What analytical technique is sensitive enough to detect — from afar — traces of explosives left on a bomb-maker’s body or belongings? One that uses an eye-safe laser to detect nitric oxide.
Kate McAlpine reports for Chemistry World:
Researchers at the Massachusetts Institute of Technology, US, (MIT) have developed a laser-based explosives detector that can spot 2,4,6-trinitrotoluene (TNT) at concentrations of 1ng/cm2, from 15cm away.
Charles Wynn and his team can generate a particular signal from nitrate and nitro-bearing explosives with a laser. McAlpine explains that the detector uses “photodissociation laser-induced fluorescence to (PD-LIF) to break the explosive molecule into fragments — nitric oxide (NO) — and probes the NO with the same UV laser pulse.” (Vibrational energy distinguishes NO in explosives from NO in atmospheric smog.)
“In addition to demonstrating that PD-LIF can detect minute concentrations of TNT, the researchers also discovered that the signal from the TNT scales with the area covered by it — not with the mass concentration,” McAlpine adds. The researchers have also shown that the method can detect other explosives such as DNT, C4, and PETN.
The MIT team found that PD-LIF could detect explosives residue on wafers directly treated with solutions of TNT. The concentration and distribution of TNT on those wafers was confirmed with a microscope study. To see how the technique would do with a more real-world scenario, they also analyzed silicon wafers that had been handled with TNT-tainted fingers. PD-LIF detected the residue on the wafers.
Other researchers told Alpine that the technique’s sensitivity at short distances is impressive. And though it wouldn’t be fast enough to scan for a roadside bomb, they suggested that PD-LIF could help at checkpoints by easily scanning around a car door handle in less than a second.
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.