[Fluorescence spectroscopy study on photobleaching properties of photosensitizers in photodynamic therapy].

The photobleaching and formation of photoproduct of hematoporphyrin monomethyl ether (HMME) was investigated in solution by fluorescence spectroscopy. Irradiation was performed by 532 nm double-frequency Nd : YAG laser at a fluence rate of 100 mW x cm(-2), meanwhile the collection of fluorescence spectra was implemented an by optical multi-channel analyzer (OMA). Utilizing the basis spectra constructed and least-square fitting, the intensity of HMME fluorescence (613 nm), photoproduct fluorescence (639 nm) and autofluorescence can be resolved respectively from the single measured spectrum. The correlation between fluorescence intensity and the concentration of HMME is consistent with linear function at concentrations not exceeding 10 microg x mL(-1). Monitoring the fluorescence spectroscopy during irradiation, three kinds of information were obtained, including photobleaching of HMME, formation and bleaching of photoproduct, as well as variation to fluorescence intensity due to the change of sample optical properties. Product generated by bleaching of photoproduct causes significant in sample optical properties. The implementation of fluorescence spectroscopy measurement and spectral analysis method presented here can be utilized effectively for both ex vivo investigation of photobleaching characteristics of photosensitizer and in vivo monitoring for dosimetry in photodynamic therapy.