Liquid Surface X-ray Studies of Gold Nanoparticle-Phospholipid Films at the Air/Water Interface

TL;DR

This study uses liquid surface X-ray scattering to investigate how gold nanoparticles and phospholipids organize in composite films at the air/water interface, revealing phase separation and network formation relevant to biological membranes.

Contribution

It provides new insights into the structural organization and phase separation of nanoparticle-phospholipid films at the air/water interface, advancing understanding of nanoparticle interactions with biological membranes.

Findings

Phase separation of DPPC and Au-NPs observed

Low Au-NP content results in isolated nanoparticle islands

High Au-NP content forms interconnected nanoparticle networks

Abstract

Amphiphilic phospholipids and nanoparticles functionalized with hydrophobic capping ligands have previously been extensively investigated for their capacity to self-assemble into Langmuir monolayers at the air/water interface. However, understanding of composite films consisting of both nanoparticles and phospholipids, and by extension, the complex interactions arising between nanomaterials and biological membranes, remains limited. In this work, dodecanethiol-capped gold nanoparticles (Au-NPs) with an average core diameter of 6 nm were incorporated into 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers in area ratios ranging from 0.1 to 20% area coverage at a surface pressure of 30 mN/m. High resolution liquid surface X-ray scattering studies revealed a phase separation of the DPPC and Au-NP components of the composite film, as confirmed with atomic force microscopy after the film was transferred to a substrate. At low Au-NP content, the structural organization of the phase-separated film is best described as a DPPC film containing isolated islands of Au-NPs. However, increasing the Au-NP content beyond 5% area coverage transforms the structural organization of the composite film to a long-range interconnected network of Au-NP strands surrounding small seas of DPPC, where the density of the Au-NP network increases with increasing Au-NP content. The observed phase separation and structural organization of the phospholipid and nanoparticle components in these Langmuir monolayers are useful for understanding interactions of nanoparticles with biological membranes.