Evanescent wave immunobiosensors use antibodies immobilized at the surface of a waveguide to form a sensing device. Fluorescence-based evanescent wave biosensors form a fluorescent complex at the surface of the waveguide when the antigen of interest is present (e.g., a sandwich assay or direct binding of a fluorescent analyte) or alternatively, the nonfluorescent analyte may compete with a fluorescent analog of the analyte for binding, as in a competitive immunoassay format. Light propagating through the waveguide extends a short distance into the surrounding medium and excites the immobilized fluorophore. The waveguide also collects the emitted fluorescence and carries this light to a photodetector.