A recirculating-flow fluorescent oxygen sensor

An immersible oxygen sensor was constructed by circulating small quantities of ruthenium tris-(2,2′-bipyridyl) II dichloride oxygen-sensitive fluorescent dye through a loop of oxygen-permeable silicone tubing immersed in test medium. The fluorescence intensity of the dye was subsequently measured as it exited the flow loop and related to oxygen tension. This method of measuring the oxygen tension, through diffusive transport to a flowing stream of dye and recirculating it in the sensor, has been found to give a stable response and relatively long sensor lifetime without major recalibration. The sensor showed good stability over at least a week's duration and showed no degradation due to leaching of the dye through membranes or photobleaching that commonly affects fluorescent sensors with immobilized chemistries.