A team from MIT has produced a cheap, lightweight wireless sensor that can detect toxic chemical agents. The new sensors, which are made from chemically altered carbon nanotubes (CNTs), can be easily integrated into wireless devices such as light radio-frequency identification (RFID) badges or smartphones to identify trace amounts of hazardous gases or chemical weapons on the battlefield or protect those working with dangerous chemicals.
The sensor comprises a circuit containing many thousand single-walled CNTs covered in an insulating material to maintain them in a highly resistive state. On being exposed to certain toxic gases, the insulating material comes apart allowing the CNTs to become much more conductive, transmitting a readable signal that can be picked up by near-field communication technology.
The sensors are highly sensitive to “electrophilic” chemical substances, which are often toxic and used for chemical weapons, aided by a new metallo-supramolecular polymer made of metals binding to polymer chains. The polymer insulates, wrapping each sensor’s CNTs, keeping them apart and highly resistant to electricity. However, such electrophilic substances provoke the polymer into disassembling so that the CNTs re-unite and improve conductivity.
The team created an NFC tag that can turn on when its electrical resistance goes below a certain threshold. With smartphones emitting short pulses of electromagnetic fields that resonate with an NFC tag at radio frequency, this induces an electric current that transmits information to the phone. As lead author Timothy Swager points out, “We are matching what you could do with benchtop laboratory equipment, such as gas chromatographs and spectrometers that is far more expensive and requires skilled operators to use”.