ALBERT

Beschreibung: The covalent organic framework LZU1 (Lan Zhou University-1) is one of the imine-based covalent organic frameworks (COFs) that possesses attractive properties such as structural regularity, stability and good porosity. This work reports on the in-situ synthesis of COF-LZU1 on the inner walls of capillary column for open-tubular capillary electrochromatography (OT-CEC). The fused-silica capillary was first modified with 3-aminopropyltriethoxysilane and glutaraldehyde. Epitaxial growth of COF-LZU1 on the inner walls was accomplished by Schiff base reaction. The formation of COF-LZU1 was confirmed by SEM and FT-IR. The COF-LZU1 coating increases the interactions between analytes and coating, which remarkably improves the CEC separation selectivity of neutral analytes, amino acids and nonsteroidal anti-inflammatory drugs. The COF-LZU1-modified column exhibits good stability and repeatability. The precisions (relative standard deviations) for intra-day, inter-day and column-to column are 〈1.6%, 5.6% and 6.8%, respectively. Hence, the imine-based COFs represent attractive stationary phase for application in CEC separations. Graphical abstract Covalent organic framework (COF-LZU1) was in situ synthesized on the inner wall of a capillary column for electrochromatographic separation of nonsteroidal drugs and amino acids.

Beschreibung: Urchin-like NiCo 2 O 4 hollow microspheres were synthesized by a solvothermal method and characterized by using X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller surface area, and zeta potential measurements. It was used as an adsorbent for the solid phase extraction of Pb(II) from water, food and street dust samples prior to its extraction with dilute HCl and its determination by FAAS. Figures of merit include a preconcentration factor of 30, a detection limit of 5.9 μg L −1 and a relative standard deviation of 2.4%. The major advantage of the method is the fast equilibration during extraction without the need for vortexing or shaking. The method was successfully accurated by analyzing certified reference materials (BCR-482 Lichen, TMDA-70 Lake water and RM 8704 Buffalo River Sediment) and by analyzing spiked sea water, wastewater, well water, apple, eggplant, broccoli, ginger, lentil and street dust samples. Graphical abstract Schematic of the preparation of urchin-like NiCo 2 O 4 microspheres and their application to the solid phase extraction of lead(II) ions

Beschreibung: The authors describe the preparation of desert rose-like gold nanoparticles (DR-GNPs) with a plasmon resonance band at 620 nm which gives them a blue color. They have a hydrodynamic diameter of ∼72 nm and were prepared by a seeding growth approach. The DR-GNPs were characterized by UV-vis spectroscopy, transmission electron microscopy and dynamic light scattering. These nonspherical GNPs were used as a label for the antibody in an immunochromatographic strip test (ICST). Despite their particular shape and the higher surface area compared to spherical gold nanoparticles, the DR-GNPs are useful blue labels for the GNP-based strip test. A multicolor ICST for aflatoxin B1 and fumonisins is described that employs both blue DR-GNPs and red spherical GNPs. It allows for simultaneous rapid determination of the two mycotoxins in maize flour, with visual cut-off levels of 2 μg⋅kg -1 for aflatoxin B1 and of 1000 μg⋅kg -1 for fumonisins. Graphical abstract Blue desert rose-like gold nanoparticles (DR-GNPs) were synthesized, characterized and applied as label for the ImmunoChromatographic Strip Test (ICST) technique, in which red spherical GNPs (s-GNPs) are usually employed. The combined use of the blue DR-GNP and red s-GNPs allowed developing of an intuitive multicolor ICST for the simultaneous detection of aflatoxin B1 and fumonisins in maize flour.

Beschreibung: The article describes a method for preconcentration and speciation of Cr(III) and Cr(VI) in river waters. It is based on ultrasound-assisted magnetic solid phase extraction employing a nanocomposite prepared from magnetite nanoparticles, manganese oxide and alumina oxide, and then functionalized with [3-(2-aminoethylamino)propyl] trimethoxysilane (AAPTMS). By taking advantage of the oxidative properties of MnO 2 , the Fe 3 O 4 @MnO 2 ,Al 2 O 3 nanocomposite was used for the preconcentration of total chromium. The AAPTMS-modified nanocomposite, in turn, is selective for Cr(VI). The concentration of Cr(III) can be calculated as the difference between total chromium and Cr(VI). The preconcentrated chromium species were quantified using ICP-OES. The method was optimized using response surface methodology. Under optimal conditions, the limit of detection and quantification are 20 and 50 pg ⋅ mL −1 , respectively. The intraday and interday precisions of the method, expressed in terms of relative standard deviation, are 2.6 and 4.9%, respectively. In addition, the effects of potentially interfering ions were examined. The method was successfully applied to the speciation of chromium in spiked river water and a certified reference material. Graphical abstract The magnetic Fe 3 O 4 @MnO 2 ,Al 2 O 3 was used as an adsorbent for preconcentration of total chromium in aqueous samples, while Fe 3 O 4 @MnO 2 ,Al 2 O 3 modified with [3-(2-aminoethylamino)propyl] trimethoxysilane (AAPTMS) was used for speciation of Cr(VI). The concentrations of Cr(III) was calculated from total Cr and Cr(VI).

Beschreibung: The authors described gold nanoclusters (AuNCs) for use on an “on − off − on” NIR fluorescent probe for the determination of citrate and Cu(II) ion. The AuNCs were prepared by a microwave-assisted method using BSA as both the stabilizing and reducing agent. The resulting BSA-capped AuNCs display NIR fluorescence peaking at 680 nm under 500 nm excitation, a quantum yield of ~6.0%, an average size of 2.8 ± 0.5 nm, water-dispersibility, stability and biocompatibility. The on−off probe for Cu(II) is based on the interaction between Cu(II) and BSA which causes the fluorescence of the BSA−AuNCs to be quenched. The quenched fluorescence is recovered on addition of vitamin C (VC), obviously due to complexation of Cu(II) by citrate. The probe was employed to image Cu(II) and citrate in HeLa cells and in aqueous solutions. The method works in the 20 nM to 0.1 mM concentration range for Cu(II), and in the 8 nM to 120 μM concentration range for VC. Graphical abstract Schematic presentation of the gold nanocluster based probe whose fluorescence is quenched by Cu(II) ions and then restored by addition of vitamin C. This is demonstrated for both aqueous solutions and living cells.

Beschreibung: The authors report on a rapid voltammetric method for simultaneous determination of the pathogens E. coli and Salmonella typhimurium ( S. typh .) by detecting the rfbE gene of E. coli O157:H7 and gyrB gene of S. typh ., respectively, and by using polymerase-assisted target recycling amplification. The assay was constructed by self-assembly of the respective hairpin probes (labeled with the electrochemical probes Methylene Blue and ferrocene) on the surface of a gold electrode. After hybridization between target DNA and hairpin probes (HPs) has occurred, the primers hybridize with the open-chain HPs and initiate extension reactions in the presence of polymerase and deoxyribonucleoside triphosphates. This results in the release of the redox labels from the electrode surface and the target dissociating from the HPs. The released target will bind to other HPs to activate new cycles, which results in enhanced suppression of current, measured best at −0.27 V and +0.36 V (vs. Ag/AgCl) for parallel detection of E. coli DNA and S. typh . DNA, respectively. The method presented here based on target recycling amplification and its integration into multiplexed electrochemical detection of pathogens was successfully applied to quantitative determination of E. coli O157:H7 and S. typh . in synthetic samples. In our perception, the strategy presented here represents a rapid and universal platform for sensitive and multiplexed quantitation of pathogens and related molecular diagnostic targets of relevance in food safety control.

Beschreibung: The capability of multi-level logic operations in biological diagnosis is far from being fully realized. In particular, the simplification of logic judgments to realize rapid, on-site complex diagnoses is still a key issue in bioelectronics. The authors here describe the construction of a colorimetric multilevel DNA circuit that incorporates two IMPLY gates and a sample extraction technology (SET) with anti-BPA aptamer as a co-recognizing element and the color of gold nanoparticles as the output signal. The circuit can perform multi-bioanalysis of the plasticizers and hormone mimetics bisphenol A (BPA) and bisphenol S (BPS). The assay is based on the finding that the aptamer against BPA can recognize both BPA and BPS. This DNA logic detection system is simple, fast, sensitive and selective because of the utilization of a co-recognition element which decreased input numbers. This, in turn, cascades multiplex Boolean logic gates and simplifies the diagnostic challenge. Both BPA and BPS can be determined by photometry at 620 nm, the limit of detection being 1.5 ng⋅mL −1 for BPA and 1.3 ng⋅mL −1 for BPS. Application to (spiked) water samples shows good analytical performance in terms of recovery (95.4 to 106.8%), linear range (4.4 to 66 ng⋅mL −1 for BPA, 2.5 to 75 ng⋅mL −1 for BPS) and correlation coefficients (〉0.98). In our perception, the method represents a simple route for the fabrication of colorimetric multi-level DNA circuits. It may shorten the gap between bioelectronic logic circuits and high throughput real sample analysis. Graphical abstract Illustration of sample extraction treatments (SET) of bisphenol A (BPA) and bisphenol S (BPS) and the three-input IMPLY1-IMPLY2 logic operation with BPA, BPS and anti-BPA aptamer as inputs.

Beschreibung: The synthesis of rattle-type nanostructured Fe 3 O 4 @SnO 2 is described along with their application to dispersive solid-phase extraction of trace amounts of mercury(II) ions prior to their determination by continuous-flow cold vapor atomic absorption spectrometry. The voids present in rattle-type structures make the material an effective substrate for adsorption of Hg(II), and also warrant high loading capacity. The unique morphology, large specific surface, magnetism property and the synergistic effect of magnetic cores and SnO 2 shells render these magnetic nanorattles an attractive candidate for solid-phase extraction of heavy metal ions.The sorbent was characterized by transmission electron microscopy, scanning electron microscopy, FTIR, energy-dispersive X-ray spectroscopy and by the Brunnauer-Emmett-Teller technique. The effects of pH value, adsorption time, amount of sorbent, volume of sample solutions, concentration and volume of eluent on extraction efficiencies were evaluated. The calibration plot is linear in the 0.1 to 40 μg·L −1 concentration range, and the preconcentration factor is 49. The detection limit is 28 ng·L −1 . The sorbent was applied to the analysis of (spiked) river and sea water samples. Recoveries ranged from 97.2 to 100.5%. Graphical abstract A yolk-shell structure based on a Fe 3 O 4 core and SnO 2 shell was developed as an efficient MSPE sorbent. A middle silica layer was etched by alkaline solution. The resulting sorbent was utilized for preconcentration of mercury ions from aqueous media.

Beschreibung: The authors describe an inexpensive electrode for the sensitive amperometric determination of the pesticide methyl parathion. A glassy carbon electrode was modified with a nanocomposite consisting of molybdenum disulfide nanosheets (MoS2) and graphene that was prepared via a hydrothermal process. Its morphology, elemental composition, diffraction, impedance and voltammetric characteristics were studied. The modified electrode displays excellent electrocatalytic ability towards methyl parathion, and the reduction peak current, measured typically at −0.60 V (vs. Ag/AgCl) is related to the concentration of methyl parathion. The effect of concentration, scan rate and solution pH value were optimized. The calibration plot is linear in the 10 nM to 1.9 mM concentration range, with a 3.2 nM detection limit (at a signal-to-noise ratio of 3). The electrode is selective, stable, adequately repeatable and reproducible. The method was successfully applied to the determination of methyl parathion in spiked samples of homogenized apple, kiwi, tomato and cabbage. Graphical Abstract A reliable and robust methyl parathion sensor has been developed using heterostructured MoS 2 /graphene. The linear range is 10 nM–1.9 nM and detection limit is 3.2 (±0.8) nM. The method was successful in real sample determination of spiked methyl parathion in food samples such as apple, kiwi, tomato and cabbage.

Beschreibung: The authors describe a flow cytometric immunoassay for aflatoxin B1 (AFB1). It has three distinct features: (a) Magnetic microspheres encoded with upconverting nanocrystals (UCNMMs) are used as fluorescent labels. These have the advantage of non-overlapping spectra and lacking crosstalk between the encoding signal and reporter signal via the low-energy near-infrared (NIR) light excitation; (b) phycoerythrin-labeled secondary antibodies are used to amplify the reporter signal; (c) The use of magnetic nanoparticles facilitates the rapid separation and specific purification of the analyte (AFB1). This assay has a detection limit of 9 pg·mL −1 and a broad working range for AFB1, requires a 50 μL sample only, and can be completed within 2 h with good accuracy and high reproducibility. It is perceived that such multifluorescent UCNMMs, whose color depends on the kind of dopants (Yb, Er, Tm, Mn) in the NaYF 4 host lattice, represent a promising tool for the analysis of mycotoxins and other analytes. Graphical abstract Schematic of the UCNMM-based indirective competitive immunoassay for AFB1 using the flow cytometric analysis (FCA) technology. The UCNMMs are prepared by doping the upconversion nanocrystals and magnetic nanoparticles inside the mesoporous polystyrene microspheres as the self-healing encapsulation strategy.

Beschreibung: The authors describe a non-enzymatioc glucose assay that has three features: (a) The use of a boronic acid as the recognition element; (b) the aggregation of gold nanoparticles (AuNPs), and (c) the use of graphene oxide quantum dots (GOQD) whose fluorescence matches the absorption of the AuNPs and thereby results in an inner filter effect (IFE). The GOQD display an orange colored fluorescence that is filtered off by the AuNPs due to an IFE. In the presence of 3-aminobenzeneboronic acid, glucose is bound to form a cationic species that causes the aggregation of AuNPs to form large assemblies. This is accompanied by a color change from red to blue, and the IFE no longer does occur so that the orange fluorescence of the GOQD pops up again. These findings were used to design an assay witha linear response in the  2.5 to 75 μmol L −1  glucose concentration range, with a detection limit of 0.65 μmol L −1 . The method was applied to the determination of glucose in spiked diluted serum and gave satisfactory results. Graphical abstract Schematic of the detection of glucose based on inner filter effect of dispersed AuNPs on the orange fluorescence of graphene oxide quantum dots.

Beschreibung: A nanocomposite prepared from reduced graphene oxide (rGO) and silver nanoparticles (AgNPs) is used in an electrochemical aptasensor for the sensitive and selective determination of the antibiotic chloramphenicol (CAP). The nanocomposite was obtained by electrostatic assembly of AgNPs on the surface of polyelectrolyte-functionalized rGO and then used to modify a glassy carbon electrode. The biosensor is then obtained by immobilizing the aptamer against CAP. When incubated with solutions of CAP, the sensor surface is loaded with CAP due to aptamer recognition. The captured CAP can be electrochemically reduced to yield a current that is strongly enhanced as a result of the excellent electrocatalysis property of the graphene/AgNP-nanocomposite. Under optimum conditions, the calibration plot is linear in the 0.01 to 35 μM concentration range, with a 2 nM detection limit (at 3σ). The sensor is reproducible, stable, selective over homologous interferents, and performs excellently when analyzing CAP in milk samples. Graphical Abstract A graphene/silver nanoparticle-based electrochemical aptasensor is designed for the selective determination of the antibiotic chloramphenicol (CAP). The excellent electrocatalytic reduction of CAP specifically captured onto the electrode surface enables the sensitive electrochemical signal transduction of the biosensor by linear sweep voltammetry (LSV).

Beschreibung: The costs of current genotyping methods limit their application to personalized therapy. The authors describe an alternative approach for the detection of single-point-polymorphisms using recombinant polymerase amplification as an allele-specific technique. The use of short and chemically modified primers and locked nucleic acids allowed for a selective isothermal amplification of wild-type or mutant variants at 37 °C within 40 min. An amplification chip platform containing 100 wells was manufactured with a 3D printer and using thermoplastic polylactic acid. The platform reduces reagent consumption and allows parallelization. As a proof of concept, the method was applied to the genotyping of four SNPs that are related to the treatment of tobacco addiction. The target polymorphisms included rs4680 (COMT gene), rs1799971 (OPRM1 gene), rs1800497 (ANKK1 gene), and rs16969968 (CHRNA5 gene). The genotype populations can be well discriminated. Graphical abstract Schematic of the allele-specific recombinase polymerase amplification for genotyping of polymorphisms. The isothermal discrimination reaction occurs in a multi-well amplification chip manufactured with a 3D printer and by using thermoplastic polylactic acid.

Beschreibung: A novel voltammetric assay for the simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RS) by using an electrochemically treated pencil graphite electrode modified with cobalt-phthalocyanine is described. Differential pulse voltammetric results showed three well-distinct oxidation peaks for HQ, CC and RS at 102 mV, 203 mV and 591 mV (vs. Ag/AgCl), respectively. Thus, the method can be applied to direct simultaneous determination without previous separation. The detection limits are 3.38 × 10 −7  mol L −1 for HQ, 3.40 × 10 −7  mol L −1 for CC and 7.23 × 10 −7  mol L −1 for RS. The method was successfully applied to the direct determination of dihydroxybenzene isomers in tea samples, and the results were compared with chromatographic data. Graphical abstract A novel assay for electrochemical detection of hydroquinone (HQ), catechol (CC) and resorcinol (RS) based on an electrochemically treated pencil graphite electrode (PGE*) modified with cobalt phthalocyanine (CoPC) was investigated. The differential pulse voltammetric (DPV) method provide a new means for direct determination of a multi-component system.

Beschreibung: The authors describe the preparation of a graphene oxide based poly(2,6-diaminopyridine) composite by in-situ polymerization. The material was characterized by Fourier transform infrared spectrometry, powder X-ray diffraction and scanning electron microscopy. The composite was placed in a column and used for solid phase extraction (SPE) of Cd(II) ions from water samples. The adsorbed Cd(II) was then eluted with HCl and injected into a flame atomic absorption spectrometer. The effects of pH values, volume and flow rate of sample, and the kind, volume and concentration of eluent were optimized. The calibration plot for the assay is linear in the 2 to 100 μg.L −1 Cd(II) concentration range. Other figures of merit include (a) a 0.47 μg.L −1 limit of detection, (b) a relative standard deviation of 1.6% (for n  = 7; at 20 μg.L −1 of Cd(II)), and (c) a preconcentration factor of 50. The method was validated by analyzing the certified reference material NIST SRM 1643f and spiked real samples. The method was successfully employed to the determination of Cd(II) in tap, river, seawater and wastewater samples. Graphical abstract Graphene oxide (GO) was used as an ideal platform for in-situ polymerization of 2,6-diaminopyridine. The material was characterized by scanning electron microscopy and spectrometry techniques. GO based poly(2,6-diaminopyridine) composite (GO-PDAP) was utilized as a sorbent for the separation and preconcentration of Cd(II) in water samples.

Beschreibung: The authors describe a visual genotyping assay for the rapid and simultaneous detection of four novel variant alleles within the SIRT1 promoter region. These alleles may be considered as a risk biomarker for the onset of Parkinson disease. An amplified DNA fragment, flanking the four SIRT1 polymorphisms, is subjected to a multiplex primer extension reaction in the presence of biotin-dUTP. Extension of primers and, consequently, incorporation of the biotin-dUTP occurs only if primers are perfectly complementary to the target sequence. Detection of the extension products is achieved by a DNA biosensor that functions in a lateral-flow mode and carries multiple test spots. Each spot comprises a suspension of polystyrene microspheres functionalized with capture probes. The primer extension reaction products hybridize, through specific sequence tags, to the capture probes of the biosensor. Biotinylated extended primers are visualized by means of anti-biotin-conjugated gold nanoparticles. The genotype is simply read out by observing the formation of red test spots. The method was optimized and evaluated by analyzing three recombinant DNA fragments carrying the novel polymorphisms and 48 clinical samples from patients with sporadic Parkinson disease and from healthy individuals. The proposed genotyping method is accurate, sensitive, and cost effective. As low as 6 fmol of amplified genomic DNA was found to be sufficient to generate detectable spots for correct genotyping. The total time required for the accumulation of genotyping results takes ∼2 h. Graphical abstract Schematic of a multi-allele genotyping assay. (a) Amplification product is subjected to primer extension reaction in the presence of biotin-dUTP. (b) The reaction product is analysed by multi-allele dipstick assay. The result is positive if a red color appears both in the test (TS) and the control spot (CS). If a red color appears only in the control spot, the result is negative. N-normal Primer; M-Multant Primer; B-biotin.

Beschreibung: This article describes a useful sorbent for separation and preconcentration of trace amounts of gold(III), palladium(II) and silver(I) ions. Graphene oxide (GO) nanoparticles were synthesized by a modified Hummers method and magnetized by MnFe 2 O 4 nanoparticles to give a sorbent referred to as mag-GO. Addition of sodium dodecyl sulfate creates admicelles on the surface of the mag-GO. Then the metal chelating agent 2-mercaptobenzothiazole (MBT) was immobilized on mag-GO to give a mag-GO-MBT type material. This adsorbent was applied to the preconcentration of gold(III), palladium(II) and silver(I) ions. Following ion desorbed with a solution of thiourea, the ions were quantified by flow injection coupled to ICP-OES. Effect of sample pH value, type and volume of eluent, amount of adsorbent, sample volume, time of adsorption and desorption were optimized. Under optimized condition, the calibration plots are linear in the 2.5 to 25,000 μg.L −1 concentration range. The limits of detection range from 0.045 to 0.076 μg.L −1 , and enhancement factors are 160, 160 and 140 for gold, palladium and silver ions, respectively. Precisions, expressed as relative standard deviation for 100 μg.L −1 of each ion are 〈3.1%. The nanosorbent applied to selective adsorption, extraction and preconcentration of Au(III), Pd(II), and Ag(I) from water, ore and automobile catalyst samples. Graphical abstract Schematic of a nanocomposite for preconcentration of gold(III), palladium(II) and silver(I) ions from water, ore and automobile catalysts. It was obtained from graphene oxide that was magnetized by using MnFe 2 O 4 and then modified with 2-mercaptobenzothiazole.

Beschreibung: An amino-functionalized grooved polyacrylonitrile nanofiber mat was modified by both functional groups and in terms of surface morphology. The mat is shown to represent a viable adsorbent for solid-phase extraction of six priority phenolic pollutants and three phenolic xenoestrogens (phenol, 3-methoxyphenol, 4-nitrophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol, 4-tert-octylphenol, 4-nonylphenol and bisphenol A) from environmental water samples. Under optimized conditions, the analytes were completely extracted from 90 mL of water sample by using only 9 mg of the mat material. Following elution with an ammoniacal methanol-acetone mixture, the eluent was directly submitted to UPLC-MS/MS or HPLC with DAD detection. Satisfied linearity in range of 50 pg·mL −1 to 100 ng·mL −1 was achieved. The detection limits ranged from 4 to 60 pg·mL −1 which revealed the excellent sensitivity of the method in comparison to standardized and other techniques. The recoveries ranged from 82.4% to 111.4%, with the relative standard deviations of 4.0% to 11.4% (for n  = 6). The method was applied to the determination of nine phenolic pollutants in water samples collected from sixteen inflow rivers and six Taihu Lake regions. Graphical abstract Amino-functionalized grooved nanofibers mat-based solid-phase extraction for simultaneous determination of nine phenolic pollutants in environmental water

Beschreibung: The simultaneous detection and evaluation of the coinfection of a cell by multiple viruses or even multiple subtypes still is a difficult challenge. The authors introduce a method for simultaneous imaging, detection and quantitative evaluation of multiple viruses in single cells by using multicolor quantum dot (QD) probes and in a single staining cycle. The multicolor QD probes were fabricated via interaction between QDs conjugated to Staph. aureus protein A (SpA-QDs) and virus-specific antibodies. A cocktail of differently colored QD-SpA-MAbs probes were loaded into the same cells containing multiple viruses, and this enabled the different viruses to be fluorescently imaged and analyzed simultaneously. Specifically, influenza A viruses of type H1N1, H3N2, and H9N2, as well as human adenovirus species B type 3 (HAdV-B3) were imaged and detected in virus-infected cells or in their co-infected cells. In our perception, the method provides a flexible platform for simultaneous detection of multiple viruses in co-infected cells. Hence, it offers new opportunities for the molecular diagnosis of virus coinfection and for studies on virus-cell interactions. Graphical abstract Multicolor QD probes were fabricated via interaction between Staph. aureus protein A-conjugated QDs (SpA-QDs) and virus-specific antibodies. A cocktail of differently colored QD-SpA-MAbs probes were applied for simultaneously detection and quantitative evaluation of H1N1, H3N2, H9N2 and HAdV viruses.

Beschreibung: The authors describe a template-free method for the electrodeposition of ultra-long copper nanowires on titanium foils. Scanning electron microscopy shows that the nanowires are around 50 nm in diameter and 30 μm in length. The titanium foils enable nonenzymatic sensing of glucose in 0.1 M NaOH solution because the nanowire-modified electrodes exhibit excellent electrocatalytic activity towards glucose oxidation at a typical working voltage of 0.7 V (vs. Ag/AgCl). Figures of merit include (a) a sensitivity of 4985 μA·mM −1 ·cm −2 , (b) a linear response extending from 1 μM to 6.0 mM of glucose, (c) good reusability (a 2.5% relative standard deviation of one electrode in five detections), and (d) an excellent reproducibility (a 3.3% RSD of five electrodes to one sample). Graphical abstract Copper nanowires with high length-diameter ratio were electrodeposited on titanium foils as nonenzymatic sensors of glucose. Benefitting from the good conductivity, abundant active sites and facilitated mass transport, the nanowire-modified electrodes exhibit excellent electrocatalytic activity towards glucose oxidation.

Beschreibung: The authors describe an aptamer based assay for the model analyte diclofenac (DCF). It is based on the use of amino-functionalized magnetite and gold nanoparticles (Fe 3 O 4 /AuNPs) that were used to decorate carbon nanotubes (CNTs) to form a highly conductive film on the surface of a glassy carbon electrode. An amino-modified DNA capture probe (ssDNA1) was placed on the Fe 3 O 4 /AuNPs using glutaraldehyde as the linker. A DCF-specific aptamer (referred to as ssDNA2) acting as the detection probe was then attached to the surface of the modified electrode via hybridization. On addition of DCF, the conformation of the aptamer undergoes a change from a random coil structure to a rigid tertiary structure (like a pocket). This change can be traced by measuring the decrease of the current observed by differential pulse voltammetry using hexacyanoferrate as a redox probe, typically at a working voltage of 0.22 V vs. Ag/AgCl. The method has a 3.4 fM detection limit and two linear responses that cover the 0.01 to 1 pM and 10 to 1300 pM DCF concentration ranges. Graphical abstract (A) Schematic illustration of the preparation of amino-functionalized Fe 3 O 4 NPs. (B) Schematic representation of different steps of aptasensor fabrication.

Beschreibung: The authors describe a nanostructured zinc(II)-imprinted polymer carrying Alizarin Red S as a ligand for separation and preconcentration of ultra-trace levels zinc(II). The adsorbent was obtained by bulk polymerization of a mixture of Zn(II) nitrate, Alizarin Red S, methacrylic acid, ethylene glycol dimethacrylate and 2,2′-azobis(isobutyronitrile). Zn(II) was then removed by treatment with ethanol and 2.0 mM HNO 3 . The imprinted nanoadsorbent was characterized by FT-IR spectroscopy and scanning electron microscopy. Following sorption of Zn(II) from the sample, it is desorbed with 3.0 M HCl and then quantified via electrothermal atomic absorption spectrometry. Under optimized conditions, the calibration plot is linear in the 3.0 to 250 ng L −1 Zn(II) concentration range, the detection limit is 0.7 ng L −1 , and the relative standard deviation is ±4.0% (for n  = 8). The method was successfully applied to the determination of Zn(II) in (spiked) water samples and hair, and in a certified reference material (MA-1b; reference gold ore) which corroborates the utility of the method. Graphical abstract Schematic of a Zn-imprinted polymer obtained by using Alizarin Red S (ARS) as a water soluble ligand via bulk polymerization method. This nanoadsorbent was applied to the separation and preconcentration of Zn(II) ion prior to its determination by electrothermal AAS.

Beschreibung: The authors describe a three-dimensional (3D) structure composed of graphene and DNA for use in a voltammetric dopamine (DA) sensor. The material was deposited on a gold electrode, and the enhanced charge-transfer performance and deposition of DNA were confirmed by electrochemical analysis. Atomic force microscopy shows the graphene-DNA composite to have been assembled on the modified gold electrode. The modified gold electrode possesses excellent electrocatalytic activity for determination of DA, best at a working voltage of 0.1 V (vs. SCE). Ascorbic acid does not interfere. Response to DA is linear in the 0.1 to 100 μM concentration range, with a 30 nM detection limit even in the presence of 1.0 mM of ascorbic acid. Graphical abstract Schematic of a voltammetric dopamine sensor based on the use of a 3D structure composed of graphene and DNA. The sensor displays an enhanced charge-transfer rate, excellent electrocatalytic activity towards dopamine, and a 30 nM detection limit.

Beschreibung: The authors describe a novel recyclable substrate for highly sensitive surface-enhanced Raman scattering (SERS) studies. It consists of gold nanorods (AuNRs) self-assembled on a TiO 2 film and combines the high SERS enhancement of assembled AuNRs with the self-cleaning property of the TiO 2 film. It overcomes limitations of conventional SERS substrates such as limited sensitivity, high costs, and poor recyclability. The packing density of the AuNRs on the TiO 2 film can be well adjusted, and therefore the SERS enhancement factor of the substrates can be tuned. For the optimized substrate, the SERS enhancement factor is as high as 5.4 × 10 10 (Raman laser at 782 nm with 10% of 1.15 mW). This indicates extremely high sensitivity and is promising in terms of single molecule detection. Raman mapping experiments showed the SERS signal to be homogeneously distributed over the whole surface, with a maximal deviation of 3.5%. The SERS activity of this substrate can be restored by degradation of the probe molecules through TiO 2 photocatalysis under UV irradiation. In our perception, these findings open a new venue for developing ultra-sensitive and recyclable SERS substrates. Graphical abstract Bilayer composites composed of gold nanorods (AuNRs) and titanium dioxide (TiO 2 ) show strong surface enhanced Raman scattering enhancement under 782-nm laser excitation and display high sensitivity and good recyclability.

Beschreibung: Okadaic acid (OA) is a low molecular weight marine toxin from shellfish which causes diarrheic shellfish poisoning (DSP). Due to its frequent occurrence, OA has become a serious threat to human health and seafood industry. The authors describe a competitive fluorophore-linked aptamer assay for OA that is based on rolling circle amplification (RCA). It consists of the following steps: (a) The wells of a microplate are modified by fixing the OA aptamer on their surface; (b) The aptamer is hybridized with an aptamer-complementary sequence-primer complex; (c) the RCA reaction is performed; (d) the FAM labelled signal probe is added. OA competes with the detection probe for the immobilized aptamer. After the competitive reaction has occurred, the supernatants containing released detection probes are removed and then read with a microplate reader. This method, unlike in competitive assays where the signals negatively correlate with OA concentrations, has a positive correlation between fluorescence intensity and OA concentration. The optimized assay has a lower detection limit (1 pg·mL −1 ) and a wider linear range (from 1 pg·mL −1 to 100 ng·mL −1 ) owning to signal amplification via RCA. It also is highly specific, repeatable, has good recovery and can be used to detect OA in seafood. Graphical abstract Schematic of a microplate assay for okadaic acid assisted by rolling circle amplification (RCA) and using a fluorophore-linked aptamer. The signal intensities are directly proportional to the concentrations of OA. The assay without RCA was also performed and compared to.

Beschreibung: The authors describe the construction of a molecularly imprinted electrochemical sensor for enantiomeric recognition of L-phenylalanine (L-Phe). Firstly, thiolated β-cyclodextrin (β-CD) and L-cysteine were used to functionalize gold nanoparticles via gold-thiol chemistry and to act as a basis for the formation of a microporous metal-organic framework (MOF). A MOF imprinted polymer was deposited on the functionalized gold nanoparticles by electropolymerization in the presence of the template L-Phe and the functional monomer 4-aminothiophenol. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy in the presence of hexacyanoferrate acting as the redox probe. The electrode, operated best at 0.2 V vs. Ag/AgCl, exhibits excellent selectivity for L-Phe, with an enantioselectivity coefficient of 2.12 over D-Phe. In addition to its good enantiomeric selectivity, the sensor has a 0.33 pM detection limit which is much lower than that reported for other electrodes. The sensor has been successfully applied to the analysis of urine spiked with L-Phe. Graphical abstract Schematic of a microporous metal organic framework imprinting sensor for the analysis of enantiomers. Combined with MOF and β-CD, the sensor exhibits excellent selectivity and sensitivity for chiral assay of L-phenylalanine.

Beschreibung: The authors describe the synthesis of carbon dots (CDs) that are highly doped with both nitrogen and phosphorus. Synthesis is accomplished via a hydrothermal reaction starting from diethylenetriaminepenta(methylenephosphonic acid) and m-phenylenediamine as the precursors. The high N,P -doping ratios renders the codoped CDs excellently water soluble, photostable over a wide range of pH values, and photostable in the presence of various metal ions. Ferric ions acts as a strong quencher of fluorescence. Their low cytotoxicity and strong green fluorescence (with excitation/emission peaks at 440/510 nm and a quantum yield of 0.32) make the CDs well suited for purposes of cell imaging, and this is demonstrated by fluorescent bioimaging of human lung carcinoma cells (type A549) and human breast cancer cells (type KB). Furthermore, the CDs were used as an effective probe for monitoring Fe(III) in both aqueous solution and living cells. Graphical abstract A highly N,P -codoped carbon dots (CDs) were synthesized for high-quality cellular Imaging and monitoring Fe 3+ in living cells. This water soluble CDs displayed high biocompatibility and emitted strong green fluorescence.

Beschreibung: An on-demand, disposable and portable surface-enhanced Raman scattering (SERS) array has been prepared by modifying the surface of cellulose paper and patterning it with silver nanoparticles (AgNPs) via pen-writing technique. The paper is initially modified with hexadecenyl succinic anhydride to generate a hydrophobic top layer that is capable of concentrating melamine (and other hydrophobic analytes) by preventing the mainly aqueous sample from spreading on the paper. The AgNPs are subsequently written onto the hydrophobic paper with a high degree of control to form large-scale SERS sensing arrays. The resulting arrays demonstrate outstanding Raman scattering enhancement as demonstrated for the fluorescent dye Rhodamine 6G which can be detected by SERS with an 80 pM limit of detection (LOD) without interference by fluorescence. The reproducibility in the preparation of spots has a relative standard deviation of 〈15% (for n  = 128 spectra). The arrays were applied to the determination of the illicit milk additive melamine. The plot of SERS intensity at Δν = 681 cm −1 versus the logarithm of melamine concentration is linear in the concentration range from 0.3 to 20 mg·L −1 , and the LOD is 0.27 mg·L −1 . In our perception, the disposable arrays presented here integrate the advantages of easy production and reliable reproducibility, and therefore are an ideal choice for use in SERS detection. Graphical abstract An on-demand, disposable and portable surface-enhanced Raman scattering (SERS) array has been developed by pen writing. Such a SERS array can be applied for the highly sensitive determination of the illicit milk additive melamine, which holds great promise for field-deployable applications.

Beschreibung: The authors report on a nonenzymatic catechol sensor that is based on the immobilization of ferrocene (Fc) on graphene oxide (GO). A glassy carbon electrode (GCE) was modified with GO which then was silanized with (3-aminopropyl)trimethoxysilane. Ferrocenecarboxaldehyde was then immobilized on GO via formation of a Schiff base. The immobilization process was monitored stepwise by using FTIR spectroscopy, X-ray diffraction, cyclic voltammetry (CV) and electrochemical impedance spectroscopy. Investigation of the modified electrode by CV revealed a pair of well-defined redox peaks with anodic and cathodic peak potentials at +0.380 and +0.277 V, corresponding to the Fc/Fc + redox couple. The Fc modified electrode exhibits excellent electrocatalytic activity towards the oxidation of catechol at a typical working voltage of +0.45 V (vs. Ag/AgCl). The response is linear in the 3 to 112 μM catechol concentration range, the detection limit is 1.1 μM, and the sensitivity is 1184.3 μA·mM −1 ·cm −2 . The sensor is stable, reproducible and reasonably selective. It was successfully applied to the determination of catechol in spiked tap water and lake water samples. Graphical abstract Schematic presentation of the covalent immobilization of ferrocene on graphene oxide through (3-aminopropyl)trimethoxysilane via Schiff base condensation for nonenzymatic catechol determination. The use of the electrode with covalently linked ferrocene and a graphene oxide host results in faster and enhanced amperometric response.

Beschreibung: This article describes the construction of a sandwich-type of DNA biosensor for detecting a specific DNA sequence of Mycobacterium tuberculosis (MTB). A polyaniline-reduced graphene oxide (PANI-rGO) composite with favorable electrochemical activity was used as a redox nanoprobe for the generation of the voltammetric signal. The composite was decorated with gold nanoparticles (AuNPs) onto which the signal probe was immobilized to form the tracer label. After hybridization between target DNA and tracer label, the voltammetric signal resulting from the polyaniline-reduced graphene oxide (PANI-rGO) redox probe can be apparently observed. The biosensor can detect the specific IS6110 DNA sequence of MTB in the 0.1 pM to 10 nM concentration range, and the detection limit is as low as 50 fM (at an S/N ratio of 3). The biosensor is also highly specific and does not recognize mismatches. It was applied to the determination of denatured PCR products in clinical samples such as sputum, and the results agreed with those obtained by gel electrophoresis. This assay provides a versatile and powerful tool for detection of MTB, and probably for other pathogens if appropriate molecular markers are available. Graphical abstract Schematic of an electrochemical DNA biosensor for the ultrasensitive detection of Mycobacterium tuberculosis (MTB). It uses a redox nanoprobe (rGO-PANI) for signal amplification. MCH: 6-mercapto-1-hexanol; PANI: polyaniline; rGO: reduced graphene oxide; rGO-PANI: polyaniline-reduced graphene oxide nanocomposite.

Beschreibung: Photodynamic therapy (PDT) uses photosensitizers, light and molecular oxygen to generate cytotoxic reactive oxygen species. Its effectiveness is limited to 〈1 cm due to the limited penetration depth of light. The present study compares the PDT effectivity of the photosensitizer verteporfin (VP) conjugated to gold nanoparticles (AuNPs) (a) by using deeply penetrating X-rays administered in standard radiotherapy doses, and (b) by using red light (690 nm). VP was conjugated to AuNPs of around 12 nm size to enhance the interaction of ionizing radiation with PS. For comparison, VP also was directly exposed to X-rays. It is found that VP alone is stimulated by X-rays to generate singlet oxygen. The conjugate to AuNPs also generated a significant amount of singlet oxygen on irradiation with X-rays in comparison to illumination with 690-nm light. It is also found that the rate of singlet oxygen generation is amplified in case of AuNP-conjugated VP compared to VP alone. The performance of the AuNP-VP conjugate and of the VP alone was tested in Panc 1 cells. Their viability was impaired much more in these two scenarios than with the X-ray radiation only. This suggests excellent perspectives for PDT based on VP and with X-ray stimulation, both as a stand-alone photosensitizer and in Au-NP conjugates. Moreover, both VP and AuNP-VP conjugates show bright fluorescence in physiological media for excitation/emission wavelengths in the range of 405/690 nm; hence they can also be used for simultaneous bioimaging. Graphical abstract Pancreatic cancer cells (Panc 1) administered with gold nanoparticle- verteporfin conjugate (AuNP-VP) showed an efficient cell killing effect with the generation of singlet oxygen ( 1 O 2 ) from triplet oxygen ( 3 O 2 ) under 690 nm irradiation and X-ray radiation.

Beschreibung: The authors report on a rapid and direct visual test for the detection of influenza A virus using a carbon nanotag based lateral flow assay. Carbon nanoparticles in the form of nanostrings are acting as reporters. As carbon nanotags accumulate in the test zone due to formation of an antibody-antigen-carbon nanotag antibody complex, and this allows for the direct visualization of the analytical signal. Under optimal conditions, influenza A virus can be determined in allantoic fluid inoculated with the virus with a limit of detection of 350 TCID 50 .mL −1 (i.e., the 50% tissue culture infectious dose). No interference is found for several other tested proteins, and for closely related viruses. Cell lysates containing different seasonal strains of influenza A viruses (including the H1N1 and H3N2 strains) collected from clinical samples were analyzed. It is demonstrated that the method can detect both influenza A viruses without interference by biological matrices. In our perception, this method has a wide potential in that it may be extended to a generally applicable platform for rapid diagnosis influenza A viruses. Graphical abstract Schematic of a rapid and direct visual test for the detection of influenza A virus using a carbon nanotag based lateral flow immunoassay. The presence of the virus induces an accumulation of the carbon nanotag conjugates, thereby providing a signal visualization.

Beschreibung: The authors describe a nanostructured hybrid platform for amperometic determination of the plasticizer bisphenol A (BPA). It consists of two dimensional sheets of reduced graphene oxide (rGO) that are decorated with Mn 3 O 4 nanoparticles. The enzyme tyrosinase was immobilized on the surface of the hybrid nanosheets placed on an ITO electrode. The larger surface area and enhanced charge transfer properties of the rGO/Mn 3 O 4 nanosheets provide a synergistic effect that results in excellent sensing performance including fast electron transfer kinetics, high electroactivity, good reproducibility and selectivity compared to other electrodes of that kind. Figures of merit include a sensitivity of 93.2 μA⋅nM −1 ⋅cm −2 , an analytical range that extends from 0.01 to 100 μM, and a 10 nM lower detection limit. Its long-term stability of 8 weeks suggests the use of such enzyme electrodes as potential tools in clinical diagnostics. Graphical abstract Schematic of the fabrication of graphene based hybrid electrode using reduced graphene oxide and colloidal Mn 3 O 4 nanostructures in presence of chitosan polymer. Further we demonstrate the electrochemical assay of the hybrid electrode for Bisphenol A detection.

Beschreibung: This study reports on the use of dispersed multi-walled carbon nanotubes (MWCNTs) as a novel pseudostationary phase in capillary electrophoresis for the separation and determination of mono- and divalent metal ions. The use of a background electrolyte containing 1 μg⋅mL −1 of dispersed MWCNTs results in good analytical linearity, in detection limits in the range from 18.5 to 124 ng⋅mL −1 , and in limits of quantifications in the range from 61 to 409 ng⋅mL −1 . The method was applied to the analysis of the ions K(I), Ba(II), Ca(II), Na(I), Mg(II), Co(II), Ni(II), Zn(II), Li(I) and Cd(II) in spiked honey, and mean recoveries were found to be between 80.0 and 106.7%. Graphical abstract Dispersed carbon nanotubes were used as pseudostationary phase in capillary electrophoresis for the separation and determination of metal ions in honey samples.

Beschreibung: An Al-doped ZnO@Fe 3 O 4 nanocomposite was synthesized and used as a magnetic sorbent for solid-phase extraction of Cd(II) prior to its determination by flame atomic absorption spectrometry (FAAS). The size and morphology of the nano-sorbent were characterized via X-ray diffraction analysis, scanning electron microscopy and FTIR. Following its desorption with acetic acid, cadmium was quantified by FAAS. Factors affecting the extraction of the Cd(II) were optimized. Under optimized experimental conditions, the calibration graph is linear in the 0.6 to 60 ng mL −1 concentration range. The limit of detection is 0.17 ng mL −1 and the pre-concentration factor is 50. The inter- and intra-day relative standard deviations for six replicate determinations at a Cd(II) level of 40 ng mL −1 are 3.8% and 2.5%, respectively. The method was successfully applied to the trace determination of Cd(II) in spiked water samples. The accuracy of the method was confirmed by analyzing the certified reference material NIST SRM 1643e. Graphical abstract Schematic of the synthesis of an Al-doped ZnO@Fe 3 O 4 nanocomposite and its application as a magnetic sorbent for solid-phase extraction of Cd(II) prior to its determination by flame atomic absorption spectrometry (FAAS).

Beschreibung: Serum alpha-fetoprotein (AFP) is present in enhanced concentrations in patients with liver cancer. Thus, sensitive detection of AFP plays an important role in the early diagnosis and treatment of cancer. In this study, a novel chiroplasmonic assay is presented for the determination of AFP. It is based on (a) the use of DNA-induced chiroplasmonic assemblies of gold nanoparticles (AuNPs) and (b) the high specificity and affinity constants between AFP and its aptamer. First, the AFP aptamer is hybridized with its complementary sequence immobilized on AuNP. As a result, the DNA-modified AuNPs are assembled to form AuNPs dimers which display strong chiroptical activity. If, however, AFP is added, it will bind to the aptamer and this results in a destruction of the aptamer-DNA hybrid and a reduction of the CD signal. Under optimized conditions, the CD intensity drops linearly with the log of the concentration of AFP in the range from 0.02 to 5 ng⋅mL −1 . Compared to the established method, this assay does not require bisulfite conversion, PCR amplification or separation. Amounts as low as 11 pg⋅mL −1 (S/ N  = 3) AFP can be detected. The method was applied to spiked human serum samples and gave recoveries ranging from 92.0% to 106%, and the relative standard derivations ranged from 4.6% to 6.3%. To the best of our knowledge, this is the first chirality based assay for AFP. Graphical abstract Schematic presentation of the novel chiroplasmonic assay for the determination of AFP. It is based on (a) the use of DNA-induced chiroplasmonic assemblies of gold nanoparticles (AuNPs) and (b) the high specificity and affinity constants between AFP and its aptamer.

Beschreibung: The authors describe an impedimetric method for the quantitation of the DNA of the human papilloma virus (HPV) type 16. A glassy carbon electrode (GCE) was modified with gold nanosheets and is shown to be superior to a common gold disk electrode. A single-stranded 25mer oligonucleotide (ssDNA) acting as the probe DNA was immobilized via its thiolated 5′ end on both electrodes. After hybridization with target (analyte) DNA, electrochemical impedance spectra were acquired in the presence of hexacyanoferrate as a redox marker. The sensor can distinguish between complementary, non-complementary and single base pair mismatches of HPV ssDNA. At a 1 mM hexacyanoferrate concentration, the biosensors respond to target DNA in the 1 μM to 1 pM concentration range, and the detection limit is 0.15 pM. The results illustrate that the use of gold nanosheets on a GCE distinctly improves the detection and differentiation of HPV compared to using bare gold. Graphical abstract Schematic of exploiting gold nanosheets as a platform for HPV detection. The method works in the 1 μM to 1 pM HPV concentration range and has a 0.15 pM detection limit..

Beschreibung: The authors describe an electrochemiluminescence (ECL) based aptasensor for the pesticide aldicarb. The method is based on effective ECL energy transfer that occurs between the ruthenium(II) bipyridyl complex [referred to as Ru(bpy) 3 2+ ] and gold nanoparticles (AuNPs). More specifically, multiwalled carbon nanotubes were modified with dendritic poly( L -arginine) labeled with Ru(bpy) 3 2+ , and the aptamers were taggedd with AuNPs. In the absence of aldicarb, the ECL emitted by Ru(bpy) 3 2+ is enhanced by AuNPs under peak wavelength at at a wavelength of 610 nm. In the presence of aldicarb, the capture and competitive binding of aldicarb to the DNA aptamers causes their separation from the DPA6/Ru(bpy) 3 2+ /MWCNT. As a result, ECL intensity decreases linearly with increasing aldicarb concentrations in the range between 40 pM and 4 nM, with a detection limit of 9.6 pM. This aptamer switch is highly sensitive, selective and inexpensive. Conceivably, it can be adapted to formats for the determination of other pesticide residues by using different DNA aptamers. Graphical abstract Schematic of the procedure for aptamer-based detection of aldicarb using the ECL signal of the Ru(bpy) 3 2+ amplified by gold nanoparticles. This assay has high sensitivity, good selectivity, and low cost. It can presumably be transferred to other pesticide detection schemes.

Beschreibung: The authors describe an electrochemical immunoassay for the β-adrenergic agonist ractopamine (RAC). It is based on the use of chitosan-stabilized gold nanoparticles (chit-AuNPs). Antibodies against RAC (anti-RAC) readily adsorb on the surface of the chit-AuNPs due to their high bio-affinity. The amount of chitosan used to synthesize chit-AuNPs does not affect the size and distribution of the NPs but amplifies the electrochemical signal of the electrode. The assay has a detection limit as low as 2.3 pg∙mL −1 (equivalent to a 6.7 fM concentration), with a response that is linear in the 0.01 to 5 ng∙mL −1 RAC concentration range. The assay is selective, acceptably reproducible, stable, and well applicable to the detection of RAC. Graphical abstract Chitosan-stabilized gold nanoparticles (chit-AuNPs) were prepared for electrochemical immunoassay of the ractopamine (RAC). The assay exhibits a detection limit of 2.3 pg·mL −1 (equal to 6.7 fM), is highly selective, acceptably reproducible, and stable.

Beschreibung: The authors describe biocompatible nanomicelle based drug carriers that can be used for simultaneous (a) fluorescence tracking, (b) pH-controlled release of the cancer drug doxorubicin (DOX), and (c) targeting the folate receptor. The pH-sensitive triblock copolymer is composed of poly-2-(diisopropylamino) ethyl methacrylate and methoxypoly (ethylene glycol) which were prepared by radical polymerization and ‘click’ chemistry. The copolymers undergo self-assembly to form spherical micelles with diameters between 100 and 200 nm and a pH-trigger capability at pH values from 5.8 to 6.2. The micelles enabled DOX to be released at pH 5.0 at a much higher rate than at pH 7.4. Studies on cellular uptake revealed selective internalization of the DOX-loaded nanomicelles into HeLa cells where they can be imaged fluorometrically. Quantitative analysis of the green fluorescence indicated that the FITC-labeled micelles possess a transfection efficiency of about 79% while that of the nanomicellles with folate is only ∼40% under the same conditions. Confocal laser scanning microscopy indicates that the micelles invade the lysosome of HeLa cells and that the DOX released by micelles causes strong cell lethality. In our preception, this work provides useful insights in terms of designing multifunctional drug carriers and of improving the applicability of copolymer micelles for drug delivery systems. Graphical abstract Schematic of the preparation of multi-functional nanomicelles through self-assembly of amphipathic polymers. The micelles act as tumor targeting and pH-controllable drug carriers. FITC/FA/P100-M can invade the lysosome of HeLa cells and release DOX inside cells, this leading to strongt cell lethality.

Beschreibung: The authors report on a method for visual and spectrophotometric determination of silver (I) by using Prussian Blue nanoparticles (PB NPs) as a colorimetric probe. It is based on the finding that the blue PB NPs are converted into colorless silver ferrocyanide ions in the presence of Ag(I) due to the establishment of a dissolution-precipitation equilibrium. The change in absorbance at 700 nm is related to the concentration of Ag(I) in the range from 0.01 to 3 μM. The visual detection limit is 3 μM. The assay has a good selectivity for Ag(I) over other common ions. It was successfully applied to the determination of Ag(I) in spiked samples of river and lake waters. Graphical abstract Schematic presentation of a visual and spectrophotometric method for determination of silver(I) by using Prussian Blue nanoparticles (PB NPs) as optical probes.

Beschreibung: The authors describe a label-free electrochemical aptasensor for ultrasensitive and highly specific detection of the antibiotic based on cascade enzymatic recycling couple with DNAzyme amplification. The assay involves two sequential reactions: the first reaction is a λ exonuclease-assisted cyclic digestion reaction triggered by target-aptamer binding. The second reaction is a nicking endonuclease-aided cyclic nicking reaction, which produces a large amount of G-rich nucleic acid segments. These form a G-quadruplex/hemin complex in the presence of K(I) ions and hemin. Because the G-quadruplex/hemin complex acts as a horseradish peroxidase-mimicking DNAzyme with excellent redox activity, the electrochemical signal transduction is accomplished due to the electroreduction of H 2 O 2 . It appears that this work is the first example that cascade enzymatic recycling coupled to DNAzyme amplification is used for antibiotic detection. The aptasensor was applied to the quantitation of kanamycin and gave a response that is linear in the 1 pM to 10 nM kanamycin concentration range, with a detection limit as low as 0.5 pM. The working voltage (vs. Ag/AgCl) at which data can be acquired best is −0.35 V. The assay offers the advantages of remarkably improved sensitivity, use of affordable instrumentation, and simplified operation without the need for electrochemical labeling or addition of labile reagents. Thus, cascade enzymatic recycling coupled to DNAzyme amplification represents a versatile platform for highly sensitive and specific antibiotics detection. Graphical abstract ᅟ

Beschreibung: The authors describe a two-step strategy for in-situ dispersive solid phase extraction ( is -dSPE) of Cr(VI) ion (chromate) prior to its determination by using copper nanoclusters capped with 4,6-diamino-2-mercaptopyrimidine (DAMP-CuNCs) as a fluorescent probe. By emulating the formation of layered double hydroxides and taking advantage of their compositions, the extraction of chromate is accomplished by rapidly dispersing a suspension of mixed hydroxides of Mg 2+ and Al 3+ into the sample solution. After enrichment, chromate is directly quantified through selective quenching of the fluorescence of DAMP-CuNCs. This results from an inner filter effect caused by chromate only, while other anions have no effect. Under optimized conditions, the method has a linear response in the 1–7 μM chromate concentration range, and the lower limit of detection is 0.31 μM. The is -dSPE has improved detection sensitivity and has provided a highly selective response. It was successfully applied to the determination of chromate in (spiked) water samples, and the results agreed well with data obtained by ICP-OES. Graphical abstract Schematic of a two-step strategy for is -dSPE of Cr(VI) ion prior to its determination by using DAMP-CuNCs.

Beschreibung: The authors describe a method for magnetic solid phase extraction (MSPE) combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for the quantitation of eight non-steroidal anti-inflammatory drugs (NSAIDs) in wastewater and environmental water samples. Specifically, the NSAIDs were directly extracted by using a magnetic nanocomposite of type Fe 3 O 4 /MIL-101(Cr) (Matérial Institute Lavoisier, MIL) from 50 mL water samples without any further cleanup. The effects of the amount of adsorbent, pH value, salt concentration, ultrasonic extraction time, desorption solvent nature and volume and desorption time were investigated. Under the optimal conditions, UPLC-MS/MS based detection resulted in the following figures of merit: (a) Linear calibration plots that typically extend from 0.1 (0.2, 0.05, 0.02) to 50 μg·L −1 , depending on the compound; (b) detection limits between 3 to 60 ng·L −1 ; and (c), recoveries varying from 81.2% to 116.8% with relative standard deviations between 0.4% and 10.8%. The adsorption of NSAIDs on Fe 3 O 4 /MIL-101(Cr) was characterized by adsorption isotherms, kinetics and thermodynamics studies and provides a deeper insight into the adsorption mechanism. Compared to other method for pretreatment and preconcentration of NSAIDs, the new method is more rapid, sensitive, accurate and eco-friendly. The method was successfully applied to the determination of the NSAID residues in a variety of real environmental and wastewater samples. Graphical abstract Schematic of a method for determination of non-steroidal anti-inflammatory drugs (NSAIDs) in environmental water by magnetic solid phase extraction based on Fe 3 O 4 /MIL-101(Cr) combined with UPLC-MS/MS. The adsorption mechanism of NSAIDs on Fe 3 O 4 /MIL-101(Cr) was studied.

Beschreibung: Anabolic androgenic steroids (AAS) are frequently abused in human and animal sports as performance-enhancing drugs, and consequently their use is controlled by international sports authorities. Testosterone is one of the most frequently used AAS, and therefore the accurate determination of its levels in biological fluids is very important. The authors describe the selection of testosterone-binding aptamers performed using a classic SELEX approach with the target immobilized on magnetic beads. Counter selections with structurally similar steroids were implemented at different stages. Pools from different selection rounds were sequenced with Next Generation Sequencing and ten aptamer candidates were selected for further characterization. Low nanomolar range dissociation constants were calculated by a bead-based PCR assay and verified by microscale thermophoresis. Future work will focus on the development of aptamer-based platforms for the sensitive detection of testosterone in biological samples and the validation of these assays for the rapid screening of suspicious samples. Graphical abstract The selection of testosterone-binding aptamers is described via classic SELEX using the target immobilized on magnetic beads combined with Next Generation Sequencing. The process let to the identification of several unique aptamer candidates which were characterized and their binding to testosterone was evaluated.

Beschreibung: The authors describe a sensor capable of detecting methanol adulteration of ethanol. The sensor is based on the use of quartz tuning forks (QTFs) that were functionalized with polymer wires made from a combination of polystyrene (PS) and aniline. Exposure to organic vapors causes the resonance frequency of the functionalized QTF to change, and this can be used to identify the type and concentration of the analyte. A mixture of methanol and ethanol vapors in varying concentrations was exposed to the QTF polymer system. The resulting shift in the resonance frequency of the QTF was firstly used to determine the concentration of alcohol vapor, which is reflected in the amount of shift. Secondly, the nature of change in resonance frequency was used to determine the type of alcohol exposed to the sensor. The sensitivity and selectivity of the sensors to ethanol and methanol vapors has been investigated. A portable hand-held prototype sensor has been developed which displays the percentage of two alcohols it is exposed to. It can detect ethanol adulteration where the methanol concentration is as low as 5%. Graphical abstract Spring loaded Quartz Tuning Fork sensors functionalized with polystyrene-aniline wires exhibit opposite responses (increase and decrease in frequency) to vapors of ethanol and methanol respectively.The methanol adulteration of ethanol solutions may thus be detected by sensing their vapors.

Beschreibung: The authors describe an aptamer based fluorometric assay for the determination of ATP. It is based on deoxyribonuclease I-aided target recycling and signal amplification. The DNA probe consists of two regions (sequences) that represent the capture probe and the signal probe, respectively. In the absence of ATP, the probe is adsorbed by the surface of graphene oxide (GO) via π-stacking interactions. This results in quenching of the fluorescent label (carboxyfluorescein) and protects it from being cleaved by DNase. Upon adding ATP, the probe will be repelled by GO because ATP binds to the aptamer. This triggers an increase in fluorescence as measured at excitation/emission wavelengths of 480/514 nm. The detection limit is as low as 0.2 nM, and the calibration plot is linear in the 10 to 400 nM ATP concentration range. The assay is specific and sensitive, and in our perception has a large potential in terms of detecting other species including pathogenic microorganisms, small molecules, metal ions, and proteins. Graphical abstract Schematic of the fluorescent strategy for adenosine triphosphate assay by using aptamer-based target recognition and deoxyribonuclease I-aided signal amplification.

Beschreibung: The β-adrenergic agonist brombuterol (BB) is illicitly used as an additive in animal feed to enhance the lean meat-to-fat ratio. The authors describe an ultrasensitive lateral flow immunochromatographic assay (LFIA) based on the use of surface enhanced Raman scattering (SERS) for the determination of brombuterol in swine meat and urine samples. Flower-like gold-silver core-shell bimetallic nanoparticles (referred to as AuNF@Ag) displaying strong SERS enhancement were synthesized, characterized and used as the substrate for the preparation of the LFIA. Polyclonal antibody against brombuterol was immobilized on the surface of the AuNF@Ag particles carrying the Raman reporter 4-mercaptobenzoic acid (MBA). After performing an LFIA, the Raman scattering intensity of MBA on the test line was measured and used for quantitation of brombuterol. Figures of merit of this assay procedure include (a) duration of LFIA process of 15 min; (b) an IC 50 value (e.g. the concentration of brombuterol producing 50% of signal inhibition in standard curve) of 380 pg mL-1; and (c) a limit of detection as low as 0.5 pg mL-1. The LFIA is selective over the molecules salbutamol, ractopamine, phenylethanolamine A, isoproterenol and phenylephrine, but shows a 8.5% cross-reactivity to clenbuterol, probably due to the high structural similarity. Swine meat and urine samples spiked with different amounts of brombuterol were analyzed by this method and gave recoveries between 95.8 and 108.0%, and relative standard deviations between 2.0 and 6.3% (for n  = 3). Graphical abstract Schematic presentation of the lateral flow immunochromatographic assay (LFIA) based on surface enhanced Raman scattering (SERS) using flower-like gold-silver core-shell nanoparticles. It is capable of detecting brombuterol in swine meat and urine samples with high sensitivity and specificity.

Beschreibung: The amphiphilic copolymer poly(vinylbenzyl thymine-co-styrene-co-maleic anhydride) (PSVM) was synthesized by radical copolymerization of styrene, vinylbenzyl thymine, and maleic anhydride. Its chemical structure was proven by using 1 H nuclear magnetic resonance spectroscopy. PSVM was used as a host to prepare a composite consisting of carbon nanotubes and gold nanoparticles by in-situ reduction. The morphology of the nanocomposites was studied by transmission electron microscopy. A glassy carbon electrode coated with this composite is shown to be a viable sensor for the determination of dopamine (DA), paracetamol (PAT) (both at a pH value of 7), and uric acid (UA) (at pH 6). Two linear relationships exists between amperometric current and analyte concentrations. For DA, the linear analytical ranges are from 0.1 to 200 μM and from 200 to 1000 μM. For PAT, the ranges are from 0.1 to 200 μM and from 200 to 1000 μM. For UA, the ranges are from 0.05 to 1000 μM. The respective limits of detection (for S/ N  = 3) are 56, 27 and 50 nM. The sensor is highly sensitive, stable, reproducible, and selective. Graphical abstract A hybrid nanocomposite (CNT/PSVM/Au) of carbon nanotube (CNT) – Au nanoparticle composite based on the amphiphilic copolymer poly(vinylbenzyl thymine/styrene-co-maleic anhydride) (PSVM) was prepared through in situ reduction. This nanocomposite was immobilized on a glassy carbon electrode (GCE) to fabricate an electrochemical sensor to determine dopamine (DA), paracetamol (PAT) and uric acid (UA).

Beschreibung: A regenerable and ultrasensitive voltammetric biosensor is described for the determination of thrombin. It relies on a combination of (a) enzymatic catalysis, (b) a G-quadruplex/hemin DNAzyme system, and (c) AuPd nanoparticles for signal amplification. Poly(o-phenylenediamine) was decorated with AuPd nanoparticles and loaded with horseradish peroxidase (HRP) and thrombin aptamer (TBA), and the mixture was allowed to interact with hemin to form the G-quadruplex/hemin/HRP/AuPd/poly(o-phenylenediamine) bioconjugates. In the presence of thrombin, the bioconjugates remain immobilized on the surface of the modified glassy carbon electrode through a sandwich reaction. Poly(o-phenylenediamine) also acts as a redox mediator, and the electrochemical reaction of poly(o-phenylenediamine) in the presence of H 2 O 2 is efficiently catalyzed by HRP, AuPd nanoparticles and G-quadruplex/hemin as the peroxidase mimics. Thus, a remarkably amplified electrochemical signal is obtained by the triple catalytic amplification. The biosensor has a dynamic range that spans the 100 f. to 20 nM thrombin concentration range, and the detection limit is 20 fM. The biosensor can be regenerated by applying an electrochemical desorption technique that breaks the gold-thiol bond and releases the components from the surface. In our perception, the mediator-free and signal-amplified biosensor demonstrated here has a large potential with respect to the quantitation of thrombin in clinical samples. Graphical abstract Schematic of the assay: The peroxidase-like AuPd nanoparticles, G-quadruplex/hemin DNAzyme and horseradish peroxidase synergistically catalyze the electrochemical reaction of poly(o-phenylenediamine) in the presence of H 2 O 2 , thereby amplifying the electrochemical detection signal of thrombin.

Beschreibung: The authors have developed a rapid and reliable method for the capillary electrochromatographic determination of cephalosporin antibiotics in environmental waters. An open-tubular capillary column was modified with the complex [Cu(mal)(bpy)], a copper(II) complex with malic acid and 4,4′-bipyridyl, by an amide coupling method to act as the stationary phase. The simultaneous determination of the cephalosporins formulations, namely cefapirin (CP), ceftiofur (EFT) and cefixime (CFM) in environmental water samples was accomplished in buffer of pH 5.0 by applying a voltage of 8 kV and with DAD detection. Detection limits typically are 0.1 μg⋅mL −1 .The method was applied to the analysis of cephalosporins in spiked water samples from Kunming Lake to give recoveries betwen 88 and 106%. Graphical abstract A metal-organic framework (MOF) was synthesized from copper(II), malic acid and 4,4′-bipyridyl and used as stationary phase of capillary electrochromatography (CEC) by covalent immobilization on the capillary inner walls. Compared to an uncoated fused-silica capillary, improved separation of cephalosporin antibiotics can be accomplished.

Beschreibung: Iron sulfides with different atomic ratios were synthesized by a hydrothermal method and used to modify a glassy carbon electrode. The various sulfides were compared to each other for their amperometric response to H 2 O 2 . It is found that FeS is the most adequate material. Operated in 0.1 M NaOH solution at 0.4 V (vs. Ag/AgCl), the sensor based on FeS displays a linear response that extends from 0.50 μM to 20.5 mM of H 2 O 2 , with a sensitivity of 36.4 μA mM −1  cm −2 and a detection limit of 0.15 μM (at an S/N ratio of 3). The sensor is selective, stable and reproducible. Graphical abstract Schematic of the synthesis of pomegranate flower-like FeS by a hydrothermal route using ferric chloride and thiourea (SC(NH 2 ) 2 ) as the precursors, and ethanolamine (EA) as the structure-guiding auxiliary agent. A glassy carbon electrode (GCE) modified with this material allows for amperometric sensing of hydrogen peroxide in 0.1 M NaOH solution with a 0.15 μM detection limit. 

Beschreibung: The authors describe a highly sensitive and selective photoelectrochemical (PEC) assay for mercury(II) ions. It is based on a dual signal amplification strategy. The first enhancement results from the surface plasmon resonance (SPR) of Au@Ag nanoparticles (NPs) absorbed on MoS 2 nanosheets. Here, the injection of hot electrons of Au@Ag NPs into MoS 2 nanosheets produces a strong photocurrent, while background signals are strongly reduced. The second enhancement results from the use of a thymine rich ct-DNA aptamer attached to the Au@Ag-MoS 2 nanohybrid. The DNA specifically binds Hg(II) ions to form thymine-Hg(II)-thymine (T-Hg-T) complexes. This leads to the formation of a hairpin-shaped dsDNA structure. The use of a CdSe quantum dot label at the terminal end of the ct-DNA further facilitates electron–hole separation. The photocurrent of the detector is measured as a function of Hg(II) concentration at a bias voltage of 0.1 V and under irradiation of 430 nm light. Due to the two-fold amplification strategy presented here, the linear range extends from 10 pmol·L −1 to 100 nmol·L −1 , with a detection limit of 5 pmol·L −1 (at S/N = 3). Graphical Abstract The injection of hot electrons of Au@Ag into MoS 2 produces a strong photocurrent, and the formation of thymine-Hg(II)-thymine further facilitates electron–hole separation by CdSe. This dual signal amplification strategy is used to detect Hg(II) ions via a photoelectrochemical assay.

Beschreibung: CdSe:Eu nanocrystals were successfully synthesized and characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectric spectroscopy. The CdSe:Eu nanocrystals showed enhanced green electrochemiluminescence (ECL) intensity when compared to pure CdSe nanocrystals. Further, the nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen (CEA) that has a linear response over the 1.0 fg·mL −1 to 100 ng·mL −1  CEA concentration range with a 0.4 fg·mL −1 detection limit. The assay was applied to the determination of CEA in human serum samples. Graphical abstract Schematic of the assay: GCE-glassy-carbon electrode, Ab- Antibody, BSA- Bovine serum albumin, Ag- Antigen. CdSe:Eu nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen.

Beschreibung: The authors present a voltammetric immunoassay for the quantification of the prostate specific antigen (PSA), a well-established tumor marker. Biotinylated anti- PSA antibodies were immobilized on the surface of a nano-TiO2-modified carbon paste electrode using specific interaction between streptavidin and biotin. Streptavidin itself was covalently grafted to the electrode surface via 4-aminobenzoic acid film. Signal transduction was then performed using polyclonal antibodies conjugated with horseradish peroxidase (HRP) and thionine. An amplified catalytic reduction current was observed in the presence of H 2 O 2 because more than one polyclonal antibody linked to each antigen. Each step of the preparation of the immunosensor was monitored via electrochemical impedance spectroscopy. The electrode, if operated at a typical potential of 0.3 V vs. Ag/AgCl and using hexacyanoferrate as an electrochemical probe, exhibits linear responses in the 0.10 to 5.0 ng·mL −1 and 5.0 to 100 ng·mL −1 PSA concentration ranges, with a detection limit of 200 pg·mL −1 . The accuracy of the biosensor was confirmed by analyzing a certified human serum sample, and this indicated that the immunosensor is well suited for the quantification of PSA. Graphical abstract Schematic presentation of a sandwich-type electrochemical immunosensor for the prostate specific antigen. It is based on the use of a carbon paste electrode, streptavidin and biotinylated monoclonal antibody. Signal transduction is the result of the catalytic reduction of thionine.

Beschreibung: The authors report on a new approach for the determination of the breast cancer biomarker microRNA-155 (miRNA-155). It is based on the measurement of the fluorescence shift of oligonucleotide-templated copper nanoclusters (DNA-CuNC). A probe DNA was designed that acts as a template for the preparation of CuNC which, under 400 nm excitation, exhibit strong fluorescence enhancement at 490 nm and a 90 nm Stokes shift after binding to target miRNA-155 and formation of a DNA-RNA heteroduplex. Under the optimal conditions, the fluorescence of the DNA-CuNC increases with increasing concentration of miRNA-155 in the range from 50 pM to 10 nM, with a 11 pM detection limit. The assay has excellent selectivity over noncomplementary RNA. The method was applied to the determination of miRNA-155 in the presence of human plasma and saliva. Graphical abstract Schematic of the detection strategy that relies on the fluorescence shift of DNA-CuNCs resulting from the specific binding of DNA-CuNCs with target miRNA-155. Fluorescence intensities are linearly proportional to the concentrations of target RNA from 50 pM to 10 nM.

Beschreibung: Composites containing cobalt oxide (Co 3 O 4 ) nanocubes integrated with multiwall carbon nanotubes (MWCNT) were synthesized by a hydrothermal route. The fractions of MWCNTs in the composite were varied from 4, 8, 12, 16 and 20 wt.%, and the resulting materials are denoted as C1, C2, C3, C4 and C5, respectively. The formation of products with high structural crystallinity was confirmed by X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. A morphological study by field emission scanning electron microscopy and high resolution transmission electron microscopy showed the successful integration of Co 3 O 4 nanocubes to the MWCNTs with an average particle size of ∼32 nm. The surface of a glassy carbon electrode (GCE) was modified with the nanocomposites in order to evaluate the electrochemical performance of the nanocomposites. Cyclic voltammetry showed that the C4-modified GCE displays best performance in terms of oxidation potential and peak current in comparison to that of a bare GCE, Co 3 O 4 nanocubes, or GCEs modified with C1, C2, C3 or C5. The detection limit (at an S/N ratio of 3) is 0.176 nM by using chronoamperometry, and the linear range is between 1 and 20 μM. Graphical abstract MWCNT-Co 3 O 4 nanocubes were synthesized by one pot hydrothermal route. The nanocomposite is used for electrochemical detection of dopamine. The limit of detection is found to be 176 nM by chronoamperometry at a constant potential of + 0.13 V.

Beschreibung: The paper describes a colorimetric sandwich enzyme-linked immunosorbent assay (ELISA) for the determination of human IgG. It is based on the use of an Fe(II) coordination complex as a signal amplifier and of mesoporous silica nanoparticles modified with glucose oxidase (GOx) and secondary antibodies (Ab 2 ). After formation of the immuno sandwich complex, the quantity of GOx is proportional to the quantity of IgG. On addition of Fe(II) and glucose, GOx catalyzes the oxidation of glucose to produce hydrogen peroxide which oxidizes Fe(II) to Fe(III). After adding a stop solution containing the complexing ligand 1,10-phenanthroline (Phen), un-reacted Fe(II) forms an orange-red complex with Phen which can be detected by plate reader and even seen with bare eyes. This sandwich ELISA has a linear response in the 1 pg.mL −1 to 100 ng.mL −1 human IgG concentration range and a 860 fg.mL −1 detection limit. This is 20 times lower than the commercial ELISA for human IgG. The assay also is selective, stable, highly sensitive and cost-effective. Graphical abstract Schematic of a colorimetric enzyme-linked immunosorbent assay (ELISA) based on Fe(II) coordination complex as signal amplification strategy for human IgG detection. Glucose oxidase (GOx, green) and detection antibodies (Ab 2 , brown) functionalized mesoporous silica nanoparticles (MSN) were prepared as probe.

Beschreibung: The authors describe a method for speciation of thallium that is based on solid phase extraction (SPE) combined with dispersive liquid-liquid microextraction (DLLME) prior to electrothermal vaporization ICP-MS determination. The method is shown to be applicable to the determination of total, suspended, soluble, organic and inorganic Tl, and of Tl(I) and Tl(III) in tea leaves and tea infusion. The SPE step involves the use of titanium dioxide nanofibers for preconcentration of the Tl analytes and simultaneous removal of the matrix components such as polyphenols, soluble sugars, catechin, caffeine and tea pigments. Following elution of Tl with dilute HNO 3 , the eluate was further preconcentrated and separation by DLLME. After optimization of the method, it has a detection limits of 0.015 pg mL −1 for Tl(I) and of 0.020 pg mL −1 for Tl(III), with relative standard deviations of 6.5% and 7.3% (at 0.10 ng mL −1 ; for n  = 9), respectively. The technique has an enrichment factor of 450 and is highly selective. It was successfully applied to the speciation and distribution of thallium in tea leaves and tea infusions. A certified reference material of tea leaves was analyzed by this method, and the obtained values were in good agreement with the certified values. Graphical abstract Schematic of a new method for solid phase extraction (SPE) of thallium. Titanium dioxide nanofiber-based extraction was combined with dispersive liquid-liquid microextraction (DLLME) for speciation of thallium and its distribution in tea leaves and tea infusion, including total, suspended, soluble, organic and inorganic Tl, and of Tl(I) and Tl(III).

Beschreibung: The authors describe an integrated biosensor for amperometric DNA detection of Dengue virus in real time. Cu 2 CdSnS 4 (CCTS) quaternary alloy nanostructures were successfully synthesized, deposited on an oxygen-etched silicon substrate (O 2 /Si) via spin coating, and annealed at 400 °C. The nanostructures were investigated by using UV-vis spectroscopy, X-ray diffraction, atomic force microscopy and scanning electron microscopy. Interdigitated electrodes were fabricated using silver as a metal contact deposited on the CCTS/O 2 /Si substrate using a thermal evaporator vacuum coater and a hard mask. The quaternary alloy acts as a support for immobilization of a Dengue-specific DNA probe that is employed as the recognition element. Single-stranded DNA in concentrations from 100 f. to 10 nM were successfully recognized via amperometry, typically at a working voltage of 1.5 V. The lower detection limit is 17 nM. Sensitivity is found to be 24.2 μA nM −1  cm −2 . The biosensor is inexpensive, fast, highly sensitive, and has low power consumption. Graphical abstract Schematic illustration of IDEs fabrication steps. (a) Si substrate (b) O 2 /Si, (c) CCTS/O 2 /Si, (d) Ag/CCTS/O 2 /Si, (e) cross section view of the sample.

Beschreibung: The authors describe the synthesis of a nanosorbent for fast magnetic solid phase extraction of trace levels of Ag(I), Au(III), Pd(II) and Pt(II). It consists of graphene oxide sheets modified with magnetite nanoparticles (mGO) coated with silica. This material was further modified with a polypyrrole-polythiophene copolymer via oxidative polymerization to end up with a material of the type mGO@SiO 2 @PPy-PTh. Successful synthesis of the nanocomposite and its components was corroborated by FT-IR, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry and thermogravimetric analysis. The presence of nitrogen- and sulfur-containing functional groups on both sides of the nanocomposite sheets facilitates the formation of strong complexes between target (i.e. noble metal ions) and the surface of the sorbent. Following elution with thiourea-HCl, the ions were quantified by FAAS. Under optimized conditions, the lower limits of detection range from 0.1 to 1.0 μg L −1 . The maximum sorption capacities are 49, 50, 45, and 50 mg g −1 for Ag(I), Au(III), Pd(II) and Pt(II), respectively. The method was successfully applied to the extraction and determination of the analytes in wastewater (electroplating, radiological and photographical wastewater), sea water, and road dust. Graphical abstract A sorbent of the type mGO@SiO 2 @PPy-PTh (where mGO stands for magnetic graphene oxide, PPy for polypyrrole, and PTh for polythiophene) was synthesized and used as a nanosorbent for the micro solid phase extraction of the ions Ag(I), Au(III), Pd(II), and Pt(II) prior to their determination by FAAS. mGO: Magnetic graphene oxide. TEOS: Tetraethyl orthosilicate. PPy-PTh: Polypyrrole-Polythiophene copolymer.

Beschreibung: The authors have prepared organized assemblies of a hemoglobin-chitosan(CS)@Fe 3 O 4 composite on glassy carbon electrodes (GCEs) via three strategies with the aim of preparing tunable Hb-coated GCEs with good stability and long-term oxygen storage capability. The formation and morphology of the Hb - CS@Fe 3 O 4 composite was characterized by scanning electrochemical microscopy, XRD and UV–vis spectroscopy. It is shown that Hb is fully integrated into the CS@Fe 3 O 4 and can be manipulated by a magnetic field whilst maintaining its biological activity. In the absence of oxygen, a surface-controlled electrode process occurs with an interfacial electron transfer rate ( k s ) of 2.14 s −1 . The modified GCE also has a favorable oxygen storage lifetime (almost 6 h). One Hb-CS@Fe 3 O 4 film on the electrode displays particularly good electrocatalytic reduction activity towards oxygen. The linear range for detection of O 2 is 1.2 × 10 −7  ~ 2.0 × 10 −4 mol L −1 with a detection limit of 4.0 × 10 −8 mol L −1 . In our opinion, this method has great potential in terms of enhanced oxygen storage capability of Hb, which can be applied in special situations such as space operations, down hole mining, mountaineering and diving. Graphical Abstract Hb-CS@Fe 3 O 4 composites were prepared by three strategies, and oxygen carrying capability was studied. The corresponding modified electrode constructed on the basis of the magnetic field environment was superior in terms of stability, sensitivity and O 2 storage time, showing wider linear range and lower detection limit.

Beschreibung: The authors describe a graphite immobilized bismuth film electrode with enhanced sensitivity for the organophosphorus pesticide paraoxon. The film was formed by ex-situ electroplating of bismuth onto the large surface of a glassy carbon electrode modified with graphite nanopowder (Bi/Gr/GCE). The modified GCE was characterized by chronoamperometry using p-nitrophenol as a model nitro compound. The modification of the GCE results in an increase of the electroactive area (to 27.7 mm 2 ) and of the electrocatalytic activity (the catalytic rate constant being 4140 L·mol −1 ·s −1 ). This results in an enhancement of the current for the electroreduction of paraoxon by a factor of 4.3 (compared to a plain GCE). The modified GCE was applied to the sensitive determination of paraoxon by differential pulse voltammetry. At a typical working potential of −0.45 V vs. Ag/AgCl, the LOD is 2 nmol·L −1 of paraoxon, which is comparable to the LOD of some cholinesterases-based electrochemical sensors and is lower than the LOD of the organophosphorus hydrolase-based electrochemical sensors for paraoxon. In addition, the new GCE is more stable than enzyme-based sensors, and it can be renewed. Graphical abstract Schematic of a glassy carbon electrode (GCE) modified by renewable Bi film deposited ex situ. Graphite nanopowder (Gr) was incorporated in laponite as intermediate layer to form a sandwich-type structure (Bi/Gr/GCE). The Bi/Gr/GCE was applied for the sensitive paraoxon quantification with an LOD of 2 nmol L −1 . Symbols: 1-glassy carbon electrode; 2-graphite nanopowder; 3-Bi-film. GCE: glassy carbon electrode; Bi/GCE: Bi-film modified glassy carbon electrode; Gr/GCE: graphite nanopowder modified glassy carbon electrode; Bi/Gr/GCE: graphite immobilized Bi-film electrode.

Beschreibung: Polyether ether ketone (PEEK) is an ideal substrate for in tube solid-phase microextraction (SPME) because it overcomes the shortcomings of conventional silica fibers in terms of fragility and poor flexibility. Commonly used bare PEEK tubes suffer from difficult modification with selective sorbents and low inner surface areas. This problem was solved by etching with concentrated sulfuric acid, which dissolves the amorphous regions of the PEEK surface and yields a rough inner surface with plenty of microscopically small holes. The etched tube was then stepwise functionalized with polydopamine and graphene oxide which was in-situ immobilized. The modified tube displays excellent efficiency for the extraction of positively charged quaternary alkaloids by a mixed-mode extraction. Enrichment factors from 221 to 275 can be obtained for the extraction of the alkaloids jatrorrhizine, palmatine and berberine. The alkaloiods were then quantified by online SPME-HPLC-MS/MS detection. The method has detection limits of 0.1 pg mL −1 , good linearity, and good intra-day reproducibility (≤ 2.4%). It was applied to the analysis of the three alkaloids in Cortex Phellodendri herb and rat plasma after oral administration. Graphical abstract A concentrated sulfuric acid etching method was used for enhance the workability of polyether ether ketone tube (PEEK) in solid phase microextraction (SPME). The etched tube was covered with graphene oxide (GO) for extraction of protoberberines.

Beschreibung: The authors describe an electrochemical aptasensing platform for the determination of Pb(II) ions. The assay is based on the use of gold nanoparticles (AuNPs) (that facilitate electron transfer), the enzyme exonuclease III (Exo III; assisting signal amplification), and a hairpin structured complementary strand of an aptamer that prevents binding of AuNPs to the surface of the sensor electrode in the presence of Pb(II). In the absence of Pb(II), AuNPs attach to the surface of the gold electrode, and this leads to a strong voltammetric signal. In the presence of Pb(II), however, the AuNPs do not bind to the surface of the electrode because of the hairpin structure of the complementary strand. As a result, the peak current (typically measured at 0.17 V vs. silver reference electrode) remains weak. The method has a 149 pM detection limit. It was applied to the analysis of spiked tap water and human serum samples and gave recoveries between 92 and 105.25%. Graphical abstract Scheme 1. Schematic illustration of Pb 2+ recognition based on an electrochemical approach. In the presence of Pb 2+ , apt bound to Pb 2+ . So, the hairpin structure of complementary strand remained intact and protected complementary strand against digestion by Exo III and no AuNPs interacted with it, resulting in a weak electrochemical signal (a). In the absence of Pb 2+ , the apt is hybridized with complementary strand and the hairpin structure of complementary strand is disassembled. Upon the addition of Exo III, only the 3”-end of complementary strand is degraded and apt is released. The released apt hybridizes with other free complementary strand and the cycle is continued. In the presence of AuNPs, AuNPs interacts with the remains of complementary strands. Thus, a strong electrochemical signal can be detected (b).

Beschreibung: Defective few-layered graphene (dFLG) was successfully prepared by using a detergent and a sonoelectrochemical method. The fast exfoliation of dFLG with step defects results from the rapid interaction of sodium n-octyl sulfate with a highly oriented pyrolytic graphite electrode on application of an oscillation power of 192 W and a potential of around 3 V (vs. Ag/AgCl). Simultaneously, the application of an oxidation potential leads to the formation of C-O and O-C = O groups on the dFLG as confirmed by X-ray photoelectron spectroscopy. The dFLG with such defects was deposited on a glassy carbon electrode (GCE) where it displays improved electrocatalytic activity in catalyzing the oxidation of H 2 O 2 , best at a working voltage of −0.4 V (vs. Ag/AgCl). Its sensitivity (211.14 μA·mM −1 ·cm −2 ) is improved when compared to a GCE modified with reduced graphene oxide or graphene oxide and the linear analysis range extends from 0.02 to 2.9 mM. Real sample analysis of milk demonstrated the feasibility of using such a dFLG-based sensor for H 2 O 2 . Graphical abstract Defective few-layered graphene (dFLG) with step defects and few O-containing groups were prepared by a sonoelectrochemical approach. The dFLGs can act as catalysts that have significantly higher sensitivity (211.14 μA·mM −1 ·cm −2 ) for sensing H 2 O 2 when compared to chemically reduced graphene oxide and graphene oxide.

Beschreibung: The article describes a magnetic metal-organic framework (MOF) of the type MIL-101(Fe)/2-(propylamino-ethyl) dithiocarbamate on the surface of magnetite nanoparticles. The MOF is shown to be a viable material for speciation analysis of Cr(III) and Cr(VI) because it shows selectivity for Cr(VI) at pH values around 2.0, while at pH values around 5 both Cr(III) and Cr(VI) species are sorbed. Hence, preoxidation or reduction treatments are not needed. After optimization of the extraction conditions, chromium was quantified by ET-AAS. Feature of the determination of Cr(VI) include (a) a 1.0 ng L −1 limit of detection, (b) a linear analytical range that extends from 3 to 300 ng L −1 , and (c) a relative standard deviation of 6.4%. The respective values for total chromium are 1.5 ng L −1 , 4 to 325 ng L −1 and 7.5%, respectively. The method was validated by analyzing two certified reference materials. It also was successfully employed to the rapid extraction and speciation of Cr(III) and Cr(VI) in (spiked) water samples and of total chromium in tea samples. Graphical abstract A novel magnetic metal-organic framework [a MIL-101(Fe)/2-(propylamino-ethyl) dithiocarbamate modified magnetite nanoparticle composite] was synthesized and utilized for speciation analysis of Cr(III) and Cr(VI) via determination by electrothermal atomic absorption spectrometry. (a) A schematic representation for synthesis of Fe 3 O 4 @PAEDTC NPs. (b) Schematic illustration of the synthesis of MIL-101(Fe)/Fe 3 O 4 @ PAEDTC nanocomposite.

Beschreibung: The authors report on an aptamer-based method for the detection of S. Typhimurium. The aptamers were identified by using a modified cell-based SELEX method (cell-SELEX) by adopting an alternating negative-positive selection strategy. Each cross-reactive population was used separately, with a focus on generating strain-specific aptamers in order to enhance selectivity. The aptamers were characterized and chemically modified with thiol groups at the 5′ end which enables covalent binding to gold nanoparticles on a screen printed carbon electrode (GNP-SPCE). The aptamer-modified GNP-SPCE was subsequently applied to impedimetric sensing of S. Typhimurium in water and food samples. Response is linear in the 10 to 10 5  CFU⋅mL −1 concentration range, and the limit of detection is ~10 CFU⋅mL −1 . The assay can distinguish S. Typhimurium from S. Typhi and has been validated in water and spiked egg samples. Graphical abstract A modified Cell-SELEX approach for screening species specific aptamer for the impedimetric detection of non-typhoidal Salmonellosis.

Beschreibung: Laser desorption-ionization mass spectrometry (LDI-MS) is used to determine Hg(II) ions by using thymine-modified chitosan-coated magnetic nanoparticles (TCTS). TCTS nanoparticles are characterized using transmission electron microscopy, X-ray diffraction, UV-vis absorption, infrared spectroscopy and LDI-MS. TCTS acts as a preconcentration probe, supports surface enhanced LDI-MS (SELDI-MS) and acts as a capping agent for Hg(II). The separation of Hg(II) via this method combined with SELDI-MS provides a sensitive and selective tool for inexpensive and fast (5 min) detection of Hg(II) with limit of detection down to 0.05 nmol for environmental samples such as tap and sea water. Graphical abstract Schematic of laserr desorption/ionization mass spectrometry (LDI-MS) using t hymine - modified ch ito s an magnetic nanoparticles for the specific analysis of Hg(II) ions in tap and sea water. TCTS acts as preconcentration probe, supports s urface e nhanced LDI-MS, and binds Hg(II) ions.

Beschreibung: The authors describe a magnetic nanoadsorbent consisting of magnetite nanoparticles coated first with titanium dioxide and then with polypyrrole (PPy). It is shown to be a viable material for magnetic solid-phase extraction of trace amount of Pb(II). The magnetic titanium dioxide nanoparticles were synthesized first and then modified with PPy via in-situ electropolymerization. The properties, morphology, and composition of the sorbent were characterized by FTIR, scanning electron microscopy, energy-dispersive X-ray analysis and vibrating sample magnetometry. The effects of pH value, extraction time, type and concentration of eluent, and of sample volume were optimized. Under the optimum conditions, the limit of detection (for S/ N  = 3) is 0.28 μg⋅L −1 . The maximum adsorption capacity of the adsorbent is 126 mg⋅g −1 of Pb(II). The accuracy of the method was investigated by analysis of a Certified Reference Material and the obtained value (0.119 μg⋅g −1 ) was in good agreement with the certified value (0.120 μg⋅g −1 ). The method was successfully applied to the determination of Pb(II) in a gastropod and spiked environmental and marine water samples. It gave recoveries in the range from 94.4 to 103.1%. Graphical abstract Magnetic titanium dioxide nanoparticles were synthesized and modified with PPy via in situ polymerization. The Fe 3 O 4 /TiO 2 /PPy nanocomposite was used for solid-phase extraction and pre-concentration of trace amount of lead(II) ions in complex matrices.

Beschreibung: Carbon dots codoped with nitrogen and sulfur (N,S-CDs) were synthesized by a single-step hydrothermal method. The N, S-CDs were characterized by transmission electron microscopy, X-ray diffraction, FTIR and X-ray photoelectron spectroscopy in terms of surface morphology, functional groups and surface composition and elemental composition. The CDs possess intense fluorescence and excitation wavelength dependent emission wavelengths. Fluorescence is strongest at an excitation wavelength of 360 nm and typically peaks at 440 nm. The fluorescence of the N,S-CDs is quenched by Cr(VI) ion. Under the 360 nm excitation wavelength condition, fluorescence intensity decreases linearly on increasing the Cr(VI) concentration from 1 μM to 10 μM, and the LOD at a signal-to-noise ratio of 3 was about 0.2 μM. The method was applied to the quantitation of Cr(VI) in spiked real samples and gave satisfactory results. Graphical abstract Carbon dots codoped with nitrogen and sulfur (N,S-CDs) were synthesized. These possess intense fluorescence that is quenched by Cr(VI) ion. The this probe can be used for quantitative detection of Cr(VI) ion.

Beschreibung: The authors describe a voltammetric sensor for simultaneous determination of dopamine (DA), uric acid (UA), L-tyrosine (Tyr), and the diuretic drug hydrochlorothiazide (HCTZ). The assay is based on the use of graphene nanowalls deposited on a tantalum substrate. The nanowalls are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, and cyclic voltammetry. The nanowalls are vertically grown on the substrate by direct-current arc plasma jet chemical vapor deposition. The modified electrode is shown to enable simultaneous differential pulse voltammetric determination of DA, UA, Tyr, and HCTZ. The graphene nanowalls display a large specific surface, high conductivity, and a large number of catalytically active sites for oxidation of analytes. Simultaneous detection is performed best at a pH value of 7.0 and at peak potentials of 0.124 V (vs. SCE) for DA, 0.256 V for UA, 0.536 V for Tyr and 0.708 V for HCTZ. The respective detection limits are 0.04 μM, 0.1 μM, 0.6 μM and 0.4 μM. The results show that this graphene wall modified electrode is a promising tool for the design of sensitive, selective, and stable sensors. Graphical abstract The graphene-based differential pulse voltammetric sensor for simultaneous determination of dopamine, uric acid, L-tyrosine, and hydrochlorothiazide exhibits high selectivity, sensitivity, and stability.

Beschreibung: The authors describe a method for DNA target recognition and signal amplification that is based on the target-induced formation of a three way junction. The subsequent assembly of two DNA probes releases the inhibitory strand and triggers a downstream strand displacement amplification. This causes the formation of a G-rich single sequence that binds to a hemin monomer with its peroxidase-mimicking properties. The resulting peroxidase (POx) activity is quantified by using H 2 O 2 and TMB as the substrate. In the presence of an inhibitor, in contrast, the POx-like activity is strongly reduced. This forms the basis for a highly sensitive DNA assay. It has a 0.8 pM detection limit when operated at a wavelength of 450 nm and was applied to the isothermal determination of target DNA with high selectivity. Graphical abstract Schematic of the assay: Introduction of target results in the formation of a three way junction. The subsequent assembly of two probes releases the inhibitory strand and triggers a downstream strand displacement amplification, generating amount of G-rich single sequence which causes peroxidase-mimicking activity on binding to a hemin monomer.

Beschreibung: The authors describe a new chemiluminescence (CL) system composed of Si-doped carbon dots (Si-CDs), Fe(II) ions, and K 2 S 2 O 8 . The Si-CDs were prepared by a hydrothermal method and characterized by fluorescence spectra, transmission electron microscopy, energy-dispersive X-ray and FTIR spectroscopy. The weak CL of the Fe(II)-K 2 S 2 O 8 reaction is found to be intensified by a factor of ~125 in the presence of Si-CDs. The possible mechanism for CL and its enhancement was studied by recording fluorescence and CL spectra and by investigating the effect of some radical scavengers. It is found that norfloxacin exerts a strong enhancing effect on the CL intensity of the system. This finding was employed to design a CL-based norfloxacin assay that works in the 5.0 to 300 μg L −1 concentration range, with a limit of detection (3 σ) of 1.5 μg L −1 . The method was applied to the determination of therapeutic levels of norfloxacin in spiked human plasma and gave satisfactory results. Graphical Abstract Schematic of the new chemiluminescence system. It consists of silica-doped carbon dots, Fe(II) ions and K 2 S 2 O 8 and was applied to the determination of norfloxacin which exerts a strong enhancement effect.

Beschreibung: The authors describe the synthesis of a multifunctional nanocomposite with an architecture of type Fe 3 O 4 @SiO 2 @graphene quantum dots with an average diameter of about 22 nm. The graphene quantum dots (GQDs) were covalently immobilized on the surface of silica-coated magnetite nanospheres via covalent linkage to surface amino groups. The nanocomposite displays a strong fluorescence (with excitation/emission peaks at 330/420 nm) that is fairly selectively quenched by Hg 2+ ions, presumably due to nonradiative electron/hole recombination annihilation. Under the optimized experimental conditions, the linear response to Hg 2+ covers the 0.1 to 70 μM concentration range, with a 30 nM lower detection limit. The high specific surface area and abundant binding sites of the GQDs result in a good adsorption capacity for Hg 2+ (68 mg⋅g −1 ). The material, due to its superparamagnetism, can be separated by using a magnet and also is recyclable with EDTA so that it can be repeatedly used for simultaneous detection and removal of Hg 2+ from contaminated water. Graphical abstract A schematic view of preparation process for the Fe 3 O 4 @SiO 2 @graphene quantum dots nanocomposite (denoted as Fe 3 O 4 @SiO 2 @GQDs). The graphene quantum dots were covalently immobilized on the surface of silica-coated magnetite nanospheres (Fe 3 O 4 @SiO 2 ) via covalent linkage to surface amino groups.

Beschreibung: The authors describe a pipette type of biosensor for detecting target genes and using a zinc finger protein fused to luciferase (ZF luciferase). The ZF protein binds to a specific DNA sequence, and the target double-stranded (ds) DNA can be detected by monitoring the enzymatic activity of ZF luciferase. A small avidin-immobilized reaction plate is placed on a plastic pipette tip (referred to as Biologi tip). The dsDNA detection procedures are carried out by using a programmable dispensing robot equipped with a photodetector. These procedures include (a) the aspiration of an analyte to capture the biotinylated target dsDNA (a product of a polymerase chain reaction) on the small reaction plate inside the pipette tip, (b) the introduction of ZF luciferase and luciferin into the pipette tip, and (c) migration of the pipette tip to the detection port to measure bioluminescence on the small reaction plate. The emission originating from luciferase activity is observed on the reaction plate containing immobilized biotin-tagged target dsDNA, whereas plates containing non-target or biotinylated single-stranded DNA only do not yield a signal. The intensity of emission increases proportionally to the concentration of dsDNA, and the detection limit of the target dsDNA is as low as 62 pM. An actual genomic DNA sample from Escherichia coli O157 was successfully detected by this automatic analyzer using the Biologi tip equipped with a reaction plate. This indicates that this system has a large potential for practical applications, including in particular point-of-care analyses in hygiene control, food safety testing, and clinical diagnosis. Graphical abstract A pipette-type biosensor was developed to detect target genes using a luciferase-fused zinc finger protein, where a small NeutrAvidin-immobilized reaction plate was placed on the tip, and the biotinylated target double-stranded DNA was detected by monitoring the bound luciferase activity.

Beschreibung: Electrochemical DNA sensors represent a simple, accurate and economical platform for DNA detection. Gold nanoparticles are known to be efficient labels in electrochemical sensors and to be viable materials to modify the surface of electrodes thereby to enhance the detection limit of the sensor. For surface modification, gold nanoparticles are used in combination with nanomaterials like graphene, graphene oxide, or carbon nanotubes to improve electrochemical performance in general. This review (with 116 refs.) mainly covers the advances made in recent years in the use of gold nanoparticles in DNA sensing. It is divided into the following main sections: (a) An introduction covers aspects of electrochemical sensing of DNA and of appropriate nanomaterials in general. (b) The use of gold nanoparticles in DNA is specifically addressed next, with subsections on AuNPs acting as electrochemical labels, electron transfer mediators, signal amplifiers, carriers of electroactive molecules, catalysts, immobilization platforms, on silver enhancement strategies, on AuNPs modified with carbonaceous materials (such as graphenes and nanotubes), and on multiple amplification schemes. The review concludes with a discussion of current challenges and trends in terms of highly sensitive DNA based sensing using AuNPs. Graphical abstract The review describes the state of the art in the use of gold nanoparticles in the electrochemical DNA sensors and contains sections on the use of AuNPs as labels, signal amplifiers, carriers of electroactive molecules, catalyst, immobilization platform, and on silver enhancement and multiple amplification strategies.

Beschreibung: The authors describe a rapid and sensitive magnetic relaxation switch (MRSw) aptasensor for the determination of the food-borne pathogen Pseudomonas aeruginosa . An aptamer against P. aeruginosa is covalently bound to superparamagnetic iron oxide nanoparticles. On incubation with P. aeruginosa bacteria, they will be captured by the aptamer, and this affects the formation of SPIO aggregates. The resulting strong increase in the spin-spin relaxation time (T 2 ) is utilized as the analytical information to quantify the bacteria. Under optimized conditions, the assay has a linear range that extends from 100 cfu⋅mL −1 to 10 6 cfu⋅mL −1 , and a detection limit of 50 cfu⋅mL −1 (at an S/N ratio of 3). The method was applied to the detection of P. aeruginosa in (spiked) real food and drinking water samples and was validated by the established plate counting method. This aptasensor is considered to represent a promising platform for the determination of P. aeruginosa . Conceivably, the method may be extended to other food-borne bacteria or biomolecules for which respective aptamers are available. Graphical abstract Schematic of the magnetic relaxation switch aptasensor for Pseudomonas aeruginosa detection. The superparamagnetic nanoparticles act as a “switch” to detect aggregated and dispersed states with and without target , which leads to substantial changes in the T 2 relaxation time.

Beschreibung: A stainless steel wire coated with a polymeric ionic liquid (poly-IL) is shown to represent a viable new tool for solid-phase micro-extraction (SPME) of polychlorinated biphenyls (PCBs). The surface of the wire was covalently modified with 3-(trimethoxysilyl) propyl methacrylate, and susequent free-radical initiated polymerization of the ionic liquid (IL) 1-hexyl-3-vinylimidazolium bromide on the surface of the wire produced a poly-IL possessing sheet-like structure. The poly-IL fiber was evaluated with respect to its capability for extracting PCBs from water samples. The fiber aging temperature, extraction time, extraction temperature and ionic strength of the water sample were optimized. The poly-IL SPME fiber was applied to the headspace extraction of 12 kinds of PCBs (from PCB 81 to PCB 189) which, after direct injection into the port, were quantified by GC with ECD detection. The method displays good linearity in the 10 to 200 ng L −1 PCB concentration range, and limits of detection between 0.9 and 5.8 ng L −1 . The single fiber and fiber-to-fiber repeatabilities are 〈10.7% and 〈12.7%, respectively. The method was applied to the analysis of PCBs in (spiked) Yangtze River water samples to give recoveries between 86.6 and 108%. Graphical abstract A polymeric ionic liquid (poly-IL) was synthesized and anchored on the surface of a pre-treated stainless steel wire to produce a poly-IL solid-phase micro-extraction fiber that showed excellent headspace extraction of PCBs.

Beschreibung: A nanocomposite was electrochemically synthesized from polypyrrole and manganese dioxide (PPy/MnO 2 ) and deposited on a stainless-steel wire for use in electromembrane surrounded solid-phase microextraction (SPME). In order to evaluate the performance of the method, the antihistamines cyproheptadine (CYP) and ketotifen (KET) were selected as model analytes. To increase the selectivity of the method and to improve sample cleanup, an organic solvent was immobilized in the pores of the wall of a hollow fiber. The SPME fiber was placed in its lumen which was initially filled with the aqueous acceptor phase. The basic analytes (CYP, KET) were migrated, by applying an electrical field, from the aqueous sample solution through the liquid membrane into the aqueous acceptor phase. As a result, they are adsorbed by the solid sorbent which acts as the cathode. The composition of the organic liquid membrane, the pH values of the donor and acceptor phases, the applied voltages and the extraction times were optimized. Under optimal conditions, extraction recoveries are in the range of 26.8 to 46.9%, and detection limits of less than 1.1 and 0.7 ng mL −1 in water, urine and plasma samples were obtained by using GC with FID detection for KET and CYP, respectively. Response is linear in the range of 0.3 to 200 ng mL −1 in water, 1.2 to 200 ng mL −1 in urine and 1.0 to 200 ng mL −1 in plasma samples for CYP, and from 0.7 to 200 ng mL −1 in water, 1.4 to 200 ng mL −1 in urine and 1.2 to 200 ng mL −1 in plasma samples for KET. The method was applied to the analysis of CYP and KET in human urine and plasma samples, and satisfactory results were obtained. Graphical abstract A polypyrrole-manganese dioxide nanocomposite was synthesized electrochemically and used in electromembrane surrounded solid-phase microextraction.

Beschreibung: Nano-sized molecularly imprinted polymers (nano-MIPs) possessing cavities that fit nicotinic acid were synthesized via precipitation polymerization. Acrylamide, divinyl benzene, nicotinic acid (NA) and acetone were utilized as functional monomer, cross-linker, template and porogen, respectively. The nano-MIPs were placed on a graphite paste electrode doped with reduced graphene oxide (rGO). An indirect detection method was employed that makes use of Cu(II) ion as an electrochemical probe because NA itself does not generate a significant voltammetric signal. To accomplish this, the modified electrode was first incubated with a solution of nicotinic acid, then with a solution of Cu(II). It is found that a MIP-based electrode that was previously incubated with nicotinic acid solution showed a distinct signal for Cu(II), while the same electrode incubated with Cu(II) only gave a very weak signal. A non-imprinted polymer-based electrode also gave no signal. In addition, the presence of rGO in the electrode led to a significantly increased current. Various factors influencing the analytical performance were optimized. The electrode, best operated at 0.2 V (vs. Ag/AgCl), has a linear response in the 10 nM to 0.2 μM NA concentration range. The detection limit is as low as 8.0 nM (at 3 Sb/m). The method was applied to the determination of NA in spiked plasma and urine samples. Graphical abstract Schematic representation of indirect voltammetric sensing of nicotinic acid by the nano-MIP-modified electrode.

Beschreibung: Polyacrylonitrile (PAN) was grafted on silica (Si) surfaces in the form of one-dimensional (1D) gratings to form well-defined line patterns. The tethered PAN 1D gratings were then subjected to a cyano-to-tetrazole conversion reaction to generate a tethered polyvinyltetrazole (PVT) 1D grating. This results in different properties for the transverse magnetic (TM) and transverse electric (TE) polarizations, i.e. perpendicular and parallel to the line patterns, respectively. After adsorption of Cr(III), the negative charges of PVT chains were neutralized, and this results in a collapse of the polymer brushes. As a result, the effective refractive indices vary with the concentration of Cr(III). This causes a gradual color change from yellow via green to blue at incident angles of 30–40°. The adsorption of the ions Na + , Ag + , Ca 2+ , Cd 2+ , Fe 3+ , Zn 2+ and Cr 6+ ions, in contrast, does not cause significant changes in the effective refractive index. The Cr(III)-induced deswelling transitions can be reversed by treatment with acid. The assay has a limit of detection (LOD) as low as 20 μg·L −1 of Cr(III). The ions Pb(II), Cu(II) and Cr(VI) are also adsorbed by the PVT grating, but the respective LODs are higher (80, 100 and 40 μg·L −1 ). Graphical abstract Polyvinyltetrazole (PVT) is exploited to graft on silica surfaces as one-dimensional (1D) gratings. The grating-based assay exhibited high sensitivity and selectivity due to significant change of effective refractive indices in an experimentally simple setup for visualization of Cr 3+ .

Beschreibung: The authors describe an amperometric biosensor for the amino acid L-arginine (L-Arg). It is based on the use of a Nafion/Polyaniline (PANi) composite on a platinum screen-printed electrode (Pt-SPE) using a novel recombinant arginine deiminase isolated from Mycoplasma hominis . The protein was over-expressed, purified and employed as a biorecognition element of the sensor. Enzymatic hydrolysis of L-Arg leads to the formation of ammonium ions which diffuse into the Nafion/PANi layer and induce the electroreduction of PANi at a potential of −0.35 V (vs Ag/AgCl). L-Arg sensitivity is 684 ± 32 A·M −1 ·m −2 , and the apparent Michaelis-Menten constant (K M app ) is 0.31 ± 0.05 mM. The calibration plot is linear over the range 3–200 μM L-Arg, the limit of detection is 1 μM, and the response time (for 90% of the total signal change to occur) is 15 s. The sensor is selective and exhibits good storage stability (〉 1 month without loss in signal). The biosensor was applied to the analysis of L-Arg in pharmaceutical samples and of ammonium and L-Arg in spiked human plasma obtained from blood of healthy volunteers and those with a hepatic disorder. Data generated were found to be in good agreement with a reference fluorometric enzymatic assay. Graphical abstract Schematic of an amperometric biosensor for L-arginine based on a Nafion/polyaniline (PANi) composite at a platinum screen-printed electrode (Pt-SPE) using a novel recombinant arginine deiminase (ADI) from Mycoplasma hominis .

Beschreibung: A surface plasmon resonance sensor whose surface has been modified with boronic acid groups was developed in order to bind and detect transferrin. 4-Mercaptophenylboronic acid (4-MPBA) was utilized to form a self-assembled monolayer on the gold surface of the sensor chip. The surface topography of the modified gold chip was characterized by atomic force microscopy. In solutions of pH 9, the glycosyl groups of transferrin (Trf) quickly and reversibly combine with 4-MPBA on the sensor chip to result in changes of the refractive index. Thus, Trf can be sensed online by monitoring the SPR signal. Under optimized conditions, the sensor has a linear response in the 10 nM to 1.3 μM Trf concentration range, and the limit of detection is 4.4 nM (equivalent to 0.34 μg·mL −1 ). The results suggest that this 4-MPBA-functionalized sensor is a viable candidate for clinical testing of Trf which is a potential marker for severe diseases such as hypertension, primary renal disease, and diabetes. Graphical abstract Schematic of a novel SPR sensor modified with boronic acid for the determination of transferrin in human urine with high sensitivity.

Beschreibung: The authors describe the preparation of carbon nanofibers (CNFs) with a three-dimensional network structure by one-step carbonization of bacterial cellulose at 800 °C. The 3D CNFs wrapped with Nafion polymer were cast on a glassy carbon electrode (GCE) which then enables sensitive detection of Cd(II) and Pb(II). Under optimized conditions and at typical stripping peaks of around −0.80 and −0.55 V (vs Ag/AgCl), the electrode exhibits high sensitivity and a wide analytical range of 2–100 μg·L −1 for both Cd(II) and Pb(II). The detection limits are 0.38 μg·L −1 for Cd(II) and 0.33 μg·L −1 for Pb(II), respectively. The modified GCE was successfully employed to the determination of trace amounts of Cd(II) and Pb(II) in both tap water and waste water. Graphical abstract A three-dimensional carbon nanofiber network wrapped with Nafion polymer was employed to prepare a chemically modified electrode, which is shown to enable simultaneous detection of trace amounts of Cd(II) and Pb(II) in both tap water and waste water.

Beschreibung: Aligned silver nanorods wrapped with Al 2 O 3 layers about 0.85, 1.54 nm thickness were utilized to study the SERS response and adsorption behavior of uranyl ion. Relatively broad and asymmetric SERS bands were observed due to the contribution of several hydrolyzed uranyl complexes and multiple coordination between uranyl complexes and SERS substrates. The mechanism of sorption on SERS substrates is discussed. The effect of the pH value of sample solutions was also studied. Results show that the Al 2 O 3 layers enhance the stability of silver nanorod. It is found that the Al 2 O 3 layer is consumed in acidic or basic solutions, while the SERS performance of silver nanord is maintained. Uranyl ion can be quantified by this method in concentration down to 10 −9  M. Graphical abstract Schematic of an AgNR@Al 2 O 3 substrate prepared by oblique angle deposition (OAD) and atomic layer deposition (ALD) techniques in order to study the SERS response of uranyl species. It shows an excellent sensitivity with a detectable concentration down to 1 nM.

Beschreibung: The authors describe a quartz crystal microbalance based aptasensor for the determination of Pb 2+ . In order to enhance its response, oligonucleotide-embellished gold nanoparticles (AuNPs) were used to amplify the frequency changes. The method is based on the use of specific aptamers immobilized on the surface of the quartz crystal microbalance (QCM) and the binding of Pb 2+ , which prevents the self-assembly of the AuNPs on the QCM. Trace concentrations of Pb 2+ can be determined by monitoring the change in the response frequency of the QCM. The method has a 4 nmol∙L −1 detection limit and works in the 5 to 200 nmol∙L −1 Pb 2+ concentration range. This aptasensor also shows adequate selectivity for Pb 2+ over potentially interfering metal ions. Graphical abstract Schematic of the assay. The specific aptamer SAP does not readily combine with its partial complementary strand CSAP in the presence of Pb(II) ion. Thus, the mass change on the crystal is inversely proportional to the concentration of Pb(II).

Beschreibung: The authors describe a fluorescence based aptasensor for adenosine (AD), a conceivable biomarker for cancer. The assay is based on the immobilization of capture DNA on newly synthesized quaternary CuInZnS quantum dots (QDs) and the conjugation of probe DNA on gold nanoparticles (AuNPs). The capture DNA is an adenosine-specific aptamer that is partly complementary to the probe DNA. Once the capture aptamer hybridizes probe DNA, the fluorescence of the QDs (measured at excitation/emission wavelengths of 522/650 nm) is quenched by the AuNPs. However, when AD is added, it will bind to the aptamer and restrain the hybridization between capture DNA and probe DNA. Therefore, the fluorescence of the QDs will increase with increasing AD concentration. Under optimal conditions, fluorescence is linearly related to the AD concentration in the range from 50 to 400 μM, the detection limit being 1.1 μM. This assay is sensitive, selective, reproducible and acceptably stable. It was applied to the determination of AD in spiked human serum samples where it gave satisfactory results. Graphical abstract Aptamer based fluorescent assay of adenosine using quaternary CuInZnS quantum dots and gold nanoparticles

Beschreibung: An immunoassay has been developed for the determination of alpha-fetoprotein (AFP). It is based (a) on the use of a detection reaction mediated by manganese dioxide nanoparticles (MnO 2 NPs) because their good stability at room temperature, and (b) on tyramine signal amplification (TSA). The MnO 2 NPs acts as an artificial peroxidase that causes the conversion of TMB to give a colored product, and the tyramine-triggered reaction is used for signal amplification to improve the detection limit. Combined with immuno-magnetic separation and enrichment, the response of this AFP immunoassay is linear from 6.25–400 ng mL −1 , with a detection limit of 22 pg mL −1 (S/ N  = 3). This immunoassay was successfully applied to the quantification of AFP in serum samples, and gave excellent accuracy compared with the clinical results from a local hospital. The LOD and stability of this assay are better than those of the standard horseradish peroxidase-based ELISA. The strategy presented here is conceived to have a wider scope in that it may be extended to various other immunoassays. Graphical abstract Schematic of an immunoassay based on manganese dioxide nanoparticles (MnO 2 NPs)-mediated enzyme reaction and tyramine-triggered signal amplification (TSA) to detect alpha-fetoprotein (AFP).

Beschreibung: The article describes a sensitive and rapid method for the colorimetric determination of Salmonella pullorum and Salmonella gallinarum ( S. pullorum and S. gallinarum ). Silica coated magnetic nanoparticles (MNP) were modified with antibodies against S. pullorum and S. gallinarum to act as the capture probes. Horseradish peroxidase (HRP) and antibodies against S. pullorum and S. gallinarum on silica nanoparticles (HRP-IgG-SiNP) were used as detection probes (secondary antibody). In the presence of S. pullorum and S. gallinarum , the target bacteria are captured by capture probes and detection probes to form sandwich structures. This sandwich complexes were then magnetically isolated and used to catalytically oxidize the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB). The absorbance at 450 nm is proportional to the concentration of S. pullorum and S. gallinarum. Under the optimized conditions, the assay has a detection range that extends from from 8.4 × 10 3 to 8.4 × 10 7  CFU⋅mL −1 , and the limit of detection is 1.7 × 10 3  CFU⋅mL −1 . The approach is cost-effective and specific. Sample preconcentration is not required. In our perception, this immunomagnetic nanoparticle-based detection strategy holds great promise for on-site detection of a wide range of pathogens by using the respective antibodies. Graphical abstract Schematic illustration of (a) the process for preparation of IgG-MNP, (b) the process for preparation of HRP-IgG-SiNP and (c) the colorimetric sandwich assay for detection of target bacteria S. pullorum and S.gallinarum by using HRP-loaded silica nanoparticle as the signal-transduction tag. (S. pullorum and S. gallinarum: Salmonella pullorum and Salmonella gallinarum; Ab: antibodies; HRP: Horseradish peroxidase; IgG-MNP: Antibodies against S. pullorum and S. gallinarum coated magnetic nanoparticles; HRP-IgG-SiNP: Horseradish peroxidase and antibodies against S. pullorum and S. gallinarum dual labled silica nanoparticles; TMB: 3,3′,5,5′-tetramethylbenzidine; APTES: 3-aminopropyltri-ethoxysilane).

Beschreibung: The authors describe an ultrasonic-assisted headspace method for solid phase micro-extraction (UA-HS-SPME) of 7 polychlorinated biphenyls (PCBs) with codes PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180. The coating is based on a poly-dopamine metal-organic framework [PDA-MIL-53(Fe)] on a stainless steel wire. The coating can be prepared and evenly deposited on the stainless fiber by dipping the PDA fiber into a solution of MIL-53(Fe). The assay is also environmentally friendly because water is used as the solvent. The effects of extraction time, addition of salts, pH value and power of ultrasonic power were optimized. The coating is found to possess a high selectivity and adsorption capacity for PCBs compared to commercial SPME fibers such as the divinylbenzene/carboxen/polydimethylsiloxane fibers. Following desorption, the PCBs were quantified by GC-MS. The detection limits are between 50 and 90 pg⋅g −1 of PCBs in soil. The fibers can be easily prepared, and the batch-to-batch reproducibility (RDS) is 〈10% (for n  = 6). The fibers are inexpensive, re-usable and can be easily manipulated, and particularly well suited for screening polychlorinated biphenyls in soil. Graphical abstract Schematic of the preparation of an extraction fiber using stainless steel wire as substrate, PDA as adhesive, and MIL-53(Fe) as the adsorbent. It was applied to the extraction of PCBs from soil. The fiber is durable and inexpensive.

Beschreibung: The authors describe a method for the determination of the activity of alkaline phosphatase (ALP) that utilizes dsDNA-templated copper nanoparticles (CuNPs) coupled to enzymatic amplification via λ exonuclease. A hybrid of a DNA modified with a phosphate moiety at the 5′-end (P-DNA) and a P-DNA complementary sequence (cP-DNA) is employed as the dsDNA substrate for ALP. In the absence of ALP, the dsDNA is cleaved by the λ exonuclease, which hinders the formation of CuNPs which display fluorescence with excitation/emission peaks at 340/565 nm. However, ALP-mediated hydrolysis of the 5′-phosphoryl end impedes the cleavage of dsDNA by the λ exonuclease, and this promotes the formation of fluorescent dsDNA-templated CuNPs via ascorbate-mediated reduction. Under the optimized experimental conditions, this method exhibits a high specificity to ALP and has a 0.1 U⋅L −1 limit of detection. The strategy also provides the basis for a screening platform for inhibitors of ALP. Graphical abstract Schematic presentation of a fluorescence assay for the detection of alkaline phosphatase based on dsDNA-templated copper nanoparticles and exonuclease based amplification.

Beschreibung: Three-dimensional structures comprising polypyrrole nanowires (PPyNWs) and molecularly imprinted polymer (MIP) were prepared by electropolymerization on the surfaces of a glassy carbon electrode (GCE). The modified GCE possesses both large surface area and good electrocatalytic activity for oxidizing dopamine (DA), and this leads to high sensitivity. The electropolymerized MIP has a large number of accessible surface imprints, and this makes the GCE more selective. Under optimal conditions and at a working voltage of typically 0.23 V (vs. SCE), the calibration plot is linear in the 50 nM to 100 μM DA concentration range, and the limit of detection is 33 nM. The sensor has been successfully applied to the analysis of DA in injections. Graphical abstract Schematic of a three-dimensional nanocomposite based dopamine sensing platform based on the use of a molecularly imprinted polymer and poly(pyrrole) nanowires. The modified polypyrrole nanowires and molecularly imprinted polymer endowed high electrocatalytic capacity and good selectivity for dopamine recognition, respectively.

Beschreibung: The authors describe a method for the determination of cobalt(II) ions based on the use of luminescent and water-soluble ZnO quantum dots capped with β-cyclodextrin (β-CD@ZnO QDs). The modified QDs display strong yellow-green fluorescence with a peak at 537 nm under 360 nm excitation. High-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, luminescence, and UV-visible absorption spectroscopy were used to characterize the β-CD@ZnO QDs. The fluorescence of the QDs is quenched by Co(II) ions. This finding was exploited to design a quenchometric assay designed for the detection of Co(II) in water solution. The detection limit is 0.34 μM (based on the 3σ/slope criterion), and the linear range extends from 1.0 to 10 μM. The method was applied to quantify Co(II) in spiked real samples. The quenching mechanism was studied, and this showed that aggregation-induced quenching causes the main effect. Graphical abstract The fluorescence of β-cyclodextrin-capped ZnO quantum dots (β-CD@ZnO QDs) is quenched by cobalt ions, and this finding is exploited in a fluorescence assay for cobalt ions in aqueous solutions.

Beschreibung: The work describes a photoelectrochemical (PEC) biosensor for the detection of DNA. It employs oriented hierarchical ZnO flower-rod architectures (ZnO FRs) and DNA dendrimers. ZnO FRs act as photoactive material that yields a photocurrent of up to 23 μA. The photogenerated electron transfer is inhibited once the probe DNA and the target DNA oligonucleotides hybridize, and this results in a reduced photocurrent. The use of DNA dendrimers with scores of DNA branches further amplifies the signal of the PEC biosensor. The PEC sensor displays a response that is linear in the DNA concentration range from 10 fM to 0.1 μM with a detection limit of 3.7 fM (at S/ N  = 3). The sensor was applied to the determination of DNA in human serum samples and was found to work with acceptable accuracy. Due to the use of ZnO FRs and DNA dendrimers, the assay is highly sensitive, rapid, and repeatability. Graphical abstract Schematic of an innovative photoelectrochemical (PEC) biosensors based on oriented ZnO flower-rod architectures (ZnO FRs) for DNA detection. Dendrimers were employed for signal amplification to give a low detection limit of 3.7 fM.

Beschreibung: The authors describe an electrochemical approach for the preparation of a glassy carbon electrode (GCE) modified with graphene oxide and silver nanodentrites (AgNDs). The coating was obtained by using an aqueous solution containing silver nitrate, phosphate and ammonia. The phosphate anions act as a scaffold for the improved deposition of AgNDs. The effects of deposition potential and time and concentration of electrolyte on the formation of the AgNDs were optimized. The modified GCE displays good electrocatalytic activity towards the oxidation of dissolved hydrazine. The electron transfer coefficient and diffusion coefficient are 0.60 and 4.64 × 10 −5  cm 2  s −1 respectively. The electrode exhibits a linear response over the 100 nM to 670 μM hydrazine concentration range and a detection limit (LOD) of 33 nM. The sensitivity of the modified electrode is 2077 μA mM −1  cm −2 at a typical working voltage of 0.1 V (vs Ag/AgCl). This LOD is much lower than that of the allowable concentration of hydrazine in drinking water as defined by the US EPA and the WHO. Graphical abstract Schematic of the 2-step fabrication of a glassy carbon electrode (GCE) modified with graphene oxide (GO) and silver nanodendrites (AgND) for use in a hydrazine sensor. First, Ag 3 PO 4 is formed by adding AgNO 3 and phosphate. Secondly, the formed Ag 3 PO 4 is converted to a colorless complex by adding ammonia and by electrolytic growth of AgND on the GO/GCE.

Beschreibung: A sensitive and specific bioassay based on cyclic enzymatic amplification was developed for determination of microRNA (miRNA) by taking advantage of the exodeoxyribonuclease activity of T7 exonuclease (T7 Exo). In the presence of miRNA, DNA/RNA duplexes are formed by hybridization of miRNA and capture probes (Cp). Then, the Cp is digested to release miRNA into the next amplification cycle assisted by T7 Exo. This leads to the digestion of numerous Cp molecules. The broken Cp does no longer hybridize with hairpin probes (Hp) to unveil G-quadruplex DNAzyme (GDNAs). However, in the absence of miRNA, the Hp hybridizes with Cp to unveil GDNAs. The generated GDNAs form assemblies with hemin to form the G-quadruplex/hemin DNAzyme complex which is capable of catalyzing the oxidation of the substrate ABTS by H 2 O 2 . Upon cyclic enzymatic amplification, the output signal is reduced accordingly, this resulting in a “signal-off” signal best acquired at a wavelength of 418 nm. The lower detection limit is 0.69 pM (at an S/N ratio of 3). The assay involves efficient signal amplification, is homogeneous and isothermal, and enables visual detection. It provides a simple, rapid and sensitive platform for use in clinical diagnostics. Graphical abstract Schematic of a method for colorimetric and visual detection of miRNA using T7 exonuclease-based cycling signal amplification.

Beschreibung: The authors describe the preparation of magnetic cobalt/nitrogen-doped carbon microspheres (Co-N/Cs) by combining a hydrothermal procedure with a carbonization process. The textures of the Co-N/Cs were investigated by powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, nitrogen adsorption-desorption isotherms and vibration sample magnetometry. The Co-N/Cs possess a high surface area and strong magnetism. This results in good adsorption capability and enables magnetic separation. The Co-N/Cs are shown to be an effective magnetic solid-phase extraction adsorbent for the enrichment of various phthalate esters (diethyl phthalate, diallyl phthalate and diisobutyl phthalate) from sport beverages and milk samples prior to their determination by HPLC. The limits of detection (at an S/N ratio of 3) are between 0.1–0.2 and 0.08–0.3 ng mL −1 for sport beverages and milk samples, respectively. The recoveries when extracting all the spiked samples varied from 80.3% to 116.2%. Graphical abstract Magnetic cobalt/nitrogen-doped carbon microspheres (Co-N/Cs) were prepared and used as an effective magnetic solid phase extraction adsorbent for the enrichment of phthalate esters from beverages and milk samples.

Beschreibung: The authors describe a molecularly imprinted polymer (MIP) deposited on multiwalled carbon nanotubes (MIP/MWCNTs) for separation and preconcentration of L-cysteine (L-Cys). The MIP was characterized by scanning electron microscopy, X-ray diffraction and FT-IR and via adsorption kinetics and adsorption isotherms. The MIP is shown to be a viable sorbent for L-Cys which subsequently is quantified by spectrophotometry through formation of a charge transfer complex with the DDQ reagent. The experimental parameters affecting separation efficiency and spectrophotometric determination were optimized. Under optimum conditions and at an analytical wavelength of 478 nm, the calibration plot is linear in the 4.0 to 180 ng mL −1 concentration range, and the limit of detection (at an S/N ratio of 3) is 2.3 ng mL −1 . The intra-day and inter-day precision are in the range from 2.4 to 3.6%. The method was successfully applied to determination of L-Cys in spiked human serum and water samples where it gave recoveries ranging from 96.6 to 102.4%. Graphical abstract Schematic of the preparation of a  molecularly imprinted polymer coated on the multiwalled carbon nanotube (MIP/MWCNT) by functionalization of MCNTs with methacrylic acid and subsequent polymerization. The MIP/MWCNTs were successfully applied for extraction and spectrophotometric determination of L-Cys by charge transfer (CT) complexation.