Quantification of internalized gold nanoparticles in endothelial and epithelial cells by ICP-AES. Both epithelial cells (H441 and A549) and endothelial cells (HDMEC and hCMEC/D3) were incubated with 50 μM gold nanoparticles at 37°C for 24 hours. Cells were extensively washed, lysed by aqua regia (3:1 hydrochloric acid : nitric acid) and analyzed for gold concentration by ICP-AES. In (A) the total number of particles per area was calculated, while in (B) the percentage uptake of particles into cells, as a function of the total amount applied, was determined. (duplicate of three independent experiments).