DETECTION OF YERSINIA-PESTIS FRACTION-1 ANTIGEN WITH A FIBER OPTIC BIOSENSOR

A fiber optic biosensor was used to detect the fraction 1 (F1) antigen from Yersinia pestis, the etiologic agent of plague. The instrument e mploys an argon ion laser (514 nm) to launch light into a long-clad fi ber and measures the fluorescence produced by an immunofluorescent com plex formed in the evanescent wave region. This sensing area is a shor t section (12.5 cm) at the end of the optical fiber from which the cla dding has been removed and in which the silica core has been tapered. Capture antibodies, which bind to F1 antigen, were immobilized on the core surface to form the basis of the sandwich fluoroimmunoassay. The ability. to detect bound F1 antigen was provided by adding tetramethyl rhodamine-labeled anti-plague antibody to form fluorescent complexes. The evanescent wave has a limited penetration depth (<1 lambda), which restricts detection of the fluorescent complexes bound to the fiber's surface. The direct correlation between the F1 antigen concentration and the signal provided an effective method for sample quantitation. T his method achieved a high level of accuracy for determining F1 antige n concentrations from 50 to 400 ng/ml in phosphate-buffered saline, se rum, plasma, and whole blood, with a 5-ng/ml limit of detection. Subse quent blind studies, which included serum samples from patients, yield ed results in good agreement with measurements by enzyme-linked immuno sorbent assay. A major advantage of the fiber optic biosensor is that results-can be generated within minutes while isolating the user from hazardous samples. These factors favor development of this biosensor i nto a facile and rapid diagnostic device.