Research On Visual Sensor And Its Analytical Application Based On Multifunctional Nanozymes

Natural enzymes are macromolecular biocatalysts composed of most proteins and a few nucleic acids that run through the metabolic processes of life.However,most natural enzymes are easily inactivated or inhibited under non-physiological conditions,which severely limits the widespread use of natural enzymes.In addition,natural enzymes also have defects such as high storage requirements,complex production and purification processes,and high costs.With the rapid development of nanoscience and life sciences,nanozymes with high catalytic activity and versatility have been widely studied and become potential alternatives to natural enzymes.The emergence of nanozymes has greatly improved the sensitivity and stability of colorimetric visualization sensing platforms.Nanozyme-based visualization sensors are widely studied in various fields,especially in the field of detection of heavy metals and pesticide residues,due to their simple operation,short detection time,and visual recognition by the naked eye.In this paper,nanozymes with different functions were prepared by simple and low-cost synthesis methods to construct visualization sensors for the highly selective detection of heavy metals and organophosphorus pesticides,respectively.The specific work content is as follows:1.A simple colorimetric sensor was constructed for the detection of Hg²⁺by synthesizing Mn O₂nanosheets with oxidase-like activity under simple mild conditions.Mn O₂nanozymes could rapidly oxidize TMB in the presence of dissolved oxygen.Reducing GSH could reduce and etch Mn O₂nanosheets to produce Mn²⁺,which weakened the catalysis of TMB by Mn O₂nanozymes.In the presence of Hg²⁺,Hg²⁺coordinated with the sulfhydryl groups in GSH,thereby reducing the etching of Mn O₂nanozymes by GSH and allowing more Mn O₂nanozymes to catalyze the oxidation of TMB.Therefore,the greater the concentration of Hg²⁺,the more blue ox TMB were produced.In the range of 0.1～8.0μmol L^-1,the Hg²⁺concentration had a good linear relationship with the absorbance difference（△OD）of ox TMB,and the detection limit was 0.097μmol L^-1.The sensor provides a simple and effective method to detect Hg²⁺in water.2.Cu MOF with oxidoreductase properties were synthesized by a simple and rapid method for rapid and sensitive detection of Cr（VI）.TMB and Cr（VI）undergone a rapid（30 s）redox reaction under Cu MOF-mediated electron transfer.Cr（Ⅵ）were reduced to Cr（Ⅲ）,and TMB were oxidized to blue ox TMB.In the range of 0.06～20μmol L^-1,the absorbance of ox TMB increased with the increase of Cr（Ⅵ）concentration and showed a good linear relationship.The detection limit was 0.018μmol L^-1.This method provides a reliable way for rapid and sensitive detection of Cr（Ⅵ）in water.3.A Zn-Zr MOF with hydrolysis of P-O in organophosphorus was synthesized by modifying Zn²⁺on the surface of Zr MOF for colorimetric detection of profenofos.In this method,the Zn and Zr elements in the Zn-Zr MOF acted as Lewis acids by deprotonation of coordinated water to form Zn（Ⅱ）-OH and Zr（Ⅳ）-OH under weak base conditions.Coordination of Zn and Zr with profenofos activated the P-O bond and promoted nucleophilic attack of the P-O bond by water or hydroxide,and obtained the phenolic hydrolysate products4-bromo-2-chlorophenol.In the presence of the oxidant K₃[Fe（CN）₆],4-bromo-2-chlorophenol reacted with 4-amino-antipyrine to produce the pink products.In the range of 0.01～1000μg m L^-1,the concentration of profenofos had a strong linear relationship with pink products and the detection limit was 6.33×10^-3μg m L^-1.This work provides a new strategy for the highly sensitive and selective detection of profenofos.