Electron microscopy study of SPION interaction and uptake. (A) Electron microscopy images of thin sections of cells interacting with DMSA-SPION by clathrin mediated uptake (<200 nm in diameter aggregates). Scale bar represents 200 nm. (B) Two images by electron microscopy of thin sections of cells showing typical images of macropinocytosis for DMSA-SPION uptake (>200 nm in diameter aggregates). Scale bars represent 200 nm. (C) Electron microscopy images of different types of endosomes containing SPION aggregates: (a) Early endosome. (b) Multivesicular body containing intraluminal vesicles. (c) Late endosome characterized by a multilamellar morphology. (d) Late endosomes and lysosomes with multivesicular structure and large electron-dense areas. Scale bar represents 200 nm.