Graphene quantum dot functionalized by chitosan as an electrically conductive nano-material toward low potential detection: a new platform for interface science

Graphene quantum dot (GQD) with tunable sizes, (2–5 nm) especially displays unique optical and electrical properties due to the quantum confinement effect. Experiments have revealed that the band gap and HOMO/LUMO energy levels of GQDs can be independently controlled by either the lateral size or chemical functionalization. In the present work, a simple and controllable sequent electrodeposition method for the functionalization of graphene quantum dots with chitosan and preparation of a thin film on a glassy carbon electrode surface was proposed and further used for the construction of an electrochemical detector. This novel interface was constructed by two-step electrochemical deposition in solution containing graphene quantum dots and chitosan. This deposited interface possessed excellent stability by the characterization of cyclic voltammetry and wave voltammetry in phosphate buffer with pH 7.4. As the nanostructured sensing film provides plenty of active sites for the direct oxidation of vitamin C, the prepared sensor exhibited excellent electrochemical, catalytical and analytical performance at the pH 7.4. The kinetics of charge transfer and mass transport processes across the nanocomposite/solution interface were studied. The modified electrode showed an efficient electrocatalytic activity toward the oxidation of vitamin C through a surface mediated electron transfer. The catalytic rate constant and the vitamin C diffusion coefficient were reported.