17 August 1994 Photoproducts and new spectral bands during PDT probed by cw and time-gated microscopy and spectroscopy
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Intracellular modifications of sensitizers during PDT were observed with combined measurements of cw and time-gated microscopy and spectroscopy. Protoporphyrin when stimulated with 5-aminolevulinic acid (ALA) showed photobleaching after irradiation with blue light (1 - 10 J/cm2) in competition with the formation of photoproducts (i.e., photoprotoporphyrins). The anionic meso-tetra(4-sulfonatophenyl)porphyrin (TPPS4) was incubated in cells seeded at low cell density (isolated cells; 25 cells/mm2) or high cell density (confluent growing cells; 500 cells/mm2), respectively. A similar granular fluorescence pattern, cw and time-gated fluorescence spectra could be observed before light exposure in both cases. With increasing irradiation a redistribution from the cytoplasm to the nucleus in addition with a pronounced formation of a fluorescent band around 615 nm was dependent on the growth phase of the cells and could be detected mainly for isolated cells. This species was correlated with a short fluorescence decay time and detected with an `early' time gate between 0 - 5 ns, whereas the neutral TPPS4 molecule was detected within a `late' time-gate between 10 - 15 ns.
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Angelika C. Rueck, Wolfgang S. L. Strauss, Michael H. Gschwend, Karsten Koenig, Reinhard Sailer, Rudolf W. Steiner, Herbert Schneckenburger, "Photoproducts and new spectral bands during PDT probed by cw and time-gated microscopy and spectroscopy", Proc. SPIE 2134, Laser-Tissue Interaction V; and Ultraviolet Radiation Hazards, (17 August 1994); doi: 10.1117/12.182937; https://doi.org/10.1117/12.182937

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