DEVELOPMENT OF A LED-BASED PHASE FLUOROMETRIC OXYGEN SENSOR USING EVANESCENT-WAVE EXCITATION OF A SOL-GEL IMMOBILIZED DYE

In this paper we report preliminary results from an intrinsic fibre-op tic oxygen sensor based on phase fluorimetry. Phase fluorimetry is a m ethod of measuring the luminescence lifetime of a fluorophore and, whe re suitable, has many advantages over other reported optical sensing t echniques such as absorption and fluorescence intensity monitoring. Li fetime measurements are absolute quantities, which offer the possibili ty of inherent referencing, and are usually independent of indicator c oncentration, photobleaching and excitation source intensity. The long excited-state lifetimes of ruthenium polypyridyl complexes are effici ently quenched by oxygen. Sol-gel immobilization of the ruthenium comp lex (Ru-II-tris(4,7-diphenyl-1,10-phenanthroline)) on a multimode opti cal fibre yields highly durable, inert, microporous claddings which ex hibit almost complete quenching under evanescent-wave excitation, The fluorophore decay curve exhibits a double exponential behaviour consis ting of a fast and a slow component, both of which undergo quenching o n exposure to oxygen. These data are used to model the expected behavi our of the sensor in phase fluorimetric mode. The predictions are in c lose agreement with experimental measurements performed with the coate d fibre under blue light-emitting diode (LED) excitation. An optimum m odulation frequency is identified and the performance of the intrinsic oxygen sensor in real-time measurement mode is reported. The use of a n inexpensive light source, combined with a simple fabrication techniq ue and the advantages of the phase fluorimetric method, facilitates th e production of low cost, high performance optical oxygen sensors.