Fundamental sensing limit of electrochemical glucose sensors

This paper investigates the inherent sensitivity limit, deactivation of glucose oxidase, of a glucose oxidase based electrochemical glucose sensor for in vivo monitoring of blood glucose concentration. Results in this paper show that the current density sensitivity to glucose decreases from 1200 nA/mm(2)/mM at initial implantation to 100 nA/mm(2)/mM after an implantation time of 2 years, when degradation due to glucose oxidase deactivation only is considered. Even as the sensor signal strength decreases, if the sensing electronics are sufficiently discriminating then a useful measure of blood glucose concentration can be extracted. This work aims to determine both how the glucose oxidase based sensor's signal-to-noise ratio degrades over long time scales and the electronic circuit requirements to achieve multi-year device lifetimes. Two sensing amplifier techniques are presented which can be used to detect the signal generated by the sensor. The noise performance of each technique is compared with the noise performance of the sensor and mutli-year lifetimes are shown to be feasible.