Cell Viability Assay using Propidium Iodide

The cell viability assay was based on the exclusion of propidium iodide (PI) by the intact viable cells according to the protocol described in [27 (link)]. The cells were plated in 24-well tissue culture test plates (Techno Plastic Products, Trasadingen, Switzerland) at 5 × 10⁴ cells/mL and treated with QBAs for 48 h. After incubation, PI (1 μg/mL) was added and the percentage of dead (PI-positive) cells was detected using Cytomics FC 500 and/or CytoFlex flow cytometry systems (Beckman Coulter, Inc., Brea, CA, USA). A total of 10,000 cells were analyzed for each sample. Each experiment included two replicate wells and was repeated at least three times.