ALBERT

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A fluorimetric and colorimetric method is described for the determination of glutathione (GSH) and silver (I). It is based on the use of MnO〈sub〉2〈/sub〉 nanosheets that were prepared by solution mixing and exfoliation. They display oxidase-mimicking activity and can catalyze the oxidation of o-phenylenediamine (OPD) to form yellow 2,3-diaminophenazine (DAP) with an absorption maximum at 410 nm. DAP also has a yellow fluorescence (with a peak at 560 nm). The MnO〈sub〉2〈/sub〉 nanosheets can be rapidly reduced to Mn〈sup〉2+〈/sup〉 by GSH. This reduces the efficiency of the oxidase mimic MnO〈sub〉2〈/sub〉 and causes a decrease in fluorescence and absorbance intensity. However, on addition of Ag〈sup〉+〈/sup〉, a complex is formed with GSH. It prevents the destruction of MnO〈sub〉2〈/sub〉 nanosheets so that the enzyme mimicking activity is retained. A dual-method for the determination of GSH and Ag(I) was developed. It has excellent sensitivity for GSH with lower detection limits of 62 nM (fluorimetric) and 0.94 μM (colorimetric). The respective data for Ag(I) are 70 nM and 1.15 μM. The assay was successfully applied to the determination of GSH and Ag(I) in spiked serum samples.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Schematic presentation of a method for colorimetric and fluorometric determination of glutathione (GSH) and silver(I). MnO〈sub〉2〈/sub〉 nanosheets are reduced to Mn(II) by GSH. This reduces the enzyme-mimicking activity of MnO〈sub〉2〈/sub〉 nanosheets and causes a decrease in fluorescence and absorbance. On addition of Ag(I), the enzyme-like activity is increasingly retained. A decrease in fluorescence and absorbance is not observed any longer.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3613_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Carboxylic acids (CAs) have been reported as potential biomarkers of specific diseases or human body odors. A visual sensor array is described here that is based on indicator displacement assays (IDAs). The arrays were prepared by spotting solutions of the following metal complexes: Murexide-Ni(II), murexide-Cu(II), zincon-Zn(II) and xylenol orange-Cu(II), with the capability of discrimination of 15 carboxylic acids (CAs) and the quantitation of pyruvic acid (PA). Clear differences can be observed through distinctive difference maps obtained within 5 min by subtraction of red, green and blue (RGB) values of digital images after and before exposure to analytes. After an analysis of multidimensional data by pattern recognition algorithms including HCA, PCA and LDA, excellent classification specificity, and accuracy of 〉96% were obtained for all samples. The IDA array exhibited a linear range from 10 to 1500 μM with a theoretical detection limit of 3.5 μM towards PA. Recoveries of real samples varied from 84.8% to 114.3%. As-fabricated IDA sensor array showed an excellent selectivity among other organic interfering substances and a good batch to batch reproducibility, demonstrating its robustness. All these observations suggested that the IDA sensor array is one of the most promising paths for the discrimination of CAs.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Schematic diagram of indicator displacement assay (a), the procedure for acquisition of difference maps (b), and pattern recognitions for CAs (c). The method uses hierarchical cluster analysis (HCA), principal component analysis (PCA) and linear discriminant analysis (LDA)〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3601_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A multifunctional nanoprobe is described for dual sensing of acidic pH values and glutathione (GSH) by combining the pH-responsive fluorescent probe 3-acetyl-7-hydroxy-2H-chromen-2-one (AHC) and MnO〈sub〉2〈/sub〉 nanosheets. The fluorescence of the MnO〈sub〉2〈/sub〉/AHC composite is weak due to an inner filter effect. If, however, the MnO〈sub〉2〈/sub〉 nanosheets are reductively decomposed by GSH, the blue fluorescence of the pH probe AHC (with excitation/emission maximum at 417/456 nm) will be restored. The MnO〈sub〉2〈/sub〉 nanosheets also are decomposed by acidic pH values, and the fluorescence of AHC is decreased. According to absorbance and fluorescence signal changes, the pH and GSH induced responses can be easily distinguished. Thus, the nanoprobe can be used for logical analysis of acidic pH values and GSH. The nanoprobe works in the pH range from 4 to 7, and GSH can be determined in the concentration range from 0.5 to 200 μM.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Schematic presentation of a multifunctional nanoprobe for dual sensing of acidic pH values and glutathione by combining a pH-responsive fluorescent probe and MnO〈sub〉2〈/sub〉 nanosheets. According to absorbance and fluorescence signal changes, the nanoprobe can be used for logical analysis.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3590_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Two kinds of aptasensors for ampicillin (AMP) are described. The assay strategies include the use of gold nanoparticles (AuNPs) that were modified with (a) a thiolated aptamer (T-Apt), and (b) a non-thiolated polyadenine aptamer (polyA Apt). The AuNPs and the aptamers were brought to interaction prior to addition of AMP. T-Apt and polyA Apt are adsorbed on the AuNPs by different mechanisms. The adsorbed aptamer was able to bind the target while preventing non-specific interactions. Remarkably different optical absorbances (measured at 520 and 680 nm) are produced the absence and presence of AMP. The assay can selectively recognize AMP even in the presence of species of similar chemical structure. The T-Apt based assay has a linear response in the 1–600 nM AMP concentration range and a 0.1 nM limit of detection. The respective data for the polyA Apt assay are 1–400 nM and 0.49 nM.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Schematic presentation of the colorimetric aptasensor for ampicillin detection using two kinds of anti-ampicillin aptamers and gold nanoparticles. Polydiallyldimethylammonium chloride (PDDA) acts as aggregation agent.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3524_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉The authors describe an immunosensor for the prostate specific antigen (PSA). It was obtained by modifying a glassy carbon electrode (GCE) first modified with gold nanoparticles and then with reduced graphene oxide that was decorated with gold nanoparticles. The AuNPs on reduced graphene oxide provide a suitable surface for attachment of antibodies. On binding of the antigen, the square wave voltammetric signal (measured by using hexacyanoferrate as a probe) reduced. This method has two logarithmically linear analytical ranges that extend from 25 to 55 fg.mL〈sup〉−1〈/sup〉 and from 1 to 36 ng.mL〈sup〉−1〈/sup〉, respectively. The lowest detection limit is 2 pg.mL〈sup〉−1〈/sup〉. Electrochemical impedance spectroscopy was also carried out for PSA determination. EIS works in the 0.0018 to 41 ng.mL〈sup〉−1〈/sup〉 concentration range and has an LOD of 60 pg.mL〈sup〉−1〈/sup〉. This method was applied to the determination of PSA in (spiked) human serum samples. In order to survey the selectivity of immunosensor, determination of PSA was performed in human serum samples, and finally sensitivity and reproducibility were examined.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Facile label free immunosensor based on reduced graphene oxide decorated with gold nanoparticles for early diagnosis prostate cancer via ultrasensitive detection of PSA biomarker: application in human serum.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3565_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A non-enzymatic hydrogen peroxide (H〈sub〉2〈/sub〉O〈sub〉2〈/sub〉) electrochemical sensor material was prepared from silver nanoparticles and a 2D copper-porphyrin framework (MOF). The structure and morphology of the nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results showed that the MOF has a two-dimensional sheet structure, and a large number of Ag NPs are uniformly attached to it. The MOF also acts as a peroxidase mimic. The sensor has excellent catalytic performance in terms of H〈sub〉2〈/sub〉O〈sub〉2〈/sub〉 reduction. Figures of merit include (a) an electrochemical sensitivity of 21.6 μA mM〈sup〉−1〈/sup〉 cm〈sup〉−2〈/sup〉 at a typical working potential of −0.25 V (vs. SCE), (b) a detection limit of 1.2 μM (at S/〈em〉N〈/em〉 = 3), and (c) a linear response range that extends from 3.7 μM to 5.8 mM. Compared to other sensors of the same type, the linear range of the sensor is extended by an order of magnitude.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Silver nanoparticles (Ag NPs) were reduced with sodium borohydride (NaBH〈sub〉4〈/sub〉) on the surface of copper(II)-porphyrin (Cu-TCPP) nanosheets prepared with the assistance of polyvinylpyrrolidone (PVP). Their synergistic effect improved the performance of H〈sub〉2〈/sub〉O〈sub〉2〈/sub〉 sensor fabricated by immobilizing Ag NPs/Cu-TCPP nanocomposites on glassy carbon electrodes (GCE).〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3551_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Two adsorbents with covalently bound aminomethylenephosphonic acid functions (and referred to as MNPs/AMPA and MNPs/SiO〈sub〉2〈/sub〉-AMPA) were synthesized from two types of amino-functionalized magnetic nanoparticles (MNPs) via Moedritzer-Irani reaction. The sorbents with anchored dopamine ligand (MNPs/dopa) or aminopropyl groups (MNPs/SiO〈sub〉2〈/sub〉-NH〈sub〉2〈/sub〉), and the MNPs/AMPA were characterized by X-ray diffraction, FTIR, transmission electron microscopy and vibrating sample magnetometry. Surface modification does not adversely impact the physical properties of the starting magnetite. Compared to the size of the unmodified Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉 (magnetite) nanoparticles (7–12 nm), the average size of functionalized nanoparticles is increased to 10–16 nm. Similarly, the magnetic saturation decreased from 67.5 emu g〈sup〉-1〈/sup〉 to 42.0 emu g〈sup〉−1〈/sup〉, and the surface area is increased up to 205 m〈sup〉2〈/sup〉 g〈sup〉−1〈/sup〉 for MNPs/SiO〈sub〉2〈/sub〉-AMPA. The kinetics of the adsorption of Eu(III) on the sorbent is ultra-fast, and equilibria are attained within 5–10 min at room temperature. The adsorption kinetics can be described by a pseudo-second-order model. Adsorption and desorption conditions were tested with respect to the removal of Eu(III) ions from water solution. The adsorption capacities for Eu(III) at pH 7.0 are 77 mg g〈sup〉−1〈/sup〉 and 69 mg g〈sup〉−1〈/sup〉 for MNPs/AMPA and MNPs/SiO2-AMPA nanoparticles, respectively. Eu(III) was quantified by ICP-MS. The limit of detection (LOD) for Eu(III) is 0.05 ng L〈sup〉−1〈/sup〉 (based on the 3σ criterion), with an enrichment factor of 150. The selectivity over ions such as Tb(III), Fe(III), Zn(II), Cu(II), and Ca(II) ions was studied. Under optimal condition the distribution coefficient for Eu(III) relative to these ions is near 10〈sup〉5〈/sup〉 mL g〈sup〉−1〈/sup〉. The sorbents can be easily retrieved from even large volumes of aqueous solutions by magnetic separations. The method was tested for spiked water samples (with recoveries from 96.6–102.5%) and for rock minerals.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉A schematic showing the regeneration of magnetite nanoparticles (MNPs), core-shell (MNPs/SiO〈sub〉2〈/sub〉), and the structures with covalently bonded aminomethylenephosphonic acid (AMPA) after preconcentration of Eu(III) from largewater sample volumes onto a small specimen.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3520_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉A ratiometric electrochemical aptamer-based assay is described for the ultrasensitive and highly specific determination of adenosine triphosphate (ATP). It is based on ATP aptamer-mediated triple-helix molecular switch (THMS). The method uses (a) a hairpin DNA (MB-DNA-SH) labeled with the redox probe Methylene Blue (MB) at the 3′ end, and a thiol group at the 5′ end, and (b) a single strand ATP aptamer modified with two ferrocenes at each end (Fc-DNA-Fc). The labeled probe of type MB-DNA-SH was self-assembled onto the surface of a gold electrode via gold-thiol binding. On exposure to Fc-DNA-Fc, it will hybridize with MB-DNA-SH to form a stable THMS structure on electrode surface. In the presence of ATP, it hybridizes with the loop portion of Fc-DNA-Fc, and this results in the unwinding of the THMS structure. Such variation caused the changes of the differential pulse voltammetry (DPV) peak currents of both MB (at around −0.25 V) and Fc (at around 0.39 V; both vs. Ag/AgCl). A significant enhancement is found for the ratio of the two DPV peaks. Under the optimum experimental conditions, this assay has a response that covers the 0.05 to 100 pM ATP concentration range, and the detection limit is 5.2 fM (for 〈em〉S〈/em〉/〈em〉N〈/em〉 = 3). The method is highly selective for ATP over its analogs.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Schematic presentation of a novel ratiometric electrochemical aptasensor for ATP via triple-helix molecular switch (THMS) strategy. MB-DNA-SH was self-assembled on GE surface through gold-thiol binding. Fc-DNA-Fc hybridized with MB-DNA-SH to form THMS structure. ATP specifically bond with its aptamer sequence of Fc-DNA-Fc to unwind the THMS structure. The ratio of DPV peak currents of MB and Fc was applied to monitor the concentration of ATP in real samples over its analogs.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3630_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Core-shell nanoparticles (NPs) consisting of a gold core and a metal-organic framework shell (type MOF-74) were synthesized via one-pot synthesis. The NPs exhibit highly sensitive and stable SERS activity for the detection of 4-nitrothiophenol, with a specific band at 1337 cm〈sup〉−1〈/sup〉. The method has a linear response in 0.10–10 μmol·L〈sup〉−1〈/sup〉 analyte concentration range and a lower detection limit of 69 nmol·L〈sup〉−1〈/sup〉. The potential application of this novel SERS substrate was evaluated by two model reactions involving 4-nitrothiophenol. The first involves in-situ SERS monitoring of the surface plasmon-induced nitration of aromatic rings without adding conventional acid catalyst. The second involves the photocatalytic reduction of 4-nitrothiophenol to 4-thioaminophenol in the presence of Au/MOF-74 under 785-nm laser irradiation. The plasmon-assisted dimerization of 4-nitrothiophenol to form 4,4′-dimercaptoazobenzene can also be monitored simultaneously.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Schematic presentation of a nanoparticle SERS substrate consisting of gold core and MOF-74 shell, which was applied to detection of 4-nitrothiophenol. The Au/MOF-74 was successfully used for in-situ monitoring of two model reactions involving 4-nitrothiophenol by SERS.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3618_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉

Beschreibung: 〈h3〉Abstract〈/h3〉 〈p〉Light-harvesting nanoprobes were developed by self-assembly of nanoscale metal-organic frameworks (NMOFs) and stimuli-responsive polymers for fluorometric sensing of pH values and temperature. Two kinds of fluorescent NMOFs (acting as the energy donor) and stimuli-responsive polymers conjugated to fluorophores (acting as energy acceptors) were prepared and characterized. The NMOFs include zirconium(IV) and 〈em〉π〈/em〉-conjugated dicarboxylate ligands. The fluorophores inclued cyaine dyes and a Bodipy dye. The energy donor and energy acceptor form a Förster resonance energy transfer (FRET) nanosystem. In the light-harvesting system, the chain lengths of the stimuli-responsive polymers vary when the local pH value or temperature change. Ratiometric sensing of pH and temperature was accomplished by monitoring fluorescence. pH values were can be sensed between 3.0 and 8.0 under 420 nm excitation and by ratioing the emission peaks at 645 and 530 nm. Temperature can be sensed in the range from 25 to 50 °C under 550 nm excitation and by ratioing the emission peaks at 810 and 695 nm. The nanoprobes display excellent water dispersibility and cell membrane permeability. They were applied to image pH values and temperature in HeLa cells.〈/p〉 〈p〉 〈span〉 〈caption〉 〈strong〉Graphical abstract〈/strong〉 〈em〉 〈div〉Schematic presentation of an effective strategy to fabricate light-harvesting nanoprobes by self-assembly of MOFs and stimuli-responsive polymers for ratiometric pH and temperature sensing. The distance as the polymer length between energy donor and acceptor is crucial for energy transfer efficiency.〈/div〉 〈/em〉 〈/caption〉 〈span〉 〈img alt="" src="https://static-content.springer.com/image/MediaObjects/604_2019_3608_Figa_HTML.png"〉 〈/span〉 〈/span〉 〈/p〉