Self-calibration of a polyaniline nanowire-based chemiresistive pH sensor

Abstract

This paper reports on a new method to measure the pH of the solution with repeatability and low hysteresis using a polyaniline nanowire-based chemiresistive sensor. Polyaniline’s natural tendency to irreversibly lose its conductivity, especially when frequently exposed in solutions with pH greater than 4, has prevented its advancement as a reusable pH sensor. In the presented method, the polyaniline is electrochemically reduced prior to each measurement in order to reset the doping level of the polymer. Then, the potential of the polyaniline is linearly scanned, from a fully reducing (VR) to a partially oxidizing (V0) potential, and the resulting current waveforms are used to determine the pH. Here, we demonstrate that by comparing the current values at V0, the solution pH in the range 1–3 can be determined, and by comparing the peak values of the current responses from the two consecutive voltage sweep cycles, the pH of the solutions in the range 4–6 can be distinguished. Experimental results show that the proposed technique gives repeatable pH measurements even as the polyaniline nanowires undergo conductivity degradation.