In Fig. M1, the cell is still intact, as indicated by its morphology with an elongated shape with narrow branches and the bulky body center containing the cell nucleus (dark due to extremely low fluorescence intensity). Resorufin with a FLT of 2.8 ns dominates the fluorescence of the medium surrounding the cell. Hypericin with a FLT of 6.8 ns is mainly accumulated in the ER around the nucleus, but can also be found within the cytoplasm. In contrast to the fluorescence emitted from the outside medium and the cell's ER, the overall fluorescence of the cytoplasm is not dominated by a single dye but is a combination of both hypericin and resorufin fluorescence. As a result, the intensity weighted average fluorescence lifetime value (τ AvInt ) of the cytoplasm is approx. 5 ns, in between the values recorded for the two contributing dyes. With ongoing PDT progression (Fig. M2-4), overall cell and nucleus contraction and rounding can be observed, which is accompanied by a formation of cell membrane blebs. Blebs mainly occur at membrane sites around the ER and expand to create large protuberances (M4, white arrows). While the cell membrane is already severely distorted by surface protuberances in M4, its integrity is still maintained as indicated by the low fluorescence intensity inside the protuberances and no significant increase of the amount of resorufin in the cell. Between Fig. M5 and M6 rupture of the cell membrane occurs. During the final stages of PDT (Fig. M6-M8) the cell membrane stability is compromised. The decreasing τ AvInt values in the cell from approx. 5 ns in Fig. M5 to approx. 3.5 ns in M8 indicate that the cell is progressively flooded with the surrounding medium, resulting in expansion and complete rounding of the cellular body. At this stage, cell organelles are hardly visible anymore and resorufin is the dominant fluorescence emitter within the entire glioma cell.