Size-dependent interaction of hydrophilic/hydrophobic ligand functionalized cationic and anionic nanoparticles with...

We study the nature of nanoparticle (NPs)-membrane interaction as a function of nanoparticle size for different functionalization using molecular dynamics simulation. Zinc sulphide quantum dots of size, 2 nm and 4 nm are used as model NPs, and DLPC and DPPC lipid bilayers are used as model membranes. We use coarse-grained polarizable MARTINI model (MPW) to simulate the NPs and lipid bilayers. Our simulation results show that uncharged bare NPs penetrate the lipid bilayers and embed themselves within the hydrophobic core of the bilayer both in the gel and fluid phases. NPs of size 4 nm are shown to disrupt the bilayer. The bilayer recovers from the damages caused by smaller NPs of size 2 nm. In case of either purely hydrophilic or hybrid (with hydrophilic/hydrophobic ratio of 2:1) ligand-functionalized NPs of smaller size (shell size 2 nm), only cationic NPs bind to the bilayer. However, for larger NPs with a shell size of 4 nm, both anionic and cationic hybrid functionalized NPs bind to the bilayer. The performance of standard Martini (SM) force field for the charged NP/bilayer systems has also been tested and compared with the results obtained using MPW model. Although the overall trend that the cationic NPs interact strongly with the bilayers than their anionic counterparts has been captured correctly using SM, the adsorption behaviour of the functionalized NPs differ significantly in the SM force field. The interaction of anionic NPs with both fluid and gel bilayers has been observed to be least accurately represented in the SM force field.