WASHINGTON -- Researchers at the Naval Research Laboratory's Center for Bio/Molecular Science and Engineering have developed a multichannel biosensor capable of providing early detection of anthrax and other lethal biological agents. Now in advanced prototype form, the sensor soon could become an indispensable tool against biological warfare -- an area in which the US has few safeguards. The brick-size device simultaneously monitors four fluorescence-based fiber optic biosensors using a fiber array interrogation strategy. Excitation is provided by an axially located, 100-µm-core glass fiber, while fluorescence generated during the assay is detected by 500-µm, high numerical aperture fibers arrayed symmetrically around the glass fiber. Fluorescence is triggered when a toxin comes in contact with the waveguide, which is coated with an antibody. The Naval Research Laboratory's new handheld biosensor could provide another line of defense for soldiers facing increasing exposure to chemical and biological toxins. A second antibody, tagged with a fluorescent dye, interacts with the toxin and fluoresces, serving as "a highly specific Scotch tape," according to Elric Saaski, president of Research International in Woodinville, Wash., who collaborated with the Navy lab. That fluorescence triggers one of four 635-nm laser diodes from Toshiba America Electronic Components in Irvine, Calif. The intensity of the fluorescence indicates how much botulism, anthrax or ricin is in the sample. And because the device is an evanescent wave sensor, it is very sensitive. Evanescent wave sensors penetrate only a fraction of a wavelength into the sampling medium. This reduces the background fluorescence from the sample. Because the signal is generated as the binding occurs, users observe a rapid, near-real-time response.