Facile Synthesis of High-Loading Cu Single-Atom Nanozyme for Total Antioxidant Capacity Sensing

Single-atom catalysts (SACs) with atomically dispersedactive sitesand maximum atomic utilization efficiency provide new opportunitiesto develop high-performance nanozymes. However, the preparation ofSACs with a high metal content still faces serious challenges. Herein,we report a pyrolysis method for achieving a Cu single-atom catalyst(Cu-SAC) on nitrogen-doped carbon with a Cu loading of 7.98 wt %.Isolated Cu atoms with Cu-N-3-C coordinationwere confirmed by spherical aberration-corrected transmission electronmicroscopy and X-ray absorption spectroscopy. The synthesized Cu-SACdisplayed outstanding peroxidase-like activity by effectively catalyzingthe reaction between 3,3 ',5,5 '-tetramethylbenzidine(TMB) and H2O2 to show a blue color. Based onthe inhibition effect on the oxidation of TMB by ascorbic acid (AA),a colorimetric assay for AA was established with a limit of detection(LOD) of 0.63 mu M. Furthermore, the total antioxidant capacities(TACs) of practical samples including vitamin C tablets, commercialbeverages, and fresh fruit were successfully detected by the proposedcolorimetric assay. This study provided a facile method for the preparationof high-metal-loading SACs, which exhibited high enzymatic propertieswith promising applications in food and drug safety.