From IIT-M, nano-scale device to detect big explosives

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  reporated 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 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.