Unadulterated glucose biosensor based on direct electron transfer of glucose oxidase encapsulated chitosan modified glassy carbon electrode

Glucose oxidase (GOD) was encapsulated in chitosan matrix and immobilized on a glassy carbon electrode, achieving direct electron transfer (DET) reaction between GOD and electrode without any nano-material. On basis of such DET, a novel glucose biosensor was fabricated for direct bioelectrochemical sensing without any electron-mediator. GOD incorporated in chitosan films gave a pair of stable, well-defined, and quasireversible cyclic voltammetric peaks at about -0.284 (EPpa) and -0.338 V (E-pc) vs. Ag/AgCl electrode in phosphate buffers. And the peak is located at the potentials characteristic of FAD redox couples of the proteins. The electrochemical parameters, such as midpoint potential (E-1/2) and apparent heterogeneous electron-transfer rate constants (K-s) were estimated to -0.311 V and 1.79 s(-1) by voltammetry, respectively. Experimental results indicate that the encapsulated GOD retains its catalytic activity for the oxidation of glucose. Such a GOD encapsulated chitosan based biosensor revealed a relatively rapid response time of less than 2 min, and a sufficient linear detection range for glucose concentration, from 0.60 to 2.80 mmol L-1 with a detection limit of 0.10 mmol L-1 and electrode sensitivity of 0.233 mu A mmol(-1). The relative standard deviation (RSD) is under 3.2% (n = 7) for the determination of practical serum samples. The biologic compounds probably existed in the sample, such as ascorbic acid, uric acid, dopamine, and epinephrine, do not affect the determination of glucose. The proposed method is satisfactory to the determination of human serum samples compared with the routine hexokinase method. Both the unique electrical property and biocompatibility of chitosan enable the construction of a good bio-sensing platform for achieved DET of GOD and developed the third-generation glucose biosensors.