pH and ion sensitivity of a field-effect EIS (electrolyte-insulator-semiconductor) sensor covered with polyelectrolyte multilayers

Field-effect capacitive EIS (electrolyte-insulator-semiconductor) sensors have been utilised for a label-free electrical monitoring of the layer-by-layer adsorption of polyelectrolyte multilayers (PEM). Anionic poly(sodium 4-styrene sulfonate) and cationic poly(allylamine hydrochloride) have been used as model system. The effect of the number of PEMs and polarity of the terminating layer on the sensor signal have been investigated. In addition, pH and ion sensitivity of EIS sensors covered with PEM have been studied by constant-capacitance method. Alternating potential shifts, having a tendency to decrease with increasing the number of PE layers, have been observed after the adsorption of each polycation and polyanion layer. The possible mechanisms for the sensor response are discussed.