Ellipsometry measurements and impedance spectroscopy on Langmuir–Blodgett membranes on Si/SiO2 for ion sensitive sensor

LB films containing butyrylcholinestrase (BuChE) are fabricated to realize an ion-sensitive field-effect transistor (ISFET) for the detection of organophosphorus pesticides in water. A common pesticide known as trichlorfon is examined in our work. Adsorbing the enzyme molecules onto stearylamine monolayer using the electrostatic force forms the BuChE-immobilised Langmuir–Blodgett (LB) films. Enzyme/stearylamine mixed LB films are immobilized onto ISFET and treated by glutaraldehyde vapor to improve the LB film’s stability. Two techniques, the ellipsomerty and spectroscopy methods, have been used to investigate the homogeneity and stability of these films. In ellipsometry the refractive index and thickness of Si/SiO2/LB films are measured. By utilizing the spectroscopy technique the impedance spectrum of Si/SiO2 and Si/SiO2/LB films are obtained and compared to ellipsometry results.