Optical Oxygen Sensor

Abstract

Photoexcited triplet state of porphyrins and phthalocyanines is efficiently quenched by molecular oxygen and the quenching reaction is based on the first-order kinetics on the oxygen concentration. Therefore, phosphorescence measurement and lifetime measurement of the photoexcited triplet state are applied for optical oxygen sensing techniques. In the case of phosphorescence measurement platinum or palladium porphyrins, which emit only phosphorescence under room temperature and normal pressure, are suitable sensor molecules and are useful for visual oxygen sensor. The triplet lifetime measurement is independent of both the porphyrin concentration and the excitation light intensity, thus the measurement can adapt to a variety of application. Optical oxygen sensor based on phosphorescence measurement and the lifetime measurement is applied for solid surface measurement and an investigation of the oxygen concentration inside a living cell. When porphyrin is painted on solid surface, an oxygen concentration on the surface alters depending on air pressure change and phosphorescence intensity response to the change, because an oxygen concentration increases with increase in oxygen partial pressure. Phosphorescence intensity of the painted surface becomes larger at low pressure, and likewise the intensity becomes smaller at high pressure. The flow image of a flying airplane or a running car seems to be clarified by optical oxygen sensing in a wind tunnel experiment. Oxygen sensitivity and responsibility was investigated on the surface of solid oxygen sensor devices, which are porphyrin encapsulated polymer and porphyrin immobilized aluminum oxide plate. Optical oxygen sensor is also applied for an investigation and a making image of an oxygen concentration inside a living cell and development of phosphorescence lifetime measurement system combined with microscope. It is known that porphyrins accumulate inside a cell when a living cell is soaked in porphyrin solution. Therefore, the oxygen concentration inside the cell was investigated by phosphorescence lifetime of the accumulated porphyrins. Lifetime measurement is a powerful tool for the experiment, because the accumulated porphyrins are localized and are not spread over whole cell homogeneously. Pulsed Nd-YAG laser was used as an excitation light and CCD detector was set in microscope. Phosphorescence from the accumulated Pt-porphyrin inside a cell was detected through an objective lens, so that an emitting image of whole cell was directly obtained and the oxygen concentration distribution was determined from phosphorescence lifetimes at the point of CCD pixels.