Time-resolved detection of singlet oxygen luminescence in red cell ghosts generated by photosensitizers via excitation in the far red

Abstract

In recent years a lot of new far red absorbing sensitizers for photodynamic therapy (PDT) were synthesized, like derivatives of bacteriopheophorbide. The possibility of increasing the accumulation in tumor tissue by coupling these dyes to carrier molecules is investigated. The photophysical properties of these dyes can be dramatically changed as a result of covalent binding to carrier molecules, different solvents, or biological surroundings. In heterogeneous systems 1O2 is strongly quenched. Therefore, its luminescence is difficult to detect. Another difficulty is the fact that especially far red absorbing sensitizers show fluorescence at the wavelength of 1O2-luminescence at 1270 nm, which can be several magnitudes higher than the luminescence of 1O2. The efficiency of singlet oxygen (1O2) generation is of major interest because 1O2 seems to play an important role in PDT. Time resolved luminescence measurements of 1O2 generated by dyes in micelles and liposomes in D2O were already made in our group. In order to investigate more complex systems and to avoid unwanted photochemistry we changed the excitation wavelength from UV (337 nm) to VIS/NIR(ND:YAG/OPO). The excitation power was increased and the detection limit was decreased. First measurements in red cell ghosts are presented.