Electrochemical quartz crystal impedance study on immobilization of glucose oxidase in a polymer grown from dopamine oxidation at an Au electrode for glucose sensing

Glucose oxidase (GOD) was codeposited into a polymer grown from oxidation of dopamine (DA) at an Au electrode in a neutral phosphate aqueous solution for the first time. The electrochemical quartz crystal impedance analysis (EQCIA) method was used to monitor the GOD-immobilization process. Effects of concentrations of phosphate buffer, DA and GOD were investigated, and the optimal concentrations were found to be 20.0mM phosphate buffer (pH 7.0), 30.0mM DA and 5.00mgml-1 GOD. A glucose biosensor was thus constructed, and effects of various experimental parameters on the sensor performance, including applied potential, solution pH and electroactive interferents, were examined. At an optimal potential of 0.6V versus the KCl-saturated calomel electrode (SCE), the current response of the biosensor in the selected phosphate buffer (pH 7.0) was linear with the concentration of glucose from 0.05 to 9mM, with a lower detection limit of 3μM (S/N=3), short response time (within 15s) and good anti-interferent ability. The Michaelis constant (Kmapp) was estimated to be 9.6mM. The biosensor exhibited good storage stability, i.e. 96% of its initial response was retained after 7-day storage in the selected phosphate buffer at 4deg. C, and even after another 3 weeks the biosensor retained 86% of its initial response. In addition, the enzymatic specific activity and enzymatic relative activity of the GOD immobilized in the polymer from dopamine oxidation (PFDO) were estimated from the EQCIA method to be 1.43kUg-1 and 3.7%, respectively, which were larger than the relevant values obtained experimentally using poly(o-aminophenol) and poly(N-methylpyrrole) matrices, suggesting that the PFDO is a better matrix to immobilize GOD