Chemiresistive sensors have gained increasing interest in recent years due to the necessity of low-cost, effective, high-performance gas sensors to detect volatile organic compounds (VOC) and other harmful pollutants. While most of the gas sensing technologies rely on the use of high operation temperatures, which increase usage cost and decrease efficiency due to high power consumption, a particular subset of gas sensors can operate at room temperature (RT). Current approaches are aimed at the development of high-sensitivity and multiple-selectivity room-temperature sensors, where substantial research efforts have been conducted. However, fewer studies presents the specific mechanism of action on why those particular materials can work at room temperature and how to both enhance and optimize their RT performance. Herein, we present strategies to achieve RT gas sensing for various materials, such as metals and metal oxides (MOs), as well as some of the most promising candidates, such as polymers and hybrid composites. Finally, the future promising outlook on this technology is discussed.

Indium oxide microcrystals with shapes of truncated cubes and pyramids as well as microrods with square, triangular or hexagonal cross-sections are grown by a catalyst free evaporation deposition method. Size and shape control of the crystals as a function of the treatment parameters is discussed. Their luminescence properties are investigated and some features in the cathodoluminescence images are suggested to be related to the possible formation of a core dislocation. The waveguiding behaviour of the rods as well as whispering gallery resonances with improved Q-factor are demonstrated for hexagonal and square cross-section rods. The effect of tapering of the rods on the resonance wavelength is also studied and fitted to a theoretical model.