Relationship between the Microscopic and Macroscopic World in Optical Oxygen Sensing: A Luminescence Lifetime Microscopy Study

An investigation based oil confocal fluorescence lifetime imaging microscopy (FLIM) of silica-loaded silicone films doped with a molecular oxygen-sensitive ruthenium(11) polyazaheterocyclic complex is presented. The effect of the silica type (hydrophilic/hydrophobic), particle size and amount of silica filler on the luminescence decay of the immobilized indicator dye has thoroughly been Studied. A higher amount of hydrophilic silica leads to both a higher solubility or molecular oxygen into the silicone film and to higher levels of the metal indicator dye. Thus, incorporation of 10% (by wt) pyrogenic silica into silicone shortens the mean luminescence lifetime from 1.4 to 0.9 mu s. However, all excess of filler may lead to overloading of the dye into the film producing new phenomena such as triplet-triplet annihilation and excitation energy homotransfer, as observed from their influence oil the emission lifetime or the metal complex. Those phenomena do not Lake place when trimethylated silica (hydrophobic filler) is used. In this case, no increase on the oxygen or dye concentration is observed after addition of the filler and no significant reduction of the luminescence lifetime is measured. Both the addition or silica and the possible precipitation of dye crystals lead to the appearance of microdomains where the molecular probe exhibits widely different excited state lifetimes. For the first time, such microdomains within the oxygen Sensing layer are Visualized and analyzed by means of FLIM, showing the potential of this technique and the usefulness or out conclusions to the future design and development of novel luminescent oxygen sensor films for environmental and process analysis.