Michael Sailor of the University of California at San Diego has transformed ordinary silicon into a powder that can identify chemicals in the environment. This "smart dust" may someday be used to warn of a chemical or biological attack: "It could be stuck to paint on a wall or to the side of a truck or dispersed into a cloud of gas," Sailor says.
|Silicon crystals just 1/10,000 of an inch wide function as custom-tailored chemical detectors.|
Photograph courtesy of UCSD.
He and his colleagues etched tiny holes in a silicon wafer, cut the wafer into thin layers, and then blasted them with ultrasound to create particles about 1/10,000 of an inch wide. The manner in which the silicon is cut and etched determines which wavelength, or color, of light the particles reflect when illuminated by a laser beam. If a chemical binds onto one of these particles, the change in the wavelength of the returned light can identify the contaminant.
So far, Sailor's team has detected the smart dust's glow from 60 feet away, and they hope to extend its signal to a half mile. Once perfected, smart dust could be sprayed into and around buildings or mixed into a sample of drinking water, and then scanned for thousands of hazardous chemicals at once. Smart dust coated with specific compounds could also be useful as an inexpensive mobile molecular detector—screening a DNA sample for particular genes, for instance, or identifying pathogens in a patient's blood sample. The detectors can already distinguish several chemicals, and Sailor's team has begun work on recognizing biological agents.