Time-resolved in-vivo fluorescence of photosensitizing porphyrins.

Various components of photosensitizing porphyrins (e.g. monomers, aggregates, ionic species) have been recently localized in single cells by time-resolved fluorescence microscopy. Novel time-resolving techniques, based on picosecond laser diodes, a frequency-doubled Nd:YAG laser and time-gated microscopic equipment, were used for in-vivo measurements of the chick chorioallantoic membrane (CAM) exhibiting a pronounced vasculature. Changes of the fluorescence decay kinetics after light exposure were correlated with the formation of a photoproduct (Photosan, aminolaevulinic acid) or changes of the intracellular binding sites (tetraphenyl-porphyrins). Fluorescent components with different decay times were shown to be distributed differently within the tissue.