Toward Impedimetric Measurement of Acidosis with a pH-Responsive Hydrogel Sensor.

A pH-responsive, poly(2-hydroxyethyl methacrylate) [poly(HEMA)]-based hydrogel has been fashioned into an impedimetric pH sensor for the continual measurement and monitoring of tissue acidosis that can arise due to hemorrhaging trauma. Four hydrogel systems molecularly engineered to influence water distribution and ionic abundance were studied: a cationogenic primary amine, -(2-aminoethyl) methacrylate (AEMA), a tertiary amine moiety, ,-(2-dimethylamino)ethyl methacrylate (DMAEMA), and a combined AEMA-DMAEMA formulation. Electrochemical impedance spectroscopy (EIS) of hydrogel discs held between platinized Type 304 stainless steel mesh electrodes in pH-adjusted 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid sodium salt (HEPES) buffer and equivalent circuit modeling indicated that the AEMA hydrogel had the highest sensitivity containing the relevant pathophysiological range (pH 7.