The pH-static enzyme sensor offers a solution to the buffer dependency of ISFET-based enzyme sensors. A continuous coulometric titration of the reaction products keeps the pH in the enzymatic membrane at a constant level. This paper presents an automatic system to control the compensating current that is a direct measure for the substrate concentration.
van der Schoot, B. H., Voorthuyzen, H., & Bergveld, P. (1990). The pH-static enzyme sensor: design of the pH control system. Sensors and actuators, 1(1-6), 546-549. https://doi.org/10.1016/0925-4005(90)80270-A