Softening of phospholipid membranes by the adhesion of silica nanoparticles--as seen by neutron spin-echo (NSE).

Ingo Hoffmann,Michael Gradzielski,Raphael Michel,Melissa Sharp,Bela Farago,Marie-Sousai Appavou,Olaf Holderer,Frank Polzer

doi:10.1039/c4nr00774c

Abstract

The interactions between nanoparticles and vesicles are of significant interest both from a fundamental as well as from a practical point of view, as vesicles can serve as a model system for cell membranes. Accordingly the effect of nanoparticles that bind to the vesicle bilayer is very important with respect to understanding their biological impact and also may shed some light on the mechanisms behind the effect of nanotoxicity. In this study we have investigated the influence of small adsorbed silica nanoparticles (SiNPs) on the structure of zwitterionic DOPC vesicles. By a combination of SANS, cryo-TEM, and DLS, we observed that the SiNPs are bound to the outer vesicle surface without significantly affecting the vesicle structure. Most interestingly, by means of neutron spin-echo (NSE) local bilayer fluctuations were studied and one finds a small but marked decrease of the membrane rigidity upon binding of the nanoparticles. This surprising finding may be a relevant aspect for the further understanding of the effects that nanoparticles have on phospholipid bilayers.

Highlights

Liposomes are vesicles formed from phospholipids, which constitute the major part of any biological membrane.[1]
3.1 Structure and stability In order to be able to study the in uence of NP adsorption on the liposomes, a system had to be identi ed where (i) the NPs show adsorption, (ii) the structure does not change over the timescale of the neutron spin-echo (NSE) experiment and to facilitate the analysis (iii) the structure of the liposomes is not changed signi cantly by the adsorption
Even though cryo-TEM does not provide 3-dimensional information, it can be inferred from the NPs located at the edge of the vesicles, that the NPs are located on the membrane rather than inside the vesicle

Summary

Introduction

Liposomes are vesicles formed from phospholipids, which constitute the major part of any biological membrane.[1]. Growing attention has been devoted to the study of the interactions in mixed systems of liposomes and inorganic. In order to understand such rather complex systems as nanoparticles interacting with biomembranes, it is rst necessary to study simple model systems. As such a simple case we considered phospholipid vesicles to which silica

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Conclusion