Graphene quantum dots as a new substrate for immobilization and direct electrochemistry of glucose oxidase: application to sensitive glucose determination.

Graphene quantum dots (GQD) were introduced as a novel and suitable substrate for enzyme immobilization. Glucose oxidase (GOx) was immobilized on GQD modified carbon ceramic electrode (CCE) and well-defined quasi-reversible redox peaks were observed. The UV-vis photoluminescence spectroscopy, transition electron microscopy, field emission scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry techniques were used for characterizing the electrochemical biosensor. The electron transfer coefficient (α) and the heterogeneous electron transfer rate constant (k(s)) for redox reaction of GOx were found to be 0.48 and 1.12 s(-1), respectively. The developed biosensor responds efficiently to glucose presence over the concentration range 5-1270 μM with the detection limit 1.73 μM (S/N=3) and sensitivity 0.085 μA μM(-1) cm(-2). The high value of surface coverage GOx-GQD|CCE (1.8×10(-9) mol/cm(2)) and the small value of Michaelis-Menten constant (0.76 mM) confirmed an excellent loading of the enzyme and a high affinity of biosensor to glucose. High performance of the biosensor is attributed to the large surface-to-volume ratio, excellent biocompatibility of GQD, porosity of GQD|CCE, and the abundance of hydrophilic edges as well as hydrophobic plane in GQD which enhances the enzyme absorption on the electrode surface.