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 its catalytic sites are classified as type1 (T1), type2 (T2) and type3 (T3) Cu. The electron transfer distance between the T1 to T2/T3 Cu has a great effect on the electron transfer efficiency in the laccase-catalyzed reaction. To mimic the active sites of laccase, a copper-doped carbon dots (CuCDs) was synthesized by a one-step hydrothermal treatment of copper sulfate and riboflavin. Experiment characterizations and theoretical simulations revealed that the catalytic sites in CuCDs consist of N, O coordinated copper and 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 in catalytic sites of CuCDs accelerates the oxidation of the substrate dopamine (DA) to polydopamine (PDA) with a reaction rate being 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 could provide an efficient and eco-friendly nanozyme for hair dyeing in ambient condition, but also could inspire more and deeper researches in the field of mimicking natural enzyme with carbon nanomaterials.