Fig. 1. (Color online) Smart gas sensor array fabricated by different techniques assisted by artificial intelligence algorithms can find many real-life applications, exhibiting great potential as a mammalian olfactory system in the areas of air and water quality monitoring, non-invasive disease detection, and dangerous gases leakage alarming.

Fig. 2. (Color online) MOX sensor array fabrication method and morphology^[10,11]: (a) FSP set-up, (b) SEM image of porous doped SnO₂ film, (d) USP setup, (e) Cross-section of SnO₂ nanotube decorated with Pt nanoparticles, gas sensor array of (c) doped SnO₂ microsensors and (f) 3-D SnO₂ nanotube.

Fig. 3. (Color online) (a) Sensor array fabrication methods and morphology^{[12, 13]}: (a) an SEM image of organic functionalized gold nanoparticle film deposited between adjacent electrodes, (b) a TEM image of monolayer capped gold nanoparticles, (d) a TEM image of ultrathin silicon channel, (e) EDS indicating the elemental composition of a single Pd-Au CS-FET, gas sensor array of (c) gold nanoparticles, (f) CS-FET.

Fig. 4. (Color online) Artificial intelligence algorithms adopted in a gas sensor array.

Fig. 5. (Color online) Application of gas sensor array ^{[11, 17, 98]}. (a) Processes involved in breath testing, (b) gases associated with different kinds of diseases including cancer, (c) GPRS based air pollution monitoring system, (d) real-time indoor gas monitoring by smart phone in smart buildings.

Table 1. Summary of different types of gas sensor^[33–37].