Cranberry aid for assay.

Cranberry juice, often used to stave off urinary-tract infections caused by Escherichia coli, also keeps the bacteria from reducing a biosensor's specificity, scientists report.

Past research had shown that cranberry juice fights the infections by stopping E. coli from adhering to human cells. Frances S. Ligler, Brandy Johnson-White, and their colleagues at the Naval Research Laboratory in Washington, D.C., tested whether the juice would also prevent the bacteria from attaching to biosensors' glass surfaces.

On its surface, the sensor has a pattern of different antibodies that capture targets--proteins or microbes, for example--from food or clinical samples. A subsequent application of antibodies that have a fluorescent tag pinpoints the location of the target, revealing its identity.

E. coli bacteria, often found in biologic samples, bind all over the glass surface, says Ligler. Since this bacterium shares surface proteins with other microbes, the fluorescent antibodies can attach to the E. coli in a sample along with the desired target, producing areas of brightness that obscure a target's location.

When the team mixed cranberry juice with its samples, however, the juice "prevented the sticking of these very sticky bacteria" to the slides, Ligler says. A 50 percent solution of the juice eliminated almost all the background fluorescence. The researchers found no such effect with other juices, they report in an upcoming Analytical Chemistry.--A.C.