27 June 2002 Evidence for excitation of fluorescence in RPE melanin by multiphoton absorption
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Proceedings Volume 4617, Laser Tissue Interaction XIII: Photochemical, Photothermal, and Photomechanical; (2002) https://doi.org/10.1117/12.472521
Event: International Symposium on Biomedical Optics, 2002, San Jose, CA, United States
Previously, we reported that ultrashort, near infrared (NIR) laser pulses caused more DNA breakage in cultured retinal pigment epithelial (RPE) cells than did CW, NIR laser radiation delivering a similar radiant exposure. We hypothesized that this difference was due to multiphoton absorption in an intracellular chromophore such as the RPE melanin. We investigated two-photon excitation of fluorescence in a suspension of isolated bovine RPE melanosomes exposed to a 1-KHz train of approximately 50- fsec laser pulses at 810 nm from a Ti:Sapphire laser, and compared this to the fluorescence excited by CW exposures at 406 nm from a Krypton ion laser. Fluorescence was measured with a PC-based spectrometer. The CW sources excited fluorescence with a peak at 525 nm. The fluorescence intensity depended on the irradiance of the sample, as well as the melanosome concentration. Peak fluorescence was obtained with a suspension of ~2 x 107 melanin granules/ml. The 810-nm, ultrashort pulses also excited fluorescence, but with a broader, lower-amplitude peak. The weaker fluorescence signal excited by the 810-nm ultrashort pulse laser for a given melanosome concentration, compared to 406-nm CW excitation, is possibly due to the smaller two- photon absorption cross-section. These results indicate the involvement of multiphoton absorption in DNA damage.
© (2002) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Randolph D. Glickman, Benjamin A. Rockwell, Gary D. Noojin, David J. Stolarski, and Michael L. Denton "Evidence for excitation of fluorescence in RPE melanin by multiphoton absorption", Proc. SPIE 4617, Laser Tissue Interaction XIII: Photochemical, Photothermal, and Photomechanical, (27 June 2002); doi: 10.1117/12.472521; https://doi.org/10.1117/12.472521

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