Abstract
This article addresses the lateral organization of two-component lipid membranes deposited on a solid support with the addition of colloidal particles. The authors have applied synchrotron-based scanning transmission soft x-ray spectromicroscopy to image thin lipid layer patches with bound microspheres coated by a charged monolayer. The ability and current limits of scanning transmission x-ray spectromicroscopy to examine samples under physiologically relevant conditions in the presence of excess water have been tested. In particular, the authors have investigated a range of model lipids and have shown that these can be reproducibly identified from the near-edge x-ray absorption fine structure spectra at the carbon K absorption edge. Reference spectra were obtained based on a compact laser-driven plasma source, while the spectromicroscopy data were collected using synchrotron radiation at a lateral resolution of about 60 nm. The authors show that thin lipid layer sensitivity can indeed be reached under physiological conditions and that membrane colloid interaction as well as eventual lateral segregation of lipid components may be probed in the future by this technique.
Highlights
A quantitative understanding of the interactions between nanoparticles and biological interfaces, in particular, the cell membrane, is a prerequisite for the design of drug delivery systems based on synthetic nanoscale carrier systems, as well as for imaging agents such as fluorescent quantum dot markers
We have successfully used scanning transmission x-ray spectromicroscopy to image positively charged polystyrene latex microspheres binding to a supported twocomponent lipid membrane composed of charged and neutral lipid species
The presence of bilayer patches enabled us to investigate the sensitivity of scanning transmission x-ray spectromicroscopy down to the level of a thin lipid layer
Summary
A quantitative understanding of the interactions between nanoparticles and biological interfaces, in particular, the cell membrane, is a prerequisite for the design of drug delivery systems based on synthetic nanoscale carrier systems, as well as for imaging agents such as fluorescent quantum dot markers. Relevant issues are related to the binding affinity, the range of interaction, possible toxic effects due to membrane disruption or lysis, as well as the lateral reorganization of a multicomponent membrane in response to nanoparticle binding.. The dominant interaction forces between nanoparticles and membranes are electrostatic in nature since charged lipids are common and versatile constituents of biological membranes. Charges in such lipids differ in magnitude and location within the interface and can locally demix in response to charged nanoparticles.. If binding of nanoparticles to a multicomponent membrane results in a redistribution of charged and uncharged lipids, this altered membrane state will in return affect the bilayer-nanoparticle interaction, so that strong nonlinear effects can be expected. From a fundamental point of view, the interaction between two classical model systems, the lipid bilayer on one side
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