Enhanced peroxidase-like nanozyme: copper-poly(tannic acid) for advanced colorimetric assay of total antioxidant capacity

The assessment of total antioxidant capacity (TAC), a critical marker of food quality in terms of antioxidant efficacy, has garnered considerable attention in human health management. The development of an <i>in situ</i> technique that does not require complex apparatus can facilitate accurate and rapid TAC detection. Herein, we developed a specific and sensitive colorimetric assay to evaluate the TAC of fruit juices using the red-green-blue (RGB) model. We synthesized a copper-poly(tannic acid) (Cu-PTA) coordination polymer that exhibits enhanced peroxidase (POD)-like activity in the presence of H₂O₂. This Cu-PTA nanozyme, along with H₂O₂, enhances the conversion of the colorless compound 3,3',5,5'-tetramethyl-benzidine (TMB) into a visually perceptible oxTMB product. This chromogenic reaction is suppressed in the presence of antioxidants, such as ascorbic acid (AA). This colorimetric assay achieved a limit of detection of 0.06 μM across a concentration range of 0.90-5.40 μM for AA. Our findings enable the development of nanozymes for convenient <i>in situ</i> TAC analysis to assess the nutritional value of food items.