Abstract: A fluorescent optical probe employed for the analysis of the concentration of an analyte (or material to be analyzed) in a fluid, employs a permeable, transparent polymeric matrix in which a fluorophor is immobilized, with the polymeric material being directly exposed to the fluid being analyzed. The composite material of the probe may be made up of a homogeneous matrix of transparent polymer, fluorescent compound, catalyst(s) and reagents(s) and is employed to measure analyte concentration in a fluid in the environment surrounding the material. For analyzing oxygen, the fluorophor may be 9,10-diphenyl anthracene and the polymer matrix may be poly (dimethyl siloxane), or silicone, with the presence of oxygen quenching the fluorescence of 9,10-diphenyl anthracene.