A microoptode array for fine-scale measurement of oxygen distribution

A new microoptode array is presented that provides simultaneous measurement with eight oxygen microoptodes using a simple optical setup and a phase-angle detection principle. The measuring system consists of: (1) an optical unit with eight oxygen microoptodes, a special fiber-coupler array, optical filters, lenses, light sources (light-emitting diodes) and light detectors (photodiodes, photomultiplier tube); (2) a signal-processing unit with analog signal processing (phase-angle detection, filtering) and digital signal processing (central, data storage and display). The oxygen concentration is measured with tapered silica-glass fibers (tip diameter 20-30 pm) by the dynamic quenching of a luminophore. A phase-modulation technique is used to determine the phase-angle shift that is caused by the fluorescence Lifetime when the indicator is excited sinusoidally. In a time multiplex mode each sensor signal is sampled. This multisensor array system is designed for the investigation of the oxygen distribution in biofilms and aquatic sediments. The new measuring system and first applications in artificial and natural systems are presented.