SENSING OXYGEN THROUGH SKIN USING A RED DIODE-LASER AND FLUORESCENCE LIFETIMES

The most difficult impediments to transcutaneous optical sensing are t he absorbance and scatter of light caused by skin and the lack of fluo rescent sensing probes which can be excited at wavelengths over 600 nm . Furthermore, current optical sensing techniques rely on absorbance o r fluorescence intensity measurements, both of which are sensitive to drifts in lamp intensity, changes in probe concentration and inner fil ter effects. We demonstrate oxygen sensing through a layer of skin by using red light which readily penetrates skin as diffusely scattered l ight. The oxygen sensitive osmium-ligand complex used in this study ca n be excited at 635-680 nm. In addition, we measure fluorescence lifet imes, which are inherently unaffected by factors that limit absorbance and fluorescence intensity measurements. By using phase fluorimetry a nd long lived fluorophores, we are able to demonstrate the potential f or subdermal oxygen sensing with simple and inexpensive instrumentatio n. This work describes a paradigm for future non-invasive measurements of other analytes.