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 in situ 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 in situ TAC analysis to assess the nutritional value of food items.