Carbon-nanotube sensor detects rotting meat
The sensor is based on the principle that the conductivity of suitably adapted CNTs can be modified by the presence of certain gases that bond to the adoptor atom or molecule. In this case a team working under Timothy Swager, the John MacArthur Professor of Chemistry at MIT, has 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.
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.
"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 Sophie Liu, lead author of a paper on the technology in a recent edition of the journal Angewandte Chemie.
The sensor was tested in 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.
There are other sensors that can detect the signs of decaying meat, but they are usually large and expensive instruments that require expertise to operate. "The advantage we have is these are the cheapest, smallest, easiest-to-manufacture sensors," Swager says. However, it is not clear how accurate the technique is, or how the sensor would be calibrated
The device is also low power and could be included in a wireless sensor node that allows a smartphone to read output from the sensor. The researchers have filed for a patent on the technology and hope to license it for commercial development.
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