Preparation Of Four Copper-based Nano Enzymes And Their Application In The Detection Of Antioxidant Capacity In Fruits And Vegetables

Enzyme has the advantages of high catalytic activity and strong specificity,can participate in many important biochemical processes in the body,but natural enzymes have extremely strict requirements for living conditions,easy denaturation and inactivation,limiting its wide application,the study of simulated enzymes came into being,with the rapid development of nanotechnology,nanoenzymes have become a research hotspot in the field of simulated enzymes.Nanoenzymes refer to nanomaterials with enzyme-like activities,and nanozymes have the advantages of low cost and good thermal stability,but the catalytic efficiency of nanozymes is lower than that of natural enzymes.Metal-organic frameworks（MOFs）have the advantages of large specific surface area,more active sites,tunable structure and function,etc.,so the construction of nanoenzymes based on MOFs can improve this shortcoming.MOFs-based nanozymes can be used in many fields,among which the sensing field is currently the most widely used field.In this paper,four novel metal-organic framework materials（Cu-TCPP,Cu O-TCPP,Cu₂O-TCPP,Cu-Cu₂O-TCPP）were studied and prepared with copper nanoclusters as the core,and optical sensors with high detection and high sensitivity were constructed based on four MOFs and applied to the detection of the total antioxidant capacity of eight vegetables and fruits.The results of the study are as follows:Cu-TCPP,Cu O-TCPP,Cu₂O-TCPP,and Cu-Cu₂O-TCPP nanocomposites with two-dimensional layered loose porous structures were prepared by in-situ polymerization.The prepared new MOF material improves the characteristics of three-dimensional structure that is not easy to disperse in aqueous solution,provides more catalytic sites for L-Ascorbic acid,and greatly improves the catalytic activity and efficiency.A variety of characterization techniques were used to characterize the four new composites,and the structures were observed to be two-dimensional layered structures,and the specific surface areas of the four materials were 1.6048 m²/g,0.9868 m²/g,13.9671 m²/g and 10.9755 m²/g,respectively.The catalytic conditions of four MOF materials were optimized.The optimized test conditions were nanoenzyme concentration of 1.5 mg/ml,TMB concentration of 15 m M,H₂O₂volume of 0.05 ml,and reaction time of 15 min.The kinetic characterization of the four nanomaterials was carried out,the Km value was the substrate concentration when the reaction speed reached half of the maximum reaction speed,the smaller the Km value,the higher the affinity of the catalytic substrate and enzyme,and the Km value of the four nanoenzymes were smaller,0.27 m M,0.57 m M,0.52 m M,respectively,which proved that the affinity of the four nanoenzymes and the catalytic substrate TMB was higher.A standard curve of L-Ascorbic acid concentration and absorbance was established,and the peroxidase activity of four nano enzymes was used to detect the L-Ascorbic acid concentration and total antioxidant capacity of eight vegetables and fruits.Cu-TCPP was used to detect broccoli and oranges,with RSD of 2.11%and 1.69%,respectively;Cu O-TCPP was used to detect radish and kiwi,with RSD of 2.5%and 0.6%,respectively;Cu₂O-TCPP was used for the detection of cabbage and lemon,with RSD of 0.41%and 0.13%,respectively;Cu-Cu₂O-TCPP was used to detect kale and grapefruit with RSD of 0.38%and 0.21%,respectively.In this experiment,a complete sensing detection system was constructed by preparing two-dimensional metal-organic framework compounds（MOFs）for the detection of L-Ascorbic acid concentration and total antioxidant capacity in fruits and vegetables,combined with ultraviolet-visible spectroscopy detection technology.The whole process detection is fast and sensitive,does not involve natural enzymes,is lower cost,greener,and more efficient,and provides a reference for rapid detection of antioxidant capacity.