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.　©　2024　American　Chemical　Society