FREQUENCY-DOMAIN LIFETIME MEASUREMENTS AND SENSING IN HIGHLY SCATTERING MEDIA

For clinical chemistry, or for non-invasive sensing through skin, it i s often necessary to obtain quantitative information in highly scatter ing media. We describe two simple methods for fluorescence lifetime me asurements in highly scattering media, and in particular in an intrali pid suspension. Lifetimes can be measured using an intensity decay law that accounts for the time delays and pulse-broadening effects of mul tiple light-scattering events in the intralipid. Alternatively, the ph ase and modulation measurements can be performed relative to a referen ce fluorophore with a known lifetime. These approaches provide reliabl e lifetime data for a pH-sensitive fluorophore contained within a micr ocuvette 4 mm under the surface of the intralipid suspension. Fluoresc ence lifetime-based sensing is now recognized as a valuable methodolog y in clinical and analytical chemistry, and the possibility of lifetim e-based sensing in turbid media has been demonstrated.