Immobilizations of the modified materials and enzyme on the electrode sufrace are main factors that restrict wide use of the glucose biosensor now. Graphene and gold nanoparticles were alternately electrodeposited on the surface of glassy carbon electrode to fabricate the graphene/gold composites. The electrode was then immersed in a 2,5-di-(2-thienyl)-1- pyrrole-1-(p-benzoic acid) solution (DPB) to electrochemically polymerize and form the poly(DPB) conducting polymer film which contains a large number of free carbonyl groups. In order to fabricate the glucose biosensor, the glucose oxidase was covalently connected to the poly(DPB) conducting polymer film with the mixture solution of 1-ethyl-3-(3-dimethyl- aminepropyl)carbodiimide and N-hydroxysuccinimide as an activator. In this study, Raman spectrum, X-ray diffraction pattern and scanning electron microscope were used to characterize morphology and structure of the as-prepared graphene/gold composites, respectively. The results have demonstrated that a well-dispersible graphene/gold composites was obtained using such a alternate electrodeposition. Moreover, electrochemical properties of the biosensor were also investigated in detail. It was found that the electrochemical activity area, amounts of the immobilized enzyme and the apparent Michaelis constant of the modified electrode were 0.1403 cm², 7.73×10^-11 mol·cm^-2 and 5.23×10^-5 mol·L^-1, respectively. When the concentration of glucose ranged from 5×10^-6 mol·L^-1 to 5×10^-4 mol·L^-1, the peak current change of differential pulse voltammetric response of the biosensor will increase linearly. The detection limit was found to be 1.7×10^-6 mol·L^-1. After the biosensor was placed in 4 ℃ for 4 weeks, the electrochemical response can remain more than 95%. Due to electrocatalysis of the graphene/gold composite and covalent immobilization of the enzyme with the conducting polymer, the proposed method provides a better sensitivity, selectivity, stability and reproducibility than that of other glucose biosensors reported in literatures. It has been successfully applied to determination of glucose in various serum samples.

Key words: graphene/gold composites, functional conducting polymer, biosensor, glucose