Design of a conductimetric microsensor based on reversibly swelling polymer hydrogels

The design of a conductimetric sensor is described. Based on a planar interdigitated electrode structure coated with a polymer gel, the proposed sensor will detect changes in conductivity of a polymer hydrogel layer as the water content of the gel responds to environmental changes. A number of hydrogels were synthesized with varying chemistries so as to yield gels with a wide range of water contents and therefore conductivities. The measured conductivities were incorporated into a fields model which computes the admittance of an interdigitated electrode as a function of the properties of the gel and the electrode geometry. This permitted identification of the electrode geometries and minimum gel thicknesses needed to obtain a suitable admittance and adequate sensitivity to gel conductivity changes.<>