Enhanced ionodetection by using polyethyleneimine as an insulator material

Thin polyethyleneimine (PEI) films were deposited on p-silicon-based transducers. The polymer acts at the same time as the insulator and the sensitive membrane of an electrolyte/insulator/semiconductor (EIS) structure. Electrochemical measurements such as potentiometric or capacitance and impedance spectroscopy analyses were performed to investigate the sensitivity of this device towards ions. The PEI-modified silicon was used as copper and pH sensor. Sensitivities recorded in both cases were close to a Nernstian response: 45 mV/pH and 26 mV/pCu. Impedance spectroscopy allowed to propose equivalent circuits for the EPS structure, and has lead to a better understanding of the mass-transfer mechanisms, which are involved during the interactions between the electroactive species and the polymeric insulator.