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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]

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 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]

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]