Electroanalytical detection of glucose using a cyanometalate-modified electrode: requirements for the oxidation of buried redox sites in glucose oxidase

Modification of a nickel electrode with a mixture of iron and ruthenium cyanometalates allows one to efficiently turn over glucose oxidase in the presence of its substrate. A limit of detection for glucose of 25 μM can be obtained with an observed saturation concentration of 10 mM. Glucose detection is found to be very sensitive to the cationic environment of the electrolyte. The largest currents for glucose oxidation are observed in the presence of nonelectroactive multiply charged cations. The solid state nature of the surface-confined cyanometalate redox mediator argues against the widely held mechanism for enzyme oxidation in which the redox mediator is required to enter the enzyme active site.