Natural laccase-guided synthesis of copper-doped carbon dots with enhanced laccase-like activity†

Natural laccase, a member of the copper blue oxidase family, has catalytic sites classified as type1 (T1), type2 (T2) and type3 (T3) Cu. The electron transfer distance between T1 and T2/T3 Cu greatly influences the electron transfer efficiency in a laccase-catalyzed reaction. To mimic the active sites of laccase, copper-doped carbon dots (CuCDs) were synthesized by a one-step hydrothermal treatment of copper sulfate and riboflavin. Characterizations and theoretical simulations revealed that the catalytic sites in CuCDs consist of N,O-coordinated copper and a quinoxaline structure, which resemble the coordination environment of T2 Cu and the function of the T3 Cu center, respectively. The short electron transfer distance of 4.8 Å between the catalytic sites of CuCDs accelerates oxidation of the substrate dopamine (DA) to polydopamine (PDA) with a reaction rate 40 times faster than that of laccase. Galvanic cell experiments proved that electron transfer from DA to oxygen was achieved in the presence of CuCDs. Therefore, this study not only provides an efficient and eco-friendly nanozyme for hair dyeing under ambient condition but could also inspire further research in the field natural enzyme mimics based on carbon nanomaterials.