When building a gas sensor, it is important to bare in
mind the selectivity for detecting a specific gas in different
environments. Other requirements are the sensitivity, selectivity and reversibility operating at different temperatures.
In addition, it is also important to note that these sensors should be compact and of low costs. To date, a wide
variety of sensors has been fabricated based on semiconducting oxides, metal oxides, metal nanoparticles, metal
complexes, organic polymers and carbon nanotubes.