 Since then there has been research into chemiresistors and chemically sensitive field effect transistors fabricated from individual single-walled nanotubes, bundles of single-walled nanotubes, bundles of multi-walled nanotubes, and carbon nanotube–polymer mixtures.It has been shown that a chemical species can alter the resistance of a bundle of single-walled carbon nanotubes through multiple mechanisms.Carbon nanotubes are useful sensing materials because they have low detection limits, and quick response times; however, bare carbon nanotube sensors are not very selective.