MTT assay

Cells were seeded on 96 well plates at a density of 3500–5000 cells per well (depending upon cell line) in 100 µL of complete media, recovered for 24 h, and then were exposed to AgNPs or AgNO₃ (Sigma-Aldrich) as a source of Ag⁺ in 100 µL of complete media containing the indicated concentrations of silver listed in the figures. After 72 h, media containing AgNPs or Ag⁺ were replaced with 200 µL of media containing 0.5 mg/mL 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT; Sigma-Aldrich) and incubated for 2 h at 37 C. Media was removed, and cells were lysed in 200 uL of DMSO and absorbance read using a Molecular Devices (San Jose, CA, USA) Emax Precision Microplate Reader at 595 nm. To control for contributions to absorbance due to AgNPs, the absorbance of wells treated with AgNPs but which do not receive MTT also was measured. Comparisons of curve fitting and statistical analysis of background corrected and raw absorbance measurements fell within the standard deviation of normal sample variation, and therefore any contribution of AgNP absorbance was deemed negligible to the overall results.