Luminescence ratio indicators for oxygen

To improve stability of optical sensors with respect to calibration, the authors developed oxygen indicator systems which have two luminescence bands, one of which is quenched by oxygen while the other is relatively unaffected by oxygen. The measured parameter is the relative intensity of the two bands. The following systems have been evaluated: (1) In water in the presence of ..gamma..-cyclodextrin, the ratio of pyrene monomer fluorescence to pyrene dimer fluorescence decreases with increasing oxygen partial pressure. (2) In water in the presence of ..beta..-cyclodextrin, the ratio of bromonaphthalene phosphorescence to fluorescence decreases with increasing oxygen partial pressure. (3) Bromonaphthoyl derivatives extracted into ..gamma..-cyclodextrin bonded to cellulose and dried show intense oxygen-dependent phosphorescence and oxygen-independent fluorescence. Of these, system 3 is most practical because it is more stable and has higher intensities with a larger change in intensity ratio. However, it is limited to measurements in dry samples, because 100% relative humidity is sufficient to quench phosphorescence.