New MIT sensor detects spoiled meat

MIT researchers have developed an inexpensive, portable sensor that can detect gases emitted by rotting meat, allowing you to determine whether the meat in the grocery store or refrigerator is safe to eat.
The sensor, which consists of chemically modified carbon nanotubes, could be deployed in "smart packaging" that would offer much more accurate safety information than the expiration date on the package, said Timothy Swager, the John D MacArthur Professor of Chemistry at Massachusetts Institute of Technology (MIT).
The sensor is similar to other carbon nanotube devices that Swager's lab has developed in recent years, including one that detects the ripeness of fruit.

All of these devices work on the same principle: Carbon nanotubes can be chemically modified so that their ability to carry an electric current changes in the presence of a particular gas.
In this case, the researchers modified the carbon nanotubes with metal-containing compounds called metalloporphyrins, which contain a central metal atom bound to several nitrogen-containing rings.
For this sensor, the researchers used a metalloporphyrin with cobalt at its center. Metalloporphyrins are very good at binding to nitrogen-containing compounds called amines.

Of particular interest to the researchers were the so-called biogenic amines, such as putrescine and cadaverine, which are produced by decaying meat.

When the cobalt-containing porphyrin binds to any of these amines, it increases the electrical resistance of the carbon nanotube, which can be easily measured.
"We use these porphyrins to fabricate a very simple device where we apply a potential across the device and then monitor the current. When the device encounters amines, which are markers of decaying meat, the current of the device will become lower," said the paper's lead author, graduate student Sophie Liu.
In the study, the researchers tested the sensor on four types of meat: pork, chicken, cod, and salmon. They found that when refrigerated, all four types stayed fresh over four days.

Left unrefrigerated, the samples all decayed, but at varying rates.
The new device requires very little power and could be incorporated into a wireless platform that Swager's lab recently developed which allows a regular smartphone to read output from carbon nanotube sensors such as this one.