A Better Liquid-Explosives Detector

A company based in Stillwater, OK, has developed a detector for hydrogen-peroxide explosives, which are thought to be popular with certain terrorist groups. It is now working to place its liquid-explosives-detection technology in airports.

The need for such a device was highlighted last summer, when a plot to bomb airplanes using liquid-explosives ingredients was uncovered in the United Kingdom. ICx Nomadics, whose TNT detectors are now sniffing out explosives in Iraq, has developed a device that can sense hydrogen peroxide and the peroxide-based explosive triacetonetriperoxide (commonly referred to as TATP), which was used in the subway and bus bombings in London last year. The device is sensitive enough to detect peroxide even if it is inside a factory-sealed container, says Aimee Rose, a researcher with the company.

Rose says ICx Nomadics should be ready to start tests with the Department of Homeland Security (DHS) and the Transportation Security Administration (TSA) in a couple of months. If it passes those tests, the detector, based on chemically sensitive films, would represent a novel–and potentially far faster and more accurate–way to detect liquid explosives. The company’s existing TNT detectors are based on a semiconducting polymer film that was developed in the lab of Timothy Swager, a professor of chemistry at MIT. The film creates a signal when TNT vapors bind to it (see “Stopping Roadside Bombs”).

The DHS is now testing 10 commercial devices for detecting liquid explosives, according to DHS spokesman Christopher Kelly. The department uses four main types of technology: X-ray, acoustic/ultrasound, Raman spectroscopic, and electromagnetic. And all of these can detect liquid explosives through a sealed container. But these devices, while sensitive, tend to return too many false positives, making them impractical for use in airports.

The ICx Nomadics detectors work by sensing minute amounts of vapor: a specially formulated film fluoresces under certain conditions. For peroxide detection, a film starts to glow when it comes in contact with the peroxide vapors. The film coats the inside of a glass tube, through which air is drawn. The glass walls of the tube guide light from the film to a light sensor, which registers changes in light intensity. (In the TNT sensor, TNT vapors encountering an already fluorescing film cause it to darken.)

The company is working with MIT professor of material sciences Yoel Fink to further improve the clarity of the detectors’ signal by making it easier to distinguish from background noise. Fink, who has created hollow fibers that can guide light much better than the glass tubes currently used, has also incorporated light detectors directly into fibers. A device that combines these features could “offer a huge simplification in instrumentation, making these almost ubiquitous,” Rose says. In the future, soldiers could carry fibers designed to detect a variety of substances. The company is also developing polymers for detecting a variety of toxic industrial chemicals. A bundle of fibers could be used to detect more than one substance at a time.

It remains unknown whether ICx Nomadics’s liquid-explosives-detection technology will ultimately result in the federal government lifting restrictions on taking bottled water and other liquids through airport security. “That’s up to the TSA,” Kelly says.