Graphene oxide and CuO double quantum dot composites (GOQD-q-CuO) with enhanced haloperoxidase-like activity and its application in colorimetric detection of H2O2 and glucose

We report herein, double quantum dot composites of graphene oxide and CuO (GOQD-q-CuO), formed by a low-temperature solution process, possess enhanced haloperoxidase (HPO)-like catalytic activity, which catalyze the oxidation of Cl− by H2O2 to generate reactive chlorine species (RCS). A sensitive and selective colorimetric sensor was then developed via the oxidation of 3,3ʹ,5,5ʹ-tetramethylbenzidine (TMB) by the GOQD-q-CuO catalytic system through the generation of RCS for H2O2 and glucose detection, with detection limits of 0.5 and 2.5 μM and linear ranges between 2.5–200 and 5–400 μM, respectively. This sensor was further applied to glucose detection in clinical serum samples showing no significant differences with the hexokinase method. Additionally, we demonstrate that the GOQD modulates the catalytic activity of q-CuO by reversing its zeta potential, producing an overall negatively charged surface, therefore GOQD-q-CuO has much higher affinity than CuO to the positively charged chromogenic substrate TMB, yielding higher HPO-like activity. Moreover, the presence of Cl− accelerates electron transfer to facilitate Cu2+ reduction to Cu+ on the GOQD-q-CuO surface, speeding up the overall catalytic reaction for the RCS generation, therefore, higher detection sensitivity was achieved.