**2. Impedimetric Sensing Mode**

In order to describe the response of a PPy based conducting polymer electrochemical sensor towards a low amplitude sinusoidal perturbation as a function of frequency, the impedimetric sensing mode will be used. Impedimetric mode, also known as impedance, is a circuit's ability to measure the resistance towards the flow of an electrical current. To measure the impedance, an electrochemical impedance spectroscope (EIS) is used with the application of a small sinusoidal potential to the working electrode in an electrochemical cell, while measuring the resulting current response. By varying the excitation frequency, *f*, of the applied potential over a range of frequencies, one can calculate the complex impedance, i.e., the sum of the system's real and imaginary impedance components as a function of the frequency (i.e., angular frequency *w*). The results of the impedance measurement can be graphically demonstrated using the Nyquist (Cole–Cole) and Bode plot for all the applied frequencies with the real part of the impedance *Z* plotted along the *x*-axis and imaginary part plotted along *y*-axis in the latter [27].
