Electrodeposition of a biocompatible hydroxyapatite matrix to immobilize glucose oxidase for sensitive glucose biosensing

The electrochemical quartz crystal microbalance was used to quantitatively examine the electrodeposition of hydroxyapatite (HA) at a gold electrode. Potentiostatic electroreduction of p-benzoquinone (BQ) in solution containing Ca(NO3)(2), NH4H2PO4 and BQ at a potential of -0.2 V vs SCE increased the solution pH near the electrode, and thus a calcium phosphate (CP) film was precipitated on the electrode surface. A further NaOH treatment of the CP deposit led to a uniformly distributed HA coating on the electrode, as examined by quartz crystal microbalance, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. A glucose biosensor was developed by dip-coating of glucose oxidase (GOx) onto the HA-modified Au electrode, glutaraldehyde cross-linking of GOx, and then electrodeposition of an outer poly(o-phenylenediamine) film. Effects of various experimental parameters on glucose biosensing were investigated for optimizing the experimental conditions. The biosensor exhibited high sensitivity, fast response, low detection limit and good storage stability. Through nonlinear fitting of the experimental data to the Michaelis-Menten enzymatic kinetics, the apparent Michaelis-Menten constant of the immobilized GOx was calculated to be 5.2 mmol L-1.