Investigating Biomembrane-Nanoparticle Interactions with 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 investigated nanoparticles interacting with lipids in which the zwitterionic head group was inverted from its natural configuration. This inverted lipid species, referred to as DOCP, is based on 1,2-dioleoyl-glycero-3-phosphocholine (DOPC) but has the positions of the phosphate and choline groups reversed.

These interactions were investigated by fabricating giant unilamellar vesicles (GUVs) with DOPC lipids and DOCP lipids respectively, and introducing nanoparticles to suspensions of both. In the presence of charged polystyrene nanoparticles, GUVs displayed various deformational modes depending on the charge sign and size of the nanoparticles. The differences in the responses of the two lipid species were quantified according to the size changes of GUVs. These differences illuminate how the relative positions of the negative and positive charge groups on the lipid interact with charged particles. They also reveal a particle size dependence of the nanoparticle-membrane electrostatic interaction. This work provides fundamental insights regarding the nature of this interaction, which has implications for the development of new drug delivery vehicles as well as understanding the environmental toxicity of nanomaterials.