Selective room temperature nanostructured thin film alcohol sensor as a virtual sensor array

Nanostructured SiO2 thin films fabricated via glancing angle deposition on interdigitated electrodes were used as room temperature alcohol sensors. Both frequency dependent capacitance and impedance were used to analyze sensor response to methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol. Sensor responsivity was examined across the entire percent vapour saturation range for the same set of alcohols and the detection limit for ethanol, as an example, was derived. The response and recovery times for ethanol were determined from a pulse test and the responsivity curves, giving values of 66 s and 76 s, respectively. Sensor lifetime was examined for the same set of alcohols with and without irradiation from a UV-LED. We observed that sensor aging for the detection of ethanol and 1-butanol was greatly reduced under irradiation from the UV-LED whereas the UV-LED had little effect on aging for methanol, 1-propanol and 2-propanol. Using the frequency dependent responsivity curves of our sensors, we developed an algorithm that enables a single sensor to distinguish between methanol, ethanol and 2-propanol in a blind protocol test. In five out of seven trials, the algorithm successfully identified both the alcohol and concentration thereby demonstrating room temperature single sensor selectivity.