Oxygen flux fluorescence lifetime imaging

We describe a device capable of imaging distributions of surface PO2 as well as oxygen flux (e.g., into the human skin), Oxygen is monitored by a phase-angle-sensitive imaging technique using the effect of luminescence lifetime quenching of ruthenium complexes incorporated into a polymer layer system. The dyes are excited by modulated radiation of blue light-emitting diodes. The phase-shifted luminescence is detected by an intensified CCD camera. Several modulation techniques have been comparatively investigated. The obtained images correspond pixel-by-pixel to the local luminescence lifetimes, which are a direct measure for the distribution of surface PO2, or alternatively for the oxygen flux through a permeable diffusion barrier. For an illuminated sensor area of 10 cm(2) and a spatial resolution of I mm at the sensor layer, the oxygen resolution is better than Delta PO2=0.3 torr in the absence of oxygen, and better than Delta PO2=4 torr at PO2= 160 torr.