Fluorescence-based Sensor for Oxygen Permeability of Plastic Beverage Containers
Polymers used for food and beverage packaging often must have very good gas-barrier properties. Since the permeability of O2 gas through common feedstock materials such as poly(ethylene terephthalate), PET, is affected by typical stretch-blow molding processes for bottle fabrication, we are developing an optical method for determining oxygen transport through intact drink bottles. The sensor material, tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) encapsulated in silicone rubber, is applied as a thick film to the inner surface of a transparent bottle and excited using a pulsed laser operating at blue or UV wavelengths. Red fluorescence from the sensor salt is resolved on the microsecond time scale and the fitted decay rate is a function of quenching by oxygen present. Our present limit of detection for O2 is below 1000 ppmv. Fluorescence-based sensors may be applied to rapid testing of permeability through actual containers and will enable measurements of oxygen dissolved within novel micro-layered polymers being developed for advanced packaging applications.