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

Abstract

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
Pages172-179
Number of pages8
Volume4617
DOIs
StatePublished - 2002
EventLaser Tissue Interaction XIII: Photochemical, Photothermal and Photomechanical - San Jose, CA, United States
Duration: Jan 20 2002Jan 23 2002

Other

OtherLaser Tissue Interaction XIII: Photochemical, Photothermal and Photomechanical
CountryUnited States
CitySan Jose, CA
Period1/20/021/23/02

Keywords

  • 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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