TEM images of EMT cells for different naked AuNP co-culture times. A) co-culturing with 500 μM AuNP colloid for 30 min: only a few AuNPs can be found on the surface or inside the cytoplasm. The red square (B) marks the area where clusters are found. C) 1 h co-culture time: a larger number of endocytotic vesicles containing AuNPs is found in the cytoplasm. D) 6 h co-culture time: the number and the size of endocytotic vesicles containing AuNPs are even larger. Bar: 2 μm (A, C and D) and 200 nm (B).