The electrochemical glucose sensing based on the chitosan-carbon nanotube hybrid

In glucose sensors, the direct electron transfer (DET) method delivers electrons from glucose oxidase (GOx) to an electrode without the intervention of a mediator. Many researchers have developed the DET method using carbon nanotube (CNT)-based composites for the permeation into the enzyme co-factor. We synthesized chitosan (Chit) core-shelled CNTs that were hydrophilic, biocompatible, and easily prepared. Electrodes with three different Chit-CNT weight ratios were prepared, and their morphological and physicochemical properties were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), scanning electron microscopy (SEM), and transition electron microscopy (TEM). The Chit-CNT85 composite (85 wt% Chit) performed optimally by cyclic voltammetry (CV), and was covalently modified with GOx via a routine coupling protocol to form the GOx-Chit-CNT85/ITO electrode. This electrode was electrochemically characterized by impedance spectroscopy (EIS). The GOx loading and pH were optimized against the CV redox potential. The electrode exhibited a fast electron-transfer constant (k(s)) of 8.2 s(-1). The cathodic peak of GOx decreased in response to increasing glucose concentrations, but no changes were observed in the presence of physiological interfering substances such as ascorbic acid and uric acid. Therefore, our GOx-Chit-CNT85/ITO electrode has the potential for use in glucose sensing directly without a mediator.