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Quirk in antibody action yields cheap assay.

Quirk in antibody action yields cheap assay

A new sensing device that can detect cocaine quickly and cheaply may prove a time-saver for scientists, a cost-saver for the U.S. military and a life-saver for patients, as well as a roadside drug detector.

The new approach could radically broaden the commercial potential for screening technology, says Ralph O. Mumman, an environmental chemist at Penn State University in University Park. For example, it might make possible portable, easy-to-use sensors.

Developed the Naval Research Laboratory (NRL) in Washington, D.C., the "flow immunosensor" was described last week by Frances S. Ligler at the American Chemical Society meeting in Atlanta. The device's high efficiency took its inventors and other researchers by surprise, the NRL chemist says, because according to conventional wisdom, it shouldn't have worked at all.

Today, laboratories typically screen for drugs with devices that use molecules labeled with radioactive tags or fluorescent dyes. Many of these screening techniques harness antibodies, molecules that recognize specific substances--Even when those substances exist in minute amounts. Because each assay consumes a little of the costly labeled material -- whether or not screened-for material is detected -- even a simple urine test for cocaine can cost as much as $4. For the U.S. Navy, such tests now add up to $10 million a year, Ligler notes.

Though the immunosensor she helped develop borrows from that antibody approach, "the way we're using the antibody is different," Ligler explains. The Navy scientists pack tiny beads coated with cocaine-sensitive antibodies into a cylinder slightly bigger than a pencil's eraser, then add a fluorescent label to the cocaine molecules, which bind to the antibodies.

As urine flows through the cylinder, any cocaine molecules in the sample will kick their fluorescent counterparts off the the antibodies, and these tagged molecules will register a positive result as they exit past a fluorimeter. But if the sample contains no drug, no expensive tagged material is consumed, Ligler says -- and therein lies a substantial savings.

Ligler says she doubted this approach would work because the labeled cocaine should bind to these immobilized antibodies and never come off. Instead, it comes off in seconds -- much faster than in other screening tests, which take at least 20 minutes. Moreover, she notes, this sensor costs much less to build than comparable assaying equipment and requires less training and labor to operate. "You can use it in the workplace or in a police station," she says.

With different antibodies, she expects researchers can adapt the flow immunosensor for monitoring pollutants in water, drug levels and blood chemistry in patients, and elusive substances sought by scientists in their research. Though antibodies exist for some of these substances, sensors for many other compounds will require the development of new antibodies. The technique "needs more development to see how versatile it will be," says Mumma.
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Title Annotation:flow immunosensor device for drug screening
Author:Pennisi, Elizabeth
Publication:Science News
Date:Apr 27, 1991
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