In order to fabricate their "smart" silicon crystals, Frdrique Cunin and his colleagues at the University of California, San Diego, modified existing technology used to make computer chips. "The idea is that you can have something that's as small as a piece of dust with some intelligence built into it so that it could be inconspicuously stuck to paint on a wall or to the side of a truck or dispersed into a cloud of gas to detect toxic chemicals or biological materials," co-author Michael J. Sailor explains. The team first laid down nanometer-thick films that react to specific chemicals on silicon wafers and then broke the wafers up into particles having a diameter of just a few microns. "Since the particles can be encoded for millions of possible reactions," Sailor says, "it's possible to test for the presence of thousands of chemicals at the same time." The particles emit a specific wavelength of light--which can be read using a laser similar to a grocery store scanner--when they encounter an agent for which they are encoded. So far, the researchers have succeeded in identifying chemicals from nearly 20 meters away. Their goal, Sailor says, is to increase that distance to at least one kilometer.