TIME-RESOLVED FLUORESCENCE SPECTROSCOPY AND INTRACELLULAR IMAGING OF DISULFONATED ALUMINUM PHTHALOCYANINE

Spectroscopic studies were carried out on the photosensitizer disulpho nated aluminium phthalocyanine (AlS(2)Pc) which has prospective applic ations in photodynamic therapy. The fluorescence lifetimes of AlS(2)Pc were measured in a range of model systems and cultured leukaemic cell s using laser excitation and time-correlated, single-photon-counting d etection. In an investigation of non-covalent protein binding, we stud ied AlS(2)Pc in the presence of human serum albumin (HSA) in 0.1 M pho sphate-buffered saline at pH 7.4. On addition of excess concentrations of HSA, small red shifts in the fluorescence and absorbance spectra w ere observed, together with an increase in fluorescence polarization a nisotropy, consistent with binding of the phthalocyanine. Fluorescence decays could be resolved into two lifetimes for bound AlS(2)Pc with a dominant component of 5.5 ns and a minor component of 1 ns. Fluoresce nce imaging and time-resolved microfluorometry were carried out on int racellular AlS(2)Pc using leukaemic K562 cells. Microscopic imaging wi th a charge-coupled device (CCD) camera revealed that AlS(2)Pc fluores cence predominated in a discrete perinuclear region which was then pro bed selectively by a focused laser spot for fluorescence lifetime meas urements. Bi-exponential decays with lifetime components of 6.1 and 2. 2 ns were observed. On irradiation at 633 nm, the fluorescence intensi ty increased initially and subsequently declined due to photodegradati on.