Ways to improve the parameters of optical gas sensors of ammonia based on polyaniline

Abstract The possibility to improve the parameters of the optical ammonia sensors on the basis of polyaniline (PANI) has been investigated. Basing on the analysis of the PANI optical absorption spectra the possibility of a significant increase in sensitivity and selectivity of the ammonia sensors is shown using the additional measurement of optical absorption at wavelengths 800 nm (to increase sensitivity) and 720 nm (to increase selectivity). As measurement of the gas-stimulated changes has been carried out both in the visible region of the spectrum at 600 nm and in the infra-red region at 800 nm, the manufacture of the sensory elements may be realized without difficulty. It has been stated that the sensitivity to ammonia of the thin PANI films increases almost twice at the expense of simultaneous measurements of the optical absorption increase in the visible spectrum and its decrease in the nearest infra-red spectrum and the absolute values of summation of these measurements. The isobestic point of the gas-stimulated changes absence in optical absorption of PANI near 720 nm can be used as a reference point for the ammonia presence, which increases the gas sensor selectivity. We propose the method of detecting the analyte with the optical gas sensor on optoelectronic pairs with the mobile matrix of LEDs and photodiodes, and also the possibility of simultaneous registration of the parallel optocouples independent signals.