Fiber-optic immunosensor for the detection of fumonisin B₁

A fiber-optic immunosensor was developed to measure the mycotoxin fumonisin B₁ (FB₁). Monoclonal antibodies produced against FB₁ were covalently bound through a heterobifunctional silane to an etched 800 μm core optical fiber. An evanescent wave effect was utilized to excite fluorescein isothiocyanate labeled FB₁ (FB₁-FITC) molecules near the surface of the fiber. A direct competitive assay was used to measure FB₁ concentrations with the following steps: saturation of antibody binding sites by FB₁-FITC, competition of FB₁ and FB₁-FITC with displacement of the labeled toxin, and resaturation of binding sites by FB₁-FITC. The signal generated in the assay was found to be inversely proportional to the FB₁ concentration. This sensor exhibited a working range of 10-1000 ng of FB₁/mL, an IC₅₀ of 70 ng/mL, and a limit of detection of 10 ng/mL. These values compared favorably with those for currently available ELISA techniques. The sensor exhibited cross-reactivity with fumonisin B₂ but did not react with hydrolyzed FB₁, sphinganine, or tricarballylic acid. Sensor performance was also found to be unaffected in a sample matrix of methanol/water-extracted corn.