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Smoke Signals for Explosives

By Burt Helm What's the best way to find out if a material is explosive? Blow it up. That's what a group of scientists at Oak Ridge National Laboratory and the University of Nevada, Reno, are doing as they build hand-held bomb-detector wands that could replace the bulky and expensive equipment currently used at airports and security checkpoints.

Using an array of what look like tiny silicon diving boards -- each only a tenth of a millimeter long, or about half the width of a human hair -- the scientists catch tiny particles of explosive material floating in the air. Heating the boards to about 900 degrees Fahrenheit causes the explosive particles to blow up. The shock causes the silicon to flex back and forth, which is picked up by sensors. While the boards are too small to detonate anything larger than a few molecules, they create a tiny puff of smoke from the explosion.

MAN'S BEST FRIEND. The new bomb-detection method is part of a program at Oak Ridge National Laboratory. Researchers are using these "micro-cantilevers" -- the technical term for the mini-diving boards -- to detect and identify particular molecules, from TNT and water contaminates to specific proteins in the body. The work could ultimately lead to cheaper bomb detectors, an improved ability to uncover biological hazards, and better medical equipment. It's being funded by the U.S. Energy Dept.'s Office of Biological & Environmental Research, as well as the Justice Dept. and the Homeland Security Dept.

The research team -- led by Oak Ridge Labs scientist Thomas Thundat, and assisted by Lal Pinnaduwage of Oak Ridge and Jesse Adams, a professor at the University of Nevada, Reno -- sees a bright future for the technology in bomb detection. Current detection machines are huge and can cost anywhere from $40,000 to $1.3 million. Other than these machines, "the best technology out there is a [bomb-sniffing] dog," says Adams.

Clearly, the market needs a lower-cost alternative. The new detectors are as sensitive as a dog, being able to detect as little as 70 picograms of an explosive. That's about one-ten-millionth the mass of a grain of sand. The cantilevers are so small they could be installed in a hand-held wand, or placed throughout a building's ventilation system.

DANGEROUS OR DAPPER? The cantilever program began with a simple premise 10 years ago: Every chemical compound has a match -- another compound to which it can't help but bind. By coating one side of these diving boards with that attractive chemical, the target substance -- say TNT -- latches on. Because of surface tension, the board bends, and a sensor picks that up.

But a problem with the early design emerged. Other chemicals, like cologne or perfume, latched onto the micro-cantilevers as well. In a crowded airport, telling the difference between the dangerous and the merely dapper would be impossible. The group fixed the problem by introducing bare silicon cantilevers that would be superheated. TNT particles would blow up on contact. Chanel No. 5 would not.

Because the explosion method isn't as sensitive as the original chemical-matching method, the team is now working on combining the two technologies. The next step is using a variety of differently coated cantilevers to create an extremely sophisticated detector. The different receptors would work together "just like a sensitive nose" to accurately identify materials, says Thundat.

INTERNAL AFFAIRS. Thundat and his team have licensed the technology to two companies. The first, privately held Protoveris, has been developing it for medical use since 2001. With the proper coatings, it can detect specific proteins in the body, which will help doctors measure the effects of some drugs on patients. This week, Protoveris begins beta-testing the device for the first time at the Lombardi Cancer Center at Georgetown University.

The other business, SENSE Holdings, licensed the technology in 2003 for bomb-detection wands. SENSE execs say they're looking for development partnerships with major security-device manufacturers and say their wand will be ready for commercialization in 12 months.

In addition to saving costs for airports, "we really hope to put it into many more places that can't afford [explosive-detection] technologies right now." says Dore Perler, CEO and president of SENSE. "We think the potential is enormous." If he's right, detecting bombs will become a whole lot easier. Helm is a reporter for BusinessWeek Online in New York

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