A sensor, consisting of the carbon nanotubes, could be put in smart packaging to help retailers and consumers with more accurate safety information than the expiration date on the package.
Carbon nanotubes can be chemically modified so their ability to carry an electric current changes in the presence of a particular gas.
When the device encounters amines the current will become lower. So-called biogenic amines, such as putrescine and cadaverine, are produced by decaying meat.
Electric current change
Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT, told FoodQualityNews that the detection is from a change in electrical resistance.
“It can be put in packaging, as long as the amines diffuse, and they are volatile so they move around and permeate other structures, the tag doesn’t even have to be visible,” he said.
“It measures a change in electrical resistance which you can read wirelessly so you don’t have to physically contact the sensor.”
The device could be incorporated into a wireless platform Swager’s lab developed that allows a smartphone to read output from carbon nanotube sensors such as this one.
Researchers modified the carbon nanotubes with metal-containing compounds called metalloporphyrins, which contain a central metal atom bound to several nitrogen-containing rings.
Hemoglobin, which carries oxygen in the blood, is a metalloporphyrin with iron as the central atom.
Metalloporphyrin was used with cobalt at its center as they can bind to nitrogen-containing compounds called amines.
When the cobalt-containing porphyrin binds to any of these amines, it increases the electrical resistance of the carbon nanotube, which can be measured.
Threshold level
Swager said the system is better than colour-changing methods which require line of sight and can be subjective and is targeted at retailers for use in tracking products.
“There are several potential advantages in having an inexpensive sensor for measuring, in real time, the freshness of meat and fish products, including preventing foodborne illness, increasing overall customer satisfaction, and reducing food waste at grocery stores and in consumers’ homes,” said Roberto Forloni, a senior science fellow at Sealed Air, who was not part of the research team.
“Consumers are probably not the first place but it will reach them eventually. Retailers are more likely to be the first place this is used. It should work fine with recloseable packaging as long as it is sealed properly,” he said.
“With the amines you put a threshold on when the product is compromised. For example, a traffic light system, red means don’t eat, yellow means it is ok now but tomorrow maybe not and green is fine. You might not need yellow, red and green would tell you if it is ok or not.
“We cannot have metal packaging as we need to read the sensor wirelessly but except metal we can do anything and we are investigating different packaging with suppliers.
“It can be isolated from food so there is no contact and it works as long as the polymers are permeable to the amines. Nothing comes out of the sensor and we have spoken with people in the industry about how it might work.”
Sensor testing and development
Researchers tested the sensor on pork, chicken, cod, and salmon.
They found that when refrigerated, all four stayed fresh over four days. Left unrefrigerated, the samples decayed, but at varying rates.
There are other sensors that can detect the signs of decaying meat, but they are large and expensive instruments that require expertise to operate.
Swager said the company C2 Sense is commercialising the technology and will be in field trials soon.
A patent has been filed and the plan is to license it for commercial development.
Research was funded by the National Science Foundation and the Army Research Office through MIT’s Institute for Soldier Nanotechnologies.
The sensor is similar to other carbon nanotube devices that the lab has developed, including one that detects the ripeness of fruit.