Engineering a BSA-templated Iridium Oxide Nanozyme for Colorimetric Evaluation of Total Antioxidant Capacity in Food Samples

Antioxidants are crucial for capturing and neutralizing free radicals to prevent oxidative damage, which implies assessing the antioxidant content in foods and medications is essential. In order to quantify the total antioxidant capacity (TAC) of food samples, a straightforward and sensitive colorimetric sensing method utilizing an iridium oxide (IrOx) nanozyme was developed. By employing bovine serum albumin (BSA) as a structural template and iridium as the precursor, a biomimetic mineralization strategy was utilized to synthesize b-IrOx nanozymes exhibiting intrinsic peroxidase (POD)-like activity, enabling their effective substitution of natural peroxidases in catalyzing redox reactions. Through single electron transfer (SET) and hydrogen atom transfer (HAT) processes, antioxidants in samples can compete with substrates for •OH, causing a hue shift that depends on the antioxidant concentration. The proposed b-IrOx-based colorimetric assay was successfully used to measure the TAC of mango juice (948.31 ± 0.83 µM), yellow peach juice (776.72 ± 2.47 µM), and apple juice (154.77 ± 1.70 µM) with good accuracy (recovery rate: 90.49%-110.62%) and reproducibility (relative standard deviation, RSD < 3.0%). The b-IrOx nanozymes were compared with a commercial TAC standard kit to further confirm the reliability of the TMB colorimetric assay. The results showed no significant statistical difference between the two methods (p > 0.05). Therefore, the b-IrOx colorimetric assay offers a simple, low-cost approach for the rapid and precise determination of TAC in food samples.