Aimée Rose, 34

The detonation of a single pound of explosives hidden aboard an airliner flying over Lockerbie, Scotland, in 1988 was, for many, a turning point in understanding how vulnerable the public is to the actions of terrorists. The bombing of Pan Am Flight 103 and the deaths of its 259 passengers (and 11 people on the ground in Lockerbie) set off a behind-the-scenes, government-funded race to find better ways to detect explosives. That race acquired additional urgency after the September 11 attacks, and it became frantic when IEDs--improvised explosive devices--started killing U.S. soldiers in Afghanistan and Iraq. Now, 20 years after the Lockerbie bombing, Aimée Rose is playing a key role in creating and commercializing ultrasensitive detectors that help to protect us against explosives.

Largely because of Rose's work as a scientist, engineer, and research manager, new types of portable chemical "sniffers" are now widely used to detect trace amounts of explosives in the air. These sensitive instruments are already detecting land mines, IEDs, liquid explosives in sealed containers, and even people who have been in contact with explosives. "You can pull aside as many passengers in security lines as you want, but if you don't have the ability to detect explosives on them, it won't do much good," says Susan Martonosi, an operations researcher at Harvey Mudd College in Claremont, CA, who studies homeland security. "That has long been a weakness in the system."

Rose's chemical sniffers are part of a growing effort to develop explosives detectors that go beyond x-ray scanners, the large instruments commonly found in airports. Whereas x-ray scanners look for the characteristic shapes of bombs and can easily be fooled by tricks such as embedding explosives in electronic devices, the new kinds of detectors find explosives by picking out their distinctive chemical composition. But it's a complex problem, because those chemical signatures are diverse and often extremely faint. (Trained dogs that sniff out the vapor given off by explosives are still the most reliable and sensitive bomb detectors, but they're in short supply.) Airports have largely relied on ion-mobility spectrometers that examine the chemicals in either swabs from luggage or puffs of air blown at passengers in sealed chambers. Swabs can easily miss a well-hidden explosive, though, and analyses of air samples are frequently thrown off by dirt, dust, and other contaminants. Rose's technology, on the other hand, is the first explosives detector that matches the sensitivity of dogs. What's more, it's handheld and easy to use, and it's the only device capable of detecting the hidden liquid explosives that have become a serious security concern in the past few years.

Rose was in college when she first tackled the problem of detecting chemicals and toxic materials. "I wanted an opportunity to put something in people's hands that could affect their lives and maybe make them safer," she says. She was planning to do her graduate work in materials science at Harvard, until she was awakened at six one morning by a phone call from a stranger who spoke in long, enthusiastic rushes. "It was as if he couldn't get the words out fast enough," she recalls. "I was half asleep and very irritated." After a few minutes she was able to make out that the man was a chemistry professor who had just set up shop at MIT, complete with a new grant from the U.S. Defense Advanced Research Projects Agency to develop a chemical sensor capable of detecting land mines. He had seen her application to MIT, an application that everyone else in the department had ignored; would she consider visiting?