| Luminescence-based oxygen sensors are of growing analytical importance. Applications include aerodynamic studies of automobiles in wind tunnels, monitoring of oxygen concentration during fermentation processes and in bioreactors, measurement of biological oxygen demand, and imaging of oxygen in biological samples. Significant problems in the design and manufacture of polymer-supported, luminescence-based oxygen sensors include nonlinearity of the Stern-Volmer plot and multi-exponential lifetime decays, which are attributed primarily to heterogeneity of the sensor molecule within the polymer support. Despite the fact that polymers have a tremendous effect on sensor properties, neither the detailed role of the polymer in controlling the photophysical behavior of sensors, nor the relationship between film fabrication and response is understood. Consequently, the design of sensors with performance characteristics required for a given application remains a challenge.;New materials were developed to study sensor response as a function of structure and composition. The potential of a solvatochromic ruthenium complex to probe the effect of local environment on quenching was explored, and osmium complexes were developed for red diode laser excitation. Polymers were prepared for use as pressure sensitive paints (PSPs), and poly(trimethylsilylmethyl methacrylate) was used as a PSP in a wind tunnel. Methods were developed to measure oxygen diffusion and solubility in polymers to ascertain the relationship between properties of the polymer and sensor response. Quenching response was not dictated by bulk physical properties of the polymer, but was influenced by the local environment of the molecule. Fluorescence microscopy (FM) techniques proved useful in the study of sensor heterogeneity. Conventional fluorescence microscopy was exploited to resolve nonuniform emission intensity and oxygen quenching within sensor films and to quantitate the degree of heterogeneity to correlate microscopic quenching behavior to the macroscopic sensor response. Microcrystallization, and probably nanocrystallization of the complex within sensor films caused the observed heterogeneity. Conventional FM was used to investigate the photochemistry exhibited by ruthenium alpha-diimine complexes. Confocal and two-photon FM were used to detect microcrystallization. The experimental approach and methods of measurement used in these investigations and the implications of the results in the rational design and mass production of luminescence-based oxygen sensors are discussed. |
