Thursday, March 11, 2010

Army Seeks Super-Sniffer to Detect Explosives, Bio-Agent


Coverage of the new technology of metamaterials has tended to focus on the possibility of a real-life invisibility cloak. That kind of application is a long way off, but in the much shorter term the Army is developing new materials to build an ultra-sensitive sensor capable of detecting the faintest trace of a scent: a nose like no other.

No artificial sensor has ever been able to match the sensitivity of, say, a sniffer dog. But that might change if a research effort by the US Army’s Aviation and Missile Research Development and Engineering Center (AMRDEC) comes to fruition. This is based on the technology of plasmonics, which involves capturing light waves.

What does light have to do with sniffing? This particular super-sniffer would be based on Surface Enhanced Raman Spectroscopy (SERS). As with other types of spectroscopy, it allows a substance to be analyzed by looking at the spectrum of light coming off it. Normally you need a large amount of the material in order to get a reading, but in SERS the scattering effect is boosted. The right shape of micro-structure can capture photons, trapping them as surface waves known as plasmons. These plasmons will interact with specific molecules and hugely increase the scattering effect, so that a tiny sample is needed. Under the right conditions, this technique is hundreds of millions of times more sensitive than it would be without the surface effect.

SERS means a detector can pick up the tiniest traces of a substance in the air; in theory, one could detect a single molecule. Sound outlandish? Nature already has sensors this good: a male silkworm moth can detect a single molecule of scent released by a female .

Some SERS detectors already exist, but the technology is in its infancy and the underlying physics is not well understood. Early work used a simple roughened surface to capture plasmons, but AMRDEC would take the technology to a new level by the precise fabrication of a metal surface. Computer modeling is used to determine an effective shape, and this is then created by drilling very precise microscopic holes in metal foil using a beam of high-energy ions. This image – a view magnified 20,000 times — illustrates.

What is the potential application? In the first instance, AMRDEC want novel detectors to detect bacteria and chemical warfare agents. Unlike a dog, a detector can tell you which specific agent it can sense. Other possible applications might include spotting explosives from a distance — warning of the presence of a booby trap, car bomb or suicide vest. The same technology could be used to detecting smuggled drugs or airborne pollutants.

The AMRDEC team is still evaluating how effective their different designs are for plasmon-trapping material. Once this is completed, they will then be able to integrate it into a sensor. It may not be as glamorous as an invisibility cloak, but a new ultra-sensitive sniffer might be just as useful for saving lives.


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