MINIATURIZED LUMINESCENCE LIFETIME-BASED OXYGEN SENSOR INSTRUMENTATION UTILIZING A PHASE MODULATION TECHNIQUE

Optical oxygen sensors are mainly based on the principle of luminescen ce quenching. In contrast to already existing intensity-based systems, the measurement of the luminescence lifetime provides certain advanta ges, such as insensitivity to photobleaching or leaching of the dye or changes in the intensity of excitation light. This facilitates the us e of simple optical systems or optical fibers. Phase measurement techn iques have shown to be a powerful tool for indirect measurement of lum inescence lifetimes. Here, dyes with luminescence decay times in the o rder of tens or hundreds of microseconds allow the use of simple opto- electronic circuitry and low-cost processing electronics. An optical o xygen sensor module has been developed with the dimensions of only 120 x 60 x 30 mm. The instrument is based on the measurement of the decay time of the luminophore by measuring the phase shift between the squa re-wave excitation and the detected square-wave of the emission coming from the sensor. The instrument is based on semiconductor devices (li ght-emitting diodes, photodiodes) and may be used for the detection of oxygen in gaseous or liquid samples. Platinum(II) octaethylporphyrin- ketone, which is incorporated in an oxygen-permeable polymer and which has an unquenched lifetime of approximately 60 mu s, is used as the o xygen-sensitive dye. The typical measurement range of the device is fr om 0 to 200 hPa oxygen partial pressure with a resolution of <1 hPa ov er the whole measurement range. Measurement accuracy of <+/-1 hPa has been obtained for periods of 24 h of continuous measurement. The senso r response times t(90) are typically <1 s for gases and 1-5 min for li quid samples.