Electrochemical sensor for nitrite determination based on thin films of sulfamic acid doped polyaniline deposited on Si/SiO2 structures in electrolyte/insulator/semiconductor (E.I.S.) configuration

Sulfamic acid doped polyaniline (abbreviated PANI-SFA), previously used as an optical sensor for reagentless nitrite determination, has been tested as a potential electrochemical sensor for this anion. Cyclic voltammetry measurements of PANI-SFA and, for comparative reasons, PANI-HCl clearly show that electrochemical activity of the former is strongly dependent on the presence of nitrite in the electrolyte, even at low concentrations of this anion (C = 10−6 M). Inspired by this finding we have constructed an electrochemical sensor by deposition of a thin PANI-SFA layer on the Si/SiO2 substrate to obtain an electrolyte–insulator–semiconductor (E.I.S.) structure. The electrochemical sensing properties of PANI-SFA towards nitrite, in the E.I.S. configuration, have been tested in acidified (pH 2) solutions by capacitance voltage measurements C(V) method. Transfer and ion diffusion process of nitrite anions in the polymer membrane have been investigated. A specific feature of the sensor tested is a monotonic change of its flat band potential (ΔVfb) with increasing nitrite concentration, observed for the concentration range from C = 10−6 M to C = 10−1 M. The sensitivity of the detection is however significantly enhanced only for concentrations exceeding 5 × 10−4 M, for lower nitrite concentrations the capacitance-based detection is inferior to the previously studied optical one.