H ₂ O ₂ -free colorimetric sensing platform of Mn-doped carbon dots with oxidase-mimetic activity for the detection of glutathione in liver disease serum

The level of glutathione (GSH) is a crucial indicator in various pathological processes. Developing a sensitive and selective method for GSH detection is of great importance for the evaluation of the human health. In this work, Mn-doped carbon dots (Mn-CDs), which exhibit a simulated oxidase activity, were utilized to construct an H₂O₂-free colorimetric sensor for the detection of GSH. Mn-CDs catalyse the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to ox-TMB without the need for unstable H₂O₂, and this catalysis is inhibited by GSH, leading to a decrease in the absorbance at 652 nm. The colorimetric sensor detection of GSH demonstrated a strong linear relationship in the range of 0.5-800 µM, with a detection limit as low as 0.167 µM, a 96.5%-108.5% recovery rate, and excellent selectivity for GSH among 10 main interfering substances in human serum. Furthermore, we established a method for the visual estimation of GSH concentration based on the H₂O₂-free Mn-CDs colorimetric sensor, greatly simplifying the detection process. Compared with a commercial kit, our colorimetric sensor method provided consistent results and offered advantages in terms of cost, convenience, and potential for point-of-care testing. Importantly, we successfully applied the sensor to detect GSH levels in the serum of patients with liver disease, finding significant differences compared with healthy individuals. Overall, these results demonstrated that the H₂O₂-free Mn-CDs colorimetric sensor for detecting GSH has the characteristics of a wide linear range, excellent minimum detection limit, strong anti-interference capabilities, low cost, convenience, and stability and can be used to assess the human health.