Morphology-dependent nanoplasmonic assay: a powerful signaling platform for multiplexed total antioxidant capacity analysis

Assessing the total antioxidant capacity (TAC) in biological samples, such as saliva, is essential for health monitoring and disease prevention. TAC plays a critical role in protecting cells from damage caused by free radicals and oxidative stress, which are associated with various conditions, including cancer, cardiovascular diseases, and aging. Key antioxidants, including ascorbic acid (AA), cysteine (CYS), glutathione (GSH), and uric acid (UA), significantly contribute to this protective effect, with salivary levels of these antioxidants reflecting their concentrations in the bloodstream. Therefore, there is a strong demand for a robust, non-toxic colorimetric sensor that can effectively monitor these antioxidants using an innovative approach. This study introduces a multi-colorimetric probe capable of generating high-resolution, naked-eye-detectable color readouts for evaluating salivary TAC. The probe utilizes the morphology-dependent properties of plasmonic nanostructures as recently developed colorimetric sensors, enabling precise and efficient analysis of salivary antioxidants. The assessment of antioxidants was conducted using the probe in combination with pattern recognition analysis for accurate identification and regression analysis for quantification. The probe exhibited linear responses to pure antioxidants and TAC over a broad concentration range: 3.1-60.0, 2.6-60.0, 1.2-20.0, 0.8-20.0, and 0.7-14.0 μmol L^-1, 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-mixture, respectively. Moreover, performance metrics highlight the robustness and efficacy of the probe in detecting and quantifying antioxidant levels in saliva samples. The efficacy of the developed multi-colorimetric probe was rigorously validated through the analysis of real saliva samples for on-site TAC monitoring. This rapid, cost-effective, user-friendly, non-toxic, and non-invasive method allows for a comprehensive analysis of both individual and total antioxidants, making it highly applicable for health monitoring and disease prevention. Additionally, the probe generates unique response profiles based on varying ratios of endogenous antioxidants, enabling precise TAC quantification in saliva-an essential factor for clinical diagnostics.