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

Single-atom catalysts (SACs) with atomically dispersed active sites and maximum atomic utilization efficiency provide new opportunities to develop high-performance nanozymes. However, the preparation of SACs 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–N3–C coordination were confirmed by spherical aberration-corrected transmission electron microscopy and X-ray absorption spectroscopy. The synthesized Cu-SAC displayed outstanding peroxidase-like activity by effectively catalyzing the reaction between 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2 to show a blue color. Based on the 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 μM. Furthermore, the total antioxidant capacities (TACs) of practical samples including vitamin C tablets, commercial beverages, and fresh fruit were successfully detected by the proposed colorimetric assay. This study provided a facile method for the preparation of high-metal-loading SACs, which exhibited high enzymatic properties with promising applications in food and drug safety.