Conducting Polymer Based Gel Electrolytes for pH Sensitivity

The evaluation of concentration of ions and molecules with the help of biosensors have been regarded as an emerging technology. Bio and chemical sensors have a variety of applications in the field of medicine, military, environmental and food industries alike. With an estimated investment growth of over 4.31% in the development of pH sensors in the next five year, the objective of a developing a robust measurement system is all the more required. The scope of this research is to evaluate the ability of conducting polymer-based gel electrolytes for pH sensitivity, as a function of the transistor characteristics using an Extended Gate Field Effect Transistor or a conducting film in an electrochemical cell. Polymer gels were prepared by dissolving a suitable conducting polymer in an acidic media. The interaction of the gel with a buffer solution of known pH was collected as electric signals using a glassy carbon as an electrode. The electrochemical cell was further connected to the gate of a Metal-Oxide-Semiconductor Field Effect transistor (MOS-FET). The drain current was measured under two conditions; a) voltage across the gate (VGS) was kept constant, with varying voltage across the drain (VDS) and b) voltage across drain was fixed, while gate voltage changed. The drain current versus voltage of the transistor was plotted as a function of the ion interaction between the gel and the buffer. Different plots were recorded for different values of pH solutions. Final results were plotted to calculate the change in threshold voltage, for every change in pH of the observed solution. pH sensitivity of the gels was further tested through the Electrochemical Impedance Spectroscopy method, using a potentiostat and a three-electrode electrochemical cell. With a small excitation, the AC current flowing through the circuit at different frequencies were recorded and the plots discussed, to evaluate sensitivity to pH