CHARACTERIZATION OF LONG PATHLENGTH CAPILLARY WAVEGUIDES FOR EVANESCENT FLUORESCENCE APPLICATIONS

The optical properties of a novel fused silica fiber-optic capillary waveguide (FOCap) for fluorescence spectroscopy were evaluated. Evanescent fluorescence from samples in the FOCap was measured by coupling the FOCap to a light source and a fluorescence spectrophotometer. The FOCap has negligible excitation light loss over long lengths (20 m or more) for a range of wavelengths. The evanescent fluorescence was linear up to at least 20 m for a solution in the core and up to at least 15 m for a fluorophore covalently attached to the inner surface. Evanescent fluorescence measurements in 50, 150, and 250 µm inner diameter FOCaps indicate that greater sensitivity is achieved with thinner-walled capillaries which have more internal reflections. FOCaps can be fined tuned for a desired sensitivity by manipulating their physical dimensions. The ability of the FOCap to function as an indirect chemical sensor for nitroaromatic compounds is demonstrated with a pyrene-labeled waveguide