Flexible chemical sensors are not a new concept. Traditional chemical sensors based on conductive polymers over polymer substrates are generally flexible. However, with the advent of high-quality nanowires and nanotubes, and the rapid development of flexible electronics which involoves many breakthroughs in the synthesis and manipulation of these nanoscale materials, significant progress has been made in modern flexible chemical sensors.

In traditional conducitve polymer chemical sensors, self-organization in many solution-processed, semiconducting conjugated polymers results in complex microstructures, in which ordered microcrystalline domains are embedded in an amorphous matrix. This has important consequences for the electrical properties of these materials, i.e. charge transport is usually limited by the most difficult hopping processes and is therefore dominated by the disordered matrix, resulting in low charge carrier mobilities.

SWNTs, graphene and high quality nanowires and nanotubes as the sensing materials have been reviewed. Owing to the superior quality of SWNTs, high sensitivity ,low detection limit and fast response time have been observed in these nanowire and nanotube -based chemical sensors.

For highly crystalline metal oxide nanowires, a few sensing reactions occurred at room temperature instead of at high temperature. Ingenious nanowire and nanotube assembly and alignment open up many possibilities for high- performance multifunctional flexible chemical sensor development. Large integrated sensors with built-in intelligence are also on the horizon. The future of flexible chemical sensors is indeed very promising.