Search

The threat of glyphosate to food safety has attracted widespread attention. Consequently, it is highly urgent to develop a sensitive and accurate method for glyphosate detection. Herein, a turn-on fluorescent method for glyphosate detection using polydopamine-polyethyleneimine (PDA-PEI) copolymer as a fluorescent probe and p-nitrophenylphosphate (PNPP)/alkaline phosphatase (ALP) as a fluorescence quenching system is developed. The PDA-PEI copolymer was prepared by a one-pot method under mild condition, and its fluorescence kept almost unchanged after storing in a refrigerator for one month. ALP catalyzed the hydrolysis of PNPP to p-nitrophenol (PNP) that caused the fluorescence quenching of PDA-PEI copolymer via the inner filter effect. However, glyphosate inhibited ALP activity, thereby preventing the formation of PNP and restoring the fluorescence signal. Under the optimized conditions, the fluorescence of PDA-PEI copolymer depended on glyphosate concentrations ranging from 0.2 to 10 μg/mL with a detection limit of 0.06 μg/mL. Moreover, this assay was applied to detect glyphosate in real samples using the standard addition method. The recoveries were in the range from 88.8% to 107.0% with RSD less than 7.78%. This study provides a novel insight for glyphosate detection and expands the applications of fluorescent copolymer. [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]

Understanding the relationship between composition and activity is essential for the rational design of metal‐nitrogen‐Carbon (M−N−C) electrocatalysts for the oxygen reduction reaction (ORR). Here, a series of Fe‐N co‐doped porous carbon (Fe‐N−C) electrocatalysts are successfully prepared through the pyrolysis of ZIF‐8 doped with different amount of hemin. The catalyst (Fe55‐N−C) exhibits impressive ORR performance with an onset potential (Eonset) of 1.02 V (vs. RHE) and a half‐wave potential (E1/2) of 0.892 V in alkaline media, outperforming commercial Pt/C. Meanwhile, the average kinetic current density (Jk) of Fe55‐N−C at 0.850 V is 17.5 mA cm−2, which is 3.3‐fold higher than that of commercial Pt/C. Besides, it also delivers anti‐methanol poisoning ability and high durability. The high performance stems from the hierarchical porous structure, large specific surface area, and high dispersion of Fe‐Nx active sites in Fe55‐N−C. These findings could inspire new perspectives for rationally designing and synthesizing economical and practical non‐precious‐metal oxygen reduction electrocatalysts. [ABSTRACT FROM AUTHOR]

This study provides a unique method for the rapid deposition of amorphous Co−B nanosheets on Ni foam (Co−B/NF) by alternatively dipping Ni foam into cobalt salt and borohydride solutions. The as‐prepared Co−B/NF can act as a highly efficient electrocatalyst for the oxygen evolution reaction (OER). The catalyst affords a current density of 20 mA cm−2 at 265 mV overpotential during the OER in 1.0 M KOH solution, ranking it among the best reported nonprecious OER electrocatalysts. This strategy for constructing electrocatalysis electrodes prevails over the conventional method of drop‐coating metal boride dispersions on the electrode, having better intrinsic stability and fully exposed active site surfaces. Given the low cost, ease of fabrication, good controllability, and high OER electrocatalytic activity and stability, Co−B/NF has great potential as a high‐performance anode catalyst for water splitting. [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]

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]

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]