Gold Nanobipyramid-Based Photothermal Sensors for the Portable Evaluation of Total Antioxidant Capacity

Antioxidants are highly effective in preventing oxidative damage and reducing the risk of various diseases. To comprehensively evaluate the antioxidant content in food or nutrients, simple, portable, and cost-effective assays must be developed for measuring the total antioxidant capacity (TAC). In this study, gold nanobipyramids (AuNBPs) with a tunable photothermal effect were utilized as a probe to develop a straightforward method for photothermally sensing and assessing the TAC. Owing to the high refractive sensitivity of AuNBPs, antioxidant-triggered silver deposition induced drastic changes in their absorption spectra and photothermal effects. By this means, the TAC information can be converted into temperature signals easily captured using an affordable portable thermal camera. With our photothermal sensing strategy, the detection limit for ascorbic acid (a model antioxidant) is 0.08 μM, within the linear range of 0.1–100 μM. Furthermore, our method was successfully applied in practical applications for evaluating the TAC in honey and vitamin C tablets. The developed AuNBP-based photothermal assay exhibits considerable potential for portably assessing TAC.