The single mode tapered optical fibre loop immunosensor

A novel single mode tapered optical fibre loop biochemical sensor based on fluorescence spectroscopy has been developed. The fundamental fibre mode propagates through the tapered portion of an optical fibre and generates an evanescent field which penetrates into the aqueous environment surrounding the fibre where the bio-recognition event occurs. A two-step assay was used, in which the analyte was labelled secondarily with a fluorescent dye, fluorescein isothiocyanate or tetramethyl rhodamine. When excited by the input argon ion laser light from the near end of the taper, generated fluorescence is coupled into the guided mode of the fibre and collected at the far end of the taper. Methods of making the sensor chemically reusable were investigated. The high sensitivity (75 pg/ml) of the single mode tapered loop device, combined with a simple immobilization protocol, provides a powerful tool for performing immunoassays.