Interactions between charged nanoparticles and giant vesicles fabricated from inverted-headgroup lipids

The surface chemistry of the cell membrane plays an important role in how cells interact with particulate species. These interactions are dictated in large part by lipid headgroup charge. To investigate the nature of electrostatic interactions between lipid bilayers and nanoparticles in solution, we studied nanoparticles interacting with the zwitterionic lipid 1,2-dioleoyl-glycero3- phosphocholine (DOPC), and its inverted-headgroup analog DOCP. These interactions were investigated by fabricating giant unilamellar vesicles (GUVs) with DOPC lipids and DOCP lipids respectively, and introducing nanoparticles to suspensions of both. GUVs displayed various deformational modes depending on the charge and size of the nanoparticles as well as the compositions of the GUVs. The differences in the responses of the two lipid species illuminate how the phosphate and choline groups on the lipid interact with charged nanoparticles. This study suggests that the phosphate group dominates the lipid-nanoparticle electrostatic interaction. We speculate that the formation of water clathrate structures around the choline group inhibits interactions between negatively charged nanoparticles and the positively charged choline.