The single mode tapered optical fibre immunosensor. I. Characterisation with model analytes

A novel single mode tapered optical fibre loop biochemical sensor based on fluorescence spectroscopy has been developed. The fundamental fibre mode propagating through the tapered portion of the waveguide has evanescent fields which penetrate into the aqueous environment where the biochemical recognition event occurs. The model measurands were conjugated with a fluorescent dye, fluorescein isothiocyanate. When excited by the input laser light from the near end of the taper, generated fluorescence is coupled into the guided mode ofthe fibre and collected at the far end of the taper. Several radioactive and fluorescent quantification methods have been explored to determine the density of available binding sites immobilised on the fibre, and thus the ultimate sensitivity of the device. A generic avidin-biotin system has been tested as a model immunological diagnostic system. The high sensitivity of a single mode tapered loop device combined with a simple immobilisation method provides a powerful tool for performing immunoassays.