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US Army scientists demonstrate rapid detection of nerve agents

27 September 2012

Scientists at the US Army Research Laboratory (ARL) are exploring ways to quickly alert Soldiers to deadly gaseous nerve agents in the air using multi-wavelength photoacoustics.

Dr Kristan Gurton
Dr Kristan Gurton

Dr Kristan Gurton, an experimental physicist in the Battlefield Environment Division, Computational and Information Sciences Directorate at ARL, recognised early in his career that the photoacoustic technique was an extremely sensitive spectroscopic method, able to detect chemical compounds at parts-per-million (ppm) or parts-per-billion (ppb) concentrations.

But he also realised that traditional laser photoacoustic spectroscopy would not be appropriate as a viable approach for solving a real time chemical/biological detection problem.

Photoacoustic spectroscopy, or the photoacoustic effect, is the measurement of light's absorption by matter, its subsequent heating and conversion to sound.

"What we needed was a low-cost, easy-to-use method that would quickly and accurately detect one of about 12 common, deadly gasses," Gurton said. "It had to be fast and it had to be extremely sensitive to detect hazardous gases at trace levels."

Because traditional laser photoacoustic spectroscopy is designed to measure a single absorption parameter at a time, it was not suited to produce the type of detailed information needed to detect and identify complex gaseous molecular compounds, Gurton said.

The solution was a non-traditional approach to conventional laser photoacoustic spectroscopy that is pretty straight-forward.

"We used multiple laser sources in a single, untuned, flow-through hollow cylindrical cell, like a straw, filled with the gas and equipped with a small microphone in the centre of the cell. Each laser modulated at a different frequency, which caused the gas to heat. The effect was a faint acoustic wave that could detect gaseous nerve agent stimulants at trace levels in real time," he said.

The novelty of the method is the propagation of multiple laser beams through a single, untuned, flow-through photoacoustic cell, Gurton said.

A goal of the basic research is to find ways to reinforce Soldiers' ability to detect minute levels of harmful gases on the battlefield, said physicist, Dr. Yongle Pan, the authors' BED colleague. "The sensor brings us closer to protecting the Soldier from potentially lethal hazards."

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