Fluorometer and tapered fiber optic probes for sensing in the evanscent wave

To develop an improved fiber optic biosensor both the optical component selection and the signal coupling efficiency were investigated. The emission filter and fiber connectors were carefully chosen to reduce their contribution to noise in the system. We used long, fused silica fibers that had several centimeters of cladding removed along the distal end. This exposed core is coated with the recognition molecules that bind analyte-fluorophore complexes from the sample solution. A fluorescent signal generated in the evanescent wave region of the unclad, immersed portion of the probe is lost as it enters the cladded portion of the fiber because of a V-number mismatch. To minimize the mismatch, the core radius is reduced along the uncladded region to form a continuous taper. An assay using the tapered fiber and the described optical configuration is presented that demonstrates instantaneous signal generation in response to nanogram amounts of a toxic material.