Design of a conductimetric pH microsensor based on reversibly swelling hydrogels

Abstract

The design of a conductimetric pH sensor is described. Based on a planar interdigitated electrode structure coated with a pH-sensitive polymer gel, the proposed sensor will detect changes in conductivity of the hydrogel layer resulting from pH-dependent swelling of the gel. A pH-sensitive hydrogel has been synthesized, and the water content and conductivity measured as a function of pH. The measured conductivities are incorporated into a fields model which computes the impedance of an interdigitated electrode array. The effects of gel-layer thickness, device geometry, and interfacial impedance on device sensitivity are analyzed using the model.