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Core-shell palladium cube@CeO2 (Pd cube@CeO2) nanoparticles are shown to display oxidase-like activity. This is exploited in a method for determination of the activity of alkaline phosphatase (ALP). The Pd cube@CeO2 nanoparticles were thermally synthesized from Ce(NO3)3, L-arginine and preformed Pd cube seeds in water. The Pd cube@CeO2 nanoparticles catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by oxygen. This results in the formation of oxidized TMB (oxTMB) with an absorption peak at 652 nm. Ascorbic acid (AA) is generated from the hydrolysis of L-ascorbic acid 2-phosphate (AAP) catalyzed by ALP. It can reduce oxTMB to TMB, and this results in a decrease of the absorbance. The method allows for quantitative determination of the activity of ALP in the range from 0.1 to 4.0 U·L−1 and with a detection limit down to 0.07 U·L−1. Endowed with high sensitivity and selectivity, the assay can quantify ALP activity in biological system with satisfactory results. [ABSTRACT FROM AUTHOR]

Hemin, the most common biological iron form, serves many biological functions. However, studies on hemin detection are scarce. As an unusual natural peroxide, artemisinin is quite stable in the presence of common species. While, it can decompose to generate superoxide radicals in the presence of hemin. And the as-obtained superoxide radicals can effectively oxidize thiamine to form fluorescent thiochrome. Inspired by this, a simple and novel fluorescent assay for hemin detection based on artemisin-thiamine is developed. Based on the linear relationship between the fluorescence intensity and concentration of hemin, the developed artemisinin-thiamine assay can be utilized for sensitive detection of hemin in the concentration range of 2.0–300.0 nM with a detection limit of 0.68 nM. Moreover, this assay shows high selectivity over other cations and biomolecules. Besides, hemin can be detected in serum samples with satisfactory results, which demonstrates its great potential for real sample analysis. The designed assay is free of any fluorescent nanomaterials or probes by just mixing these reagents together, and all the detection processes is performed within 20 min. Therefore, it can offer a simple, highly sensitive and selective sensing platform for fluorescence detection of hemin. [ABSTRACT FROM AUTHOR]

In this work, we propose a fluorescence method for the simultaneous detection of glutathione (GSH) and histidine (His) based on the Cu(ii)-thiamine (Cu(ii)-TH) system. It is well established that non-fluorescent thiamine (TH) can be oxidized by Cu(ii) to generate fluorescent thiochrome (TC) under alkaline conditions. The introduction of GSH and His can inhibit the oxidation of TH by Cu(ii) due to the strong affinity between Cu(ii) and GSH or His. With this strategy, the detection limit for GSH and His is 10.5 nM and 26.4 nM, respectively. The developed method shows several obvious advantages: (1) simplicity in design and operation without the utilization of fluorescent nanomaterials or probes; (2) time-saving detection process since all the detection process is completed within 15 min; (3) cost-effectiveness by using TH as the fluorescent substrate; and (4) higher sensitivity and good selectivity. Therefore, it shows great potential in biosensing fields. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) is a significant biomarker for diagnostics. Simple, selective and sensitive detection of ALP activity is thus of critical importance. In this study, an artful fluorescence assay for ALP is proposed based on adenosine triphosphate (ATP) hydrolysis-triggered disassociation and fluorescence quenching of cerium coordination polymer nanoparticles (CPNs). ATP, a recognized natural substrate of phosphatase, can serve as a superb “antenna” to sensitize the luminescence of Ce3+ with the aid of tris(hydroxymethyl) aminomethane (Tris), forming Ce3+–ATP–Tris CPNs. In the presence of ALP, ATP will be catalytically converted into adenosine and inorganic orthophosphate, however neither of them can sensitize Ce3+ in alkaline media. As a result, the obtained CPNs are disassociated, inducing the quenching of the fluorescence. On this basis, a straightforward fluorescence assay for ALP activity is rationally developed. The fluorescence quenching efficiency shows a linear relationship for ALP within the activity range from 0.1 to 10 mU mL−1 with a detection limit of 0.09 mU mL−1 under the optimal experimental conditions. Moreover, this facile yet effective fluorescence method featured simplicity, cost-effectiveness, high sensitivity and high selectivity and can be successfully utilized for the quantitative detection of ALP in human serum samples. [ABSTRACT FROM AUTHOR]

In this work, a simple, highly selective and sensitive method for detecting biothiols based on I − -H 2 O 2 -3,3’,5,5’-tetramethylbenzidine (TMB) system is developed. The main determination mechanism of the colorimetric assay is that iodide could catalyze the oxidation of TMB in the presence of H 2 O 2 to form oxidized TMB (ox-TMB). With the introduction of biothiols, the biothiols cause the reduction of ox-TMB, accompanied with the color of the solution changing from the original blue to colorlessness. UV–vis absorption spectrum shows that the intensity of peak at 652 nm reduces largely. Other 20 kinds of amino acids have also been studied for proving the high sensitivity and selectivity of current approach. This colorimetric analysis method can be successfully applied to the practical sample determination with satisfactory results. The results indicated that this work is a facile, time-saving and cost-effective method for detecting biothiols. [ABSTRACT FROM AUTHOR]

The poly(thymine) (poly T) can effectively template the in situ formation of copper nanoparticles (CuNPs) within several minutes under ambient conditions, offering great potential as fluorescence probe for biochemical analysis without complicated modifications. However, the exploration of poly T-templated CuNPs (poly T-CuNPs) for biochemical applications is still at its very early stage. Herein, a novel fluorescent assay has been developed for acetylcholinesterase (AChE) and its inhibitor detection based on poly T-CuNPs. In the absence of AChE, the high affinity between Cu 2+ and thymine leads to the formation of fluorescent CuNPs. In the presence of AChE, the fluorescence of poly T-CuNPs is quenched based on the reaction between Cu 2+ and thiocholine generating from the hydrolysis of ATCh by AChE. This detection assay is simple without the requirement for complex labeling of probe DNA and the multiple preparation procedure of fluorescent compounds. The detection assay is highly sensitive for sensing AChE in the concentration ranging from 0.11 to 2.78 mU mL −1 with a detection limit of 0.05 mU mL −1 and is feasible for screening AChE inhibitor. This method paves a new way for exploring the biosensing applications of the poly T-CuNPs. [ABSTRACT FROM AUTHOR]

In this paper, a novel, convenient and sensitive colorimetric assay for acetylcholinesterase (AChE) activity and its inhibitor screening is successfully proposed based on the peroxidase-like activity of Prussian blue nanocubes (PB NCs). PB NCs can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H 2 O 2 to develop a blue color and an absorption peak centered at 652 nm. AChE mediates the hydrolysis of acetylthiocholine (ATCh) to yield a reducing agent thiocholine (TCh) that cause the reduction of oxidized TMB and it can also chelate with Fe 3+ , both of which result in a blue color fading and a decrease of the absorbance. The generation of TCh is inhibited and the absorbance intensity is recovered after the introduction of AChE inhibitor. Consequently, the assay is also utilized in AChE inhibitor screening. The PB NCs-H 2 O 2 -TMB based platform is highly sensitive for AChE activity sensing with a low detection limit of 0.04 mU/mL. In addition, this assay has great potential in discriminatively determining AChE over other enzymes. The proposed method is fairly novel, simple and sensitive, which may pave the way for the detection of other hydrolytic enzyme activities with properly selected substrates. [ABSTRACT FROM AUTHOR]

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 HO 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, HO and a sample containing AChE and photometric measurement. It works in the 0.05 to 5 mU•mL enzyme activity range and has a detection limit as low as 30 μU•mL. 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. [ABSTRACT FROM AUTHOR]

A novel colorimetric method for the detection of acetylcholinesterase (AChE) and its inhibitor by taking utilization of Ag [I] ion–3,3′,5,5′-tetramethylbenzidine (TMB) detection system has been proposed. Ag [I] ion could oxidize TMB to induce a blue color and an absorption peak centered at 652 nm. In the presence of AChE, acetylthiocholine (ACh) was hydrolyzed to thiocholine. Ag [I] ion could interact with thiocholine and thiocholine can reduce the oxidized TMB (oxTMB) to TMB, both of which suppressed the oxidation capacity of Ag [I] ion, resulting in a blue color fading and a decrease of the absorbance at 652 nm. The developed assay is highly sensitive with a low detection limit of 4.3 μU/mL. Moreover, the method was also applied in AChE inhibitor sensing. The obtained assay is fairly simple, inexpensive and sensitive without the utilization of nanomaterials, which may be not only used for the sensing of other hydrolytic enzyme activities with properly selected substrates, but also used for the screening of potential inhibitor drugs. [ABSTRACT FROM AUTHOR]

In this work, a facile approach to sensitively detect sulfide ions is developed. The proposed method is based on the findings that silver ions could oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to induce a blue color and an absorption peak centered at 652 nm. The introduction of sulfide ions leads to the formation of Ag 2 S nanoparticles which act as catalyst to enhance the oxidation capacity of silver ions, resulting in a blue color burning and increase of the absorbance at 652 nm. Based on the above facts, a facile method is developed to qualitatively and quantitatively detect sulfide ions by naked eyes and UV–vis spectroscopy, respectively. The color changes of the detection system in the presence of nanomolar level of sulfide ions could be distinguished by naked-eyes, demonstrating the high sensitivity of the method. Highly sensitive detection of sulfide ions can be achieved in the range of 1.0 × 10 −9 M to 8.0 × 10 −8 M, with a detection limit of 0.2 nM. In addition, this method shows excellent selectivity toward sulfide ions detection and has been successfully applied to detect sulfide ions in tap water and lake water samples. Moreover, this method is simple without the preparation of nanomaterials and the need of complex readout instruments. [ABSTRACT FROM AUTHOR]

In this paper, a novel biosensor based on Carbon dots (C-dots) for sensitive detection of hydroquinone (H 2 Q) is reported. It is interesting to find that the fluorescence of the C-dots could be quenched by H 2 Q directly. The possible quenching mechanism is proposed, which shows that the quenching effect may be caused by the electron transfer from C-dots to oxidized H 2 Q-quinone. Based on the above principle, a novel C-dots based fluorescent probe has been successfully applied to detect H 2 Q. Under the optimal condition, detection limit down to 0.1 μM is obtained, which is far below U.S. Environmental Protection Agency estimated wastewater discharge limit of 0.5 mg/L. Moreover, the proposed method shows high selectivity for H 2 Q over a number of potential interfering species. Finally, several water samples spiked with H 2 Q are analyzed utilizing the sensing method with satisfactory recovery. The proposed method is simple with high sensitivity and excellent selectivity, which provides a new approach for the detection of various analytes that can be transformed into quinone. [ABSTRACT FROM AUTHOR]

In this study we propose a simple and sensitive colorimetric aptasensor for the quantitative analysis of abrin by using catalytic AuNPs for the first time. AuNPs possess the peroxidase-like activity that can catalyse 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, leading to color change of the solution. It is interesting to find that the peroxidase-like activity of AuNPs can be improved by surface activation with a target-specific aptamer. However, with a target molecule, the aptamer is desorbed from the AuNPs surface, resulting in a decrease of the catalytic abilities of AuNPs. The color change of the solution is relevant to the target concentration, and this can be judged by the naked eye and monitored by using a UV-vis spectrometer. The linear range for the current analytical system was from 0.2 nM to 17.5 nM. The corresponding limit of detection (LOD) was 0.05 nM. Some other proteins such as thrombin (Th), glucose oxidase (GOx), and bovine serum albumin (BSA) all had a negligible effect on the determination of abrin. Furthermore, several practical samples spiked with abrin were analyzed using the proposed method with excellent recoveries. This aptamer-based colorimetric biosensor is superior to other conventional methods owing to its simplicity, low cost, and high sensitivity. [ABSTRACT FROM AUTHOR]

In this work, a novel facile nanoparticle autocatalytic sensor based on the inhibition of the Ag autocatalytic reaction for the determination of Hg2+ was developed. o-Phenylenediamine (OPD) tended to be oxidized into 2,3-diaminophenazine (OPDox) by silver ions (Ag+) followed by the formation of silver nanoparticles (AgNPs). Employed as a catalyst, the thus-formed AgNPs would further promote the reaction between OPD and Ag+. When Hg2+ was introduced, Hg2+ adsorbed on the surface of the AgNPs, thus inhibiting the oxidation process mentioned above and achieving weakened fluorescence intensity. A linear relationship between fluorescence intensity and Hg2+ concentration (within the range from 10 nM to 2500 nM) was obtained and the detection limit reached as low as 8.2 nM. The proposed method was also applied for the determination of Hg2+ in real water samples with satisfactory results. The protocol showed excellent advantages of sensitivity and selectivity for Hg2+ over various metal ions and anions. Meanwhile, this method was simpler and more cost-effective compared with many reported nanomaterial- and DNA-based approaches. Furthermore, an “INHIBIT” logic gate based on the Ag+–Hg2+–OPD system has also been designed. [ABSTRACT FROM AUTHOR]

Glutathione (GSH) plays an important role in the biological system and serves many cellular functions. Since all of the biothiols possess similar functional groups, it is still challenging to selectively detect GSH over cysteine (Cys) and homocysteine (Hcy). In this work, a novel and simple colorimetric method for discriminative detection of glutathione (GSH) over Cys and Hcy is developed. The proposed method is based on the fact that Ag [I] ion could oxidize 3,3′,5,5′,-tetramethylbenzidine (TMB) to the oxidized TMB to induce a blue color and an absorption peak centered at 652 nm. However, the introduction of GSH could cause the reduction of oxidized TMB and it could also combine with Ag + , both of which result in a blue color fading and a decrease of the absorbance at 652 nm. Based on this finding, we propose a method to qualitatively and quantitatively detect GSH by naked eyes and UV–vis spectroscopy, respectively. The proposed method shows a low detection limit of 0.1 µM by naked eyes and 0.05 µM with the help of UV–vis spectroscopy. In addition, this method has great potential in discriminatively detecting GSH over other amino acid and biothiols. More importantly, this method is simple and fast without the preparation of nanomaterials and has also been successfully applied to the detection of GSH in biological fluids. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a facile method to sensitively detect melamine and highly improve the peroxidase-like activity of bare gold nanoparticles (Au NPs) at the same time is proposed for the first time. It is interesting to find that the addition of melamine could improve the peroxidase-like activity of Au NPs. By coupling with 3,3′,5,5′-tetramethlybenzidine (TMB)–H2O2 chormogenic reaction, a novel method for colorimetic detection of melamine is developed. The detection limit of this method is as low as 0.2nM with the help of UV–vis spectroscopy and 0.5µM by naked-eye observation, both which are far below the US food and Drug Administration estimated melamine safety limit of 20µM. In addition, the present method is successfully applied for the detection of melamine in raw milk and milk powder. More importantly, the proposed method could also improve the peroxidase-like activity of Au NPs, which may not only provide a new approach to develop effective nanomaterials-based mimetic enzyme, but also irradiative to develop new applications for Au NPs in varieties of cost-effective and simple sensors in medicine, biotechnology and environmental chemistry. [Copyright &y& Elsevier]

Abstract: We reported a synthesis of manganese dioxide–silver hybrid nanowire. The fast development of detecting small molecules inspired us to study the electrochemical properties of the nanocomposite. The hybrid nanowire was fabricated as a novel nonenzymatic hydrogen peroxide sensor with rapid, stable, and reliable response with a detection limit of 0.24μM. The enhanced electrochemical signal characteristic of silver can be easily distinguished which can be assigned to the small amount decoration of silver nanoparticles on the nanowire. [Copyright &y& Elsevier]

A fluorescent assay for total antioxidant capacity (TAC) detection based on the light-responsive oxidase-like activity of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) has been developed. Thiamine (TH) as the peroxidase substrate usually works at alkaline conditions and thus limits its practical applications. Here, by utilization the light-responsive oxidase-like activity of BSA-AuNCs, TH is oxidized to fluorescent thiochrome under neutral condition in two minutes due to the single oxygen generated by BSA-AuNCs upon light irradiation. After the introduction of antioxidants into the BSA-AuNCs-TH system, the formation of thiochrome is inhibited resulting in the fluorescence decrease. On the basis of the above facts, BSA-AuNCs-TH-based assay has been fabricated and applied successfully to detect antioxidants and the TAC of vitamin C tablets as well as some commercial fruit juice with satisfied results. This work may provide novel insights into developing light-responsive nanozymes-based fluorescent assays. [Display omitted] • A fluorescent assay for the detection of total antioxidant capacity was constructed. • BSA-AuNCs can catalyze the oxidation of TH at neutral condition in short time. • Sensitive and time-saving detection of total antioxidant capacity was achieved. • This study may expand the applications of light-responsive nanozymes. [ABSTRACT FROM AUTHOR]

A fluorescent assay for alkaline phosphatase detection is proposed based on inner filter effect by in-situ formation of fluorescent azamonardine. • A facile, sensitive and selective method for alkaline phosphatase detection is proposed. • Dopamine can react with resorcinol to form fluorescent azamonardine under alkaline condtion. • The strategy is based on the inner filter effect of p -nitrophenol (PNP) on the in-situ formation of azamonardine. • This method shows great potential in real sample detection. A simple and sensitive fluorescent assay for determination of alkaline phosphatase (ALP) activity has been developed based on the inner filter effect (IFE) of p -nitrophenol (PNP) through the in-situ formation of azamonardine. Herein, p -nitrophenylphosphate (PNPP) was used as ALP substrate, which could be hydrolyzed to PNP with an absorption band centered at 405 nm. Under the alkaline condition, the introduction of resorcinol into the oxygen-containing dopamine solution would trigger the formation of fluorescent azamonardine with an intense emission band centering at 460 nm when excited at 415 nm. As a result, the fluorescence of azamonardine could remarkably decrease in the presence of PNP via IFE due to the absorption spectrum of PNP overlaps with the excitation spectrum of azamoardine. An IFE-based fluorescent assay has been thereby proposed for the ALP activity detection showing a linear range from 0.1 to 6.0 mU mL−1 with the detection limit down to 0.07 mU mL−1. Moreover, the developed fluorescent assay was successfully applied to probe ALP in human serum samples with satisfactory results. This IFE-based detection strategy exhibits several merits such as high sensitivity, good anti-interference ability, time-saving and easy operation simply by mixing the commercial reagents together. Therefore, it may promote the development of simple and sensitive fluorescent assays for the enzyme activity detections. [ABSTRACT FROM AUTHOR]

A colorimetric and fluorescent dual-channel method for ALP activity detection is proposed. • A colorimetric and fluorescent dual-channel method for ALP detection is developed. • BSA-AuNCs can catalyze the oxidation of TMB by H2O2 to obtain oxidized TMB. • The oxidized TMB causes the fluorescence quench of BSA-AuNCs. • This assay shows high sensitivity, selectivity and accuracy for ALP detection. Here, based on their bifunctional peroxidase-mimicking activity and fluorescence of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs), we develop a colorimetric and fluorescent dual-channel assay for alkaline phosphatase activity determination. The peroxidase-like activity of BSA-AuNCs makes it possible to catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into its blue product (oxTMB) in the presence of H 2 O 2 , and result in the fluorescence quench of BSA-AuNCs simultaneously due to the inner filter effect between oxTMB and BSA-AuNCs. While the ascorbic acid generating form alkaline phosphatase (ALP)-catalyzed hydrolysis of L-ascorbic acid-2-phosphate can inhibit the oxidation of TMB, thereby inducing decolorization of oxTMB and fluorescence recovery of BSA-AuNCs. Based on these findings, a dual-readout assay for ALP activity sensing using BSA-AuNCs has been reported for the first time. The detection limitation can reach as low as 0.26 and 0.16 mU mL-1 by colorimetric and fluorescent method, respectively. Moreover, the developed assay has been successfully applied to detect ALP in human serum samples with satisfactory results. This method may not only offer new idea for simple, sensitive and accurate detection of ALP activity, but also broaden the applications of BSA-AuNCs in bioanalysis. [ABSTRACT FROM AUTHOR]

The oxidase-like activity of nanoceria is low. This limits its practical applications. It is demonstrated here that pyrophosphate ion (PPi) can improve the oxidase-like activity of nanoceria. Specifically, nanoceria catalyzes the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to give a blue product (oxTMB) with an absorption peak at 645 nm in the presence of PPi. If, however, alkaline phosphatase (ALP) is present, it will hydrolyze PPi, and this results in a decreased oxidase-like activity of nanoceria. Hence, less blue oxTMB willl be formed. On the other hand, if the ALP inhibitor Na3VO4 is added to the system, the oxidase-like activity of nanoceria is gradually restored. On the basis of the above results, a spectrophotometric method was developed for determination of the activity of ALP. It works in the 0.5 to 10 mU.mL−1 activity range and has a 0.32 mU.mL−1 detection limit. Na3VO4 causes a 50% ALP inhibition if present in 71 μM concentration. The assay was successfully applied to the determination of ALP in spiked human serum and gave good recoveries. [ABSTRACT FROM AUTHOR]

The authors describe a fluorometric method for determination of the activity of alkaline phosphatase (ALP) and its inhibitors. Nitrogen and boron co-doped carbon dots (C-dots) with excitation/emission peaks at 490/540 nm act as the fluorescent probe. The C-dots were prepared by hydrothermal carbonization starting from 3-aminophenylboronic acid as the sole precursor. On the basis of the boronic acid-triggered specific reaction with cis-diols, the boronic acid modified C-dots can bind to ascorbic acid that is generated by ALP-catalyzed hydrolysis of ascorbic acid 2-phosphate. This results in particle aggregation and quenching of fluorescence. If the ALP inhibitor Na3VO4 is introduced into the system, the activity of ALP is reduced and the fluorescence of C-dots recovers. This fluorometric method allows for the determination of ALP activity in the range from 0.2 to 6.0 mU mL−1 with a detection limit of 0.16 mU mL−1. The IC50 value for the inhibitor Na3VO4 is 3.6 μM. The method is convenient and cost-effective. It does not require complicated operations and in our perception widens the scope of applications of C-dots in bioanalytical sciences.Schematic presentation of the nitrogen and boron co-doped carbon dot-based fluorometric method for determination of alkaline phosphatase (ALP) activity. [ABSTRACT FROM AUTHOR]

Direct electrochemical production of hydrogen peroxide (H2O2) through two‐electron oxygen electrochemistry, for example, the oxygen reduction in fuel cells or water oxidation in water electrolyzers, could provide an attractive alternative to locally produce this chemical on demand. The efficiency of these processes depends greatly on the availability of cost‐effective catalysts with high selectivity, activity, and stability. In recent years, various novel nanostructured materials have been reported to selectively produce H2O2. Through combined experimental and theoretical approaches, underlying mechanisms in the electrochemical synthesis of H2O2 via oxygen electrochemistry have been unveiled. Considering the remarkable progress in this area, the authors summarize recent developments regarding the direct production of H2O2 through two‐electron electrochemical oxygen reactions. The fundamental aspects of electrochemical oxygen reactions are first introduced. Various types of catalysts that can effectively produce H2O2 via two‐electron oxygen electrochemistry are then presented. In parallel, the unique structure‐, component‐, and composition‐dependent electrochemical performance together with the underlying catalytic mechanisms are discussed. Finally, a brief conclusion about the recent progress achieved in electrochemical generation of H2O2 and an outlook on future research challenges are given. Direct electrochemical production of hydrogen peroxide (H2O2) through two‐electron oxygen reduction and water oxidation is summarized. The structure, components, and composition of the electrocatalysts show strong correlation with their selectivity, activity, and durability. This review also provides some guidelines for rational design of highly efficient electrocatalysts toward electrochemical H2O2 generation on demand. [ABSTRACT FROM AUTHOR]

A fluorometric assay is described for sulfide ions determination. It is based on the finding that the oxidation of the non-fluorescent substrate thiamine (TH) by Cu(II) in basic solution to form fluorescent thiochrome is inhibited by sulfide ions. This results in a decrease in fluorescence intensity which is proportional to the concentration of sulfide ions. Under the optimized conditions, the decrease in fluorescence, best measured at excitation/emission wavelengths of 370/440 nm, decreases linearly in the 0.03 to 2.5 μM sulfide ions concentration range. The detection limit is 20 nM. The method shows excellent selectivity over many potentially interfering ions and has been successfully applied to the determination of sulfide ions in spiked tap water, lake water and the synthetic wastewater samples. The method is time-saving and environmentally friendly, and in our perception shows a great potential in water quality inspection and environmental monitoring.A fluorescent assay for sulfide ions detection is proposed based on its inhibitory effect on the oxidation of thiamine by Cu(II) ions. [ABSTRACT FROM AUTHOR]

A multifunctional TiO 2 /Ag nanoparticles (AgNPs) complex substrate was prepared via a three-step approach, which included the hydrothermal route on a Ti substrate, the deposition of Ag by photo-reducing method and the annealing treatment under high temperature. The effect of the annealing process on the morphology, structure and surface-enhanced Raman scattering (SERS) performance of the substrate was systematically investigated, and the optimal substrate was obtained. Herein, 4-aminothiophenol (4-ATP), methylene blue (MB) and crystal violet (CV) were employed as probe molecules to test the sensitivity and UV-cleanable property of the hybrid SERS substrate. The results suggested that the substrate exhibited relatively high enhancement ability, good stability, reproducibility, and recyclability. The synthesised SERS-active substrate was further used to detect thiram molecules, a kind of pesticides, and the limitation of detection in ethanol, apple juice and apple peel reached 10 −7 M, 10 −6 M and 240 ng/cm 2 , respectively. The detection limit of thiram in the apple juice was below than the maximal residue limit of 7 ppm (2.9 × 10 −5 M) in fruit prescribed by the U.S. Environmental Protection Agency (EPA). These results demonstrated that TiO 2 /AgNPs complex substrate exhibited promising application with respect to its potential use for on-site detection of residual pesticides. [ABSTRACT FROM AUTHOR]

Hexavalent chromium is a highly toxic substance, which will pose a serious threat to human life and health and the entire ecosystem. Therefore, it is crucial to establish a simple and rapid detection method for hexavalent chromium. In this work, we fabricated bovine serum albumin–stabilized silver nanocluster (BSA-Ag13 NC) which exhibited photoresponsive oxidase-like activity, catalyzing the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to the blue oxidized state TMB (oxTMB) in a short time. Interestingly, 8-hydroxyquinoline (8-HQ) can significantly inhibit the color reaction of TMB oxidation while Cr(VI) can interact specifically with 8-HQ to restore this chromogenic reaction. Based on the above facts, a colorimetric sensing system for detecting Cr(VI) was developed. The sensing system shows a wide linear range, and good selectivity, with a low detection limit of 2.32 nM. Moreover, this sensing system could be successfully applied to the detection of Cr(VI) in lake water, tap water, and sewage with satisfactory results. [ABSTRACT FROM AUTHOR]

[Display omitted] In this work, we report a novel MoS x /Mn 0.3 Cd 0.7 S composite catalyst that has been designed and fabricated by in situ coupling MoS x nanoclusters with 1D Mn 0.3 Cd 0.7 S nanorods for photocatalytic H 2 production. The catalyst features a 1D nanostructure with MoS x nanoclusters uniformly dispersed along the Mn 0.3 Cd 0.7 S nanorod. It was found that an intimate interface is built between MoS x nanoclusters and Mn 0.3 Cd 0.7 S nanorods thanks to the facile in situ photoreduction route, which contributes to a high-efficiency interfacial charge separation. The resulting MoS x /Mn 0.3 Cd 0.7 S photocatalyst shows a dramatically enhanced visible-light-driven photocatalytic H 2 production activity compared with the control samples, owing to more efficient spatial charge separation as well as enriched active sites. This work is expected to provide an optimized structure model for rational design and constructing novel, inexpensive, efficient and stable cocatalyst/metal sulfide photocatalyst systems for H 2 production. [ABSTRACT FROM AUTHOR]

Abstract: NiCo2O4 nanoflake composites were synthesized by using DNA molecules as templates via in-situ assembly and subsequent thermal treatment. The obtained NiCo2O4 composites were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Cyclic voltammetry and chronopotentiometry tests were used to investigate the electrochemical properties of the as-prepared composites. Superior performances with a good specific capacitance (1468 F/g), an extraordinary rate capability (64.9% capacity retention at 16 A/g) and an excellent cycling stability (85.5% retention after 5000 cycles) were achieved. The DNA templates were introduced as the binder of NiCo2O4 and as the conductive matrix to facilitate the electron transmission between electroactive materials and outside current collectors, which resulted in the excellent electrochemical performances of the synthesized NiCo2O4 composites. It is believed that our NiCo2O4 nanocomposites could be used as effective electrode materials for supercapacitors. [Copyright &y& Elsevier]

• CDs@NC is successfully obtained through two-step pyrolysis. • The peroxidase-like activity of CDs@NC can be adjusted by the content of glucose. • CDs@NC nanozymes are successfully used for detection of D-amino acids. • Patients with early gastric cancer can be easily distinguished from healthy people. The concentrations of D-Proline (D-Pro) and D-Alanine (D-Ala) in the saliva of early-stage gastric cancer patients are prominently higher than those of healthy people. Therefore, precisely monitoring the concentrations of D-Pro and D-Ala has essential implications for gastric cancer diagnosis and treatment. Here, through pyrolysis of ZIF-8 precursor filled with glucose (G@ZIF-8), the carbon dots confined in N-doped carbon (CDs@NC) are successfully obtained. The CDs@NC can readily act as peroxidase-like nanozyme for the colorimetric detection of D-amino acids that associated with early gastric cancer. Intriguingly, the peroxidase-like activity of CDs@NC can be tuned easily by adjusting the content of glucose precursors. Further study of the catalytic mechanism shows that the superoxide radical (O 2 −) may be the critical Reactive oxygen species (ROS) involved in the peroxidase-like catalytic reactions. The excellent results of saliva tests suggest that the colorimetric method could be used to quickly distinguish patients with early gastric cancer from healthy people. [ABSTRACT FROM AUTHOR]

A convenient and sensitive antioxidant assay with high performance is essential for assessing food quality and monitoring the oxidative stress level of biological matrices. Although coordination polymer nanoparticles (CPNs)-based nanozymes have emerged as candidates in the analytical field, strategies to improve the catalytic activity of CPNs have been scarcely revealed and studied. Herein, we demonstrate a manganese (Mn) doping strategy to enhance the peroxidase-mimetic activity of Fe-based CPNs. By tuning the Mn doping amounts and selecting 2,5-dihydroxyterephthalic acid (H4DHTP) as ligands, the produced nanozymes in amorphous state followed the catalytic activity order of Fe5Mn-DHTP > Fe8Mn-DHTP > Fe2Mn-DHTP > Fe-DHTP > Mn-DHTP. Ulteriorly, benefitting from the best catalytic performance and definite catalytic mechanism of Fe5Mn-DHTP, versatile colorimetric assays for ultrasensitive detection of one exogenous antioxidant (ascorbic acid, AA) and two endogenous antioxidants (glutathione, GSH; cysteine, Cys) have been deftly devised based on the inhibition of the 3,3′,5,5′-tetramethylbenzidine chromogenic reaction in presence of H2O2. It was found that mercaptan (GSH and Cys) and AA exhibited different inhibition mechanisms. Practically, such a colorimetric assay was viable to determine the total antioxidant capacity of drugs and foods with desirable results. This work proposes a feasible strategy for embellishing CPN nanozymes used for designing sensitive and convenient assays for various antioxidants based on an explicit detection mechanism. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Highly dispersed ultrasmall ruthenium nanoparticles with a clean surface are deposited onto graphitic carbon nitride (C3N4‐Ru) through spontaneous redox reaction between the C3N4 sheets and Ru salt without the use of any reductant. The as‐prepared C3N4‐Ru exhibits distinct peroxidase‐like activity. A nanozyme based method is successfully developed for detecting the H2O2 generated in‐situ by the two‐electron oxygen reduction strategy. The C3N4‐Ru nanozyme can realize the detection of H2O2 with a wide linear range and a low detection limit. The testing results are also compared with the conventional modified titration method, and show greater possibility for the practical detection of H2O2 produced via the electrochemical oxygen reduction for its higher selectivity. [ABSTRACT FROM AUTHOR]

A convenient and sensitive colorimetric assay for acetylcholinesterase (AChE) and its inhibitor has been designed based on the oxidase-like activity of {100}-faceted Pd square nanoplates which are grown in situ on reduced graphene oxide (PdSP@rGO). PdSP@rGO can effectively catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) without the assistance of H2O2 to generate blue oxidized TMB (oxTMB) with a characteristic absorption peak at 652 nm. In the presence of AChE, acetylthiocholine (ATCh), a typical AChE substrate, is hydrolyzed to thiocholine (TCh). The generated TCh can effectively inhibit the PdSP@rGO-triggered chromogenic reaction of TMB via cheating with Pd, resulting in color fading and decrease in absorbance. Thus, a sensitive probe for AChE activity is constructed with a working range of 0.25–5 mU mL−1 and a limit of detection (LOD) of 0.0625 mU mL−1. Furthermore, because of the inhibition effect of tacrine on AChE, tacrine is also detected through the colorimetric AChE assay system within the concentrations range 0.025–0.4 μM with a LOD of 0.00229 μM. Hence, a rapid and facile colorimetric procedure to sensitively detect AChE and its inhibitor can be anticipated through modulating the oxidase-like activity of PdSP@rGO. [ABSTRACT FROM AUTHOR]

Enzyme-mimetic properties of nanomaterials can be efficiently tuned by controlling their size, composition, and structure. Here, ultrathin PdCu alloy nanosheet–assembled three-dimensional (3D) nanoflowers (Pd1Cux NAFs) with tunable surface composition are obtained via a generalized strategy. In presence of H2O2, the as-synthesized Pd1Cux NAFs can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to the oxidized form of TMB (oxTMB) with a characteristic absorption peak at 652 nm. Interestingly, Pd1Cux NAFs show obviously composition-dependent peroxidase-like catalytic activities because of the synergistic interaction of nanoalloy. Additionally, different from 2D Pd nanosheets, the distinctive 3D superstructures are featured with rich approachable sites and proper layer spacing, which are in favor of fast mass transport and electron transfers during the catalytic process. Among the studied Pd1Cux NAFs, the Pd1Cu1.7 NAFs show the highest enzyme-like activities and can be successfully applied for the colorimetric detection of glucose with a low detection limit of 2.93 ± 0.53 μM. This work provides an efficient avenue to fabricate PdCu NAF nanozymes in biosensing toward glucose detection. [ABSTRACT FROM AUTHOR]

The facile detection of total antioxidant capacity (TAC) is limited by in-situ analysis, because it usually requires complex laboratory equipments. Here, a colorimetric assay for TAC detection is developed based on the peroxidase-like activity of iron-doped carbon nitride (Fe/NC) and the smartphone platform. The peroxidase-like activity of carbon nitride is greatly improved by the introduction of Fe atoms, and the active sites turn to Fe-N x coordination groups in the Fe/NC. The inhibition mechanism of the chromogenic reaction for different kinds of antioxidants is also studied. The colorimetric assay is fabricated by the relationship of absorbance-color-antioxidant content and applied successfully to the TAC detection of several fruit juicesand commercial beverages. This work not only provides a promising approach for convenient in-situ TAC assay without the use of large instruments, but also expands the application of nanozymes in nutritional value assessment of foods. The Fe atom-containing carbon nitride shows greatly improved peroxidase-like activity and can be conveniently used for the on-site smartphone-based colorimetric assay of total antioxidant capacity of foods. [Display omitted] • The peroxidase-like activity of C 3 N 4 is greatly improved by Fe atom doping. • The newly formed Fe-N x serve as the main active sites in the Fe/NC nanozyme. • The antioxidants content are tested and different mechanisms are proposed for AA or GSH/Cys. • RGB model of smartphone can be used for on-site colorimetric assay of TAC in food samples. [ABSTRACT FROM AUTHOR]

An ultrasensitive fluorometric and colorimetric dual-mode assay is described for the determination of the activity of alkaline phosphatase (ALP). ALP catalyzes the decomposition of 2-phospho-L-ascorbic acid, and the ascorbic acid thus generated reduces silver ions. In the presence of gold nanoparticles, gold-silver nanoparticles (Au@Ag NPs) are formed. This is accompanied by a color change form pink to deep yellow. The Au@Ag NPs reduce the fluorescence of blue fluorescent graphene quantum dots due to spectral overlap. The changes of absorbance (measured at 410 and 520 nm) and fluorescence (measured at excitation/emission wavelengths of 346/415 nm) correlate well with the ALP activity in the 0.01–6 mU·mL−1 (absorption) and 0.01–2 mU·mL−1 (fluorescence) ranges, and the detection limits are 9 and 5 μU·mL−1 individually. [ABSTRACT FROM AUTHOR]

In this paper, a novel, selective and eco-friendly biosensor has been fabricated and applied for sensitive detection of antibiotic oxytetracycline (OTC). This fluorescent biosensor was based on carbon quantum dots (CDs), H 2 O 2 and Fe 3 O 4 magnetic nanoparticles (Fe 3 O 4 MNPs). Herein, we firstly demonstrated that the fluorescence of CDs decreased apparently in the presence of OTC, H 2 O 2 and Fe 3 O 4 MNPs. The fluorescence quenching of CDs not only is caused by the hydroxyl radical produced from the Fenton reaction and complexation of Fe 3 O 4 MNPs with OTC, but also might be related to the inner filter effect (IFE) between CDs and OTC, which improved the selectivity and sensitivity of the fabricated biosensor. Under the optimal experiment conditions, the relative fluorescence intensity of the CDs decreased linearly with the increasing concentration of OTC from 25 nM to 1.75 μM. The detection limit of the fabricated biosensor on OTC was 9.5 nM at a signal-to-noise ratio of 3. Compared with other current protocols, the method described here displayed a few advantages including simplicity, low cost and rapid detection. The precision and reproducibility of the proposed sensor were also acceptable Significantly, the practicality of this sensitive sensor for OTC detection in drugs was further validated, revealing the advantages of high simplicity, sensitivity and selectivity. Hence, the developed biosensor might provide a useful and practical tool for OTC determination and related food safety analysis and clinical diagnosis. [ABSTRACT FROM AUTHOR]

• SA-Co/NC is obtained by wet chemical method combined pyrolysis process. • Theoretical calculations and experiments prove oxidase-like activity of SA-Co/NC. • A time-based visualization scheme for TAC detection is proposed. • TAC monitoring of skin care products is achieved by smartphone platform. Reactive oxygen species (ROS) are an important cause of oxidative skin aging and can be removed by adding some antioxidant ingredients to skin care products. However, total antioxidant capacity (TAC) assays generally require sophisticated laboratory equipment, which greatly limits their daily application. Fortunately, the adoption and development of portable smartphone platforms could promises to solve this challenge. Herein, we report a cobalt single atom-based portable smartphone platform which can realize dynamic-time visualization monitoring the TAC of skin care product. Theoretical calculations and specific experimental results show that single-atom cobalt catalysts (SA-Co/NC) present excellent oxidase-like activity and can effectively convert dissolved oxygen into strongly oxidizing reactive oxygen species. More interestingly, based on the unique sacrificial inhibition catalytic mechanism of ascorbic acid (AA), it can be combined with a portable smartphone platform to detect the TAC of real samples by fitting a time-color-concentration standard curve and recording the change of color RGB values during the reaction. Compared with the traditional scheme, this scheme is convenient, low cost, and can realize visual detection of mobile terminals. This work provides a new scheme for miniaturization, convenience and home-based of TAC detection. [ABSTRACT FROM AUTHOR]

A novel colorimetric biosensor for the determination of tetracyclines (TCs) based on the Fe 3 O 4 magnetic nanoparticles (Fe 3 O 4 MNPs) is presented in this paper. TCs are known to have a strong tendency to complex with metal ions such as Fe(II) and Fe(III) on the surface of Fe 3 O 4 MNPs. Experiments results show that the complexation of Fe 3 O 4 MNPs and TCs could lead to the accelerated catalysing H 2 O 2 -mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by Fenton chemistry. The reaction starts with oxidation of Fe 3 O 4 MNPs-TCs complex by dissolved oxygen to generate reactive oxygen species (ROS), primarily ·OH, leading to deepen the color of the solution. Analysis results can be seen with the naked eye and monitored by UV–vis spectra. Under the optimal conditions, the detection limits are 26 nM for oxytetracycline (OTC), 45 nM for tetracycline (TC) and 48 nM for doxycycline (DOX). Moreover, this method has been applied for the determination of OTC content in drugs with satisfactory results. The proposed colorimetric biosensor is advantageous over other conventional methods in terms of convenient operation without any complicated chemical synthesis, modification, or tedious experimental procedures and its simple signal generation and detection by the naked eye. To the best of our knowledge, this is the first report on the enhancement effect of TCs on Fe 3 O 4 MNPs-TMB-H 2 O 2 reaction and its application in colorimetric TCs analysis. The designed colorimetric strategy may provide a promising alternative detection for TCs in clinical samples. [ABSTRACT FROM AUTHOR]

The pod-like Cu 2 O nanowire arrays (denoted as Cu 2 O PLNWs/Cu foam) grown on the three-dimensional copper foam is synthesized by a low-cost and convenient method. The morphology and composition of the Cu 2 O PLNWs/Cu foam are characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction, respectively. The high conductivity of Cu foam as current collector can facilitate the charge and mass transfer, and the Cu foam with opened framework provides large amounts of anchoring sites for the deposition of Cu 2 O NWs during the synthesis of the Cu 2 O PLNWs/Cu foam. Accordingly, The Cu 2 O PLNWs/Cu foam is used as electrocatalysts for the detection of glucose and H 2 O 2 . The Cu 2 O PLNWs/Cu foam electrode shows extremely high sensitivity of 6.6807 mA mM −1 cm −2 and a low detection limit of 0.67 μM for the electrocatalytic oxidation for glucose. The nonenzymatic sensor also demonstrates good response toward hydrogen peroxide with high sensitivity of 1.4773 mA mM −1 cm −2 and the detection limit of 1.05 μM. Due to the excellently high sensitivity, stability and anti-interference ability, the Cu 2 O PLNWs/Cu foam will be the potential candidate for constructing practical non-enzymatic glucose and hydrogen peroxide sensors. [ABSTRACT FROM AUTHOR]

A facile, low cost and time-saving method to synthesize porous NiCo 2 O 4 nanoplatelet and nanorod structures is developed via a simple two-step route. A flakes assembled precursor containing Ni-Co hydroxides is firstly prepared via a facile, low-cost chemical bath coprecipitation process only using diluted ammonia solution as a precipitant to govern over the nucleation, growth, and agglomeration processes.Then, porous NiCo 2 O 4 nanoplatelet and nanorod structures are successfully obtained through pyrolyzing the above precursor. The influence of the calcination temperature is mainly studied on the pyrolysis reaction. The calcination temperature has statistically significant effects on the morphology and structure evolution, crystallinity, electronic conductivity and the electrochemical performances of the products. The optimized, nanoplatelet predominated NiCo 2 O 4 spinel, calcinated at 300 ∘C for 6 h (denoted as NC300), has excellent crystallinity and electric conductivity. It shows a superior-specific capacitance of 1362F g −1 at a current density of 1 A g −1 .When the current density increases to 16 A g −1 , the specific capacity still retains 964 F g −1 (70.8% capacity retention). Ragone plot indicates maximum energy density of our porous NC300 electrode is 75.67 W h kg −1 at a power density of 499.82 W kg −1 . Cycle-life tests show that the specific capacitance of NC300 is nearly stable between 300 and 1500 cycles, indicating its potential use in energy-storage field.The simplicity and practicability of the modified pyrolysis process may facilitate the successful commercial applications in electrochemical capacitors for nanostructured NiCo 2 O 4 spinel. [ABSTRACT FROM AUTHOR]

It’s almost hardly to realize the large-scale practical application of fuel cells if the costly noble metal-based electrocatalysts for oxygen reduction reaction (ORR) cannot be replaced by other efficient, stable, and low-cost non-precious metal or even metal-free ORR electrocatalysts. Herein, we report the novel design and synthesis of N and S dual-doped hierarchical micro/mesoporous carbon (NS-MC) foams via high temperature treatment of polyaniline coated sulfur sphere composite without any side products. The highlight of our method lies in its environmental concept of green synthesis and simplicity for no use of toxic gas (NH 3 or H 2 S) or templates (SiO 2 or MgO). The main focus of this research is to develop a high-performance metal-free ORR electrocatalyst as well as to gain insight into the synergistic effects originating from multiple-element doping on ORR performance. It is found that much graphitic-N and thiophene-S binding configurations formed for NS-MC foams at 1000 °C, which shows excellent electrocatalytic activity (high onset potential (0.051 V vs. Ag/AgCl (sat.KCl)), large diffusion-limiting current density (5.61 mA cm −2 at 1600 rpm) and kinetic current density (22.22 mA cm −2 at −0.25 V)), high selectivity towards methanol and long durability compared to commercial Pt/C with a nearly four-electron transfer passway when they are employed as metal-free catalyst for ORR. Besides, the desired NS-MC1000 shows a strong amperometric response towards ethanol indicating its potential application as an anode metal-free electrocatalyst in the alkaline direct ethanol fuel cell. [ABSTRACT FROM AUTHOR]

In this work, we proposed a facile, environmentally friendly and cost-effective assay for melamine with BSA-stabilized gold nanoclusters (AuNCs) as a fluorescence reader. Melamine, which has a multi-nitrogen heterocyclic ring, is prone to coordinate with Hg2+. This property causes the anti-quenching ability of Hg2+ to AuNCs through decreasing the metallophilic interaction between Hg2+ and Au+. By this method, detection limit down to 0.15µM is obtained, which is approximately 130 times lower than that of the US food and Drug Administration estimated melamine safety limit of 20µM. Furthermore, several real samples spiked with melamine, including raw milk and milk powder, are analyzed using the sensing system with excellent recoveries. This gold-nanocluster-based fluorescent method could find applications in highly sensitive detection of melamine in real samples. [ABSTRACT FROM AUTHOR]

This study demonstrates a cocaine sensing method employing graphene oxide (GO), gold nanoparticles and a structure switching aptamer, which can fold into a three-way junction in the presence of cocaine. On the observation of gold nanoparticles (Au NPs) induced graphene oxide fluorescence quenching, a structure switching aptamer of cocaine was introduced as the linker between the two parts. Firstly, two fragments of a cocaine aptamer were immobilized covalently onto GO and Au NPs, respectively. Then when the three-way junction formed, the Au NPs were drawn near to the GO surface and induced a fluorescence intensity decrease. The limit of detection was 0.1 μM for cocaine in purified water, and well defined results were also obtained in biological fluids and the specificity experiment, which expands the feasibility of the as-prepared sensor for practical applications. [ABSTRACT FROM AUTHOR]

Abstract: Here, we report a new and facile method to prepare silver nanoparticles (Ag NPs) film for surface-enhanced Raman scattering (SERS)-based sensing. The porous Ni foam was used as a template to generate high quality of Ag NPs by seed-mediated growth of metallic nanoparticles. The preparation process is very economic and environment-friendly, can achieve the recovery of the raw materials. We found that the type of silver-plating solution and the growth time are two key factors to determine the magnitude of SERS signal enhancement. Using rhodamine 6G (R6G) and 4-animothiophenol (4-ATP) as probe molecules, the created Ag NP films exhibited relatively high enhancement ability, good stability, and well reproducibility. The synthesized SERS-active substrate was further used to detect melamine molecules, an illegal additive in infant milk powder, and the limitation of detection can reach 1μM. [Copyright &y& Elsevier]

Electrochemical reduction and electrodeposition are two effective methods for the preparation of new nanomaterials for electrochemical sensing. In this work, the reduced graphene oxide-nickel nanoparticles composite (RGO-NiNPs) was synthesized using both methods mentioned above. The fabrication process was simple and easily performed. Then, the RGO-NiNPs composite was characterized by SEM, EDS, and XRD. Furthermore, for the strong catalytic ability of the high-valent oxyhydroxide species (NiOOH) formed in alkaline media, the composite was used as the matrix for nonenzymatic detection of glucose. Comparing with NiNPs modified glassy carbon electrode (NiNPs/GCE), the RGO-NiNPs/GCE showed better sensitivity and stability. A low detection limit of 0.1 µM with a wide linear range from 2 µM to 2.1 mM ( R=0.996) was obtained. [ABSTRACT FROM AUTHOR]

• Fe-N-C nanozyme is successfully prepared by pyrolyzing hemin trapped zeolitic-imidazolate-frameworks (Hemin@ZIF-8). • Remarkable peroxidase-mimetic activities can be achieved. • The peroxidase-mimetic activity of the Fe-N-C catalysts is effectively adjusted. • Fe-N x moieties are demonstrated to be main active sites to mimic peroxidase. • The Fe-N-C nanozyme is used successfully in detection of ascorbic acid-generating bio-enzymes. Revealing the relationship between composition and enzyme-like activities is essential for the rational designs of nanozymes and related assays with improved performances. Here, a series of Fe-N co-doped porous carbon (Fe-N-C) nanozymes containing different Fe contents have been successfully prepared by facilely pyrolyzing hemin trapped zeolitic-imidazolate-frameworks (Hemin@ZIF-8). The special doping agent hemin will endow Fe-N-C with exceptionally high peroxidase-mimetic activities due to the hierarchically porous structure, high specific surface area, and high dispersed Fe-N x sites. Notably, the optimal Fe 55 -N-C nanozymes are used to detect bio-enzymes, by taking alkaline phosphatase (ALP) as a model, based on the inhibition of nanozymatic activity by ascorbic acid (AA). A linear activity range of 0.05–20 U/L is obtained with a low detection limit of 0.03 U/L, which is superior to the most published optical ALP assays. This work provides not only a new method for the design of the transition metal-N-C nanozyme with enhanced peroxidase-like activity but also a promising strategy for the detection of ascorbic acid-generating bio-enzymes with the assistance of specific substrates. [ABSTRACT FROM AUTHOR]

• A novel 0D/1D direct Z-scheme structural model is designed and constructed. • Efficient separation of interior and surface carriers is simultaneously realized. • W 18 O 49 /CdS shows excellent photocatalytic H 2 evolution performance and stability. • This novel Z-scheme exhibits potential in photocatalytic overall water splitting. Rational design and construction of unique transmission channel in photocatalyst system is of great significance for promoting the efficient spatial separation of photo-induced charge carriers. This work reports a novel 0D/1D direct Z-scheme heterojunction photocatalyst synthesized by in-situ anchoring W 18 O 49 QDs onto the surface of CdS NRs. Due to this unique structural design, both bulk and surface photogenerated carriers are separated efficiently, achieving a dramatically improved photocatalytic H 2 evolution performance. The optimal of H 2 production rate of the W 18 O 49 /CdS heterostructure is as high as 55.24 mmol·h−1·g−1, with lactic acid as sacrificial reagents under visible light irradiation, which is approximately 110.5 and 3.7 times as that of pure CdS NRs and Pt/CdS, respectively. Even in the absence of hole scavengers, the optimal WCS300 composite exhibits an obvious photocatalytic H 2 evolution activity accompanied by the generation of considerable H 2 O 2. This work provides a new protocol for the development of efficient photocatalyst systems. [ABSTRACT FROM AUTHOR]