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Optical Sensor Detects Trace Amounts of Explosives

A novel optical fibre sensor can detect minute concentrations of explosives in only a few minutes, according to research published in Sensors and Actuators B: Chemical.

“Traditionally explosives detection has involved looking for metals that encase them, such as in land mines,” says project leader Dr Georgios Tsiminis of the University of Adelaide’s Institute for Photonics and Advanced Sensing.

“In today’s world, however, home-made improvised explosive devices will often have no metal in them, so we need to be able to detect the explosive material itself. This can be difficult as they often don’t interact with chemicals and we don’t want them near electricity in case they explode.”

Instead, the researchers are using a plastic material that emits red light when illuminated with green laser light. The amount of red light emitted declines in the presence of explosives.

Three tiny holes at the core of special optical fibres are coated with a thin layer of polymer. The explosives sample is drawn up the holes in the fibre by capillary action, and the amount of red light emitted is measured.

“This has high sensitivity, and we can detect tiny quantities of an explosive in a small sample,” says Tsiminis. “And not only do we know if explosives are there, we can quantify the amount of explosive by looking at how the light emission changes over time.”

Tsiminis says the sensor is ideal for forensics investigations to determine whether explosives have been present in a particular location. It’s inexpensive, quick and easy to use, and could be done on-site to detect trace amounts of explosive. “So forensic investigators would be able to take swabs from various surfaces, place them in some organic solvent and, within a few minutes, know if there have been explosives present.”