Metal-phenolic networks derived CN-FeC hollow nanozyme with robust peroxidase-like activity for total antioxidant capacity detection.

A tannate-iron network-derived peroxidase-like catalyst loaded with Fe ions on carbon nitride (C3N4) was reported for detection of total antioxidant capacity (TAC) in food in this study. Metal-phenolic networks (MPNs) was employed to form a low coordination compound on C3N4, and calcined catalyst formed hollow structure with abundant and uniform Fe sites and surface folds. CN-FeC exhibited significant peroxidase-like activity and high substrate affinity. The homogeneous distribution of amorphous Fe elements on the C3N4 substrate provides more active sites, resulting in provided excellent catalytic activity to activate H2O2 to ·OH, 1O2 and O2·-. The established CN-FeC/TMB/H2O2 colorimetric system can detect AA in the concentration range of 5-40 µM, with the detection limits of 1.40 µM, respectively. It has good accuracy for the detection of vitamin C tablets, beverages. Taken together, this work shows that metal-phenolic networks can be an effective way to achieve efficient utilization of metal atoms and provides a promising idea for metal-phenolic networks in nanoparticle enzyme performance enhancement.

Rational construction of a robust metal-organic framework nanozyme with dual-metal active sites for colorimetric detection of organophosphorus pesticides.

While nanomaterials with enzyme-mimicking activities are emerging as promising candidates in the colorimetric detection of organophosphorus pesticides (OPs), the catalytic activities and recognition ability to analyte of most nanozymes are inherently deficient. In this work, we introduced manganese ions into a typical iron based MOF (Fe-MIL(53)) via a one-pot hydrothermal reaction strategy, which brought out a catalytically favorable bimetallic Mn/Fe-MIL(53) MOF nanozyme. The catalytic performance of Mn/Fe-MIL(53) is superior to that of pure Fe-MIL (53) and the mechanism for superior catalytic activity of material is revealed by active species scavenging experiments and X-ray photoelectron spectroscopy (XPS). Besides, the introduction of manganese endows the material with the characteristic of being specially destroyed by choline, which motivates the establishment of a simple, selective and sensitive colorimetric strategy for OPs detection. The proposed colorimetric strategy could quantify the methyl parathion and chlorpyrifos in the concentration range of 10-120 nM and 5-50 nM, respectively. The low detection limit of 2.8 nM for methyl parathion and 0.95 nM (3 S/N) for chlorpyrifos were achieved. Good recoveries were obtained when applied in the real sample detection. Our work paves the way to boost catalytic performance of MOF nanozymes, which will be useful in biosensing.

Dextran-stabilized Fe-Mn bimetallic oxidase-like nanozyme for total antioxidant capacity assay of fruit and vegetable food.

The total antioxidant capacity (TAC) has become increasingly vital for evaluating antioxidant food quality in the field of healthcare. Herein, a convenient and sensitive method for TAC assay was proposed based on the absorbance difference of reaction systems between various antioxidants existed in food and Dex-FeMnzyme/oxTMB. Under the optimum condition, the limit of detection (LOD) of the colorimetric sensor was 1.17 µM with the linear concentration range from 1 µM to 30 µM. The analysis results demonstrated the excellent feasibility of practical application in fruit and vegetable food, which offered a new avenue for the establishment of colorimetric biosensors.

Lycium Barbarum Polysaccharide-Iron (III) Chelate as Peroxidase Mimics for Total Antioxidant Capacity Assay of Fruit and Vegetable Food.

Quantitative evaluation of the antioxidant capacity of foods is of great significance for estimating food's nutritional value and preventing oxidative changes in food. Herein, we demonstrated an easy and selective colorimetric method for the total antioxidant capacity (TAC) assay based on 3,3',5,5'-tetramethyl-benzidine (TMB), hydrogen peroxide (H2O2) and synthetic Lycium barbarum polysaccharide-iron (III) chelate (LBPIC) with high peroxidase (POD)-like activity. The results of steady-state kinetics study showed that the Km values of LBPIC toward H2O2 and TMB were 5.54 mM and 0.16 mM, respectively. The detection parameters were optimized, and the linear interval and limit of detection (LOD) were determined to be 2-100 µM and 1.51 µM, respectively. Additionally, a subsequent study of the determination of TAC in six commercial fruit and vegetable beverages using the established method was successfully carried out. The results implied an expanded application of polysaccharide-iron (III) chelates with enzymatic activity in food antioxidant analysis and other biosensing fields.