Mtt cell viability assay

HeLa cells (ATCC, USA) and MCF-7 cells (ATCC, USA) were grown in DMEM (Gibco, Life Technologies, MA, USA) with culture media containing 10% fetal bovine serum (Gibco, USA) and penicillin–streptomycin (Gibco, USA). Cells were cultured in a Nu-4750 incubator (NuAire, USA) at 37 °C with a CO₂ level of 5%. The concentrations of silica nanoparticles or exosome-encapsulated silica nanoparticles for HeLa cell intake experiments were 10 µg/mL in a culture medium for 6 h. After changing the culture medium to discard free nanoparticles, a fluorescent cell imager (Bio-Rad, USA) was used, capturing the silica distribution within the cell. For drug delivery experiments, exosome-encapsulated silica nanoparticles loaded with doxorubicin and free doxorubicin were added to the culture medium to a final doxorubicin concentration of 2.5 µg/mL. MTT cell viability assays (Thermo Fisher, USA) and fluorescence microscopy were used to analyze the viability of HeLa and MCF-7 cells and intracellular doxorubicin fluorescence 3, 6, 12, and 24 h after culturing. A confocal microscope (Zeiss, Germany) was used to record the doxorubicin and silica nanoparticle fluorescence distribution 6 h after culture, including lysosome staining by LysoTracker Green (Thermo Fisher, USA) during this period.

MTT cell viability assays (Thermofisher, Waltham, MA, USA) according to the manufacturer’s protocol, as previously reported (10). Cells were seeded in a 96-well plate at a density of 25,000 cells/well. Following knockdown and/or treatments, media was replaced with fresh media. MTT dye was added and incubated at 37 °C for 2 h. DMSO was added to solubilize the formazan and absorbance was read at 540 nm. Blank wells were included and non-specific absorbance subtracted from final absorbance readings. Cell viability was computed as percentage of vehicle treatment or control RNA control.