The Massachussets Institute of Technology has developed a carbon
nanotube sensor modified with a metalloporphyrin that can be used to
detect gases emitted by 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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