Evidence for excitation of fluorescence in RPE melanin by multiphoton absorption

Randolph D. Glickman, Benjamin A. Rockwell, Gary D. Noojin, David J. Stolarski, Michael L. Denton

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations


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 × 10 7 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.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
EditorsS.L. Jacques, D.D. Duncan, S.J. Kirkpatrick, A. Kriete
Number of pages8
StatePublished - 2002
EventLaser Tissue Interaction XIII: Photochemical, Photothermal and Photomechanical - San Jose, CA, United States
Duration: Jan 20 2002Jan 23 2002


OtherLaser Tissue Interaction XIII: Photochemical, Photothermal and Photomechanical
Country/TerritoryUnited States
CitySan Jose, CA


  • Damage
  • Fluorescence
  • Laser
  • Melanin
  • Melanosome
  • Multiphoton absorption
  • RPE
  • Ultrashort pulse

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Condensed Matter Physics


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