(723f) Nanoparticle Interactions with Lipid Bilayer Studied with Ghost Tweezers Method

Using dissipative particle dynamics (DPD) simulations, we explore the interactions of nanoparticles with freestanding lipid bilayers. In order to study nanoparticle-bilayer interactions, we introduce a novel “ghost tweezers” technique that emulates a lab experiment performed with optical tweezers. Ghost tweezers represent a virtual harmonic potential applied between the  nanoparticle and a chosen system point. The nanoparticle is tethered by the ghost tweezers to a given point by a spring and experiences thermal fluctuations around this point. The average spring force is used to measure the effective force of nanoparticle-bilayer interaction as a function of the particle coordinate. The free energy landscape of the nanoparticle near the bilayer is evaluated as the mechanical work needed to bring the particle from the bulk solution to a particular distance from the substrate surface.

 Hydrophobic particles adsorb lipids in a a form of a self-assembled monolayer with the tail facing the hydrophobic particle and heads facing the surrounding water. As the nanoparticle approaches the bilayer, it caused deformation of the latter, associated with a free energy penalty. The deformation is followed by a spontaneous fusion of the freestanding bilayer and the adsorbed monolayer and particle incorporation inside the bilayer hydrophobic segement. Particle escape from the bilayer membrane is also associated with bilayer deformation and a free energy penalty. Using the ghost tweezers method, we explore the free energy landscape of the nanoparticle in the bilayer vicinity and evaluate the free energy barriers associated with particle adhesion and penetration. We vary nanoparticle diameter, degree of hydrophobicity and the surface tension of the bilayer membrane.