Figure 1. Schematic illustration of the long-term AuNP accumulation model.

Endothelial cells (HUVECs) are cultivated under standard growth conditions in tissue culture plates. Additionally, their culture media were supplemented with AuNPs at a constant dose of 8 μg/mL, which is just below the acute lethal level. Based on this model, cells are expected to uptake AuNPs during the growth phase of the cell cycle, and then, typically, undergo mitosis and presumably halve their nanoparticle content into each of the offspring. Nevertheless, the continuous exposure to the nanoparticles in the medium leads to steady intracellular accumulation over time. In the early term, i.e., approximately first two weeks, cells are observed to steadily accumulate AuNPs until a maximum peak level followed by a steady decrease for the next following weeks approaching to the ground zero level.