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Image of nerve gas sensor Credit: Moria Feighery-Ross,
UCSD CHEMISTS DEVELOP PORTABLE
NERVE GAS SENSOR
a silicon chip and parts from an inexpensive CD player, chemists
at the University of California, San Diego have developed a
portable nerve-gas sensor capable of detecting "G-type"
nerve agents, such as sarin, soman and GF.
The achievement should
eventually permit the development of a large number of small and
inexpensive sensors that could be deployed by soldiers across a
battlefield or by police after a terrorist explosion to rapidly detect
the presence of certain nerve agents and to track the movements of the
"With multiple sensors
that have a radio transmitter attached to them, you can tell how big the
cloud is and where it is moving and relay that information to a base
station," says Michael J. Sailor, a professor of chemistry and
biochemistry at UCSD. He will provide details of his group’s
achievements today at the 220th national meeting of the
American Chemical Society in Washington, DC.
The innovative silicon sensor
was constructed by a team that included William C. Trogler, a professor
of chemistry and biochemistry, and postdoctoral associates Sonia Letant
and Honglae Sohn. It works by selectively detecting compounds with a
phosphorus-fluorine chemical bond, such as sarin, at very low
To accomplish this, the
scientists used a catalyst that Trogler and his co-workers had developed
for the Army to detoxify materials containing nerve agents and other
deadly chemicals with phosphorus-fluorine bonds. This catalyst breaks
the phosphorus-fluorine bond in "G"-type nerve agents,
resulting in the production of hydrogen fluoride, which is used
commercially to etch and frost glass.
sensor detects the presence of hydrogen fluoride through a silicon
interferometer—a stamp-sized silicon wafer, similar to a computer
chip, with an optical coating containing the catalyst. The rainbow-colored
optical coating, which is akin to the sheen left by a thin film
of oil on water, changes color when molecules of hydrogen fluoride
hit its surface. "These silicon interferometers can detect
very, very small changes in color," says Sailor.
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
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
"The advantage of this new
development is that we’ll be able to reduce the false-alarm
rate," adds Sailor, whose team published the technical details of
their development in a recent issue of the Journal of the American
Chemical Society. "The disadvantage is that we’re specific to
only one type of nerve agent."
Although the UCSD researchers
have not tested their sensor on nerve gas, they have demonstrated that
it can detect a compound called diisopropylfluorophosphonate, or DFP,
which is structurally related to sarin and soman, at a level of 800
parts per million. They plan to test the UCSD sensor on live nerve gas
at an Army research laboratory later this year.