ALBERT

Description: We describe a new type of NADH sensor based on a screen-printed electrode (SPE) modified with reduced graphene oxide (RGO) and poly(allylamine hydrochloride) (PAH). A mixture of graphene oxide (GO) and PAH was deposited on the surface of a carbon working electrode, and RGO was prepared in-situ by electrochemical reduction of GO. The oxidation peak of NADH was recorded at +450 mV (vs . silver pseudo-reference). Under optimized conditions, the electrode exhibits high electrocatalytic activity toward NADH oxidation, expressed by a high rate constant and a stable response up to 0.8 mM concentrations. The sensitivity is 108.6 μA·mM −1 ·cm −2 , the response time is 20 s (for 95 % of the steady state current), and the detection limit is 6.6 μM (at an S/N ratio of 3). A peak separation of about 300 mV was achieved in differential pulse voltammetric determination of NADH in the presence of ascorbic acid. This makes the new sensor a useful tool with potential analytical application in different dehydrogenase based systems. Graphical abstract ᅟ

Description: We describe an electrochemical immunosensor for the simultaneous determination of alpha-fetoprotein (AFP) and prostate specific antigen (PSA) via a modified glassy carbon electrode. Silica nanoparticles (200–300 nm i.d.) with good monodispersity and uniform shape were synthesized, and the following species were then consecutively immobilized on their surface: gold nanoparticles (AuNPs; 5–15 nm i.d.), secondary antibody (Ab 2 ) and the redox-probes Azure A or ferrocenecarboxy acid (Fc). In parallel, two types of primary antibodies (Ab 1 ) were co-immobilized on the surface of the dissolved reduced graphene oxide sheets (rGO) that were also decorated with AuNPs. In the presence of antigens (AFP or PSA), the Ab 2 /Si@AuNPs carrying Azure A and Fc are attached to the AuNP/rGO conjugate via a sandwich type immunoreaction. Differential pulse voltammetry (DPV) was employed to measure the resulting changes in the signal of Fc or Azure A. Two well-resolved oxidation peaks, one at −0.48 V (corresponding to Azure A) and other at + 0.12 V (corresponding to Fc; both vs. SCE) can be observed in the DPV curves. Under optimal conditions, AFP and PSA can be simultaneously determined in the range from 0.01 to 25 ng mL‾ 1 for AFP, and from 0.012 to 25 ng mL‾ 1 for PSA. The detection limits are 3.3 pg mL‾ 1 for AFP and 4.0 pg mL‾ 1 for PSA (at a signal-to-noise ratio of 3). The method was applied to (spiked) real sample analysis, and the recoveries are within 96.0 and 107.2 % for PSA, and within 100.9 and 105.8 % for AFP, indicating that this dual immunosensor matches the requirements of clinical analysis. Graphical abstract (A) Two types of signal labels preparation process. (B) The immunosensor preparation and detection process.

Description: A nanocomposite consisting of coral-like gold nanostructures on reduced graphene oxide (RGO) was synthesized with the assistance of dimethylbiguanide (DMBG). It was then fabricated on a glassy carbon electrode, coating with cysteamine in order to enable the immobilization of acetylcholinesterase (AChE) as a model enzyme whose activity of hydrolyzing the substrate of acetylthiocholine is inhibited by the pesticide triazophos. The biosensor has response to acetylthiocholine in the 0.3 ~ 300 μM concentration range at 0.65 V (vs. SCE). The inhibition of the enzyme by triazophos can be determined in concentrations of up to 210 ppb, with a detection limit of 0.35 ppb of triazophos ( S / N  = 3). The biosensor is highly reproducible and acceptably stable. Graphical Abstract Coral-like gold nanostructures supported on reduced graphene oxide were synthesized with the assistance of dimethylbiguanide to fabricate an acetylcholinesterase (AChE) biosensor, which exhibited high reproducibility and good stability, providing a good platform for the detection of organophosphorus pesticides.

Description: We have performed a study on the performance of two microbial glucose sensors based on immobilized Gluconobacter oxydans ( G. oxydans ). The first one was prepared by modifying a glassy carbon paste electrode (GCPE) containing the microbial cells with graphene oxide (GO), the other one by modifying it with graphene-platinum hybrid nanoparticles (graphene-Pt NPs). The electrode was characterized by following the voltammetric signals of the oxidation of hexacyanoferrate(II) to hexacyanoferrate(III) via the oxidative enzymes contained in G. oxydans which convert glucose to gluconic acid. Optimizations were conducted with a conventional GCPE containing G. oxydans . After material optimization, the biosensors were applied to the determination of glucose. The linear and analytical ranges for GO based biosensor range from 1 to 75 μM (linear) and 1 to 100 μM (analytical), respectively, with a limit of detection (LOD) of (3 s/m) 1.06 μM (at an S/m of 3). On the other hand, the graphene-Pt hybrid nanoparticle based biosensor showed two linear ranges (from 0.3 to 1 µM and from 1 to 10 μM), a full analytical range from 1 to 50 μM, and an LOD of 0.015 μM. The graphene-Pt hybrid NP based sensors performs better and was applied to the determination of glucose in synthetically prepared plasma samples where it gave recoveries as 101.8 and 104.37 % for two different concentrations. Selectivity studies concerning fructose, galactose, L-ascorbic acid and dopamine were also conducted. Graphical Abstract The electrochemical performances of graphene oxide and graphene-platinum hybrid nanoparticle modified G. oxydans biosensors were compared.

Description: Copper nanoclusters (Cu-NCs) were fabricated by chemical reduction of Cu(II) ions using formaldehyde as the reductant and poly(vinyl pyrrolidone) as the protecting agent. The resulting Cu-NCs were characterized by TEM, FT-IR, UV–vis and XPS and fluorescence spectroscopy. The Cu-NCs display a luminescence quantum yield of about 13 %, and the emission peaks shift from 398 to 457 nm on increasing the excitation wavelength from 310 to 390 nm. The Cu-NCs possess a storage stability of at least 2 months and are stable in the presence of high concentrations of salt. Their fluorescence is strongly quenched by hypochlorite, while other common cations, anions and hydrogen peroxide have minor (or no) effects on fluorescence. On this basis, a fluorometric hypochlorite assay was developed that has a 0.1 μM detection limit and a linear range that extends from 1 to 30 μM. The method was successfully used to the determination of hypochlorite in local tap water samples, and the results agreed well with those obtained by a colorimetric method. Graphical Abstract Hypochlorite ion is found to quench the fluorescence copper nanoclusters synthesized by reduction of Cu(II) ion by formaldehyde in the presence of poly(vinyl pyrrolidone) serving as protecting agent. This finding resulted in a new fluorescence assay for hypochlorite.

Description: A nanoporous carbon derived from an aluminum-based metal-organic framework was deposited on stainless steel wires in a sol–gel matrix. The resulting fibers were applied to the solid-phase microextraction of the polycyclic aromatic hydrocarbons (PAHs) naphthalene, acenaphthene, fluorene, phenanthrene and anthracene from water and soil samples. The fiber was then directly inserted into the GC injector and the PAHs were quantified by GC-MS. The effects of salt addition, extraction temperature, extraction time, sample volume and desorption conditions on the extraction efficiency were optimized. A linear response to the analytes was observed in the 0.1 to 12 μg∙L −1 range for water samples, and in the 0.6 to 30 μg∙kg −1 for soil samples, with the correlation coefficients ranging from 0.9934 to 0.9985. The limits of detection ranged from 5.0 to 20 ng∙L −1 for water samples, and from 30 to 90 ng∙kg −1 for soil samples. The recoveries of spiked samples were between 72.4 and 108.0 %, and the precision, expressed as the relative standard deviations, is 〈12.8 %. Graphical Abstract A MOF derived nanoporous carbon coated fiber for use in solid-phase microextraction was prepared via sol–gel technology. The coated fiber has a porous, rough and wrinkled structure, and shows a high thermal stability, good extraction repeatability and long lifetime. The established HS-SPME-GC-MS method is suitable for the determination of the PAHs from water and soil samples.

Description: We describe uniform and high-temperature-stable mesoporous TiO 2 beads functionalized with gold nanoparticles (AuNPs-TiO 2 ) for use in conductometric sensing of gases and organic vapors. The size of the interconnected main mesopores of the TiO 2 beads ranges from 8 to 15 nm, and the AuNPs have diameters between 8 and 10 nm. The mesoporous TiO 2 beads are formed during calcination while the structure-directing template agent is removed. Monodispersed AuNPs are formed by reduction in-situ and are placed inside the mesoporous TiO 2 framework. This prevents aggregation of the AuNPs even at 500 °C. The materials were characterized by UV–vis spectroscopy, scanning and transmission electron microscopy, nitrogen adsorption-desorption, and X-ray diffraction. Comb-type gold electrodes were then fabricated on an alumina substrate and are shown to display excellent properties in terms of sensing ammonia, ethanol, methanol or acetone. The sensitivity (defined as the ratio of resistivities under vapor and air) of a typical AuNPs(0.5 %)-TiO 2 gas sensor for ethanol reached up to 5.65 at above 600 ppm at 75 °C. Response time and recovery times (t 90  ≤ 20 s) are faster than (or comparable to) other metal-doped TiO 2 sensors, and working temperatures are much lower. An interesting observation was made in that the changes in the conductivity of the sensor change with temperature. The sensor prepared with AuNPs(0.5 %)-TiO 2 is of the p-type (in its response to ammonia gas) at 45 °C, but becomes n-type at 20 °C. Obviously, rather slight changes in temperature lead to a complete change in the direction of the conductometric signal change. This may provide a new aspect in terms of selective and highly sensitive detection of ammonia at ambient and slightly elevated temperatures. Graphical abstract We describe uniform and high-temperature-stable mesoporous TiO 2 beads functionalized with gold nanoparticles (AuNPs-TiO 2 ) for use in conductometric sensing of gases and organic vapors. Interestingly, the changes in the conductivity of typical sensors were opposite with the increasing of temperature.

Description: Humidity and temperature sensors were fabricated from a nanocomposite consisting of CeO 2 -Co 3 O 4 hybrid nanoparticle-silicone adhesive and CeO 2 -Co 3 O 4 hybrid nanoparticle-polymer adhesive, respectively, to fix the material on a glass supported copper electrode. The impedance of the sensor decreases by a factor of 960 at a working frequency of 100 Hz, and by a factor of 800 at 1 kHz, on increasing relative humidity (RH) from 30 to 90 %. In parallel, the capacitances increase by factors of 567 and 355, respectively, under the same experimental conditions. The effect of temperature in the range from 25 to 70 °C on impedance (again at 100 Hz and 1 kHz) was also studied and found to decrease with increasing temperature. On going from 25 to 70 °C, the impedance measured at 100 Hz and 1 kHz decreases 2.22 and 1.58 times, respectively, in surface type sensors, while in sandwich type sensors this decrease is 3.0 and 2.08 times. The calculated average sensitivity to temperature is −1.02 and −0.8 % °C −1 for the surface type and −1.5 and −1.2 % °C −1 for the sandwich type sensors at frequencies of 100 Hz and 1 kHz, respectively. Graphical abstract A highly sensitive sensor with dual functionality for humidity and temperature has been fabricated by using CeO 2 -codoped Co 3 O 4 nanoparticles with silicone and polymer adhesive.

Description: Single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT) and graphene have been tested as carbon allotropes for the modification of carbon screen-printed electrodes (CSPEs) to simultaneously determine melatonin (MT) and serotonin (5-HT). Two groups of CSPEs, both 4 mm in diameter, were explored: The first includes commercial SWCNT, MWCNT and graphene, the second includes SWCNT, MWCNT, graphene oxide nanoribbons and reduced nanoribbons that were drop casted on the electrodes. The carbon nanomaterials enhanced the electroactive area in the following order: CSPE 〈MWCNTs 〈SWCNTs 〈graphene. This allowed the simultaneous determination of 5-HT and MT at the working potentials of +50 mV and +390 mV (vs. Ag), respectively. The use of carbon nanomaterials, in particular of graphene oxide nanoribbons on CSPEs, represents an excellent and disposable tool for sensing the two target molecules in even small sample volumes. Figures of merit for MT and 5-HT include (a) detection limit of 1.1 and 0.4 μM for MT and 5-HT, respectively; (b) an inter-electrode reproducibility with RSD ≤ 8 %; (c) 120 s response time, and (d) recoveries (in case of spiked samples) ranging from 94 to 103 % (with an RSD 〈 1 %). Graphical Abstract Carbon nanomaterials on screen-printed electrodes: smart electrochemistry for fast, simultaneous and reliable detection of serotonin the molecule of happiness and melatonin the molecule of darkness.

Description: We describe a sensitive photoelectrochemical (PEC) sensor for the determination of the herbicide clethodim. The PEC sensor was constructed by using amino-MIL-125/TiO 2 (MIL stands for Materials from Institute Lavoisier), an amino-functionalized metal-organic framework (MOF) modified with TiO 2 . The amino-MIL-125/TiO 2 was synthesized by a simple one-step solvothermal method and placed on a glassy carbon electrode where it displays photoelectrocatalytic activity. Scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and X-ray diffractometry (XRD) were used to characterize the amino-MIL-125/TiO 2 . In the sensing process, amino-MIL-125/TiO 2 is illuminated by visible light to produce electrons. These excited electrons are delivered to the glassy carbon electrode, leaving positively charged holes (h + ) on the surface of the amino-MIL-125/TiO 2 . The holes react with H 2 O to generate hydroxy radicals (•OH). Clethodim rapidly attacks the hydroxy radicals and improves the efficiency of charge separation, this leading to an enhanced photocurrent. Under the optimal experimental conditions, this photoelectrochemical method enables clethodim to be quantified in the concentration range from 0.2 to 25 μmol L −1 , with a detection limit (3 S/N) of 10 nmol L −1 . The assay was applied to the determination of clethodim in soil samples, and results were in acceptable agreement with data obtained by liquid chromatography/mass spectrometry. Graphical Abstract An amino-functionalized metal-organic framework (MOF) modified with titanium dioxide was synthesized and used as a new platform for photoelectrochemical sensing of the herbicide clethodim.

Description: We report on a new amplification strategy for use in an immunoassay for influenza virus subtype H7N9. Graphene sheets were first placed on a glassy carbon electrode (GCE), and gold nanoparticles were then electrodeposited as a support for a layer of alcohol dehydrogenase (ADH) in a sol–gel containing thiol groups. Protein A was used to properly orientate immobilized antibody against H7N9 on the sol–gel, and this is shown to result in strongly improved specificity of the antigen-antibody binding. Thus, a sensitive and specific immunosensor was obtained in which a quadruple signal amplification strategy is employed, viz. (a) via the use of graphene sheets, (b) via a hybridization chain reaction, (c) the use of hemin/G-quadruplex DNAzyme concatamers, and (d) the use of ADH. The hemin/G-quadruplex is a typical DNAzyme, which simultaneously acts as NADH oxidase and HRP-mimicking DNAzyme. The hybridization chain reaction-based DNAzyme concatamers assembled on multi-walled carbon nanotubes (MWCNTs) and the ADH represent a triple electrocatalytic enzyme cascade system. Sandwich immunoreactions occurred between the capture antibody on the electrode and the secondary antibody labeled with MWCNTs. Positively charged Methylene Blue (MB) was then used as an intercalator to detect the DNAzyme concatamer formed. The differential pulse voltammetric signals for MB are related to the concentration of H7N9 in the range from 8 to 60 pg · mL −1 , and the detection limit is 0.81 pg · mL −1 (at an S/N ratio of 3). This immunoassay is very sensitive, specific and robust. Graphical Abstract An electrochemical sandwich immunosensor has been developed for sensitive and specific detection of influenza virus subtype H7N9. Protein A was used to properly orientate antibody. The hybridization chain reaction based DNAzyme concatamers assembled on multi-walled carbon nanotubes (MWCNTs) and the ADH represent a triple electrocatalytic enzyme cascade system.

Description: We describe a turn-off fluorescence-based strategy for the detection of ATP by making use of aptamer-triggered dsDNA concatamers. This sensitive and easily controlled method is based on consecutive hybridization induced by ATP aptamers and their sectional complementary DNAs to form dsDNA concatamers. The intercalator SYBR Green I (SGI) was employed as a fluorescent probe. In the absence of ATP, the probe produces a strong signal. However, on addition of ATP, the binding of aptamer and ATP cause the concatamers to collapse and to release SGI whose fluorescence then is quenched. The effect was exploited to design a selective ATP assay by relating the decrease in fluorescence to the ATP concentration. A lower detection limit of 6.1 μM and a linear response in the 0 to 5000 μM concentration range was accomplished. The strategy was applied to cellular ATP assays, and the results obtained by this strategy and by the gold standard method are in good agreement. The method is sensitive, simple and cost efficient, and hence is promising in terms of future applications to determine ATP in cellular and other systems. Graphical Abstract A turn-off fluorescence-based strategy for the selective detection of ATP by using aptamer-triggered dsDNA concatamers.

Description: A molecularly imprinted polymer (MIP) was prepared by self-polymerization of dopamine in the presence of bovine hemoglobin (BHb) and then deposited on the surface of an electrode modified with gold nanoparticles (AuNPs). Scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry were employed to characterize the modified electrode using the hexacyanoferrate redox system as an electroactive probe. The effects of BHb concentration, dopamine concentration, and polymerization time were optimized. Under optimized conditions, the modified electrode selectively recognizes BHb even in the presence of other proteins. The peak current for hexacyanoferrate, typically measured at + 0.17 V (vs. SCE), depends on the concentration of BHb in the 1.0 × 10 −11 to 1.0 × 10 −2  mg mL −1 range. Due to the ease of preparation and tight adherence of polydopamine to various support materials, the present strategy conceivably also provides a platform for the recognition and detection of other proteins. Graphical Abstract Gold nanoparticles and molecularly imprinted self-polymerization dopamine were modified on gold electrode surface to recognize and determine bovine hemoglobin. Under the optimized conditions, the modified electrode showed specific adsorption, selective recognition, and sensitive detection of bovine hemoglobin.

Description: We report on an electrochemical method for the determination of the activity of trypsin. A multi-functional substrate peptide (HHHAKSSATGGC-HS) is designed and immobilized on a gold electrode. The three His residues in the N-terminal are able to recruit thionine-loaded graphene oxide (GO/thionine), a nanocover adopted for signal amplification. Once the peptide is cleaved under enzymatic catalysis by trypsin (cleavage site: Lys residue), the His residues leave the electrode, and the GO/thionine cannot cover the peptide-modified electrode anymore. Thus, the changes of the electrochemical signal of thionine, typically acquired at a voltage of -0.35 V, can be used to determine the activity of trypsin. A detection range of 1 × 10 −4 to 1 U, with a detection limit of 3.3 × 10 −5  U, can be achieved, which is better than some currently available methods. In addition, the method is highly specific, facile, and has the potential for the detection of trypsin-like proteases. Graphical abstract Graphene oxide was adopted as a nanocover for the development of a sensitive electrochemical method to detect the activity of trypsin.

Description: We report on the microwave-assisted synthesis of ultrasmall Ce 3+ and Tb 3+ -doped SrF 2 nanocrystals (NCs) capped with glutathione (GSH). The NCs have an average size of about 5 nm and show bright green fluorescence upon photoexcitation at 290 nm. Fluorescence is strongly quenched by Hg(II) and Pb(II). This finding was applied to design a method for the fairly selective determination of these ions. The detection limits (for the 3σ/slope criterion) are 20 μM and 30 μM for Hg(II) and Pb(II) ions, respectively. The intensity of the luminescence can be restored by the addition of ethylenediaminetetraacetic acid (EDTA), and this suggests that these NCs can be used as reusable fluorescent probes. Graphical Abstract Scheme illustrating the metal induced change in the binding modality of GSH ligand upon addition of metal (M) ions and EDTA solution through metal-ligand interaction.

Description: We describe a novel magnetic nanosorbent that consists of nanowires consisting of a core of metallic iron and an iron (III) oxide shell. These nanowires were then deposited on graphene oxide to form a composite of the type Fe@Fe 2 O 3 /GO. Specifically, the magnetic composite is formed via electrostatic interaction between negatively charged GO nanosheets and positively charged Fe@Fe 2 O 3 nanowires in aqueous solution. The material was successfully applied to the extraction of the endocrine-disrupting phenols bisphenol A, triclosan and 2,4-dichlorophenol from water samples. Compared to neat graphene oxide, the composite material exhibits improved properties in terms of microextraction where both the hydrophilic graphene oxide and the Fe@Fe 2 O 3 nanowires participate in the adsorption of the hydrophilic analytes. The amount of adsorbent, pH of water sample, extraction time and desorption time, type and volume of desorption solution were optimized. Following extraction for the absorbent, the phenols were quantified by HPLC. The three phenols can be determined in 0.5 to 100 ng∙mL −1 concentration range, with limits of detection (at an S/N ratio of 3) ranging from 0.08 to 0.10 ng∙mL −1 . The repeatability was investigated by evaluating the intra- and inter-day precisions with relative standard deviations of lower than 7.5 % ( n  = 5). The recoveries from spiked real water samples were in the range from 84.8 to 92.0 %. The results indicate that the novel material can be successfully applied to the extraction and analysis of phenols from water samples. Graphical Abstract Scheme 1 procedure for the synthesis of Fe@Fe 2 0 3 /G0

Description: Immobilization of proteins on a solid support is critical with respect to the fabrication and performance of biosensors and biochips. Protein attachment with a preferable orientation can effectively avoid its denaturation and keeps its active sites fully exposed to solution, thus maximally preserving the bioaffinity or bioactivity. This review (with 140 refs.) summarises the recent advances in oriented immobilization of proteins with a particular focus on antibodies and enzymes. Following an introduction that describes reasons for oriented immobilization on (nano)surfaces, we summarize (a) methods for (bio)chemical affinity-mediated oriented immobilization (with sections on immunoglobulin G (IgG)-binding protein as the capture ligand, DNA-directed immobilization, aptamer- and peptide-mediated immobilization, affinity ligand and fusion tag-mediated immobilization, material-binding peptide-assisted immobilization); (b) methods for covalent oriented immobilization (with sections on immobilization via cysteine residues or cysteine tags, via carbohydrate moieties; via enzyme fusion or enzymatic catalysis, and via nucleotide binding sites of antibodies); (c) methods based on molecular imprinting techniques; (d) methods for characterization of oriented immobilized proteins; and then make conclusions and give perspectives. Graphical Abstract This review summarises recent advances in oriented immobilization of proteins based on strategies via bio−/chemical affinity, covalent bonding, and molecular imprinting techniques. Advantages and disadvantages of each approach are discussed.

Description: Magnetic oleate-coated Fe 3 O 4 nanoparticles were applied to the extraction of PCBs from fruit juices that were quantified by gas chromatography coupled to triple quadrupole mass spectrometry. Two methods were evaluated: The first method involves a two-step procedure that combines dispersive liquid-liquid microextraction with dispersive micro-solid phase extraction, and the second one involves magnetic solid-phase extraction (mSPE) carried out in a single step. The mSPE procedure is shown to be more sensitive, and therefore, it was optimized and applied to the analysis of PCBs in juices. The detection limits for all target PCBs are below 6 ng∙L −1 for apple juice, and 3 ng∙L −1 for grape juice. The enrichment factor is 125. Analysis of spiked fruit juice samples gave relative recoveries higher than 70 % for all PCBs except for PCB28 and PCB52. Graphical Abstract Diagram of the extractive methods using magnetic nanoparticles (MNPs): A ) two-step method combining dispersive liquid-liquid microextraction (DLLME) with dispersive micro solid-phase extraction (D-μ-SPE) and B ) one-step magnetic solid-phase extraction (mSPE) procedure

Description: Thin-layered molybdenum disulfide (MoS 2 ) was intercalated, via ultrasonic exfoliation, into self-doped polyaniline (SPAN). This material, when placed on a glassy carbon electrode (GCE), exhibits excellent electrical conductivity and synergistic catalytic activity with respect to the detection of bisphenol A (BPA). The electrochemical response of the modified GCE to BPA was investigated by cyclic voltammetry and differential pulse voltammetry. Under optimal conditions, the oxidation peak current (measured best at 446 mV vs. SCE) is related to the concentration of BPA in the range from 1.0 nM to 1.0 μM, and the detection limit is 0.6 nM. Graphical Abstract Thin-layered molybdenum disulfide (MoS 2 ) was intercalated into self-doped polyaniline (SPAN) via ultrasonic exfoliation. The special conjugated structure and functional groups of MoS 2 -SPAN composite help to adsorb BPA easily. MoS 2 -SPAN has a synergistic effect for catalyzing the oxidation of BPA. The BPA electrochemical sensor based on MoS 2 -SPAN has a high sensitivity and low detection limit.

Description: We have synthesized nitrogen-doped graphene nanoribbons (N-GrNRs) by unzipping multi-walled carbon nanotubes (CNTs) under strongly oxidizing conditions and subsequent doping with nitrogen by a low-temperature hydrothermal method. The N-GNRs were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy, and assembled on a disposable screen-printed carbon electrode to give a sensor for H 2 O 2 that was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry and chronoamperometry. The nano-modified electrode displays enhanced electron transfer ability, and has a large active surface and a large number of catalytically active sites that originate from the presence of nitrogen atoms. This results in a catalytic activity towards H 2 O 2 reduction at near-neutral pH values that is distinctly improved compared to electrodes modified with CNTs or unzipped (non-doped) CNTs only. At a working potential of −0.4 V (vs. Ag/AgCl), the amperometric responses to H 2 O 2 cover the 5 to 2785 μM concentration range, with a limit of detection as low as 1.72 μM. This enzyme-free electrochemical sensor exhibits outstanding selectivity and long-term stability for H 2 O 2 detection. Graphical Abstract Nitrogen-doped graphene nanoribbons (N-GrNRs) were expediently synthesized for highly sensitive and selective detection of H 2 O 2 .

Description: We have investigated the possibility of sampling ammonium ion using the diffusive-gradients-in-thin-films technique (DGT) by introducing a novel binding agent that is based on micro-sized zeolite. The performance of zeolite-DGT was characterized by measurement of the following parameters: (1) the diffusion coefficient of ammonium ion in hydrogel; (2) the adsorption rate of ammonium ion by the zeolite binding gel; (3) the elution efficiency, and (4) the effects of pH, ionic strength and interfering ions on DGT. The method was validated by studying the uptake of ammonium ion from in freshwaters by zeolite gels which was found to be fast enough to meet the requirements of DGT. The concentrations determined via DGT agreed well with the concentrations determined in bulk solutions. Sampling of ammonium ion using zeolite-DGT was consistent over the pH 3 to 8 range and the 0.001 to 10 mM ionic strength range. The method also performs predictably in natural waters containing various metal ions. The technique is considered to be a viable passive tool for sampling ammonium from aqueous solutions. Graphical Abstract Schematic representation of the principle of DGT and the determination of mass accumulated on the binding gel.

Description: We report on a method for the determination of magnetic bead-labeled C-reactive protein (CRP), a biomarker of cardiovascular diseases and inflammations. It is using a flexible giant magnetoimpedance (GMI)-based platform. Micro-patterned GMI sensing elements were prepared from a cobalt-based commercial amorphous ribbon (Metglas® 2714A) using micro electro-mechanical system (MEMS) technology. A gold film was then deposited on the GMI sensing element to act as a support for the immuno platform. Sandwich assays are performed using antibody-antigen combinations and biotin-streptavidin interactions on the gold film substrate surface via self-assembled layers. The GMI ratios of the sensors with different concentrations of antigen against CRP were investigated. The results show that the presence of CRP antigens on the biosensor improves the GMI effect owing to the induced magnetic dipole of superparamagnetic beads, and that the GMI ratios show distinct changes at high frequency. This bioassay for CRP has a linear detection range between 1 to 10 ng·mL −1 . This new method in our perception provides a widely applicable basis for rapid diagnostic testing and will pave the way for future development of electrochemical point-of-care diagnostic devices for cardiac diseases. Graphical Abstract (a) Graphical illustration of CRP test setup. (b) Magnetic field arrangement of the beads under an applied magnetic field. (c) GMI changes in relation to the concentration of the CRP

Description: We describe the fairly easy preparation of thiol stabilized water soluble cadmium sulfide quantum dots and the modification of their surface with the human transferrin protein siderophiline. The particles are shown to enable targeted imaging of human breast adenocarcinoma cell (type MCF7). The fluorescence quantum yield of the modified QDs is ~0.74. The particles have an average diameter of 8.1 ± 0.1 nm as determined in solution by dynamic light scattering. The cancer cells were imaged by fluorescence microscopy of the QDs which display strong green fluorescenece under 350 nm excitation. A cytotoxicity assay showed 66 and 78 % cell viabilities, respectively, after 24 h of incubation with the QDs and modified QDs. Graphical Abstract Water-soluble cadmium sulfide QDs were modified with siderophiline (transferrin) and applied to fluorescent and targeted imaging of breast cancer cells. Left: control (human breast cancer cells (type MCF-7) were treated with QDs without siderophiline); right: human breast cancer cells (type MCF-7) treated with siderophiline modified QDs

Description: We describe the preparation of carbon dots (CDs) from glucose that possess high stability, a quantum yield of 0.32, and low toxicity (according to an MTT assay). They were used, in combination with the fluorogenic zinc(II) probe quercetin to establish a fluorescence resonance energy transfer (FRET) system for the determination of Zn(II). The CDs are acting as the donor, and the quercetin-Zn(II) complex as the acceptor. This is possible because of the strong overlap between the fluorescence spectrum of CDs and the absorption spectrum of the complex. The method enables Zn(II) to be determined in the 2 to 100 μM concentration range, with a 2 μM detection limit. The method was applied to image the distribution of Zn(II) ions in HeLa cells. Graphical Abstract Based on the fluorescence resonance energy transfer (FRET) between carbon dots and quercetin (QCT)-Zn 2+ , the fluorescence indicator was established, which displays high sensitivity and selectivity in the detection of Zn 2+ . The method was also applied to image the distribution of Zn(II) ions in HeLa cells.

Description: Sensitive detection of engineered nanoparticles (NPs) in air and in liquid samples is an important task and still a major challenge in analytical chemistry. Recent work demonstrated that it can be performed using surface plasmon microscopy (SPM) where binding of single NPs to a surface leads to the formation of characteristic patterns in differential SPM images. However, these patterns have to be discriminated from a noisy background. Computer-assisted recognition of nanoparticles offers a solution but requires the development of respective tools for data analysis. Hereby a numerical method for automated detection and characterization of images of single adsorbing NPs in SPM image sequences is presented. The detection accuracy of the method was validated using computer generated images and manual counting. The method was applied for detecting and imaging of gold and silver NPs adsorbing from aqueous dispersions and for soot and NaCl NPs adsorbing from aerosols. The determined adsorption rate was in range 0.1–40 NPs per (s mm 2 ) and linearly dependent on the concentration of nanoparticles. Depending on the type of NPs and signal to noise ratio, a probability of recognition of 90–95 % can be achieved. Graphical Abstract A computer-assisted method is presented for the detection and characterization of images of single adsorbing nanoparticles in surface plasmon microscopy images. The method was validated and can be applied to detecting and imaging of nanoparticles absorbed from aqueous dispersions and aerosols.

Description: This article describes a new procedure for multi-element preconcentration of heavy metal ions, specifically of Cr(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II) ions. The method is based on dispersive micro solid-phase extraction (DMSPE) of the metal complexes of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) by graphene oxide nanoparticles prior to energy dispersive X-ray fluorescence spectrometric (EDXRF) determination. The effects of pH, amount of graphene oxide, concentration of complexing reagent, sample volume and sorption time were optimized. The influence of commonly encountered other ions was also investigated. Under optimal conditions, the calibration plots cover the 2 to 150 ng mL −1 range for each element. The precision (at a 20 ng mL −1 level for n  = 10) is lower than 4.8 %, and the detection limits range is from 0.07 to 0.25 ng mL −1 . The DMSPE-EDXRF procedure was successfully applied to the determination of heavy metal ions in water and spiked water samples with recoveries between 94.4 and 103.5 %. Graphical Abstract Schematic of the dispersive solid-phase microextraction of metal complexes of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) using graphene oxide nanoparticles, followed by their energy dispersive X-ray fluorescence spectrometric determination.

Description: Alloy nanoparticles of the type Pt x Fe (where x is 1, 2 or 3) were synthesized by coreduction with sodium borohydride in the presence of carbon acting as a chemical support. The resulting nanocomposites were characterized by scanning electron microscopy and X-ray diffraction. The nanocomposite was placed on a glassy carbon electrode, and electrochemical measurements indicated an excellent catalytic activity for the oxidation of glucose even a near-neutral pH values and at a working voltage as low as 50 mV (vs. SCE). Under optimized conditions, the sensor responds to glucose in the 10.0 μM to 18.9 mM concentration range and with a 3.0 μM detection limit (at an S/N ratio of 3). Interferences by ascorbic acid, uric acid, fructose, acetamidophenol and chloride ions are negligible. Graphical Abstract Nonenzymatic sensing of glucose is demonstrated at neutral pH values and low working potential using a glassy carbon electrode modified with platinum-iron alloy nanoparticles on a carbon support.

Description: A single glass conical nanopore functionalized with 6-carboxymethyl-chitosan (CMC) was applied to study the binding of bovine serum albumin (BSA) because of both hydrophobic and hydrophilic interactions. The interactions between the CMC-modified nanopore and BSA within the confined space were studied via the ionic current passing the nanopore by measuring the current–voltage (I–V) curves in 10 mM KCl solution. The hydrophilicity of CMC was varied by adjusting the pH values. Significant changes in the ionic current were observed following attachment of BSA. The relative contributions of hydrophobic and hydrophilic interactions depend on whether solutions are acidic or basic. A linear relationship exists between the concentration of BSA (up to 500 nM) and the ionic current at pH 12. This suggests a potential application of the method for sensing proteins via sweep voltammetry on a nanoscale. The nanodevice described here can be made reversible by ultrasonication to remove the attached BSA molecules. Graphical Abstract A single glass conical nanopore functionalized with 6-carboxymethyl-chitosan (CMC) was used to study the hydrophobic/hydrophilic association with BSA molecules both in acid and basic conditions by using sweep voltammetry. A linear relationship between the concentration of additional BSA and the ionic current of the nanopore at pH 12 was achieved, which suggests a promising application in biosensing of proteins.

Description: Co@Pt core-shell nanoparticles (NPs) were synthetized by a two-step reductive method using carbon (Vulcan XC-72) as a solid support. The NPs were characterized by X-ray diffraction, field emission gun scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. Their electrochemical performance was evaluated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry, and these showed that the Co@Pt NPs display an electrocatalytic activity towards the oxidation of glucose that is much better than that of plain Pt NPs. Under optimized conditions and at pH 7.0, the oxidation current of glucose at a working potential of −50 mV (vs. SCE) is linearly related to its concentration in the 1.0 to 30 mM range, and the detection limit is 0.3 mM (S/N = 3). It therefore covers the clinical range. The sensor also exhibits excellent stability and repeatability. Graphical abstract Co@Pt core-shell nanoparticles (NPs) display an electrocatalytic activity towards the oxidation of glucose that is much better than that of plain Pt NPs. The oxidation current for glucose is linearly related to its concentration in the 1.0 to 30 mM range, and the detection limit is 0.3 mM (S/N =3).

Description: We report on a simple, sensitive and regenerable fluorescent nanoprobe for Zn(II) ion. It is based on the use of glutathione capped CdTe quantum dots (GSH-CdTe Q-dots). The bright fluorescence of these Q-dots is quenched on addition of diethylenetriaminepentaacetic acid (DTPA) due to the binding of DTPA to GSH. If, however, Zn(II) is added, it will bind DTPA and detach it from the surface of the Q-dots, this resulting in the fluorescence recovery. Under optimum conditions, the intensity of the restored fluorescence is proportional to the concentration of Zn(II) in the 0.48 to 90 μmol · L −1 range, with a limit of detection of 0.14 μmol · L −1 . The nanoprobe was applied to the determination of Zn(II) in spiked tap water and river water and gave satisfactory results. The findings were also applied to design a molecular logic gate where DTPA acts as the first input to the system by quenching the fluorescence of the GSH-CdTe Q-dots. Zn(II) acts as the second input and causes the detachment of DTPA from the Q-dots and a restoration of fluorescence. This system therefore represents a new IMP (IMPLICATION) logic gate. Graphical Abstract We describe a fluorescent nanoprobe for Zn(II) based on quantum dots, and its use in an IMP molecular logic gate. The nanoprobe was successfully applied to the determination of Zn(II) in spiked tap water and river water.

Description: We describe a nonenzymatic electrochemical sensor for uric acid. It is based on a carbon nanotube ionic-liquid paste electrode modified with poly(β-cyclodextrin) that was prepared in-situ by electropolymerization. The functionalized multi-walled carbon nanotubes and the surface morphology of the modified electrodes were characterized by transmission electronic microscopy and scanning electron microscopy. The electrochemical response of uric acid was studied by cyclic voltammetry and linear sweep voltammetry. The effects of scan rate, pH value, electropolymerization cycles and accumulation time were also studied. Under optimized experimental conditions and at a working voltage of 500 mV vs. Ag/AgCl (3 M KCl), response to uric acid is linear in the 0.6 to 400 μΜ and in the 0.4 to 1 mΜ concentration ranges, and the detection limit is 0.3 μΜ (at an S/N of 3). The electrode was successfully applied to the detection of uric acid in (spiked) human urine samples. Graphical Abstract SEM images of ( a ) carbon ionic liquid electrode (CILE) ( b ) MWNT-CILE ( c ) β-CD/CILE ( d ) β-CD/ MWNT-CILE. The surfaces of carbon ionic liquid electrode (CILE) ( a ) and MWNT-CILE ( b ) were homogenous and no separated carbon layers can be observed; After β- cyclodextrin (CD) was modified on CILE and MWNT-CILE, the surfaces of β-CD modified electrodes ( c and d ) exhibited loose and porous morphologies.

Description: The authors describe an electrochemical immunoassay for α-fetoprotein (α-FP) using a glassy carbon electrode (GCE) modified with a nanocomposite made from gold nanoparticles, graphene oxide and multi-walled carbon nanotubes (AuNPs/GO-MWCNTs) and acting as a signal amplification matrix. The nanocomposite was synthesized in a one-pot redox reaction between GO and HAuCl 4 without using an additional reductant. The stepwise assembly of the immunoelectrode was characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy. The interaction of antigen and antibody on the surface of the electrode creates a barrier for electrons and causes retarded electron transfer, this resulting in decreased signals in differential pulse voltammetry of hexacyanoferrate which is added as an electrochemical probe. Using this strategy and by working at a potential of 0.2 V (vs. SCE), a wide analytical range (0.01 - 100 ng∙mL‾ 1 ) is covered. The correlation coefficient is 0.9929, and the limit of detection is as low as 3 pg∙mL‾ 1 at a signal-to-noise ratio of 3. This electrochemical immunoassay combines the specificity of an immunological detection scheme with the sensitivity of an electrode modified with AuNPs and GO-MWCNTs. Graphical Abstract Schematic illustration of the fabrication procedure of the immunosensor

Description: We describe an electrochemical sensor for nitric oxide that was obtained by modifying the surface of a nanofiber carbon paste microelectrode with a film composed of hexadecyl trimethylammonium bromide and nafion. The modified microelectrode displays excellent catalytic activity in the electrochemical oxidation of nitric oxide. The mechanism was studied by scanning electron microscopy and cyclic voltammetry. Under optimal conditions, the oxidation peak current at a working voltage of 0.75 V (vs. SCE) is related to the concentration of nitric oxide in the 2 nM to 0.2 mM range, and the detection limit is as low as 2 nM (at an S/N ratio of 3). The sensor was successfully applied to the determination of nitric oxide released from mouse hepatocytes. Graphical abstract NO electrochemical sensor based on CTAB-Nafion/CNFPME was fabricated through a simple method and applied to detect NO released from mouse hepatocytes successfully.

Description: Two-dimensional carbon nanomaterials ranging from single-layer graphene to defective structures such as chemically reduced graphene oxide were studied with respect to their use in electrodes and sensors. Their electrochemical properties and utility in terms of fabrication of sensing devices are compared. Specifically, the electrodes have been applied to reductive amperometric determination of hydrogen peroxide. Low-defect graphene (SG) was obtained through mechanical exfoliation of natural graphite, while higher-defect graphenes were produced by chemical vapor deposition (CVDG) and by chemical oxidation of graphite and subsequent reduction (rGO). The carbonaceous materials were mainly characterized by Raman microscopy. They were applied as electrode material and the electrochemical behavior was investigated by chronocoulometry, cyclic voltammetry, electrochemical impedance spectroscopy and amperometry and compared to a carbon disc electrode. It is shown that the quality of the graphene has an enormous impact on the amperometric performance. The use of carbon materials with many defects (like rGO) does not result in a significant improvement in signal compared to a plain carbon disc electrode. The sensitivity is 173 mA · M −1  · cm −2 in case of using CVDG which is about 50 times better than that of a plain carbon disc electrode and about 7 times better than that of rGO. The limit of detection for hydrogen peroxide is 15.1 μM (at a working potential of −0.3 V vs SCE) for CVDG. It is concluded that the application of two-dimensional carbon nanomaterials offers large perspectives in amperometric detection systems due to electrocatalytic effects that result in highly sensitive detection. Graphical abstract Graphene materials prepared by different techniques were studied as electrode material for the electrochemical detection of H 2 O 2 . Materials comprising a less defective structure showed a significantly higher sensitivity.

Description: A pH responsive nanogel composed of magnetite (Fe 3 O 4 ), silica and poly(4-vinylpyridine) was designed and utilized as an adsorbent for the simultaneous separation of ultra-trace amounts of cadmium, lead, copper and nickel ions. This solid phase extraction system was characterized by Fourier transform infrared spectrometry, transmission electron microscopy and X-ray diffraction analysis. The sorbent can be separated from the sample solution by applying an external magnetic field, and the analytes eluted with 1 M hydrochloric acid. The extracted ions were quantified by flame atomic absorption spectrophotometry. Effects of pH value, adsorption and desorption time, type, concentration and volume of the eluent, breakthrough volume, and effect of potentially interfering ions were studied. Under optimized conditions, the extraction efficiency is 〉98 %, the limits of detection are 0.03, 0.2, 0.6 and 0.9 ng mL −1 for Cd(II), Cu(II), Ni(II) and Pb(II), respectively, and the adsorption capacities for these ions are 52, 61, 75 and 65 mg g −1 . The sorbent has a high affinity for the above target ions. Eventually, the pH responsive system was used for rapid, efficient, fairly selective and highly sensitive extraction of these ions from various water samples. Graphical Abstract We describe a magnetite-silica-poly(4-vinylpyridine) nanogel that is pH-responsive and can act as a sorbent for the extraction of Cd(II), Cu(II), Ni(II) and Pb(II).

Description: We describe a facile method for the preparation of magnetic microparticles consisting of a metal-organic framework (MOF) of Cu(II)-BTC (BTC = 1,3,5-benzenetricarboxylate) for rapid magnetic solid-phase extraction (MSPE) of the dye Congo Red (CR) from aqueous solution. Magnetization of the MOF and solid-phase extraction of CR was simultaneously accomplished by mixing, under ultrasonication, the MOF and silica-coated magnetite microparticles in the solution to be extracted. Under optimized conditions, the magnetic MOF hybrid exhibits a fast adsorption rate and a high removal efficiency (〉97 %) toward CR even over 15-fold reuse, which also features high adsorption capacity of 97.7 and 92.5 % for cationinc Methylene Blue (MB) and Crystal Violet (CV), respectively. The desorption of CR from the magnetic MOF was realized by washing it with ethanol and water. The material is considered to be a promising new adsorbent for use in wastewater treatment and in analytical preconcentration. Graphical abstract We report on a method for magnetization of a Cu-BTC metal-organic framework for use in rapid magnetic solid phase extraction of Congo Red from aqueous solutions. The material maintains its high removal efficiency (of 〉97 %) over 15 recyclable experiments.

Description: We describe a nanostructured immunosensor for the cardiovascular biomarker netrin 1. A glassy carbon electrode was consecutively modified with multi-walled carbon nanotubes (MWCNTs), nafion (to retain the MWCNTs), thionine-coated gold nanoparticles (Thi@AuNPs), and monoclonal antibodies against netrin 1. The modified electrode was characterized by transmission electron microscopy, cyclic voltammetry, differential pulse voltammetry, UV-visible spectrophotometry and X-ray diffraction. The presence of Thi@AuNPs warrants direct and convenient immobilization of the antibody. This immunoelectrode enables netrin 1 to be determined, best at a voltage of −300 mV (vs. SCE), with a limit of detection of 30 fg mL −1 (at an S/N ratio of 3) after a 50 min incubation time. The detection range extends from 0.09 to 1800 pg∙mL −1 . The method is simple, sensitive, specific and reproducible. We presume this stable and reproducible biosensor to be useful for the early detection of cardiovascular diseases. Graphical Abstract A high sensitivity immunoassay was developed for the detection of netrin 1 based on multi-walled carbon nanotubes, thionine and gold nanoparticles. Its excellent performance is ascribed to the good conductivity of MWCNTs and the combination of materials.

Description: We describe a simple, highly sensitive, and selective colorimetric kinetic assay for the determination of potassium(I) by exploiting the specific recognition capability of an appropriate aptamer and catalytic signal amplification by gold nanoparticles (AuNPs). Amplification is based on the reduction of 4-nitrophenol by borohydride which is catalyzed by AuNPs. This leads to a color change of the solution from yellow to colorless, and the color change can be recognized with bare eyes or via photometry. The K(I)-selective aptamer is placed on the AuNPs and forms a tightly bound G-quadruplex with K(I) which partially masks the surface of the AuNPs and prevents 4-nitrophenol to be reduced at the catalytically active surface of the AuNPs. Hence, the rate of decoloration is retarded. The assay displays high selectivity for K(I) over other cations, has a linear response in the 0.1 nM to 10 μM concentration range, and a detection limit as low as 0.06 nM. In addition, these findings pave the way to novel analytical methods based on the use of gold nanoparticle-catalyzed chemical reactions. Graphical Abstract A simple, highly sensitive, and selective colorimetric kinetic assay for the determination of potassium(I) was represented.

Description: We describe a single-step solvothermal method for the preparation of nanocomposites consisting of graphene oxide and Fe 3 O 4 nanoparticles (GO/Fe 3 O 4 ). This material is shown to be useful as a magnetic sorbent for the extraction of flavonoids from green tea, red wine, and urine samples. The nanocomposite is taking advantage of the high surface area of GO and the magnetic phase separation feature of the magnetic sorbent. The nanocomposite is recyclable and was applied to the extraction of flavonoids prior to their determination by HPLC. The effects of amount of surfactant, pH value of the sample solution, extraction time, and desorption condition on the extraction efficiency, and the regeneration conditions were optimized. The limits of detection for luteolin, quercetin and kaempferol range from 0.2 to 0.5 ng∙ mL −1 in urine, from 3.0 to 6.0 ng∙mL −1 in green tea, and from 1.0 to 2.5 ng∙mL −1 in red wine. The recoveries are between 82.0 and 101.4 %, with relative standard deviations of 〈9.3 %. Graphical abstract The article describes a method for magnetic solid-phase extraction (MSPE) of trace amounts of natural substances in complex samples by using graphene oxide (GO)-Fe 3 O 4 nanoparticles as the sorbent.

Description: The surface of CdTe quantum dots (Q-dots) was modified with thioglycolic acid (TGA) and these Q-dots were then covalently conjugated to amino-functionalized silica-coated carbon dots (C-dot@SiO 2 ) via carbodiimide chemistry. The Q-dots form kind of “satellites” on the surface of the C-dot@SiO 2 nanoparticles. The nanoparticle conjugates display dual emission (with peaks at 441 nm and 605 nm) under UV excitation and were further characterized by transmission electron microscopy, UV–vis absorption and FTIR spectroscopy. The C-dot@SiO 2 @Q-dots hybrid spheres are shown to represent a ratiometric fluorescent probe for Cu 2+ in that the emission of the Q-dots is quenched by Cu 2+ , while the emission of the C-dots (which are coated with SiO 2 ) is not quenched. The ratio of the fluorescence intensities at 441 and 655 nm is related to the concentration of Cu 2+ in the range from 0.1 to 1.0 μM, with a 0.096 μM lower detection limit. The ratiometric probe was successfully applied to the determination of Cu 2+ in (spiked) vegetable and fruit samples by the standard addition method, and recoveries ranged from 96.7 to 100.8 %. Graphical Abstract Carbon dots were first coated with silica and then with CdTe quantum dots to give nanoparticles with an architecture of the type C-dot@SiO 2 @Q-dots. These are shown to be a viable ratiometric fluorescent probe for the detection of Cu(II).

Description: Alumina (Al 2 O 3 ) with an average particle size of 63 μm was modified with the anionic surfactant sodium dodecyl sulfate (SDS) and then applied to (i) solid phase extraction and separation of both thallium(I) and thallium(III), and (ii) preconcentration of Tl(III) from waste water samples. Only Tl(III), in the form of its complex with diethylenetriaminepentaacetate (DTPA), was retained on the sorbent, from where it can be eluted with 40 % nitric acid. Thallium species were then quantified by ICP MS. The method was characterized by a LOD of 25 pg of Tl(I) and 160 pg of Tl(III) in 10 mL samples. A large excesses of Tl(I) over Tl(III) was tolerated, and relatively high levels of other metal ions, such as a 500-fold excess of Pb(II) and Cd(II), and a 2000-fold excess of Zn(II), respectively, do not interfere. The sorbent was easily prepared and possesses a high loading capacity, and these properties make it an attractive material for rapid and efficient extraction and speciation of Tl. Graphical abstract: Schematic of the SPE procedure for separation (with preconcentration) of Tl(III) from Tl(I) was developed and applied to direct speciation analysis of thallium in wastewater. Self-made columns packed with alumina coated with SDS were used. The method is resistant to interferences from Pb, Cd, Zn and tolerates a large excess of Tl(I) over Tl(III).

Description: Reduced graphene oxide (RGO) was used to construct a bienzyme biosensor containing horseradish peroxidase (HRP) and glucose oxidase (GOx). A poly(toluidine blue) (pTB) film containing RGO acted as both enzyme immobilization matrix and electron transfer mediator. The bienzyme biosensor was characterized by electrochemical techniques and displays a highly sensitive amperometric response to glucose and hydrogen peroxide (H 2 O 2 ) at a potential as low as −0.1 V (vs. SCE). It is shown that use of RGO causes a strong enhancement on the amperometric responses. H 2 O 2 formed by the action of GOx in the presence of oxygen can be further reduced by HRP in the pTB film contacting the RGO modified electrode. In the absence of oxygen, glucose oxidation proceeds by another mechanism in which electron transfer occurs from GOx to the electrode and with pTB acting as the mediator. Amperometric responses to glucose and H 2 O 2 follow Michaelis-Menten kinetics. The experimental conditions were optimized, and under these conditions glucose can be determined in the 80 μM to 3.0 mM range with a detection limit of 50 μM. H 2 O 2 , in turn, can be quantified in up to 30.0 μM concentration with a detection limit of 0.2 μM. The bienzyme biosensor is reproducible, repeatable and stable. Finally, it has been successfully applied to the determination of glucose in plasma samples. Graphical Abstract Schematic representation of glocuse detection at GCE/RGO/pTB-HRP-GOx.

Description: The authors describe an efficient method for microextraction and preconcentration of trace quantities of cationic nitrogen compounds, specifically of anilines. It relies on a combination of electrochemically controlled solid-phase microextraction and on-line in-tube solid-phase microextraction (SPME) using polypyrrole-coated capillaries. Nanostructured polypyrrole was electrically deposited on the inner surface of a stainless steel tube and used as the extraction phase. It also acts as a polypyrrole electrode that was used as a cation exchanger, and a platinum electrode that was used as the anode. The solution to be extracted is passed over the inner surface of the polypyrrole electrode, upon which cations are extracted by applying a negative potential under flow conditions. This method represents an ideal technique for SPME of protonated anilines because it is fast, easily automated, solvent-free, and inexpensive. Under optimal conditions, the limits of detection are in the 0.10–0.30 μg L‾ 1 range. The method works in the 0.10 to 300 μg L‾ 1 concentration range. The inter- and intra-assay precisions (RSD%; for n  = 3) range from 5.1 to 7.5 % and from 4.7 to 6.0 % at the concentration levels of 2, 10 and 20 μg L‾ 1 , respectively. The EC-in-tube SPME method was successfully applied to the analysis of methyl-, 4-chloro-, 3-chloro and 3,4-dichloroanilines in (spiked) water samples. Graphical Abstract ᅟ

Description: Novel nanocomposites were prepared from graphene oxide (GO) and octahedral tin dioxide (SnO 2 ) through a facile process that included synthesis of octahedral SnO 2 and the reduction of GO with ascorbic acid. The morphology and structure of the nanocomposites were characterized by UV–vis spectroscopy, transmission electron microscopy, and Raman spectroscopy. The nanocomposites were placed on a glassy carbon electrode where they displayed excellent performance in terms of differential pulse voltammetric determination of dopamine (DA). This is attributed to (a) the synergetic interactions between reduced graphene oxide (r-GO) and octahedral SnO 2 , and (b) the presence of a large number of active sites on the nanocomposites surface. The sensor responds to DA in the concentration range of 0.08 to 30 μM, with a 6 nM detection limit if operated at 0.24 V (vs. Ag/AgCl). The modified electrode also widely suppresses the background current resulting from excess ascorbic acid and uric acids. The method was applied to the determination of DA in spiked human urine and gave satisfactory results, with recoveries in the range from 96.4 to 98.2 %. Graphical Abstract Green and facile synthesis of reduced graphene oxide-octahedral SnO 2 (r-GO-SnO 2 ) nanocomposites for the sensitive and selective electrochemical detection of dopamine.

Description: We report on the synthesis of cobalt dihydroxide [Co(OH) 2 ] nanorods and their deposition on a 3-dimensional graphene network via chemical bath deposition. The structural characterization reveals deposited Co(OH) 2 to consist of flower-like nanorods on a 3-dimensional graphene foam. The nanocomposite was used for glucose sensing by electrocatalytic oxidation of glucose in 1 M KOH solution. Cyclic voltammetry and amperometric studies revealed a high sensitivity for glucose (3.69 mA mM −1 cm −2 ) and a 16 nM detection limit. The nanocomposite offers a large effective surface (11.4 cm 2 ) and is very selective for glucose over potentially interfering materials such as dopamine, ascorbic acid, lactose, fructose and urea, not the least due to a relatively low working potential of 0.6 V (vs. Ag/AgCl). The high sensitivity, low detection limit and very good selectivity of free-standing nanocomposite electrodes are attributed to the synergistic effect of (a) the good electrocatalytic activity of the NRs, and (b) the large surface area with high conductivity offered by the 3D graphene foam. Graphical Abstract Cobalt hydroxide [Co(OH) 2 ] nanorods were deposited on three dimensional graphene (3DG) by a chemical bath deposition method, and the resulting material was used as an electrode for non-enzymatic and specific sensing of glucose in 1 M KOH solution.

Description: A glassy carbon electrode (GCE) modified with polymeric nanocomposite consisting of palladium nanoparticles and a conductive polymeric ionic liquid was prepared. The modified GCE was applied to sensitive and fairly selective electrochemical determination of the mycotoxin zearalenone. Electrocatalytic oxidation is performed in a solution containing 20 % ( V /V) acetonitrile and 80 % ( V /V) of 1 M perchloric acid. Cyclic voltammetry and square wave voltammetry revealed a well-defined electrocatalytic peak current at overpotential of +0.69 V versus Ag/AgCl. Under optimized experimental conditions, there is a linear relationship between anodic peak current and zearalenone concentration in the range from 0.03 to 35 ng⋅mL‾ 1 , and the detection limit is 0.01 ng⋅mL‾ 1 . The method was successfully applied to the analysis of zearalenone in spiked food samples and gave recoveries between 95.6 and 104.0 %. Graphical abstract The nanocomposite (PdVC-PIL) was prepared by polymerization of ionic liquid monomer (PIL) in presence of Pd nanoparticles on Vulcan XC-72R carbon (PdVC). The solution containing nanocomposite was placed on the glassy carbon electrode (GCE). The voltammetry activity of modified electrode (PdVC-PIL/GCE) was compared to a bare GCE for zearalenone determination.

Description: We describe a sensitive and selective colorimetric method for the determination of the activity of the enzyme acetylcholinesterase (AChE) and its inhibitors. Detection is based on the fact that acetylthiocholine iodide (ATCI) catalyzes the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by H 2 O 2 to form a blue product (ox-TMB) with an absorption peak at 652 nm, but that oxidation is suppressed if ACTI previously is hydrolyzed by AChE to form thiocholine which decolorizes ox-TMB. In the presence of inhibitor, the activity of AChE is inhibited, thereby inducing the recovery of the blue coloration. Based on these findings, a highly sensitive method is developed for the determination of AChE and its inhibitors. The assay only requires mixing of buffer, solutions of ATCI, TMB, H 2 O 2 and a sample containing AChE and photometric measurement. It works in the 0.05 to 5 mU•mL −1 enzyme activity range and has a detection limit as low as 30 μU•mL −1 . The inhibitor neostigmine causes 50 % enzyme inhibition in 14.5 nM concentration. This analytical system has a wide scope in that it may be applied to the determination of the activity of various other hydrolases with proper substrates. Graphical abstract The blue product formed by the iodide-catalyzed oxidation of 3,3′5,5′-tetramethylbenzidine (TMB) by hydrogen peroxide is decolorized if acetylthiocholine iodide (ATCI) is hydrolyzed by acetylcholinesterase (AChE) to form thiocholine. If, however, AChE is inhibited, color formation will take place again.

Description: The author describes the preparation of a magnetic metal organic framework of type MOF-199 containing magnetite (Fe 3 O 4 ) nanoparticles carrying covalently immobilized 4-(thiazolylazo) resorcinol (Fe 3 O 4 @TAR). This material is shown to represent a viable sorbent for separation and preconcentration of Cd(II), Pb(II), and Ni(II) ions. Box-Behnken design was applied to optimize the parameters affecting preconcentration. Following elution with 0.6 mol L −1 EDTA, the ions were quantified by FAAS. The capacity of the sorbent ranged between 185 and 210 mg g −1 . The limits of detection are 0.15, 0.40, and 0.8 ng mL −1 for Cd(II), Ni(II), and Pb(II) ions, respectively. The relative standard deviations are 〈8.5 %. The method was successfully applied to the rapid extraction of trace amounts of these ions from sea food and agri food. Graphical abstract (a) A schematic diagram of Fe 3 O 4 functionalization by TAR (4-(thiazolylazo) resorcinol). (b) The schematic illustration of the magnetic metal organic framework-TAR nanocomposite. H 3 BTC: benzene-1,3,5-tricarboxylic acid; TEA: triethylamine; 3-CPS: 3-chloropropyl triethoxysilane.

Description: A composite material obtained by ultrasonication of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) was loaded with manganese dioxide (MnO 2 ), poly(diallyldimethylammonium chloride) and gold nanoparticles (AuNPs), and the resulting multilayer hybrid films were deposited on a glassy carbon electrode (GCE). The microstructure, composition and electrochemical behavior of the composite and the modified GCE were characterized by transmission electron microscopy, Raman spectra, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode induces efficient electrocatalytic oxidation of dopamine at a rather low working voltage of 0.22 V (vs. SCE) at neutral pH values. The response is linear in the 0.5 μM to 2.5 mM concentration range, the sensitivity is 233.4 μA·mM‾ 1 ·cm‾ 2 , and the detection limit is 0.17 μM at an SNR of 3. The sensor is well reproducible and stable. It displays high selectivity over ascorbic acid, uric acid and glucose even if these are present in comparable concentrations. Graphical abstract Gold nanoparticles were self-assembled onto the surface of the MnO 2 decorated graphene oxide-carbon nanotubes composites with poly(diallyldimethylammonium chloride) (PDDA) as a coupling agent. Further, a sensitive electrochemical sensor of dopamine was developed via immobilizing this nanocomposite on a glassy carbon electrode (GCE).

Description: We report on a novel kind of mitochondria-targeted theranostic nanoparticles (NPs). The NPs are doped with the oxygen-sensitive probe Pt(II)-porphyrins (PtTFPP) which exerts a dual role in acting as a diagnostic tool that can sense oxygen via quenching of luminescence, but also acts as an agent in photodynamic therapy (PDT) of cancer. In addition, it allows therapeutic efficacy to be assessed in-situ. Upon appropriate high-energy photoirradiation, the NPs generate singlet oxygen by energy transfer from triplet PtTFPP to ground state oxygen, and cell death is induced via PDT. Under low-energy light irradiation, in contrast, the NPs can be utilized to detect oxygen consumption rate via time-resolved luminescence measurements in order to study the efficacy of PDT. This is the first report where a single nanoagent is used to stimulate PDT and also to assess the efficacy of PDT. In our perception, the method provides a promising platform for testing anti-cancer drugs. Graphical abstract We report on a kind of mitochondria-targeted theranostic nanoparticles (NPs) doped with Pt(II)-porphyrins for oxygen sensing via quenching of luminescence, efficient photodynamic therapy (PDT) of cancer and quantitative assessment of therapeutic response in-situ.

Description: This paper describes a rapid method for fabrication of a paper substrate coated with gold nanoparticles (GNPs) that results in the formation of a large number of hot spots on the surface and allows an adequate control of the active area. The resulting substrate is shown to be a viable material for use in quantitative surface-enhanced Raman spectroscopy (SERS) analysis. The influence of the amount of GNPs on the SERS signals (using crystal violet as a sample analyte) was correlated with field-emission scanning electron microscopy, UV-visible and theoretical studies. The use of this substrates results in larger enhancement of Raman signals and in comparably repeatability when compared to commercially available substrates. The substrate was applied to SERS-based determination of nicotine and uric acid in aqueous solution, and the respective limits of detection are 20 and 30 μg L −1 . The results indicate that the SERS substrates may be applied to the quantification of a wide variety of molecules. Graphical abstract A novel and rapid procedure for preparation of sensitive and reproducible paper-based SERS substrates has been successfully developed and applied to quantitative detection of nicotine and uric acid.

Description: The authors describe an electrochemical aptamer based assay for the determination of the serine protease lysozyme in very low (pM) concentrations. The method is based on the formation of a complex between anti-lysozyme aptamer fragments and lysozyme, and on electrochemical detection by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The surface of a glassy carbon electrode was modified with a nanocomposite consisting of gold nanoparticles and electrochemically reduced graphene oxide nanosheets (AuNPs/erGO), and the thiolated aptamer was then linked to the AuNPs by self-assembly through Au-S bonds. The interaction of immobilized aptamers with lysozyme leads to the decreased peak current in DPV and increased charge transfer resistance (R ct ) in EIS when using hexacyanoferrate or Methylene Blue as a redox probe. The calibration plot, when applying EIS and working at a typical voltage of −0.22 V (vs. SCE), is linear over 1.0 to 104.3 pM concentration range, with a detection limit of 0.06 pM (at a signal-to-noise ratio of 3). The respective data for DPV are a 9.6–205.5 pM linear range with a detection limit of 0.24 pM. Depending on the redox marker applied, the method works in the “signal-off” or “signal-on” mode in DPV and EIS protocols, respectively. The sensing interface is high specific for lysozyme and not affected by other proteins. The method was applied to the determination of lysozyme in spiked diluted human serum, and the results agreed well with data obtained with a standard ELISA. Graphical abstract The surface of a glassy carbon electrode was modified with a nanocomposite consisting of gold nanoparticles and electrochemically reduced graphene oxide nanosheets (AuNPs/erGO). Then, the thiolated aptamer was linked to the AuNPs by self-assembly through Au-S bonds. The modified electrode was applied to the determination of lysozyme with “signal off” and “signal on” strategies.

Description: An electrochemical non-enzymatic glucose sensor based on copper nanorods (CuNRs) was developed. The CuNRs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy. The results display a layer of rough cuprous oxide that is formed on the surface of CuNRs. The CuNR- modified glassy carbon electrode exhibits an outstanding capability in terms of nonenzymatic sensing of glucose. The sensor displays high sensitivity (1490 μA•mM −1 •cm −2 ), fast response time (less than 5 s), a low detection limit of 8 nM (S/ N  = 3), long term stability, and excellent anti-fouling ability. The sensor was applied to the detection of glucose in (spiked) human serum and in black ice tea, with relative standard deviations (for n  = 6) of 1.7 % and 1.9 %, respectively. Graphical abstract The surface of Cu nanorods was covered with cuprous oxide, which increased the surface area of the nanorods and provided more catalytic active sites for the electro-oxidation of glucose. Good linearity and selectivity were obtained in glucose sensing.

Description: The authors describe dual-emission carbon nanodots containing blue emitters (BE; peak emission at 385nm under 315 nm excitation) and yellow emitters (YE; peak emission at 530 nm under 365nm excitation), and how they can be applied to direct and indirect determination of tetracyclines (TCs). The direct detection scheme is based on the finding that tetracycline (TET), oxytetracycline, chlortetracycline and doxycycline quench the two emissions of the carbon dots. While direct determination is rapid and convenient, it cannot differentiate between TCs. The indirect detection scheme, in contrast, is based on the finding that Al (III) ions enhance the fluorescence of the YE in the carbon dots, and that they cause a blue shift in emission. It is, however, known that TET forms a strong complex with Al (III), and this can inhibit the interaction between Al (III) and the YE, so that the fluorescence of YE is not enhanced and blue-shifted by Al (III) in the presence of TET. This finding is exploited in a fluorescence turn-on/off assay for TET that can distinguish TET from other TCs. The linear range of indirect determination for TET extends from 1 nM to 30 μM, and the limit of detection is 0.52 nM. The indirect method was successfully applied to the determination of TET in spiked milk, fish and pork, and recoveries ranged from 91.7 to 102 %. Graphical abstract High concentrations of tetracyclines quench the dual (blue and green) emission of carbon dots. Additionally, based on the fluorescence enhancement of yellow emitters by Al 3+ , an indirect turn-on/off detection of tetracycline is established with high selectivity and sensitivity.

Description: This article reports on the synthesis of water dispersible carbon quantum dots (CDs) by a one-step hydrothermal method using polyamidoamine (PAMAM) and (3-aminopropyl)triethoxysilane (APTES) as a platform and passivant. The resulting CDs are highly uniform and finely dispersed. The synergistic effect between PAMAM and APTES on the surface of the CDs results in a fluorescence that is much brighter than that of CDs modified with either APTES or PAMAM only. The fluorescence of the co-modified CDs is quenched by Hg(II) ions at fairly low concentrations. Under the optimum conditions, the intensity of quenched fluorescence drops with Hg(II) concentration in the range from 0.2 nM to 10 μM, and the detection limit is 87 fM. The effect of potentially interfering cations on the fluorescence revealed a high selectivity for Hg 2+ . The fluorescent probe was applied to the determination of Hg(II) in (spiked) waters and milk and gave recoveries between 95.6 and 107 %, with relative standard deviation between 4.4 and 6.0 %. Graphical abstract Strongly fluorescent carbon quantum dots (CDs) modified with polyamidoamine (PAMAM) and 3-aminopropyltriethoxysilane (APTES) were synthesized by one-step hydrothermal strategy. The resulting co-modified CD s were used as fluorescent probe for sensitive and selective detection of Hg 2+ .

Description: The authors describe an electrochemical sensing strategy for highly sensitive and specific detection of target (analyte) DNA based on an amplification scheme mediated by a multicomponent nucleic acid enzyme (MNAzyme). MNAzymes were formed by multicomponent complexes which produce amplified “output” signals in response to specific “input” signal. In the presence of target nucleic acid, multiple partial enzymes (partzymes) oligonucleotides are assembled to form active MNAzymes. These can cleave H0 substrate into two pieces, thereby releasing the activated MNAzyme to undergo an additional cycle of amplification. Here, the two pieces contain a biotin-tagged sequence and a byproduct. The biotin-tagged sequences are specifically captured by the detection probes immobilized on the gold electrode. By employing streptavidinylated alkaline phosphatase as an enzyme label, an electrochemical signal is obtained. The electrode, if operated at a working potential of 0.25 V (vs. Ag/AgCl) in solution of pH 7.5, covers the 100 pM to 0.25 μM DNA concentration range, with a 79 pM detection limit. In our perception, the strategy introduced here has a wider potential in that it may be applied to molecular diagnostics and pathogen detection. Graphical abstract An electrochemical strategy for sequence-specific DNA detection based on multicomponent nucleic acid enzyme (MNAzyme) -mediated signal amplification.

Description: Microcystin-RR (MC-RR) is a highly acute hepatotoxin produced by cyanobacteria. It is harmful to both humans and the environment. A novel aptamer was identified by the systemic evolution of ligands by exponential enrichment (SELEX) method as a recognition element for determination of MC-RR in aquatic products. The graphene oxide (GO) SELEX strategy was adopted to generate aptamers with high affinity and specificity. Of the 50 aptamer candidates tested, sequence RR-33 was found to display high affinity and selectivity, with a dissociation constant of 45.7 ± 6.8 nM. Aptamer RR-33 therefore was used as the recognition element in a fluorometric assay that proceeds as follows: (1) Biotinylated aptamer RR-33 is immobilized on the streptavidinylated wells of a microtiterplate, and carboxyfluorescein (FAM) labelled complementary DNA is then allowed to hybridize. (2) After removal of excess (unbound) cDNA, sample containing MC-RR is added and incubated at 37 °C for 2 h. (3) Displaced free cDNA is washed away and fluorescence intensity measured at excitation/emission wavelengths of 490/515 nm. The calibration plot is linear in the 0.20 to 2.5 ng·mL −1 concentration range, and the limit of detection is 80 pg·mL −1 . The results indicate that the GO-SELEX technology is appropriate for the screening of aptamers against small-molecule toxins. The detection scheme was applied to the determination of MC-RR in (spiked) water, mussel and fish and gave recoveries between 91 and 98 %. The method compares favorably to a known ELISA. Conceivably, this kind of assay is applicable to other toxins for which appropriate aptamers are available. Graphical abstract The aptamer RR-33 specific for microcystin (MC-RR) was identified by using the graphene oxide (GO) SELEX process. This aptamer was used for determination of MC-RR by a fluorometric displacement assay.

Description: A nanocomposite composed of graphene oxide and magnetite (Fe 3 O 4 ) was coated with the ionic liquid (IL) 1,3-didecyl-2-methylimidazolium chloride and used to capture and separate hemin from serum samples. The critical parameters affecting the extraction of analyte, such as pH, surfactant and adsorbent amounts, and desorption conditions were studied and optimized. Following magnetic separation and desorption with a 5:1 mixture of acetic acid and acetone, hemin (an iron porphyrin complex) was quantified by FAAS of iron. Under optimum conditions, the enrichment factor was 96. The calibration curve was linear in the 4.8 to 730 μg L −1 concentration range, the limit of detection was 3.0 μg L −1 , and the relative standard deviations (RSDs) for single-sorbent repeatability and sorbent-to-sorbent reproducibility were less than 3.9 % and 10.2 % ( n  = 5), respectively. The adsorbent displayed adsorption capacity as high as 200 mg g −1 , indicating IL-coated Fe 3 O 4 /GO to be a good sorbent for the adsorption of hemin. The method was validated by determining serum hemin in the presence of a large excess (480-fold) of Fe 3+ without considerable interference. The results compare well to those obtained with a commercial hemin assay kit. The results show that this method can be successfully applied to the enrichment and determination of hemin in acid digested serum samples of breast cancer patients. Graphical abstract Fe 3 O 4 /GO nanocomposites were coated with the ionic liquid 1,3-didecyl-2-methylimidazolium chloride and used as the sorbent for the separation and preconcentration of hemin from blood serum samples prior to determination using by flame AAS.

Description: The article describes the preparation of an electrode for amperometric detection in capillary electrophoresis (CE). It consists of a copper wire that was coated with a composite consisting of carbon nanotubes and polyurethane that was fabricated by in-situ polyaddition from a mixture of polyurethane prepolymer, curing agent, and carbon nanotubes (CNTs) inside a fused silica capillary. The structure of the composite was characterized by scanning electron microscopy, X-ray diffraction, thermogravimetry and FT-IR. The results indicated that CNTs were well dispersed and embedded throughout the composite to form an interconnected conducting network. The performance and advantages of the detection electrode are demonstrated by the separation and detection of standard mixtures of the hesperidin, hesperetin, naringenin and naringin by CE. The four flavanones are well separated within 12 min in a 40 cm long capillary at a separation voltage of 12 kV using a 50 mM sodium borate buffer (pH 9.2). The CNT-based electrode offers lower detection potential (0.8 V), enhanced detection limits (0.22–0.31 μM), lower costs of operation, high resistance to surface fouling, and improved stability. It shows long-term stability and repeatability, and relative standard deviations are 〈5 % for the peak current (for n  = 15). The method was applied to the determination of flavanone in the peels of citrus fruits. Graphical abstract A copper electrode modified with a composite consisting of carbon nanotubes and polyurethane for amperometric detection in capillary electrophoresis

Description: The 16 kDa heat shock protein (16 kDa HSP) against Mycobacterium tuberculosis (MT), expressed during the growth phase of MT, is a potential target in diagnostic tests for tuberculosis (TB). We describe here a method for impedimetric determination of the antigen by using a nanogapped dielectric surface consisting of a silver support coated with a thin finger-shaped coating made from zinc oxide and gold and patterned through a lift-off process. The electrode was characterized by scanning electron microscopy, field emission scanning electron microscopy, atomic force microscopy, and energy-dispersive X-ray spectroscopy. Surface chemical functionalization and immobilization of antibody against the 16 kDa HSP was evidenced by FTIR. In order to improve the detection limit, the antigen was conjugated to 10 nm gold nanoparticles. The resulting biosensor is capable of detecting the 16 kDa HSP in concentrations as low as 100 fM. The method covers a wide analytical range that extends from 100 fM to 1 nM. Graphical abstract Schematic presentation of the nanogapped impedimetric immunosensor for the diagnosis of tuberculosis

Description: The authors describe a colorimetric method for the determination of the staphylococcal enterotoxin B (SEB) that also allows for visual readout. The assay is based on the growth of gold nanoparticles (AuNPs) mediated by a hemin/G-quadruplex DNAzyme which generates a color change from red to blue in the presence of SEB. The method is enzyme-free and does not require a label. The kinetics of the formation of the AuNPs is controlled by the hemin/G-quadruplex DNAzyme and this is key to the signal generation mechanism. In the presence of SEB, the reactions between aptamer and target modulated the amount of single probe G strands that form DNAzyme capable of consuming hydrogen peroxide. The growth process of AuNPs is influenced by the resulting concentration of H 2 O 2 and leads to the color change. Under optimal conditions, a linear relationship exists between absorbance and SEB concentration in the range from 0.1 to 500 pg·mL‾ 1 which covers the clinically relevant range. In case of visual detection, the lower limit of detection is 1 pg·mL −1 . The assay described here is sensitive, comparably inexpensive and can detect SEB rapidly without the need for sophisticated equipment. In our perception, the method has a wide scope in that it may be adapted to various nucleic acids, proteins and other biomolecules if respective aptamers are available. Graphical abstract Colorimetric determination of Staphylococcal enterotoxin B via DNAzyme-guided growth of gold nanoparticles

Description: We have developed an ultrasensitive homogeneous fluorometric assay for Hg(II) ion. It is based on the different affinities of gold nanoparticles (AuNPs) for unfolded and folded aptamers. AuNPs are capable of recognizing conformational changes of aptamers under conditions of high ionic strength. A highly Hg(II)-specific T-rich aptamer was selected and adsorbed on the surface of AuNPs. This prevents the salt-induced aggregation of AuNPs. The red AuNP/aptamer system reduces the green fluorescence of cysteamine-capped CdTe quantum dots (CA-CdTe QDs). However, in the presence of Hg(II), the aptamer specifically reacts with Hg(II) to form a “T-Hg(II)-T” structure, and the AuNPs therefore form blue aggregates because they are not protected by the aptamer under conditions of high ionic strength. The blue aggregates cannot quench the fluorescence of the CA-CdTe QDs. Therefore, on addition of Hg(II), the fluorescence of the CdTe QDs is recovered. Fluorescence intensity is linearly proportional to the concentration of Hg(II) in the 50 pM to 1.0 nM concentration range, with a 2.5 pM detection limit. This ultrasensitive method in our eyes holds a large potential for environmental monitoring Hg(II) ion, and of other ions if respective aptamers are available. Graphical abstract An aptamer-based aggregation assay is developed for ultrasensitive detection of mercury ions.

Description: Mass spectrometry (MS) is the most powerful tool in phosphoproteomics research. However, phosphopeptides usually are present in low concentrations and their preconcentration therefore is highly desired. We describe a two-step method for the synthesis of a metal organic framework of the type MIL-101(Cr) that is modified with urea (then designated as MIL-101(Cr)-UR 2 ). It possesses large surface area, good solvent stability and high affinity for some phosphates. Due to the presence of modified urea functions, this material allows for selective and effective enrichment of phosphorylated peptides. It was successfully applied to the enrichment of phosphopeptides from non-fat-milk. The method was applied to the detection of phosphopeptides in a tryptic digest of β-casein where is showed a detection sensitivity as low as 10 −10  M. Graphical abstract A two step method was designed to synthesis MIL-101(Cr)-UR 2 and the prepared green solid was successfully applied to recognize phosphopeptides. (Amino functionalized metal-organic framework (MOF-NH 2 ); urea modified metal-organic framework (MOF-UR 2 ); matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS))

Description: In order to develop an aptamer based fluorescence resonance energy transfer (FRET) assay for 19-nortestosterone, a 76-mer 17β-estradiol aptamer was split into two pieces (referred to as P1 and P2, respectively). P1 was labeled with a quencher (BHQ), and P2 with a fluorophore (6FAM). The two aptamer pieces were employed to detect NT via FRET quenching in a homogeneous solution. This method has a low detection limit (5 μM) within a wide dynamic range (5 to 1000 μM). The approach was used to analyze spiked urine samples, and the results showed that the average recovery of three samples containing different NT concentrations ranged from 58 to 118 % with a relative standard deviation (RSD) of less than 1 %. In our perception, the method has a wide scope for future applications to other analytes by using dually labeled split aptamers. Graphical abstract A split aptamer-based fluorescence resonance energy transfer assay for 19-nortestosterone was developed with a wide dynamic range of 5 to 1000 μM and low detection limit (5 μM). The average recovery from spiked urine samples ranged from 58 to 118 %, with a relative standard deviation (RSD) of less than 1 %.

Description: A glassy carbon electrode (GCE) was anodically oxidized by cyclic voltammetry (CV) in 0.05 M sulfuric acid to introduce hydroxy groups on its surface (GCE ox ). Next, an imidazolium alkoxysilane (ImAS) is covalently tethered to the surface of the GCE ox via silane chemistry. This electrode is further modified with graphene oxide (GO) which, dispersed in water, spontaneously assembles on the electrode surface through electrostatic interaction and π-interaction to give an electrode of type GO/ImAS/GCE. Electroreduction of GO and GCE ox by CV yields electroreduced GO (erGO) and an electrode of the type erGO/ImAS/GCE. This electrode displays excellent electrocatalytic activity for the oxidation of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Three fully resolved anodic peaks (at −50 mV, 150 mV and 280 mV vs. Ag/AgCl) are observed during differential pulse voltammetry (DPV). Under optimized conditions, the linear detection ranges are from 30 to 2000 μM for AA, from 20 to 490 μM for UA, and from 0.1 to 5 μM and from 5 μM to 200 μM (two linear ranges) for DA. The respective limits of detection (for an S / N of 3) are 10 μM, 5 μM and 0.03 μM. The GCE modified with erGO and ImAS performs better than a bare GCE or a GCE modified with ImAS only, and also outperforms many other reported electrodes for the three analytes. The method was successfully applied to simultaneous analysis of AA, DA and UA in spiked human urine. Graphical abstract Differential pulse voltammetric simultaneous determination of ascorbic acid, dopamine and uric acid is achieved on a glassy carbon electrode modified with electroreduced graphene oxide and imidazolium groups, through anodic treatment of glassy carbon and silane chemistry.

Description: The authors describe a colorimetric method for the determination of Hg(II) ions by exploiting the peroxidase-lile activity of few-layered MoS 2 nanosheets (MoS2-NSs). These were prepared by sonication-induced exfoliation of bulk MoS 2 crystals in aqueous surfactant solution. The MoS2-NSs were found to acts as a peroxidase mimic that is capable of oxidizing the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) to give a blue product with an absorption maximum at 652 nm. The addition of Hg(II) strongly accelerates the kinetics of this reaction. It is shown that the enzyme mimic possesses a high affinity for TMB and a lower pseudo-Michaelis-Menten constant. The stimulating effect of Hg(II) is seriously influenced by the change of surface charge. The use of nanosheets covered with (negatively charged) polystyrene sulfonate results in a decrease in the formation of blue dye, while those covered with (cationic) poly(diallyldimethyl ammonium) ions cause a small increase. Under optimal conditions, the peroxidase-like activity of MoS2-NSs is affected by Hg(II) in the 2.0 to 200 μM concentration range. The method has a detection limit (LOD) of 0.5 μM which is much below the allowed level in cosmetics (1 ppm; ca. 5 μM). The method display excellent sensitivity, selectivity and stability. It was applied to the determination of total mercury in cosmetic samples, and results compared well with results obtained by ICP-AES. Graphical abstract A spectrophotometric assay for mercury - (II) determination is reported that is based on Hg 2+ -stimulation effect on the 3,3′,5,5′-tetramethylbenzidine (TMB)-H 2 O 2 reaction system catalyzed by MoS 2 nanosheets.

Description: The article describes the synthesis of core-shell magnetic nanoparticles (MNPs) of the type Fe 3 O 4 @MIL-100 (MIL standing for Material Institut Lavoisier), and their application as sorbent for magnetic solid-phase extraction (MSPE) of triclosan. The MNPs were prepared via circular self-assembly of ferric chloride and benzenetricarboxylic acid. The functionalized MNPs were characterized by transmission electron microscopy, FTIR and thermogravimetry. Following extraction, triclosan was eluted with ammoniacal methanol and then submitted to HPLC with UV detection. The amount of magnetic microspheres, sample pH and ionic strength, adsorption time, desorption time, desorption solvent and the volume of the eluent were optimized. Under optimum conditions, the method showed good linearity in the 0.1 to 50 mg·kg −1 triclosan concentration range in toothpaste samples. Other features include (a) intra-day and inter-day relative standard deviations (RSD, for n  = 4) of 〈5.5 %, (b) a 30 μg·kg −1 limit of detection, and (c) extraction recoveries between 90.86 % and 101.1 %. The method was successfully applied to the determination of triclosan in children’s toothpaste. Graphical abstract The article describes the synthesis of core-shell magnetic nanoparticles (MNPs) of the type Fe 3 O 4 @MIL-100, and their application as sorbent for magnetic solid-phase extraction (MSPE) of triclosan.

Description: Disposable screen-printed carbon arrays modified with gold nanoparticles (AuNPs) are described. The AuNP-modified screen-printed carbon arrays, designated as AuNP-SPCE arrays, were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The AuNP-SPCE arrays display excellent electrocatalytic activity towards lead and copper. Two well-defined and fully resolved anodic stripping peaks, at 20 mV for Pb(II) and at 370 mV for Cu(II), both vs. Ag/AgCl, can be seen. Square wave anodic stripping voltammetry was used to simultaneously analyze Pb(II) and Cu(II) in their binary mixtures in tap water. The linear working range for Pb(II) extends from 10 μg.L −1 to 100 μg.L −1 with a sensitivity of 5.94 μA.μg −1 .L.cm −2 . The respective data for Cu(II) are a working range from 10 μg.L −1 to 150 μg.L −1 with a sensitivity of 3.52 μA.μg −1 .L.cm −2 . The limits of detection (based on 3× the baseline noise) are 2.1 ng.L −1 and 1.4 ng.L −1 , respectively. In our perception, this array is particularly attractive because Pb(II) and Cu(II) can be determined at rather low working potentials which makes the method fairly selective in that it is not significantly interfered by other electroactive species that require higher reduction potentials. Graphical abstract Fabrication, characterization and electrochemical behavior of gold nanoparticles modified screen-printed carbon arrays towards lead and copper in tap water.

Description: The authors describe an SPR sensor chip coated with gold nanoparticles (AuNPs) that enables highly sensitive determination of genetically modified (GM) crops. Detection is based on localized surface plasmon resonance (LSPR) with its known sensitivity to even minute changes in refractive index. The device consists of a halogen light source, a light detector, and a cuvette cell that contains a sensor chip coated with AuNPs. It is operated in the transmission mode of the optical path to enhance the plasmonic signal. The sample solution containing target DNA (e.g. from the GM crop) is introduced into the cuvette with the sensor chip whose surface was functionalized with a capture DNA. Following a 30-min hybridization, the changes of the signal are recorded at 540 nm. The chip responds to target DNA in the 1 to 100 nM concentration range and has a 1 nM detection limit. Features of this sensor chip include a short reaction time, ease of handling, and portability, and this enables on-site detection and in-situ testing. Graphical abstract A localized surface plasmon resonance (LSPR)-based nanoplasmonic spectroscopic device enabling a highly sensitive biosensor is developed for the detection of genetically modified (GM) DNA founded in Roundup Ready (RR) soybean.

Description: We have prepared graphene quantum dot-europium(III) complex composites by noncovalently connecting chelating ligands dibenzoylmethane (DBM) and 1,10-phenanthroline (Phen) with graphene quantum dots (GQDs) first, followed by coordination to Eu(III). The resulting composites are well water-soluble and display red fluorescence of high color purity. The composites were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Aqueous solutions of the composites under 365 nm excitation display fluorescence with a peak at 613 nm and a quantum yield as high as 15.5 %. The good water solubility and stable photoluminescence make the composites very different from other Eu(III)-based coordination complexes. The composites are cell viable and can be used to label both the cell membrane and the cytoplasm of MCF-7 cells. They are also shown to act as bioprobes for in-vivo localization of tumorous tissue. In our perception, such composites are expected to possess wide scope because of the many functionalizations that are possible with GQDs. Graphical abstract Synthesis of red fluorescent graphene quantum dot-europium complex composites for use in bioimaging.

Description: The authors report on a new electrochemical aptasensing strategy for the determination of adenosine - 5’-triphosphate (ATP) at picomolar levels. First, manganese dioxide (MnO 2 ) nanosheets with an average size of ~70 nm were synthesized via a hot-injection method on the basis of reaction between potassium permanganate and the cationic detergent cetyltrimethylammonium bromide. The resulting MnO 2 nanosheets were then immobilized onto a pretreated screen-printed carbon electrode which readily binds the ferrocene-labeled ATP aptamer through the van der Waals force between the nucleobases and the basal plane of the nanoflakes. The immobilized ferrocene-aptamer conjugates activates the electrical contact with the electrode and produces a strong signal in the potentials scanned (0.0 to 1.0 V vs. Ag/AgCl). Upon addition of ATP, it will react with the aptamer and cause the dissociation of the ferrocene-aptamer from the nanosheets, this resulting in a decrease in the electrical signal. Under optimal conditions, this platform exhibits a detection limit as low as 0.32 nM of ATP. The repeatability and intermediate precision is below 10.7 % at a 10 nM concentration level. The method was applied to analyze blank fetal calf serum spiked with ATP, and the recoveries (at 3 concentration levels) ranged between 91.3 and 118 %. This detection scheme is rapid, simple, cost-effective, and does not require extensive sample preparation or multiple washing steps. Graphic abstract MnO 2 nanosheets are used as the sensing platform for electrochemical detection of ATP based on target-induced dissociation of ferrocene-labeled aptamer.

Description: The authors report on the fabrication of Co(OH) 2 -enfolded Cu 2 O nanocubes on reduced graphene oxide (rGO), and the use of this material in an electrochemical caffeine sensor. The rGO/Cu 2 O/Co(OH) 2 composite was characterized by X-ray powder diffraction pattern analysis, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. A rotating disc glassy carbon electrode covered with the nanocomposite displays enhanced electrocatalytic activity towards the electro-oxidation of caffeine. The peak oxidation potential is at 1.4  V (vs. Ag/AgCl) and hence is strongly shifted to the negative side when compared to other modified electrodes. The calibration plot is linear in the 0.83 to 1200 μM concentration range, with a 0.4 μM detection limit (at a signal-to-noise ratio of 3). The modified electrode is sensitive, selective and stable. It was successfully applied to the determination of caffeine in (spiked) caffeine-containing beverages and coffee powder and gave recoveries that ranged from 95.7 to 98.3 %. Graphical abstract Co(OH) 2 enfolded Cu 2 O nanocubes on reduced graphene oxide (rGO) for the caffeine sensor

Description: A DNA-based biosensor is presented that can be applied to the detection of DNA damage caused by UV-C radiation (254 nm) in the presence of CdTe quantum dots (QDs). The sensor is composed of a glassy carbon electrode whose surface was modified with a layer of dsDNA and another layer of CdTe QDs. The response of this sensor is based on (a) the intrinsic anodic signal of the guanine moiety in the DNA that is measured by square-wave voltammetry, and (b) the cyclic voltammetric response of the redox indicator system hexacyanoferrate(III/II). Depending on the size of the QDs, they exert a significant effect on the rate of the degradation of dsDNA by UV-C light, and even by visible light. Time-dependent structural changes of DNA include opening of the double helix (as indicated by an increase in the redox response of the guanine moiety due to easy electron exchange with the electrode when compared to the original helix state and by an increase in the voltammetric peak current of the hexacyanoferrate(III/II) anion after degradation of the negatively charged DNA backbone on the electrode). The effects of QDs were verified for salmon sperm DNA and calf thymus DNA, and further corroborated by experiments in which DNA solutions were irradiated in the presence of QDs. Graphical Abstract Scheme of the DNA-based biosensor with a layer CdTe QDs under the UV-C irradiation. The QDs enlarge damage to DNA demonstrating their size-dependent toxic effect. Two independent electrochemical methods (CV and SWV) prove a relationship between DNA degradation and exposure of the DNA biosensor to UV-C irradiation. The CdTe QDs increase damage to DNA demonstrating their size-dependent toxic effect.

Description: We report that graphene quantum dots (GQDs) are viable fluorescent probes for the determination of chromium(VI) and ascorbic acid in an on-off-on mode. The fluorescence of GQDs is strongly quenched by Cr(VI) mainly due to an inner filter effect and static quenching. This shifts the system to the “off” status. The quenching mechanism of this fluorescent system was investigated in some detail. Fluorescence intensity is inversely proportional to the concentration of Cr(VI) in the 0.05 to 500 μM concentration range with a 3.7 nM detection limit. The fluorescence of GQDs-Cr(VI) system is converted back to “on” by adding ascorbic acid which will reduce yellow Cr(VI) ion, thereby eliminating the inner filter effect and static quenching. The relative intensity of restored fluorescence is directly proportional to the concentration of ascorbic acid in the 1.0 to 500 μM range, and the limit of detection is 0.51 μM. There are almost no interferences to commonly encountered other substances. The methods were applied to the determination of Cr(VI) in spiked tape, lake and river waters, and of ascorbic acid in a tablet and human urine. Both gave satisfactory results. Graphical abstract Graphene quantum dots are viable fluorescent probes for the determination of chromium(VI) and ascorbic acid in an on-off-on mode.

Description: A new SPR sensing substrate was fabricated that is based on the use of graphene oxide (GO) and gold bipyramids (GBPs). It can substantially improve the sensitivity of wavelength modulation SPR biosensors. First, a support consisting of a sheet of single layered GO was prepared, and its morphology and thickness were determined by atomic force microscopy (AFM). GBPs were synthesized and modified with staphylococcal protein A (SPA) for the oriented immobilization of antibody. GBPs modified with SPA were assembled on GO sheets through covalent attachment. The resulting SPR biosensor exhibits a highly sensitive response to rabbit IgG in the 0.15–40 μg mL −1 concentration range. The limit of quantification is better by factors of 4 and 16 compared to those obtained with gold nanoparticle-based, and conventional gold film-based sensors, respectively. In our expectation, this GBP-based SPR biosensor has a wide scope in that it may be employed to develop detection schemes for many other biomolecules by changing the corresponding receptor on its surface. Graphical Abstract A new sensing substrate based on graphene oxide and gold bipyramids was fabricated. The resulting SPR biosensor exhibits a sensitive response to rabbit IgG.

Description: This article describes the preparation of a La(III) ion-imprinted nanoparticles (NPs) containing the La(III)-chelating ligand 2,2’:6’,6”-terpyridine (terpy). La(III) forms stable 1:1 and 1:2 complexes with terpy in acetonitrile solution. The NPs were prepared from ethyleneglycol dimethacrylate (the cross-linking monomer) via precipitation polymerization in the presence of the La(III)-terpy complex. La(III) ions were then removed from the NPs with nitric acid. The NPs were characterized by IR spectroscopy, scanning electron microscopy and elemental analysis. SEM micrographs showed the colloidal NPs to be slightly irregularly shaped and to have a diameter of 50 to 100 nm. The optimum pH value for sorption is 3.5. Sorption and desorption of La(III) is complete within 2 to 30 min. La(III) was quantified by ICP-AES. Figures of merit include a sorbent capacity for La(II) of 133.8 mg g −1 , an enrichment factor of 17.5, a relative standard deviation of the determination of 1.7 % (at 3S b /m), and a detection limit of 1.4 ng mL −1 . The results indicate an increased affinity of the material toward La(III) over other multivalent metal ions of smaller ionic radius. The imprinted NPs were regenerated twenty times without a significant loss in affinity. Graphical abstract Ion-imprinted polymer nanoparticles were synthesized via precipitation polymerization and employed as a sorbent for the separation and preconcentration of trace amounts of lanthanum(III) ion from aqueous samples in the batch mode .

Description: Dispersive liquid-liquid microextraction based on solidification of floating organic droplets (DLLME-SFO) has been applied to the extraction of pharmaceutical and personal care products (PPCPs) and pesticides from water samples. The PPCPs included bisphenol A, sodium diclofenac, gemfibrozil, furosemide, glibenclamide, nifedipine, nimesulide, propylparaben and triclocarban. The pesticides included 2,4-D, atrazine, azoxystrobin, cyproconazole, clomazone, dichloran, difenoconazole, diuron, epoxiconazole, fenoxaprop-p-ethyl, fipronil, iprodione, irgarol, propanil, propiconazole, tebuconazole, and trifloxystrobin. The type and volume of extraction solvent, type and volume of disperser solvent, ionic strength and pH were optimized. All species were then quantified by liquid chromatography tandem mass spectrometry (LC-MS/MS). The limits of quantification (LOQs) ranged from 50 to 500 ng L −1 , and the linearity ranged from the LOQ of each compound up to 10,000 ng L −1 . Recoveries ranged from 63 to 120 %, with relative standard deviations lower than 14 %. It is making use of a low-toxicity and affordable extraction solvent (1-dodecanol) and was successfully applied to the analysis of surface water samples. Graphical Abstract A mixture of 1-dodecanol and methanol was applied to the extraction of pesticides, pharmaceuticals and personal care products from water samples by applying the solidification of floating organic microdroplet technique

Description: Molecularly imprinted polymer (MIP) particles for malachite green (MG) were prepared by emulsion polymerization using methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, and a combination of Span-80 and Tween-80 as an emulsifier. The MIP particles were characterized by SEM micrographs and FT-IR spectra. Their binding capacity for MG was evaluated based on kinetic and isothermal adsorption experiments and compared to non-imprinted polymer particles. Analytical figures of merit include an adsorption equilibrium time of 15 min, an adsorption capacity of 1.9 mg∙g‾ 1 in acetonitrile-water (20:80), and an imprinting factor of 1.85. The MIP particles were successfully applied to the extraction of MG from fish samples spiked with MG and the other interfering substances prior to its determination of MG by HPLC. Spiked samples gave recoveries of MG that ranged from 86 to 104 %, much higher than that of the other interfering substance. Graphical Abstract Molecularly imprinted polymer particles for malachite green (MG) were prepared by emulsion polymerization. They show adsorption capacity of 1.9 mg∙g‾¹ with imprinting factor of 1.85, and were successfully applied to the extraction of MG from spiked fish samples.

Description: A nanocomposite was prepared that consists of chitosan, reduced graphene oxide and gold nanoparticles by in-situ and simultaneous reduction of graphene oxide and hexachloroaurate whereby chitosan acts as a reducing and stabilizing agent. The nanocomposite was then deposited on a glassy carbon electrode, and glucose oxidase (GOx) was immobilized on its surface to obtain a glucose biosensor. The immobilized GOx displays fast electron transfer with a transfer rate constant of 2.80 s −1 . Operated at a working voltage of −0.45 V (vs. Ag/AgCl), the sensor gives a linear response to glucose in the 0.05 to 1.2 mM concentration range, with a sensitivity of 13.58 μA mM −1  cm −2 , and a 0.52 μM detection limit. The apparent Michaelis-Menten constant is 2.39 mM. It also possesses good selectivity, reproducibility and stability. Graphical Abstract An electrochemical sensor for glucose is presented that consists of a glassy carbon electrode modified with a one-pot synthesized nanocomposite consisting of chitosan, reduced graphene oxide and gold nanoparticles.

Description: We describe a biosensor for dopamine that is based on the use of a gold electrode modified with carbon nanoparticles (CNPs) coupled to thionine labeled gold nanoparticles (AuNPs) acting as signal amplifiers. The biosensor was constructed by first modifying the CNPs on the gold electrode and adsorbing the thionine on the surface of the AuNPs, and then linking the complementary strand of the dopamine aptamer to the AuNPs via gold-thiol chemistry. Next, dopamine aptamer is added and the duplex is formed on the surface. On addition of a sample containing dopamine, it will interact with aptamer and cause the release of the electrochemical probe which then will be adsorbed on the surface of the CNP-modified gold electrode and detected by differential pulse voltammetry. The current is linearly related to the concentration of dopamine in the 30 nM to 6.0 μM ranges. The detection limit is as low as 10 nM, and the RSD is 3.1 % at a 0.3 μM level (for n = 11). The protocol was successfully applied to the determination of dopamine in spiked human urine samples. We perceive that this method holds promise as a widely applicable platform for aptamer-based electrochemical detection of small molecules. Graphical Abstract The aptamer-based sensor for dopamine is based on the use of a gold electrode modified with carbon and gold nanoparticles for signal amplification.

Description: The α-hemolysin (α-HL) nanopore is capable of analyzing DNA as it is electrophoretically driven through the pore. Respective current vs. time (i-t) traces depend on the DNA sequence, its secondary structures, or on the physical conditions of the analysis. The current study describes the analysis of a DNA hairpin with a 5′-extension by applying α-HL nanopores in the presence of the polyamines spermine (Spm), spermidine (Spd), and putrescine (Put) and revealed i-t traces characteristic of the DNA-polyamine complex. Voltage-dependent studies also revealed that the hairpin-Spm complex formed with excess Spm cannot be unzipped and translocated through the pores even if the voltage is increased to 180 mV. The DNA hairpin sample was titrated with Spm, Spd, or Put that showed a dose-dependent response in the characteristic event patterns for hairpins bound to Spm or Spd, but not for Put. Plots of the event types vs. counts were used to calculate binding constants for the Spm or Spd hairpin interactions. The titration also demonstrated that the event rate decreased ~10-fold on increasing the Spm or Spd concentrations from 0 to 4 mM. These observations impose practical limitations on the ability to use Spm or Spd for DNA studies with the α-HL nanopore. Graphical Abstract Hairpin DNAs bearing long single-stranded tails were studied with spermine via the α-hemolysin nanopore that generated three characteristic current signatures.

Description: Nanopore-based sequencing platforms are transforming the field of genomic science. This review (containing 116 references) highlights some recent progress on nanopore-based nucleic acid analysis and sequencing. These studies are classified into three categories, biological, solid-state, and hybrid nanopores, according to their nanoporous materials. We begin with a brief description of the translocation-based detection mechanism of nanopores. Next, specific examples are given in nanopore-based nucleic acid analysis and sequencing, with an emphasis on identifying strategies that can improve the resolution of nanopores. This review concludes with a discussion of future research directions that will advance the practical applications of nanopore technology. Graphical Abstract A review with 116 references that highlights the progress made in nanopore-based nucleic acid analysis and sequencing, and the mechanisms operative in analytical methods based on the use of nanopores

Description: We are presenting an aptasensor for the sensitive determination of fumonisin B1 (FB-1) via electrochemical impedance spectroscopy (EIS) and applying aptamer-based biorecognition. A thiolated aptamer for FB-1 was anchored onto the surface of gold nanoparticles (AuNPs) on a glassy carbon electrode. A significant increase in resistance (R et ) is found on interaction with FB-1 in the 0.1 nM to 100 μM concentration range, and the detection limit is as low as 2 pM. The assay was applied to determine FB-1 in spiked maize samples and gave recovery rates ranging from 91 to 105 %. The results demonstrate this method to present new possibilities in the application of aptamers in food safety analysis. Graphical abstract The electrodeposited AuNPs create a nanomaterial platform in situ for anchoring of FB-1 aptamers serving as recognition elements. The change in EIS signals induced by aptamer-target interactions was measured and a significant increase in resistance (R et ) is found on interaction with FB-1 in the 0.1 nM to 100 μM concentration range.

Description: A nanomaterial of the chemical composition Cu 2 (OH) 3 Cl-CeO 2 and with a large surface area is shown to be a viable peroxidase mimetic. It was synthesized by co-precipitation of an aqueous solution containing Ce(III) chloride, Cu(II) chloride and hexamethylenetetramine by adding an ionic liquid. The material was characterized by scanning electron microscopy and X-ray powder diffractometry. The composite possesses peroxidase-like activity and catalyzes the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine by H 2 O 2 to produce a blue product. Based on this finding, a simple, rapid and selective colorimetric method was worked out for the determination of glucose and cholesterol by using the respective oxidases and by quantifying the H 2 O 2 formed. Both glucose and cholesterol can be determined by this method at levels as low as 50 µM. Graphical abstract We found that the newly synthesized Cu 2 (OH) 3 Cl-CeO 2 composite material possesses intrinsic peroxidase-like activity, and this finding was applied to design a rapid and selective colorimetric assay for H 2 O 2 , glucose and cholesterol.

Description: We have developed a simple, sensitive and practical substrate for surface enhanced Raman scattering (SERS). It consists of a column material that is obtained by modifying the surface of (glycidyl methacrylate)-co-(ethylene dimethacrylate) capillary monoliths with silver nanoparticles. This new SERS column substrate was applied to the determination of 4-mercaptopyridine (4-Mpy) and Rhodamine 6G (R6G) to give detection limits as low as 100 and 10 pM, respectively. The calculated enhancement factor is approximately 1.2 × 10 8 . This represents a substantial improvement over conventional colloidal substrates. The new substrate was applied to the determination of residues of the pesticide phosmet and gave a detection limit of 3 μg∙L −1 , with a linear response in the 3 to 1000 μg∙L −1 concentration range (R 2  = 0.995). Additionally, 0.2 mg∙kg −1 of phosmet on apples and oranges, and of 0.5 mg∙kg −1 on tea leaves were detectable via SERS using this column along with a simple extraction process. The above LODs are well below the tolerance level prescribed by National Standard of China. Thus, this simple method is highly efficient, sensitive, and affordable and introduces a SERS–based trace detection suitable for real-world applications, especially for the determination of pesticides. Graphical Abstract A simple, sensitive and practical substrate is developed which introduces SERS–based trace detection suitable for real-world applications, especially for the determination of pesticides.

Description: The article describes a calix[4]arene derivative for use as a recognition element in an SPR sensor for norepinephrine (NE). The calix[4]arene carries a crown ether and a thiol group that enables the formation a self-assembled monolayer (SAM) on a gold surface. NE is recognized by the calix[4]arene via its positively charged amino group that has a high affinity for the crown moiety of the calixarene. The modified gold surface was characterized by Fourier transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The binding process to the sensor surface was monitored by SPR. Under optimized condition, the sensor has a linear response to NE in the 10 pM to 100 nM concentration range, and the detection limit is 0.12 pM. Graphical Abstract Schematic diagram of sensor chip configuration (left) and SPR angle increase according to treatment with different concentration of NE (right).

Description: An enzyme-free electrochemical sensor for glucose was prepared by electrochemical anodization of iron foil, followed by in situ annealing under a flow of hydrogen to give a one-dimensional Fe 3 O 4 nanorod array (NRA). The morphology, structure, and composition of the NRAs were characterized and the fabrication process was investigated. The array possesses a large specific surface area and a crystal structure that facilitates electron transfer. Operated at 0.6 V (vs. SCE) in pH 13 solution, the sensor displays a distinctly improved sensitivity to glucose (compared to their Fe 2 O 3 nanotube counterpart). Two linear response ranges can be observed. The first extends from 0.5 to 766 μM (with a sensitivity of 406.9 μA∙cm −2 ∙mM −1 ), the other from 765 μM to 3.7 mM (with a sensitivity of 134.1 μA∙cm −2 ∙mM −1 ). The detection limit is 0.1 μM (at an S/N of 3). The sensor is stable and can be applied to real sample analysis with minimal interferences. Graphical abstract A nonenzymatic electrochemical sensor for glucose with a sensitivity of 406.9 μAcm −2 ∙mM −1 was prepared by electrochemical anodization of iron foil, followed by in situ annealing under a flow of hydrogen to give a one-dimensional Fe 3 O 4 nanorod array.

Description: We report on a non-enzymatic electrochemical sensing strategy for ultrasensitive detection of hydrogen peroxide (H 2 O 2 ) at nanomolar levels. A glassy carbon electrode (GCE) was modified with a hybrid material consisting of multiwalled carbon nanotubes (CNT) and molybdenum disulfide (MoS 2 ). Transmission electron microscopy and Raman spectroscopy were employed to characterize the hybrid nanostructures. GCEs modified with carbon nanotubes, or nanoscaled MoS 2 , or with the CNT-MoS 2 hybrid were investigated with respect to sensing H 2 O 2 , and this revealed that the GCE modified with the CNT-MoS 2 hybrid performed best and resulted in a limit of detection as low as 5.0 nM. A repeatability and intermediate precision of 9 % was accomplished. The method was applied to determine H 2 O 2 in spiked sterilized milk and gave satisfactory results. Graphical Abstract A nonenzymatic electrochemical sensing strategy was developed for ultrasensitive detection of hydrogen peroxide at the nanomolar level by using multi-walled carbon nanotube-MoS 2 hybrid nanostructures as peroxidase mimics.

Description: We report on an indirect optical method for the determination of glucose via the detection of hydrogen peroxide (H 2 O 2 ) that is generated during the glucose oxidase (GOx) catalyzed oxidation of glucose. It is based on the finding that the ultraviolet (~374 nm) and visible (~525 nm) photoluminescence of pristine zinc oxide (ZnO) nanoparticles strongly depends on the concentration of H 2 O 2 in water solution. Photoluminescence is quenched by up to 90 % at a 100 mM level of H 2 O 2 . The sensor constructed by immobilizing GOx on ZnO nanoparticles enabled glucose to be continuously monitored in the 10 mM to 130 mM concentration range, and the limit of detection is 10 mM. This enzymatic sensing scheme is supposed to be applicable to monitoring glucose in the food, beverage and fermentation industries. It has a wide scope in that it may be extended to numerous other substrate or enzyme activity assays based on the formation of H 2 O 2 , and of assays based on the consumption of H 2 O 2 by peroxidases. Graphical Abstract We report the application of ZnO nanoparticles (NPs) in a biosensor for monitoring glucose at a large concentration range. The biosensor is based on the indirect detection of hydrogen peroxide via the respective change of the UV and visible PL of ZnO NPs.

Description: Folic acid-conjugated luminescent nanomaterials have long been widely used in targeted bioimaging, often simultaneously acting as vehicles for drug delivery. They often require, however, intense light sources for photoexcitation, and this often results in photobleaching, strong luminescence background, and strong light scattering. This article describes the preparation of nanoparticles (NPs) of the type Zn 1.1 Ga 1.8 Sn 0.1 O 4  doped with Cr(III) ions and surface-modified with folic acid. The functionalization of the NPs was monitored via measurement of zeta potentials, FTIR spectra and thermogravimetry. Cell viability and biocompatibility were tested using the MTT kit. The NPs have a size of 220 nm and were characterized by dynamic X-ray diffraction, light scattering, field emission scanning electron microscopy and high-resolution transmission electron microscopy. After annealing the NPs for 10 min at 300 °C and irradiating them with 254 nm light for 10 min, they display deep red emission that persists for up to 10 h. The NPs are easily dispersed, small-sized, and crystalline. In our perception, the new material with its long decay time offers quite novel features in terms of targeted optical imaging in providing high resolution, weak disturbance by background luminescence, and the absence of light scattering. They were successfully applied to image MCF-7 and A549 cells. Graphical Abstract Folic acid-conjugated nanoparticles of the type Zn 1.1 Ga 1.8 Sn 0.1 O 4 :Cr 3+ are presented that are easily dispersible, small-sized (100 nm), and well crystallized. They display a phosphorescence in the NIR that persists for 〉10 h after excitation and were used to image MCF-7 and A549 cells.

Description: A highly sensitive amperometric magnetoimmunoassay for rapid determination of lipoprotein(a) (Lp(a)), an important predictor of cardiovascular disease risk, in human serum, is described. It uses a sandwich configuration involving selective capture antibody [antiLp(a)] and biotinylated detector antibody [biotin-antiLp(a)], and a streptavidin-HRP conjugate on carboxy-modified magnetic beads (HOOC-MBs). The resulting MBs bearing the sandwiched immunoconjugates were captured by a magnet placed under the working electrode surface of a disposable screen-printed carbon electrode and the extent of the affinity reaction was monitored amperometrically at −0.20 V (vs a silver pseudo-reference electrode) in the presence of hydroquinone as an electron transfer mediator and upon addition of H 2 O 2 as the enzyme substrate. The method exhibited a wide linear response range (from 0.01 to 0.5 μg mL −1 ), a detection limit of 4 ng mL −1 , and an excellent selectivity over other serum components. The utility of the immunoassay was demonstrated by analyzing a reference serum containing a certified quantity of Lp(a). The performance of this magnetoimmunoassay compares favorably to that of an integrated amperometric immunoassay described earlier. Graphical Abstract The article describes the first disposable and highly sensitive amperometric magnetoimmunoassay for lipoprotein(a), an important predictor of cardiovascular disease risk, in human serum. It is  based on a sandwich configuration involving selective capture antibody and biotinylated secondary antibody, and a streptavidin-HRP conjugate on magnetic beads.

Description: We report on the use of amino-modified silica nanoparticles (SiNPs) as an additive to the background electrolyte solution to enhance the chiral selectivity of in capillary electrophoresis that is induced by the presence of a small quantity of carboxymethyl-β-cyclodextrin (CM-β-CD). The modified SiNPs were characterized by transmission electron microscopy, elemental analysis and their zeta potential. The method was applied to the separation of four alkaline drugs (ephedrine, chlorpheniramine, propranolol and amlodipine). The addition of the modified SiNPs to the background electrolyte results in a distinct improvement in the separation power, especially when the capillary was pretreated with high concentration of particle suspensions prior to separation. The effects of fractions of modified SiNPs and organic modifier, of the thickness of the SiNP coating layer on the capillary wall were investigated. Under optimum experimental conditions, all the racemates investigated were separated with improved resolution, thus indicating the potential of the method in the field of enantiomeric separation. Graphical Abstract SEM images of bare capillary wall, being pretreated with HCNPs for three times and the electropherograms of the enantioseparation of amlodipine. Experimental conditions: 30 mM phosphatebackground electrolyte (pH 5.0) containing 6.45 × 10 −2 mmol L −1 CM-β-CD on bare capillary column (left); 30 mM phosphate background electrolyte (pH 5.0) containing 6.45 × 10 −2 mmol L −1 CM-β-CD, with 0.3 mg mL −1 NH 2 -NPs added on HCNPs coating capillary column (right). Detection wavelength, 214 nm; injection, 10 kV × 2 s; separated voltage, +10 kV

Description: s We describe a sensitive fluorometric and colorimetric dual-readout probe for folic acid (FA). It is based on the use of the gold nanoclusters (AuNCs) and cysteamine–modified gold nanoparticles (cyst-AuNPs). The bovine serum albumin stabilized AuNCs exhibit strong fluorescence emission at 652 nm. Upon addition of cyst-AuNPs, the fluorescence intensity of the AuNCs showed dramatic decrease due to the surface plasmon enhanced energy transfer process. This is due to an FA-induced aggregation of the cyst-AuNPs which shifts the absorption peaks from 530 to 670 nm. Thus, the surface plasmon enhanced energy transfer between cyst-AuNPs and AuNCs is weakened and the fluorescence intensity of AuNCs is recovered. The fluorescence intensity of the AuNCs/cyst-AuNPs system is proportional to the concentration of FA in the range from 0.11 to 2.27 μmol L −1 . The dual-readout probe reported here was successfully applied to the determination of FA in spiked serum samples and folic acid tablets. Graphical Abstract A novel sensitive and selective fluorometric and colorimetric dual functional probe is developed for folic acid detection.

Description: The article describes a magnetic composite sorbent for the extraction of traces of polycyclic aromatic hydrocarbons (PAHs) from water samples. The composite was prepared by caging Fe 3 O 4 nanoparticles (NPs) and MWCNTs into calcium alginate beads. The large surface area of the MWCNTs and their π-interactions with the aromatic rings of PAHs obviously facilitate strong adsorption. The hydrophilicity of the calcium alginate cage, in turn, enhances the dispersibility of the sorbent in the water sample. Finally, the use of magnetic NPs facilitates a simple and fast separation of the sorbent. The composite sorbent was successfully applied to the extraction of PAHs from (spiked) water samples. PAHs were quantified by HPLC with fluorescence detection. Under optimized experimental conditions, the calibration plot is linear in the range of 5 to 50 μg∙L −1 for benzo[a]anthracene and benzo[a]pyrene, and 10 to 50 μg∙L −1 for benzo[b]fluoranthene. Other figures of merit include a limit of detection of 5 ng∙L −1 for benzo[a]anthracene and benzo(a)pyrene, and of 10 ng∙L −1 for benzo[b]fluoranthene, recoveries ranging from 92.0 to 97.7 %, and relative standard deviations of 〈5 %. The method has several attractive features including an easily prepared and eco-friendly sorbent, a convenient and fast extraction procedure, and a high extraction efficiency. Graphical Abstract A magnetic/multiwalled carbon nanotubes/alginate composite sorbent was developed for the extraction and preconcentration of the polycyclic aromatic hydrocarbons benzo[a]anthracene, benzo[a]pyrene and benzo[b]fluoranthene from water samples.

Description: A method is described for in-situ electrochemical preparation of nanoporous gold electrodes (np-GEs) via alloying and dealloying using ethylene glycol (EG) as a solvent. The np-GEs were prepared via cyclic voltammetry from a gold electrode in the presence of ZnCl 2 in EG. Effects of temperature, number of scan cycles and scan rate were investigated. It is concluded that the process involves formation of interfacial elemental zinc and the formation of a gold-zinc alloy. At a temperature of 120 °C, the alloy is formed already after the first scan cycle, and ten further cycles do not cause substantial further changes in the morphology. Changes in the morphology were corroborated by data on the electroactivity of the np-GEs. The mechanism of the formation of np-GEs in EG obviously is different from that in other solvents due to the superior smoothing ability of EG for electroplating. This results in more uniform alloy layers and in a more evenly distributed porous structure. The self-supporting np-GE without any further modification displays an amperometric response to catechol (at a working voltage of 420 mV vs. SCE) in the 0.050 to 1.0 mM concentration range, with a detection limit of 1.78 μM (at an S/N of 3), indicating that the np-GE can be applied to convenient and effective determination of catechol. Graphical Abstract A facile in-situ electrochemical alloying and dealloying route using ethylene glycol as the solvent is introduced for the fast fabrication of a self-supporting nanoporous gold electrode. It exhibits good electrocatalytic activity towards the oxidation of catechol.

Description: A highly sensitive electrode for sensing glucose has been fabricated by electropolymerization of 2-amino-5-mercapto-1,3,4-thiadiazole on a solid carbon paste substrate, and subsequent electrodeposition of multi-layer stacked copper particles as an outer surface. The individual copper particles are characterized by a large number of edges and corners of crystallites. Their preferred orientation {111} is parallel to the electrode surface. The conductive polymer interlayer results in an increase of the particle nucleation density and a further decrease of the polarization overpotential for direct (enzyme-free) oxidation of glucose in 0.1 M NaOH solution. A well-shaped voltammetric peak can be observed at around 0.3–0.5 V (vs. SCE, depending on scan rate) that is due to glucose oxidation. This potential is much lower than the one required for Cu(III) formation. A bulk electrolysis experiment using a thin-layer electrochemical cell confirmed the assumption that that glucose undergoes 2-electron oxidation. The mechanism of glucose oxidation in the absence of Cu(III) is discussed. The electrode exhibits a very high sensitivity (slope) of 3.31 mA cm −2  mM −1 , and the detection limit is 2 μM (at an SNR of 3). Features of the new sensor include the ease of fabrication, its high stability and good selectivity. Graphical Abstract A highly sensitive electrode for sensing glucose has been fabricated based on multi-layer stacked copper particles. Oxidation of glucose gives rise to a well-shaped anodic peak, which is different from the commonly observed anodic wave extending to the potential region of oxygen evolution.

Description: An electrochemical method is presented for the determination of arsenic at subnanomolar levels. It is based on potentiometric stripping analysis (PSA) using a graphene paste electrode modified with the thiacrown 1,4,7-trithiacyclononane (TTCN) and gold nanoparticles (AuNPs). The electrode surface was characterized by means of cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry and scanning electron microscopy. The modified electrode displays a 15-fold enhancement in the PSA signal (dt/dE) compared to a conventional graphene paste electrode. Under optimized conditions, the signal is proportional to the concentration of As(III) in the range from 25 pM to 34 nM (r 2  = 0.9977), and the detection limit (SD/s) is as low as 8 pM. The modified electrode was successfully applied to the determination of total arsenic [i.e., As(III) and As(V)] in pharmaceutical formulations, human hair, sea water, fruits, vegetables, soil, and wine samples. Graphical Abstract In the preconcentration step, arsenic forms stable intermetallic compounds with the gold substrate while allowing As to be reproducibly reoxidized during the stripping step. This, along with the complexing properties of the thiacrown TTCN towards As(III), results in a synergistic effect leading to a TTCN-AuNP-graphene paste electrode as a highly sensitive sensor for arsenic.

Description: We describe an electrode array and microfluidics based integrated biochip for the quantitation of the tumor marker prostate specific antigen (PSA). The surface of the chip was functionalized with a self-assembled monolayer of mercaptoundecanoic acid prior to the immobilization of the antibody against PSA. A flow of buffer or spiked human serum (75 %) and, subsequently, the detection antibody and gold nanoparticles (Au-NPs) modified with horseradish peroxidase were passed over the antibody-coated electrodes. This was followed by the injection of the substrate tetramethylbenzidine and simultaneous amperometry during the flow. This resulted in a real-time amperometric reading. The method has detection limits (LODs) of 0.2 ng∙L −1 in buffer and of 1 ng∙L −1 in 75 % human serum. The linear part of the calibration plot has an r 2 of 0.97. These LODs are well below the clinical threshold level of 4 ng∙L −1 . This assay is rapid (~15 min) which compares favorably with respect to conventional chronoamperometric analysis and to ELISA tests which require ~45 min. This new platform has a potential as an automatted point-of-care device for clinical use because it is likely to be applicable to numerous other clinical analytes for which appropriate antibodies are available. Graphical Abstract An electrode array and microfluidics based integrated biochip has been utilised for the real-time amperometric detection of the tumor marker prostate specific antigen (PSA).

Description: We describe a simple solvothermal method for preparation of reduced graphene oxide nanosheets decorated with uniform Cu 2 O nanoclusters by using poly(vinyl pyrrolidone)-poly(methacrylamide)-poly(vinyl imidazole) triblock co-polymer as a shape-directing agent and L -glutamic acid as a reducing agent. The resulting nanocomposite was deposited on a glassy carbon electrode where it displays improved electrocatalytic activity toward glucose oxidation in 0.5 M NaOH. This observation was exploited to construct a non-enzymatic amperometric sensor for glucose. It has a detection limit as low as 1.0 μM, high sensitivity (23.058 μA mM −1 ), and a dynamic (analytical) range that extends from 5.0 to 9595 μM at a working potential of 600 mV (vs. SCE). Graphical Abstract Uniform Cu 2 O nanoclusters supported on reduced graphene oxide (Cu 2 O NCs/r-GO) were prepared by a simple solvothermal method in the presence of a triblock copolymer as a shape-directing agent. The nanocomposite was used to construct a non-enzymatic glucose amperometric sensor with low detection limit, high sensitivity, and wide linear range.

Description: The article describes a fluorometric and sensitive assay for mercury(II) ions (Hg 2+ ). It is based on the following scheme and experimental steps: (1) Hg 2+ triggers the self-hybridization of thymine-rich ss-DNA labeled with a fluorescence tag to form a ds-DNA; (2) in the absence of Hg 2+ , labeled ss-DNA will be adsorbed on the surface of graphene oxide (GO) and its fluorescence is quenched; (3) the ds-DNA formed in the presence of Hg 2+ is cleaved by the catalytic action of exonuclease III; (4) the cleaved labeled DNA fragments do not adsorb on the surface of GO, this resulting in an increase in fluorescence intensity. The induction of the process by Hg 2+ leads to a strong amplification of fluorescence, while the fluorescence of uncleaved labeled ss-DNA is quenched because it is adsorbed on the surface of GO in the absence of Hg 2+ . This assay displays a detection limit of 0.1 nM (which is below the 10 nM upper limit in drinking water according to the US EPA and can be performed with 8 min. Graphical Abstract The detection scheme is based on the finding that the fluorescence of ds-DNA formed in the presence of Hg(II) ions on the surface of graphene oxide is quenched. If the DNA is cleaved by exonuclease III, fragments will be desorbed and fluorescence pops up