Such sensors could be used to detect environmental exposure to residential pesticides, monitor chemical markers of food spoilage, and could possibly serve some day as sensors for certain toxic nerve gases such as sarin, according to Science co-author Nicholas L. Abbott of the University of Wisconsin, Madison.

Techniques to detect such compounds already exist, but these methods (like mass spectrometry) are mostly confined to the laboratory--too bulky and complex to provide real-time, portable detection.

"These lab methods are extremely sensitive, but they're never going to be the basis for measuring personal exposure. We wanted to create something that could be worn like a badge, like those worn to detect radiation," says Abbott.

The sensor devised by Abbott and co-author Rahul R. Shah of the 3M Corporation (formerly of University of Wisconsin) consists of an ultrathin gold film with nanoscale corrugation. The surface of the gold film is then dotted with protruding chemical receptors that weakly anchor liquid crystal in a well-defined orientation along the film's surface.

When these receptors are exposed to the specific chemical that is the object of detection, however, they bond more strongly with that target chemical than they do with the liquid crystal. In effect, the target chemical muscles in on the liquid crystal's territory, shoving it away from the receptors. This displaces the liquid crystal into a new orientation that is controlled by the underlying surface texture, and the new orientation is visible to the naked eye as a change in the sensor's color or brightness.

On a surface with carboxylic acid receptors, for instance
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Contact: Ginger Pinholster
gpinhols@aaas.org
202-326-6421
American Association for the Advancement of Science
16-Aug-2001