Review on the utilisation of sensing materials for intrinsic optical NH₃ gas sensors

Optical approaches for NH3 gas sensing are contemplated as a reliable alternative to the conventional chemiresistive gas sensing techniques. Initially, we have briefly reviewed different types of optical waveguides for intrinsic room temperature NH3 gas sensing and the most conceivable optical NH3 sensing mechanism. While for the most part of this review, we have scrutinised the application of several materials for optical NH3 gas sensing. These materials are conducting polymers, biopolymers, metal oxides, organic dyes, carbon-based nanomaterials and metal-organic frameworks. Comprehensive qualitative and quantitative insights on typical gas sensing parameters such as sensitivity, cross-sensitivity (selectivity) and aptness to operate at room temperature were meticulously scrutinised for each material. Survey and juxtaposition of the respective parameters have emerged from various optical properties including absorbance, reflectance, and plasmonic response.