Measurement of low glucose concentrations using a microelectrochemical enzyme transistor

Using poly(aniline), with glucose oxidase immobilised in an electrochemically polymerised film of 1,2-diaminobenzene deposited on top and using tetrathiafulvalenium as a mediator, microelectrochemical enzyme transistors responsive to glucose which operate at pH 5 mere prepared. By careful control and monitoring of both the initial electrochemical deposition of the poly(aniline) and of the immobilisation of the enzyme, it was possible to achieve good reproducibility from device to device. By optimisation of the washing and resetting conditions, it was possible to achieve excellent reproducibilty for replicate measurements with a single device, Studies of the effect of the drain voltage on the device performance show that for drain voltages up to 0.35 V the mechanism of operation is unchanged and both the maximum drain current and the maximum switching rate at a given glucose concentration increase linearly with the drain voltage, Above 0.35 V, the performance of the device is degraded by other electrochemical reactions occurring on the poly(aniline). Measurements with low concentrations of glucose show that glucose concentrations in the micromolar region can be determined and that at the lowest levels the detection limit is determined by the background switching rate of the device in glucose-free buffer, For the present devices the detection limit was found to be around 40 times lower than the detection limit for the same device operated as an amperometric sensor in air-saturated buffer solution.