In vitro investigation on the pH dependence of the absorption and fluorescence properties of the photosensitizer mTHPC.
Fluorescence excitation efficiency is of great importance for photodynamic diagnosis. Because usually a difference in the interstitial pH between normal and tumor tissue occurs, it is necessary to assess the impact of pH on the fluorescence emission intensity of the photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC) in this context. The results obtained by in vitro fluorescence measurements clearly indicate that pH values below 6 lead to a significant decrease in the fluorescence intensity. In the physiological range of pH 6.5-7.2, however, no pH dependence was found. Besides the decrease in the fluorescence intensity of mTHPC for pH < 6, changes in the spectral shape of the absorption were found. These changes can be utilized for "dual-wavelength ratio imaging," using mTHPC as a pH-sensitive indicator with the excitation pair 405 nm/436 nm in the range of pH 3.5-6.
Zimmermann
Andreas
A
Institute for Medical Physics, Innsbruck, Austria. andreas.zimmermann@uibk.ac.at
Ritsch-Marte
Monika
M
Kostron
Herwig
H
D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008652:Mesoporphyrins / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000737:chemistry*; D012997:Solvents; D013050:Spectrometry, Fluorescence
D008652:Mesoporphyrins; D017319:Photosensitizing Agents; D012997:Solvents; C072269:temoporfin