Sniffer-dog phones to detect toxic chemicals

Cheap chemical sensors have been developed which will allow people to sniff out toxic gases with their smartphones.


The low-cost technology uses chemically altered carbon nanotubes which could be fitted to a range of handheld devices or even ID badges worn on the body.

MIT researchers intend to install the sensors in radio-frequency identification (RFID) badges worn by those likely to need advance warning of chemical agents, such as soldiers.

The scientists revealed that the sensors consists of a circuit loaded with carbon nanotubes. These are normally highly conductive but have been wrapped in an insulating material that keeps them in a highly resistive state. When exposed to certain toxic gases, the insulating material breaks apart, and the nanotubes become significantly more conductive. A smartphone-readable signal is then transmitted by near field communication (NFC) technology.

The sensors can identify toxic elements to within 10 parts per million in around five seconds.

The MIT researchers’ wireless chemical sensor. (Melanie Gonick)

In recent years the same lab developed other inexpensive wireless sensors, using chemically modified nanotubes called ‘chemiresistors’ for the detection of meat decay and the ripeness in fruit. The electric current alters when exposed to a target chemical.

In this instance researchers designed sensors highly sensitive to “electrophilic,” or electron-loving, chemical substances, which are often toxic and used for chemical weapons.

A metallo-supramolecular polymer (metals binding to polymer chains) material was created, acting as an insulation, wrapping around each of the sensor’s tens of thousands of single-walled carbon nanotubes, separating them and keeping them highly resistant to electricity. But electrophilic substances trigger the polymer to disassemble, allowing the carbon nanotubes to once again come together, which leads to an increase in conductivity.

To build their wireless system, the researchers created an NFC tag, which turns on when its electrical resistance dips below a certain threshold, and applied their nanotube/polymer material to the NFC tag’s antenna. When exposed to 10 parts per million of SOCl2 for five seconds, the material’s resistance dropped to the point that the smartphone could ping the tag. According to the researchers, such a wireless system could be used to detect leaks in Li-SOCl2 (lithium thionyl chloride) batteries, which are used in medical instruments, fire alarms, and military systems.