Glucose detection based on electrochemically formed Ir oxide films

Ir oxide (IrOx) films, known to be nanoporous, electronically conducting and biocompatible, were formed anodically on polycrystalline Ir substrates in neutral solutions and were used to immobilize glucose oxidase (GOx) using two different methods. The resulting electrodes were found to generate H2O2 in the presence of glucose and oxygen, yielding an excellent response to glucose (up to 70 mM) by the oxidation of H2O2 in both stirred and non-stirred neutral solutions. It was found that, while the preferred method of immobilization involves the growth of IrOx films in a ca. 130–160 U ml−1 GOx solution, these electrodes displayed relatively large K′m values (up to 190 mM), reflecting restricted diffusion of glucose inside these films. The thicker the film on the electrode, the more stable the electrode response, especially to solution agitation, but the larger were the K′m values. SEM examination of these electrodes showed that GOx deposits in the form of small clusters, with the more stable response obtained when these clusters are more uniformly distributed. These amperometric IrOx/GOx glucose sensors were found to be free of interference from ascorbic acid, uric acid and paracetamol, at their physiological concentrations.