Intrinsic peroxidase activity of carbon dots derived from expired drugs and its application in automatic detection of total antioxidant capacity

In the post-COVID-19 pandemic, the stockpiling of medicines by most households could pose a pollution risk as they may expire over time. In this study, an expired amoxicillin act as carbon source to prepare peroxide-like functional carbon dots nanozymes doped Fe (Fe-CDs). Importantly, a high-value treatment technique for expired drugs was proposed. To obtain outstanding catalytic performance, compared with other commonly doped metals, Fe-CDs catalyzed the oxidation of TMB by H2O2 with the highest efficiency. In particular, the oxidation product of TMB (oxTMB) would be alleviated in the presence of antioxidants. Significantly, antioxi-dants could briefly cause the fading of oxTMB and the fading level was correlated with various concentrations of antioxidants. Importantly, a sequential injection strategy was introduced to control the fading process caused by antioxidants to improve the accuracy. Under the optimum condition, the limit of detection (LOD) was 0.13 mg/L (for ascorbic acid) with the linear concentration range from 0.5 to 15 mg & sdot;L- 1. Finally, the total antioxidant capacity (TAC) in human serum samples were evaluated successfully.