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From IIT-M, nano-scale device to detect big
explosives
Tuesday August 28, 2012 06:22:58 PM, K.S. Jayaraman,
IANS
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Chennai: Researchers
at the Indian Institute of Technology, Madras, (IIT-M) have
developed a novel device that can visually detect even a single
molecule of TNT used in the making of powerful explosives.
Apart from national security, this ultra-sensitive and highly
selective detection method will have applications in early
identification of diseases and in radiation prevention, the IIT
researchers claim.
Chemistry professor Thalappil Pradeep and his students Ammu Mathew
and P.R. Sajanlal reported the principle behind this device in
the online issue of the leading chemistry journal Angewandte
Chemie on Aug 22. They are now building the device that may be put
to practical use soon.
The science behind this explosive detector is rather involved and
difficult to explain. In simple terms, the detector works somewhat
like an alert traffic cop who spots a violator by simply looking
at the traffic signal. In other words, if the suspected sample
being tested is clean, the detector gives off a red glow on being
irradiated with light of a particular wavelength.
But if the sample contains the explosive TNT (trinitrotoluene),
the signal changes to green. This dramatic change from red to
green that can be observed with a fluorescence microscope has been
demonstrated by the IIT team to take place in the presence of even
just one molecule of TNT -- a lower limit that has not been
achieved by any detector so far.
Pradeep heads IIT's nanoscience centre and naturally the TNT
sensor that his team has developed uses a combination of gold and
silver nano-particles, which are particles of extremely small
dimensions. The entire detector system is just four millionths of
a metre in size and its distinct star shape is of particular
advantage because it is easy to unmistakably identify the colour
change under the microscope, says Pradeep.
According to the scientists, their novel approach "can be
considered a single-particle, single-molecule detection technique
which is probably the ultimate in ultra-trace sensitivity".
The researchers have demonstrated that they can also detect
extremely low levels of mercury - an environmental contaminant --
using the same sensor strategy. They say the concept could also be
used for the detection of very low concentration of other
substances by incorporating appropriate molecules called "ligands'
on their sensor thereby opening up applications in catalysis,
bio-imaging and other areas.
(K.S. Jayaraman can be contacted at killugudi@hotmail.com)
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