In vitro investigation on the pH dependence of the absorption and fluorescence properties of the photosensitizer mTHPC |
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Authors: | Zimmermann Andreas Ritsch-Marte Monika Kostron Herwig |
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Institution: | Institute for Medical Physics, Innsbruck, Austria. andreas.zimmermann@uibk.ac.at |
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Abstract: | 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. |
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