A team of
bioengineers has developed a sensor for detecting nearby
undetonated explosives based on the same biological principles that cause
turkey skin to change colour. An accompanying app in development lets users
know whether they've just encountered explosive trinitrotoluene (TNT), or just
a spot of methanol.
Seung-Wuk
Lee of UC Berkeley led a team in the development of the system, which relies on
engineering the virus M13 filamentous bacteriophage to resemble
and behave like the collagen fibres found under turkey skin. You might not
think a turkey would inspire anything more than an annual attempt at making its
whole-roasted-self tasty, but its wattle was the source of inspiration since it
changes colour when the bird gets hot and bothered. This is down to a series of
blood vessels altering the dispersion of the collagen fibres as they inflate or
contract, depending on the turkey's temperament or activity. This, in turn,
causes lightwaves to scatter differently and the result is a colour-changing
jowl.
Rather
than visualising when rage or impatience is present, Lee and his team wanted
the biomimicry sensor to seek out substances including hexane, isopropyl
alcohol, methanol and TNT vapours. By engineering the M13 virus to develop
nanofibres interspersed in a similar fashion to those in turkey collagen, the
team was able to generate a substance sensitive to environmental changes. This
included humidity -- the sensor became bluer the drier the air was, and more
red if the air was moist as the nanostructures expanded and contracted like
blood vessels -- but the main objective was to test the aforementioned series
of chemicals.
"Both
natural materials and their synthetic analogues lack selectivity towards
specific chemicals, and introducing such selectivity remains a challenge,"
write the authors in the journal Nature Communications, where the experiment
results have been published. "Here we report the self-assembly of
genetically engineered viruses (M13 phage) into target-specific, colourimetric
biosensors."
They
found the biosensor became swollen or shrunk down depending on which chemical
was present, generating different colours that could be attached to a
particular chemical. It could then be photographed using the accompanying
iColour Analyser smartphone app, which automatically identifies the substance.
It's like a turkey-themed pH test for dangerous substances.
The
system was also tweaked to become a sensor solely for detecting TNT, by
engineering the virus to bind with particular sites within the molecule. When
the sensor was exposed to two molecules the team says are similar to TNT -- DNT
and MNT -- it was able to clearly spot the difference between them and the real
McCoy.
In a statement,
Lee said: "Our system is convenient, and it is cheap to make. We also
showed that this technology can be adapted so that smartphones can help analyse
the colour fingerprint of the target chemical. In the future, we could
potentially use this same technology to create a breath test to detect cancer
and other diseases."
"Our
tuneable, colourimetric sensors can be useful for the detection of a variety of
harmful toxicants and pathogens to protect human health and national
security," conclude the authors. Right now though, one stumbling block
will surely be the fact that by their own admission, the authors do not
comprehend the mechanisms behind the sensitivity of the blood vessel stand-ins.
They suggest it might down to water content within the virus. The success will
also depend on the system's sensitivity.
Current
proposals for new TNT detectors superior to a sniffer dog often have to increase levels of the substance present in the
air significantly in order to confirm detection. A team from India might
provide some competition as well, where a gel has been engineered that turns fluorescent when exposed to TNT.
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