2.7. In Vitro Phototoxicity Assay

In vitro phototoxicity assays were performed with MDA-MB-231 cells seeded into 96-well plates at a concentration of ~2 × 10³ cells/well in 100 μL of culture medium and allowed to grow for 24 h. The cells were then incubated for 24 h in the presence or absence of polymer (5 μM in water). After incubation with polymers, cells were submitted, or not, to light excitation (λ = 450 nm, 1.45 J cm⁻²) for 5 min. A total of 48 h after irradiation, the cytotoxicity or phototoxicity of the polymers were evaluated using an MTT assay. Briefly, the incubation of cells was performed in the presence of MTT (0.5 mg mL⁻¹) during 4 h to determine mitochondrial enzyme activity. Then, the cell medium was aspirated and the MTT precipitates were dissolved in an ethanol/DMSO (1:1) solution (150 μL) and a reading of the absorbance at 540 nm was performed.