Advances in fluorescent ion and gas sensors.

This research led to development of the first single-membrane dual sensors for oxygen and carbon dioxide. Sensing optodes used pulled or unpulled optical fibers as excitation carriers and ratiometric fluorescence measurements were used to determine analyte concentration. Errors due to photo-bleaching, sensor alignment and excitation power changes were reduced and a good signal-to-noise ratio was obtained. A one-use potassium sensor for monitoring both intracellular cytosolic and blood levels of potassium was prepared by immobilizing a potassium-selective ionophore and a luminescent pH dye in a plasticized PVC film. The optode had excellent selectivity over sodium, calcium and magnesium. A ratiometric fluorescent pH dye was encased in a polyacrylamide matrix, resulting in a fast-responding, precise, accurate, reversible and durable ratiometric pH micro-optode. Its behavior correlated well with a pH macro-electrode. The above pH probe was covered with a polymer membrane, leading to gas sensing capability. Dye leaching and ionic interference were reduced and a bio-compatible system resulted. Significant interest in measuring low aqueous oxygen and carbon dioxide concentrations led to fabrication of the dual gas sensor. Oxygen- and carbon dioxide-sensitive indicators were incorporated into a polymeric membrane for their detection by ratiometric fluorescence measurements. A reference dye, unresponsive to both carbon dioxide and oxygen, was added as an internal calibration. The cocktail was coated on a glass slide or the distal end of an optical fiber, resulting in a single polymer film that sensed both oxygen and carbon dioxide. The luminescence of one dye did not affect that of the others in the system and their fluorescence emission spectra were easily spectrally resolved. The transparent and pH-resistant polymers used were poly(vinyl chloride), silicones, polyurethane, polystyrene and sol gels. The parameters optimized were leaching, photo-bleaching and response time. The sensors were fast responding, long lasting, easily prepared and reusable. Respiration tests were conducted on rapeseeds and sensor response was unaffected by the seeds and the soil nutrient solution used. Real-time depletion of oxygen was measured and correlated well with simultaneous results from a commercial oxygen electrode.Ph.D.Analytical chemistryPolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127534/2/3029330.pd