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We use diamond nanoparticles (DNPs) wrapped in the cationic polyelectrolyte poly(allylamine) hydrochloride (PAH) and bilayers composed of either pure DOPC or a mixture of DOPC/DOPG to investigate the influence of membrane phospholipid composition and net surface charge on nanoparticle-membrane interactions and the extent of nanoparticle adhesion to supported phospholipid bilayers. Our results show that in all cases electrostatic attractions between the negatively charged bilayer and cationic PAH-DNP were responsible for the initial attachment of particles, and the lateral electrostatic repulsion between adsorbed particles on the bilayer surface determined the final extent of PAH-DNP attachment. Upon attachment, NPs attract lipids by the contact ion pairing between the ammonium groups on PAH and phosphate and glycerol groups on the lipids and acquire a lipid corona. Lipid corona formation on the PAH-DNP reduces the effective charge density of the particle and is in fact a key factor determining the final extent of NP attachment to the bilayer. Incorporation of DOPG to the bilayer leads to a decrease in efficiency and final extent of attachment compared to DOPC alone. The reduction in PAH-DNP attachment in the presence of DOPG is attributed to the adsorption of free PAH in equilibrium with bound PAH in the nanoparticle solution, thus reducing electrostatic attraction between PAH-DNPs and SLBs. This leads to an increase in hydrogen bonding interactions between lipid headgroups that limits extraction of phospholipids from the bilayer by PAH-DNP, lessening the reduction in interparticle repulsion achieved by acquisition of a lipid corona. Our results indicate that the inclusion of charged phospholipids in SLBs changes bilayer rigidity and stability and hinders the attachment of PAH-DNPs by preventing lipid extraction from the bilayer. 

The initial interactions of engineered nanoparticles (NPs) with living cells are governed by physicochemical properties of the NP and the molecular composition and structure of the cell membrane. Eukaryotic cell membranes contain lipid rafts – liquid-ordered nanodomains involved in membrane trafficking and molecular signaling. However, the impact of these membrane structures on cellular interactions of NPs remains unclear. Here we investigate the role of membrane domains in the interactions of primary amine-terminated quantum dots (Qdots) with liquid-ordered domains or lipid rafts in model membranes and intact cells, respectively. Using correlative atomic force and fluorescence microscopy, we found that the Qdots preferentially localized to boundaries between liquid-ordered and liquid-disordered phases in supported bilayers. The Qdots also induced holes at these phase boundaries. Using super resolution fluorescence microscopy (STORM), we found that the Qdots preferentially co-localized with lipid rafts in the membrane of intact trout gill epithelial cells – a model cell type for environmental exposures. Our observations uncovered preferential interactions of amine-terminated Qdots with liquid-ordered domains and their boundaries, possibly due to membrane curvature at phase boundaries creating energetically favorable sites for NP interactions. The preferential interaction of the Qdots with lipid rafts supports their potential internalization via lipid raft-mediated endocytosis and interactions with raft-resident signaling molecules. 

The composition, orientation, and conformation of proteins in biomolecular coronas acquired by nanoparticles in biological media contribute to how they are identified by a cell. While numerous studies have investigated protein composition in biomolecular coronas, relatively little detail is known about how the nanoparticle surface influences the orientation and conformation of the proteins associated with them. We previously showed that the peripheral membrane protein cytochrome c adopts preferred poses relative to negatively charged MPA-AuNPs. Here, we employ molecular dynamics simulations and complementary experiments to establish that cytochrome c also assumes preferred poses upon association with nanoparticles functionalized with an uncharged ligand, and specifically ω-(1-mercaptounde-11-cyl)hexa(ethylene glycol) (EG6). We find that the display of the EG6 ligands is sensitive to the curvature of the surface—and consequently, the effective diameter of the nearly spherical nanoparticle core—which in turn affects the preferred poses of cytochrome c.