Polymer sniffs out explosives
Device makes light work of detecting bombs.
A new material designed by a team of chemists and electrical engineers in the United States can detect explosives such as TNT with 30 times more sensitivity than current man-made detection devices.
Specially trained dogs that can sniff out the chemical vapours released by buried explosives are currently the gold standard for detecting hidden bombs, but bomb dogs are expensive to train and can work for only a limited number of hours each day. Because of these limitations, much research is being done to develop man-made devices that can detect concealed explosives with the same sensitivity as a canine.
To that end, Timothy Swager and colleagues at the Massachusetts Institute of Technology (MIT) in Cambridge developed a polymer that acts like a laser source, is stable in air, and is very sensitive to the presence of explosive vapours.
Massachusetts Institute of Technology
The new material, a semiconducting organic polymer (SOP), releases a stream of light particles like a laser beam when bombarded with ultraviolet light, in a process called lasing. The ultraviolet light excites electrons in the polymer, and when the SOP absorbs enough of these photons to reach what is called the lasing threshold, a beam of light is released.
When TNT is present, however, it sticks to the polymer and the SOP stops lasing. The disappearance of the beam of light from the polymer therefore reveals the presence of explosives nearby.
"Lasing is one way to get great sensitivity," says team member Aimée Rose. "With this polymer, we have achieved one of the lowest lasing thresholds known in organic materials." This property enables the SOP to operate for long periods of time in ambient air, conditions necessary for a sensor to work well in the field.
The new polymer, unveiled in this week's Nature1, expands the team's previous work in designing fluorescing polymers that attract TNT and other electronegative chemicals. The researchers hope that the latest polymer could be as sensitive as the nose of a trained dog.
Although it will be a year or two before a device incorporating the new polymer is in the hands of those uncovering buried explosives or screening cargo, the earlier-generation fluorescing polymers are the basis for a handheld detector developed by Nomadics for use by soldiers and security personnel.
Rose hopes that the latest development could help the ongoing effort to rid the world of landmines - according to some estimates, there are as many as 100 million spread over more than 60 countries around the globe. "To develop something in the lab and to see it manifested in a device that can save lives is extremely rewarding," says Rose.
- Rose A., Zhu Z., Madigan C., Swager T. & Bulovic V. Nature, 434. 876 - 879 (2005).