The Mechanism of Photofrin® Photobleaching and Its Consequences for Photodynamic Dosimetry

Irene Georgakoudi, Michael G. Nichols, Thomas H. Foster

Research output: Contribution to journalArticlepeer-review

221 Scopus citations


We report experimental results that support a theory of self-sensitized singlet oxygen-mediated bleaching of the porphyrin photosensitizer Photofrin. Microelectrode measurements of photodynamic oxygen consumption were made near the surface of individual, Photofrinsensitized EMT6 spheroids during laser irradiation. The progressive decrease in photochemical oxygen consumption with sustained irradiation is consistent with a theory in which bleaching occurs via self-sensitized singlet oxygen reaction with the photosensitizer ground state. A bleaching model based solely on absorbed optical energy density is inconsistent with the data. Photobleaching has a significant effect on calculated photodynamic dose distributions in 500 μm diameter spheriods. Dose distributions corrected for the effects of bleaching produce a new estimate (12.1 ± 1.2 mM) for the threshold dose of reacting singlet oxygen in this system.

Original languageEnglish (US)
Pages (from-to)135-144
Number of pages10
JournalPhotochemistry and Photobiology
Issue number1
StatePublished - Jan 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Physical and Theoretical Chemistry


Dive into the research topics of 'The Mechanism of Photofrin® Photobleaching and Its Consequences for Photodynamic Dosimetry'. Together they form a unique fingerprint.

Cite this