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Sensors Detect Biological Weapons

Photonics Spectra
Jan 1999
Kevin Robinson

Scientists at the Naval Research Laboratory have developed a lightweight, fully automatic biological weapons detection system that one day may find its way to the battlefield. The system, which researchers have tested mounted in an airplane, uses fluorescent antibodies, diode lasers, fiber optics and photodetectors to find airborne bacteria.

Researchers have designed a detector for biological weapons that is light enough to be carried by a small remote-controlled plane. Courtesy of Frances S. Ligler.

Reseachers led by Frances S. Ligler and George P. Anderson developed the detection system that, besides being lighter and more portable than other methods, uses fiber optics to carry the signal. The system is a combination of a fiber optic biosensor from Research International of Woodinville, Wash., and a specially designed air sampler. When it is mounted on an airplane, the motion of the plane pushes air into a column of water, creating a cyclone of water that traps the bacteria.

Antibodies bind to bacteria

Every five minutes the system pumps a sample of this water past four optical fibers. The fiber ends are tapered and are attached to antibodies that bind to specific bacteria. As the sample water flows over the fibers, the bacteria stick to them. Then the flow chamber is washed out, and a fluorescent antibody is introduced. These antibodies stick to the specific bacteria that are stuck to the probe. The system then pipes 635-nm light from a laser diode through the fiber, exciting fluorescence from any antibodies that have stuck to bacteria. This fluorescence signal, around 660 nm, returns through the fiber to be detected by a photodiode and is transmitted in real time to a ground-based unit.

Because this system uses antibodies that are specific to the bacteria, such as anthrax, it has very few false alarms. In fact, Ligler said that during tests against a harmless simulant bacteria, the research team had no false positives. This could be a boon for biological weapons detection, because other systems are elaborate and are often set off by diesel exhaust or dust and dirt.

Another advantage is that the system is light enough to be mounted in a remote-controlled plane. This pilotless plane can fly low and into areas where there are no soldiers and no ground-based detection systems. "You can identify a cloud before it reaches the troops," Ligler said.

The current system can test for four kinds of bacteria simultaneously, but Ligler said there is no reason why this could not be expanded to detect more. Also, she said that compared with other sensor systems for detecting biological weapons, "it is the least expensive that I know of." She did not comment on whether the system would be ready for deployment soon.

The researchers also have a handheld version of the device that is under testing, and they are beginning to develop a similar sensor based on planar array technology.

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