A new way to monitor health is to measure biological samples' total antioxidant capacity (TAC). Antioxidants are crucial in the body, as they protect cells from being damaged by free radicals. Saliva has antioxidant levels similar to those in the bloodstream, making it helpful in measuring important antioxidants like ascorbic acid (AA), cysteine (CYS), glutathione (GSH), and uric acid (UA). As a result, developing an innovative approach to monitoring antioxidants is considered significant, and a non-toxic, fast colorimetric sensor is regarded as a suitable tool for this purpose. In this study, a novel multi-colorimetric probe is improved, which is capable of generating high-resolution, naked-eye-detectable color readouts for salivary TAC evaluation. Plasmonic nanostructures are advanced colorimetric sensors that allow for accurate and efficient analysis of TAC in saliva. The measurement of antioxidants is done by combining linear discriminant analysis (LDA) and partial least squares regression (PLSR) with the colorimetric probe. Linear responses to pure antioxidants and TAC over concentration ranges of 3.1–60.0, 2.6–60.0, 1.2–20.0, 0.8–20.0, and 0.7–14.0 μmol L−1 are exhibited by the probe, with detection limits of 1.1, 0.9, 0.4, 0.3, and 0.2 μmol L−1 for AA, CYS, GSH, UA, and TAC, respectively. The accuracy and efficiency of the probe are validated by using real saliva samples for on-site TAC monitoring. A fast, economical, user-friendly, non-toxic, and minimally invasive method is provided by this approach, allowing accurate measurement of TAC in saliva for clinical diagnostics as the probe creates unique response profiles based on antioxidant levels.