Field-effect sensors for monitoring the layer-by-layer adsorption of charged macromolecules

Capacitive EIS (electrolyte–insulator–semiconductor) sensors and ISFETs (ion-sensitive field-effect transistor) have been utilised for the detection of the layer-by-layer adsorption of charged macromolecules. The field-effect-based sensors with the adsorbed multilayers have been characterised by capacitance–voltage, constant-capacitance and constant-voltage-mode methods. The effect of the number and polarity of the polyelectrolyte layers on the shift of the capacitance–voltage curves along the capacitance and voltage axis has been investigated. Alternating potential shifts of about 30–50 mV have been observed after the adsorption of each polyanion and polycation layer, respectively. The possible mechanisms for the sensor response are discussed.