Metallic deep eutectic solvents-assisted synthesis of Cu, Cl-doped carbon dots as oxidase-like and peroxidase-like nanozyme for colorimetric assay of hydroquinone and H2O2

As an emerging carbon nanomaterial, carbon dots (CDs) have drawn significant attention in the catalytic field owing to their low toxicity, high stability and superior biocompatibility. Herein, for the first time, Cu and Cl co-doped CDs (Cu, Cl-CDs) were synthesized via hydrothermal method utilizing citric acid as carbon source and metallic deep eutectic solvents (MDESs) as green solvent and passivation agent. It was proved that the prepared Cu, Cl-CDs exhibited oxidase-like (OD-like) and peroxidase-like (POD-like) catalytic activities. The catalytic performance, mechanism and steady-state kinetics of Cu, Cl-CDs were systematically investigated. Accordingly, bifunctional colorimetric platforms based on the OD-like and POD-like activities of Cu, Cl-CDs using 3,3′,5,5′-Tetramethylbenzidine (TMB) as substrate were established for determining hydroquinone (HQ) and H2O2, respectively, both of which showed high accuracy and sensitivity. HQ, as a reducing agent, could be detected by this method with a linear range of 0.1–120 µM and limit of detection (LOD) of 0.08 µM. And the degree of discoloration varied linearly with H2O2 in the range of 1–600 µM with LOD of 0.35 µM. Thus, Cu, Cl-CDs have broad prospects in catalysis and environmental chemistry, and provide rational guidance for green synthesis of carbon-based nanozymes with multi-enzyme catalytic performance.