Study On Colorimetric Detection Of Hg²⁺ And Cr（Ⅵ） In Water Based On Nanozyme

Heavy metals pollution of water,soil and air is a serious and urgent environmental problem.More and more people are exposed to the harm of heavy metals,causing a variety of diseases and even cancer.Accurate measurement of its content in the environment can provide certain support for prevention and control and removal.Traditional detection methods require professional operators,expensive instruments,and are not conducive to field detection,so there is an urgent need for some rapid detection methods.In recent years,nanomases with low cost,high stability and good catalytic activity have attracted extensive attention and exploration by researchers,and there are more and more researches in point-of-caretesting（POCT）.Metal nanomases are widely used in chemical catalysis,medical treatment and analytical sensing because of their high stability,easy surface modification and activity of various enzymes.Especially in the field of analytical sensing,metal nanomases can form sensing systems with different organic reagents to perform colorimetric,fluorescent and photothermal sensing analysis of different analytes,which provides a new opportunity for the development of simple and rapid POCT methods.However,compared with natural enzymes,most nano-enzymes still face the limitation of low catalytic activity,which greatly limits their practical application in POCT.Therefore,it is necessary to accurately understand the catalysis and activity regulation mechanism of nanase,and design reasonable activity regulation strategies for different nanase,so as to enhance the catalytic activity of nanase and further expand their sensing applications in POCT.Therefore,we regulated nanase to improve the catalytic performance of nanase and construct corresponding POCT sensing strategies.The specific work content is as follows:（1）Glutathione-modified gold nanoflowers（GSH-Au NFs）were synthesized and found to exhibit peroxidase-like mimetic activity after interacting with Hg²⁺.Using H₂O₂and 3,3’,5,5’-tetramethylbenzidine（TMB）as peroxidase-like substrates,the reaction kinetics of Hg²⁺-activated GSH-Au NFs mimicking peroxidase activity was studied.The possible free radicals produced by H₂O₂ catalyzed by GSH-Au NFs as peroxidase were analyzed by free radical scavengers.Based on the activation of GSH-Au NFs peroxidase activity by Hg²⁺,an ultra-sensitive colorimetric method for Hg²⁺detection was established.The mechanism was verified by a series of physical and chemical characterization.The designed detection method can realize Hg²⁺detection in the linear range of 10～300 n M.The detection limit is 3.9 n M,which is lower than the maximum concentration of Hg²⁺in drinking water set by the Environmental Protection Agency and the World Health Organization.The experimental results show that this method has high accuracy and specificity and has great potential in environmental monitoring.（2）By changing the molar ratio of Fe to Mn,bimetallic organic skeletons（Fe_xMn_y-MOFs）with different ratios were successfully synthesized.It was found that Fe_xMn_y-MOFs had the dual properties of mimicking peroxidase and oxidizing enzyme,and could oxidize peroxidase substrate TMB with and without H₂O₂.In addition,after comparing the catalytic activity,we found that Fe₁Mn₁-MOF had the best activity,and then selected Fe₁Mn₁-MOF as the best activity to catalyze H₂O₂ and TMB to study the reaction kinetics.Three kinds of free radicals(·OH、¹O₂、·O^2-)produced in the catalytic reaction were determined by electron spin resonance spectroscopy.The adsorption energy of H₂O₂ and O₂ on Fe₁Mn₁-MOF,and the free energy（Free Energy）of intermediates in the reaction process were studied by density functional theory（DFT）.Based on the excellent peroxidase properties of Fe₁Mn₁-MOF,a simple and rapid Cr（VI）colorimetric method was established combined with 8-HQ.The linear range is 80-3500 n M.The detection limit is 51 n M,which is much lower than the standard set by the US Environmental Protection Agency and the World Health Organization.The experimental results show that the method is sensitive and can be read by color change or UV-Vis signal.