2.4. PpIX Fluorescence Quantification

PpIX fluorescence was quantified using the Bio-tek Synergy HT plate reader (Bio-Tek Instruments Inc., Winooski, VT, USA), with an excitation wavelength of 405 ± 12 nm and an emission filter of 635 ± 12 nm. PpIX fluorescence measurements were taken immediately after test compounds were applied at 0 h, as well as at 3 or 6 h after incubation with the various test compound combinations and, finally, either immediately after irradiation or a period of darkness out of the incubator, for dark control plates. Between measurements, plates remained in the dark, incubated at 37 °C and 5% CO₂. Before experimentation, PpIX fluorescence was aligned with concentration using a relative PpIX standard curve (in a manner similar to that we have performed previously [23]), where PpIX was dissolved to different concentrations, the fluorescence of which were measured using the plate reader. The PpIX emission spectra produced in cells from the various test compounds under investigation were also compared (in a manner similar to that we have performed previously [19]) to that of PpIX without note.