Uptake of phthalocyanines into MCF-7c3 cells. Cells were incubated with the indicated concentrations of the Pc overnight (18–20 h). Following harvest by trypsinization, cells were washed, re-suspended in cold HBSS (without phenol red) and analyzed by flow cytometry. Excitation of Pc was achieved with a 355–365 nm UV laser, and emission was collected with a 650 nm long-pass filter. At each concentration, the MCF of each dye was divided by that of Pc 4 to obtain the relative fluorescence, which is plotted. Absolute values of MCF in cells loaded with 10, 50 and 100 nM Pc 4 were found to be 24 ± 5, 54 ± 12 and 100 ± 22, respectively. Each datum is the mean ± SEM of four independent measurements.