We report an innovative and useful procedure for immobilization of antibodies on to a fiber-optic silica surface. The procedure consists in the chemical oxidation of pyrrole-biotin monomers that are readily deposited as a thin film of poly(pyrrole-biotin) polymer on to the end-face of the fiber. The film was shown to be sufficiently translucent to enable photon coupling within the fiber transducer and its presence was demonstrated by means of fluorescent micrographs of bound rhodamine-labeled avidin. Fiber-optics modified with cholera toxin B subunit molecules were tested for sensitivity, non-specificity, and overall practicality. It was shown that the fiber-optic immuno-assay for the detection of anti-cholera toxin antibody was up to three orders of magnitude more sensitive than the classical enzyme-linked immunosorbent assay (ELISA).