The key to their sensitive detection is the use of a small laser, similar to that found in CD players, which measures the small changes in intensity of light reflecting from the optical coating on the surface of the silicon chip. "It turns out that if you take a laser that's at the right frequency that matches the properties of that layer, you can measure very small amounts of chemicals as they enter the coating," says Sailor.
While the diode laser that the UCSD scientists built for their sensor is a bit more sophisticated than those in inexpensive CD players, it can be reproduced cheaply. In fact, the researchers' first sensors were constructed from five inexpensive CD players they purchased at Fry's, a local electronics discounter. "Our program manager at the Defense Advanced Projects Research Agency, which sponsored our research, raised an eyebrow when I told him that story," says Sailor. "But for 24 bucks, we got an interferometer that was sensitive enough to detect chemicals in the parts per billion range."
The low-cost feature of the UCSD design should make it possible to deploy handfuls of sensors in a terrorist nerve-gas attack, like the 1995 Tokyo subway bombing, in which sarin was used. Because the laser is capable of recording the accumulation of hydrogen fluoride molecules on the silicon chip's surface, the sensor can also be used as a dosimeter. "You can tell how much nerve gas an area has been exposed to," says Sailor.
He says the main advantage of the sensor is that it is more specific to the detection of G-type nerve agents than the surface acoustic-wave devices, which are currently used to detect nerve gas, but which tend to produce an excess of false alarms.
"The advantage of this new development is that we'll be able to reduce the false-alarm rate," adds Sailor, whose team p
Contact: Kim McDonald
University of California - San Diego