Colorimetric Sensor Array Based On Metal Nanozymes For The Detection Of Sulfur-Containing Compounds And Antioxidants In Foods

Natural enzymes are widely used in food,environmental,medical,and other fields due to their strong specificity and high catalytic activity.However,their inherent limitations such as easy deactivation and high cost hinder their wider application.Nanozymes have broken the limitations of natural enzymes and greatly expanded the application of enzymes in various fields.Metal nanozymes stand out among nanozymes due to their excellent metal properties,active sites similar to natural enzymes,and flexible adjustable structures.Colorimetric sensor arrays based on nanozymes have also received widespread attention in the field of food quality evaluation due to their advantages of simple operation,low cost,and portability.Sulfur-containing compounds and antioxidants,as common harmful substances and nutrients in food,are closely related to food quality.Therefore,this article has synthesized two metal nanozymes,namely,nitrogen doped monoatomic cobalt nanozymes with oxidase like activity and gold platinum bimetallic nanozymes with peroxidase like activity.Based on these two nanozymes,a three channel colorimetric sensing array has been developed for the identification and quantitative detection of sulfur-containing compounds and antioxidants in food,combining with density functional theory（DFT）calculations,the catalytic mechanism of the two nanozymes was studied in depth.Finally,based on smartphones and gel tablets,visual detection of sulfur-containing compounds and antioxidants can be realized respectively.（1）Colorimetric sensing array based on nitrogen-doped monoatomic cobalt nanozymes for the detection of sulfur-containing compoundsMonoatomic Co nanozymes（CoN₄-G）with oxidase activity（OXD）were synthesized by embedding metal Co into N-doped graphene by the one pot hot synthesis method.Through DFT calculation,the high enzyme activity of Co N₄-G was deeply studied and explained in detail.Under the catalytic action of Co N₄-G,the degree of substrate oxidation is significantly influenced by p H and sulfur-containing compounds.Based on this,the three channel colorimetric sensing array was constructed for the simultaneous detection of Na₂S,Na₂SO₃,Na₂S₂O₃,Na₂S₂O₈.The three-channel colorimetric sensor array based on Co N₄-G nanozyme successfully distinguished four sulfur compounds with concentrations of 10、20、40、60、80 and100μmol/L,sulfur-containing compounds with different concentrations,and mixed systems of multiple sulfur-containing compounds.In the HAc-Na Ac buffer with p H=3.0,the detection range of four sulfur-containing compounds is 1.6-320μmol/L,and the detection limit is 0.0778-0.218μmol/L.The colorimetric sensor array has good anti-interference ability and successfully identifies sulfur-containing compounds in mineral water,red wine,milk and egg white.Finally,visual detection of sulfur-containing compounds was achieved based on smartphones.（2）Colorimetric sensing array based on gold-platinum bimetallic nanozymes for the detection of antioxidantsAu₂Pt bimetallic nanozymes with peroxidase（OPD）activity were synthesized by a typical co-reduction method.DFT calculation results showed that Au₂Pt nanozymes have more excellent OPD activity than monometallic nanozymes due to their unique bimetallic doping structure.Based on the colorimetric sensor array,the identification and quantitative analysis of five antioxidants（vitamin C（Vc）,glutathione（GSH）,cysteine（CYS）,gallic acid（GA）and caffeic acid（CA））were successfully realized.Not only successfully identified 4μmol/L and 16μmol/L,and successfully identified the mixed system of antioxidants with different concentrations and multiple antioxidants.Under the optimal conditions,the detection limits for Vc,GSH,CYS,GA and CA are 0.124,0.1581,0.1163,0.259 and 0.1885μmol/L,respectively.The colorimetric sensor array has good anti-interference ability,can successfully distinguish three kinds of food samples containing Vc（milk,green tea and orange）,and can also successfully distinguish fresh orange juice and orange juice exposed to air for 60 min.Finally,we immobilized Au₂Pt NPs into agarose gel tablets,and successfully realized the visual detection of samples by comparing it with the self-made standard colorimetric card.