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The main chemical in the curry spice turmeric could be the basis for cheap explosives detectors, say researchers.

The curcumin molecule is already well-known in medicine for its evident anti-cancer and anti-oxidant properties.

Now, research presented at the American Physical Society meeting suggests it could replace more complex solutions to spot explosives like TNT.

As it gathers molecules of explosive material in air, changes in its light-emitting properties can be measured.

This "fluorescence spectroscopy" is already employed in a wide array of sensing and analysis techniques.

Illuminating some chemicals causes them to re-emit light of a different colour, sometimes for extended periods - an effect exploited in, for example, glow-in-the-dark materials.

The intensity of this re-emitted light can change if different molecules bind to the fluorescent ones, and that is how sensing techniques exploit the effect.

Light idea

Now, Abhishek Kumar, of the University of Massachusetts, Lowell, and his colleagues have happened across a means of co-opting the curry ingredient's fluorescence properties for explosive detection.

"If you have a gram of TNT... and you sample a billion air molecules from anywhere in the room, you'll find four or five molecules of TNT - that's the reason they're so hard to detect," he told the conference.

"And, the US State Department estimates there are about 60 to 70 million land mines throughout the world; we need a very portable, field-deployable sensing device which is cheap, very sensitive, and easy to handle."

Mr Kumar's team - including physicist Jayant Kumar and engineer Pradeep Kurup of the university - was investigating the use of curcumin for biological applications, trying to make it easily dissolve in water, when they hit on the idea of making use of its optical properties.

"People have mainly looked at its biological applications, treating cancer and Alzheimer's and so on, but nobody has looked at making optical devices out of them," he told ���˿��� News.

The team's first trick was to use a chemical reaction to attach "side groups" to the curcumin that preferentially bind to explosive molecules.

But curcumin's helpful optical properties only worked when it was dissolved in a liquid; when evaporated to a solid, it clumped together and the fluorescence stopped.

They then hit on the idea of using a polymer called polydimethylsiloxane, which is thick and viscous at room temperature, spinning the mixture on glass plates to make extremely thin films.

The idea would be to use an inexpensive light source - the team uses LEDs - shone on to the thin films, detecting the light they then put off. In the presence of explosives, the light would dim.

By using an array of sensors, each sensitive to slightly different colours of light, a range of different materials could be detected, and, crucially, reduce the risk of false alarms.

In tests, the films can currently detect explosive levels down to 80 parts per billion, but Mr Kumar said that for high-sensitivity applications like mine detection, they needed to increase the sensitivity further, by adjusting the chemical groups attached to curcumin.

The team, which is funded in part by the US Army Research Laboratory and the National Science Foundation, is already in discussions with a company to develop the technique into a portable detector device.