Cellular uptake and distribution of graphene oxide coated with layer-by-layer assembled polyelectrolytes

We report a facile approach for the fabrication of a new class of graphene oxide (GO)-based nanoassemblies by layer-by-layer (LbL) technique. The single-layer thickness and intrinsic negatively charged carboxyl groups of GO nanosheets provide a natural platform for LbL assembly of polyelectrolyte nanofilms by electrostatic forces at mild and aqueous conditions. The general applicability of our approach is demonstrated by the preparation of GO nanoassemblies with sizes of 100-200 nm using various charged polyelectrolytes, including synthetic polymers, polypeptides, and DNA oligonucleotides. Systemic assessment of cytotoxicity and acute stress response show that no discernable signs of cytotoxicity are associated with exposure of GO and its nanoassemblies [GO/PLL (poly (L-lysine)), GO/PLL/PSS (poly(sodium-4-styrenesulfonate)), GO/PLL-PEG (PEGlayted PLL), GO/PLL/PLGA-PEG (PEGlayted poly (L-glutamic acid))] up to 1 μg/mL. Studies on cellular uptake and subcellular localization show that a representative nanoassembly, GO/PLL-PEG, can effectively cross cell membranes and localize mainly in lysosomal compartments, without induction of noticeable harmful effects as confirmed by detection of mitochondrial depolarization and lysosomal pH.