Colorimetric Sensors for Toxic and Hazardous Gas Detection: A Review

Since the industries are vastly rising, the threat of toxic and hazardous substance to human beings and demands of the accurate sensor is increasing. Colorimetric sensors that detect substances by measuring the absorbance or fluorescence spectra shift are one of the most emerging strategies these days. However, conventional colorimetric gas sensors are limited to specific application due to the limitation of detecting only liquid phase substances. For practical applications of the colorimetric sensors, it is necessary to detect low concentrations of toxic and hazardous substances in gaseous media. Besides, operation with low power consumption and excellent selectivity and sensitivity should be considered for Internet of Things (IoT) application. In this paper, various efforts on the investigation of several materials, including dyes, polymers, metal–organic complexes, and metal oxides as active sensor elements of the colorimetric gas sensors for IoT application are summarized. This paper also reviews various kinds of colorimetric gas sensor that exhibit great sensing properties to toxic and hazardous gases and introduce a brief overview of the challenges of colorimetric gas sensors as a candidate for future IoT gas sensor technology.