Analyte-sensitive fluorescence probes are coated onto the tip of a fiber. The excitation light, coming from the excitation monochromator or coming from a laser, passes the dichroic filter at the entrance of the fiber and is focused into the fiber. The excitation light travels down the fiber and excites the fluorescent probes located on the tip. The fluorescence emitted by the probes travels back through the fiber. The dichroic mirror separates the fluorescence from the excitation light, and the fluorescence is diverted to the detectors. When the fiber is immersed in a solution, the fluorescence properties of the probes (intensity, lifetime) change and such changes are detected by the spectrofluorometer. For instance, the intensity of fluorescein may change due to pH changes of the solution. The fiber is made out of silica to minimize any background fluorescence. The accessory is mounted on a baseplate for easy insertion into the spectrofluorometer.