AN EVANESCENT-WAVE BIOSENSOR .2. FLUORESCENT SIGNAL ACQUISITION FROM TAPERED FIBER OPTIC PROBES

A biosensor was developed using antibodies, fluorescence and the evane scent wave to detect antigen binding at the surface of an optical fibe r. Cladding was removed from the core along the distal end of a step-i ndex optical fiber, and recognitions antibodies were immobilized on th e declad core to form the probe sensing region. Immersing the declad p robe in aqueous solution creates a V-number mismatch between the immer sed probe and the clad fiber. Probes created with reduced sensing regi on radius exhibited improved response hy decreasing the V-number misma tch. Tapering the radius of this region has further improved probe res ponse. Ray tracing analysis of the tapered probe demonstrated that the evanescent wave penetration depth increases along the length of the t aper. Experiments correlating position of refraction along the taper w ith launch angle at the proximal end were realized lin the ray tracing model. An evanescent wave immunoassay was performed with a series of the tapered fiber probes, each tapered from the fiber core radius (100 mu m) to different end radii. An end radius of 29 mu m was Found to p roduce maximal signal from the tapered probe. Factors leading to the d etermination of the optimized probe are discussed.