Harnessing charge transfer to enhance peroxidase-like activity of Au@Pt nanozyme for assessing total antioxidant capacity.

Reliable total antioxidant capacity (TAC) detection in foods is of considerable practical importance for evidence-based dietary guidance and disease prevention. We designed a core-shell Au@Pt nanozyme with enhanced peroxidase (POD)-like activity, driven by electron transfer from the Au core to the Pt shell. This interfacial charge modulation lowers the catalytic energy barrier, as confirmed by structural characteristic characterization and density functional theory (DFT) calculations. The Au@Pt nanozyme also exhibits excellent long-term stability and low batch-to-batch variation. Leveraging these advantages, we developed a sensitive colorimetric platform for ascorbic acid detection, in which Au@Pt serves as the signal transducer and 3,3',5,5'-tetramethylbenzydine (TMB) as the chromogenic substrate. The assay relies on the ability of AA to quench reactive oxygen species and reduce oxidized TMB. This platform exhibits high selectivity, with negligible interference from common ions, small biomolecules, or other antioxidants. We further validated the method by determining total antioxidant capacity in commercial vitamin C tablets, beverages, and fresh fruit juices, with results expressed as mg AA equivalent per liter. The values obtained were consistent with those from the standard cupric reducing antioxidant capacity (CUPRAC) method. This work presents a rational nanozyme design via interfacial engineering and offers a practical tool for antioxidant assessment in complex food matrices.