New material lets smartphones detect toxic gases in seconds

Researchers have developed a new low cost sensing material that can be integrated in electronic circuits and can enable smartphones to detect toxic gases within seconds.
Researchers from National Institute for Materials Science in Japan and Massachusetts Institute of Technology (MIT) developed the chemical sensing material whose electrical conductivity dramatically increases when exposed to toxic gases.
They integrated the sensing material into the electronic circuit in a near-field communication (NFC) tag, which is embedded in smart cards like those used to get through train ticket gates.
This technology made it possible for smartphones to quickly (in five seconds) detect toxic gases at a low concentration (10 parts per million).

People in today's society are subject to risks of being exposed to toxic gases deriving from natural sources (such as volcanic gases), leak accidents or potential acts of terrorism.
Means to easily and quickly detect toxic gases are vital to minimise their harmful effect.

The currently available toxic gas sensors are expensive, bulky, heavy and difficult to operate, and it is not practical to set them at many public locations (for example subways) or for people to carry them around, researchers said.
They developed a low-cost chemical sensing material consisting of a group of carbon nanotubes (CNTs) individually wrapped with supramolecular polymers - clusters of monomers held together through weak interactions.

The material's electrical conductivity increases up to 3,000 times when it is exposed to electrophilic toxic gases.
CNTs alone are highly conductive materials, but when they are wrapped with supramolecular polymers, which serve as insulators, they become poor conductors.
The supramolecular polymers were designed so that weakly bound sites in the molecules are dissociated when these sites are exposed to toxic gases, causing the wrapping molecules to disassemble, researchers said.
As a result, the original high conductive state of CNTs is restored, they said.
The extent of change in conductivity is directly proportional to the concentration of and the duration of exposure to a toxic gas, and the conductivity change can be easily measured by a commercially available resistance metre.

"We created a toxic gas sensor whose measurement can be read on smartphones by integrating the chemical sensing material into the electronic circuit present in a commercially available NFC tag," researchers said.
"Users can readily determine the presence/absence of toxic gas by holding an NFC-compatible smartphone over a sensor-embedded NFC tag while making sure that communication between the two devices is intact," they said.
The research was published in the Journal of the American Chemical Society.