Spontaneous Graphene/Lipid Bicellar Co-assembly (NANO²-Graphene): Experiments and Computer Simulations

Using a combined experimental and computer modeling approach, we demonstrate that graphene can self-assemble with a discoidal lipid bicelle, forming a graphene incorporated nanodisc structure (NANO²-graphene) over a wide range of graphene-to-lipid ratios (from 1:2000 to 1:40 by weight). Structural characterization via dynamic light scattering (DLS), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) confirms the encapsulation of graphene in the bicelles and suggests that the presence of graphene enhances the stability of the discoidal structure and prevents the usual thermally induced bicelle-to-vesicle transition. Both molecular dynamics (MD) simulations and DSC results show that bicelles are capable of encapsulating a significant graphene content and that the graphene incorporation significantly suppresses the lipid ordered phase and decreases lipid lateral diffusion. MD simulations also reveal that, in the presence of single or stacked graphene layers, lipid tails bend and orient along the graphene surface to maintain the bilayer thickness with the lipid order parameter significantly reduced and the area per lipid increased along with water contacts with lipid headgroups. These results provide important insights into the interaction between lipid molecules and graphene that should be considered in the biomedical application of graphene-containing nanomaterials and, more broadly, the effect of graphene on lipid-containing biointerfaces.