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Hybrid fiber optical sensor for determining the oxygen partial pressure and the oxygen flux in biomedical applications

The development and improvement of oxygen sensors is continuously matter of research because it is important to quantify oxygen concentrations in biological systems. The presented hybrid fiberoptical sensor combines the common advantages of fiber optic sensors e.g. flexible connection to the place of interest and potential separation between place of measurement and measuring device with the special advantage of the optical analysis that does not consume the analyte oxygen. The O2 sensing was tested by using (1) solutions with the dissolved oxygen indicator dye (tris(1,10-phenantroline) ruthenium (II) chloride hexahydrate), and (2) and O2 flux optode. The O2 flux optode consist of an oxygen permeable membrane (test membrane) combined with oxygen optodes to measure the pO2 differences across the membrane. The O2 flux can be calculated from the pO2 gradient across the test membranes and its permeability. The developed measuring systems `FLOX' detects the phase shift between the sinusoidally modulated excitation light and the resulting fluorescence of the indicator. The phase shift is caused by the fluorescence lifetime that depends on the oxygen concentration. Many investigations have shown that measurements of lifetime are preferable to measurements of intensity because of higher stability. The FLOX system uses a blue light emitting diode (LED, (lambda) peak equals 450 nm) as light source together with optical filters and a photo multiplier tube as detector. The coupling between the place of measurement and the FLOX is performed by a bifurcated fiber bundle in which single multimode fibers are statistically mixed. Its measuring end could be either immersed directly in an aqueous solution of the fluorophore or provided with a special sensor head for the measurement of the oxygen flux into a surface, for example into the surface of the human skin. First measurements demonstrated the applicability of the FLOX system to measure the O2 flux into human skin; for example an about 20 - 50% increase of the O2 flux after stop of the circulation could be clearly shown.