New capillary optical fiber structure for fluorescence sensors

A multilayer capillary fiber was designed for optical sensor applications and its optical properties were evaluated by using a fluorescent layer immobilized on its inner surface. This fiber structure combines a large interaction surface (the inner wall of the capillary fiber) for binding of fluorescent indicators with evanescent wave fluorescence measurement, which may facilitate the design of pseudohomogeneous assays without separation of the bound from nonbound fluorescent indicator. The inner surface of the capillary was derivatized by aminosilanization, followed by biotinylation and addition of streptavidin. This biotin- streptavidin coating facilities subsequent immobilization of any biotinylated species (e.g. antibodies, antigens, etc.) participating in specific molecular recognition. We have evaluated some properties of this capillary fiber design by using fluorescent proteins immobilized on the inner wall of capillary by biotin-avidin-interaction. Fluorescence was excited by a HeNe-laser (fluorescent indicator APC; λ_em = 660 nm) and by a Ar-laser (fluorescent indicator RPE, λ_em = 578 nm), and measured with a spectrum analyzer.