Abstract: An assay apparatus employing total internal reflection of excitation radiation at the interface between an optically conductive rod or fiber and a surrounding liquid phase of lower index of refraction. Immobilized on the surface of the fiber is a component of a complex formed in an immunochemical-type reaction; a fluorophore that can be excited into fluorescence by the excitation radiation is attached to another component of the complex. The fiber is coaxially mounted in cantelivered position within a length of tubing, so that the excitation radiation can be launched into the unsupported end of the fiber and the fluorescent radiation tunneling back into the fiber may be observed at the same fiber end.

Abstract: An assay method and apparatus employing total internal reflection of excitation radiation at an activated region on the surface of an optically conductive rod or fiber surrounded by a liquid phase of lower index of refraction, so as to excite into fluorescence fluorophores in the liquid present in a thin layer around the rod surface. The induced fluorescence is then gathered and measured. Excitation occurs while flowing a sample of the liquid phase through an enclosure of fixed dimensions bounded in part by the activated region.

Abstract: An optical wave guide particularly useful in assay apparatus employing total internal reflection of excitation radiation at the interface between the wave guide and a surrounding liquid phase of lower index of refraction. The wave guide in the form of a solid, light-transmissive, elongated rod or fiber made typically of glass, crystal or plastic and having preferably a circular cross-section, is tapered gradually from an entrance face of relatively large diameter to a substantially smaller diameter at some position longitudinally displaced from the entrance face. In one form, the wave guide is formed with a tapering conical input portion coupled to a second portion having a cylindrical configuration and a diameter matched to the smaller diameter of the tapered portion.