Massachusetts Institute of Technology (MIT) has been developing gas-detecting sensors based on chemiresistors, which consist of electrical circuits modified so that their resistance changes when exposed to a particular chemical.
Measuring that change in resistance reveals whether the target gas is present.
Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT, is the senior author of a paper describing the new sensors in the Proceedings of the National Academy of Science .
Chemistry graduate student Joseph Azzarelli is the paper’s lead author with contributions from postdoc Katherine Mirica and former MIT postdoc Jens Ravnsbaek.
Food spoilage tracking
Azzarelli told FoodQualityNews that molecules are emitted from foods such as produce, fish, meat or vegetables when they start to degrade, such as the example of ethylene with fruit.
“Another example is the amines from fish, so the tag can act as an early warning system and give you an idea if you have any emissions or breakdown in the product so you know it needs to be sold or thrown out. In this way it has implications for compliance so people are not selling spoiled food," he said.
“Our thinking is can we accurately represent expiry dates rather than a predicted date, to help in the process and not throw away food and remove dangerous food from shelves.
“We see possible use from the consumer who can adopt it if the card is implemented into packaging and inside the grocery store the consumer could pick up the pack and scan it with their phone to get the information.”
Modified NFC tags
Sensors are made from modified near-field communication (NFC) tags which can be read by any smartphone that has such capability.
The phones can send out short pulses of magnetic fields at radio frequency (13.56 megahertz), inducing an electric current in the circuit on the tag, which relays information to the phone.
The MIT team modified the tags by punching a hole in the electronic circuit and reconnected it with a linker made of carbon nanotubes that are specialized to detect a particular gas.
They added carbon nanotubes by “drawing” them onto the tag with a mechanical pencil in which the usual pencil lead is replaced with a compressed powder of carbon nanotubes.
Modified tags are called chemically actuated resonant devices (CARDs).
When carbon nanotubes bind to the target gas, their ability to conduct electricity changes, which shifts the radio frequencies at which power can be transferred to the device.
When a smartphone pings the CARD, it responds if it can receive sufficient power at the smartphone-transmitted radio frequencies, allowing the phone to determine whether the circuit has been altered and the gas is present.
The researchers have filed a patent on the sensing technology and are looking at possible applications.
How would it work?
Azzarelli said he couldn’t give an exact price point due to the early stage of the project but said future applications could also centre around liquids as well as current gas based vapours.
“The tag would be pre-programme to turn off or on at certain levels of gas presence. The tag or card would be inside the pack of salmon, for example, and if ammonia or amines are above value the tag will turn off or on and change state from 0 to 1 based on a predetermined value," he said.
“What that threshold is needs to come from a standards level, from the supply chain or the market segment has to agree.
“The sensors have a short read range of 5cms but can be read through cardboard, plastic, glass but not metal.
“The whole idea is for more sophisticated information in real time so efficiency gains can be made in the supply chain to improve margins, if the technology can get to a mature state.
“We are at the proof of concept stage and are excited about the potential and would be interested in hearing about opportunities in terms of joint development to bring it to market.”