Fig. 2
Endocytic uptake and exocytosis of Au NPs by MSCs. MSCs were exposed to Au NPs (ca. 4 nm core diameter) at the indicated doses cNP for 24 or 48 h. After washing off residual NPs from the medium and the outer cell membrane, i.e. NPs which had not been internalized by the MSCs, culturing was continued in fresh growth medium for 24 or 48 h. Then, the amount of intracellular Au NP mAu (i.e. amount of elemental Au inside the cell pellet) and exocytozed Au NPs (i.e. amount of elemental Au in the medium) mAu,exo were determined by ICP-MS. Finally, the fraction of exocytosed Au NPs was determined as mAu,exo/(mAu,exo + mAu) = mAu,exo/mAu,tot. For cells labeled with cNP = 2 nM (°) the Au content in the cell medium was below the detection limit