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.
Dispersion of tubules made of diacetylenic phospholipids (DC 8,9 PC), in aqueous colloidal dispersions of magnetic nanoparticles is studied as a function of the sign of particles surface charges. In every case the tubule-vesicle transition temperature is decreased by the presence of the magnetic nanoparticles. Electrophoresis experiments on the tubules in pure water permits to conclude on a negative apparent surface charge. We study the magnetic response of the system to a static or stationary rotating field and to a magnetic field gradient. These experiments reveal an excess or a lack of magn…
The ordering of a multilayer consisting of DSPC bilayers on a silica sol substrate is studied within the model-independent approach to the reconstruction of profiles of the electron density from X-ray reflectometry data. It is found that the electroporation of bilayers in the field of anion silica nanoparticles significantly accelerates the process of their saturation with Na+ and H2O, which explains both a relatively small time of formation of the structure of the multilayer of 10^5 - 7x10^5 s and ~13 % excess of the electron density in it.
We consider patchy gold nanoparticles decorated by liquid crystalline ligands. The cases of two, three, four and six symmetrically arranged patches of ligands are discussed, as well as the cases of their equatorial and uniform arrangement. A solution of decorated nanoparticles is considered within a flat pore with the solid walls and the interior filled by a polar solvent. The ligands form physical crosslinks between the nanoparticles due to strong liquid crystalline interaction, turning the solution into a gel-like structure. Gelation is done repeatedly starting each time from freshly equilib…
Nanocrystals, used as building blocks, may self-assemble in long-range ordered assemblies socalled supracrystals. Different structures FCC, BCC but also Frank-Kasper phases have been observed and the roles of the soft ligands surrounding the rigid crystalline cores in the self-assembly process is not yet well understood and need further study. The mechanical behavior under hydrostatic pressure of 3D single FCC crystals built by gold nanoparticles has been investigated using HP-SAXS and compared with pure alkane, corresponding to the ligand chain. No structural transition has been observed up t…
Solvation of gold nanoparticles passivated with end group functionalized alkylthiols, namely CH$_3$, NH$_2$ or COOH is studied in solvents of varying degrees of repulsion-dispersion and electrostatic interactions ranging from strongly polar SPC/E water to modified hybrid water models, where the Lennard-Jones contribution to the potential energy is enhanced relative to SPC/E to completely non-polar, decane. The effects due to solvent reorganization around the nanoparticle as a function of the ligand and solvent chemistry are monitored using the nanoparticle-solvent pair correlation functions an…
We compare the light extinction spectra of elongated gold nanoparticles with different shapes (cylinder, spherocylinder and ellipsoid) and sizes of 10 to 100~nm. We argue that the equivalence of the various moments of mass distribution is the natural comparison criterion -rather than the length-to-diameter (aspect) ratio generally used in the literature- and that it leads to better spectral correspondence between the various shapes.
We describe several unexpected phenomena, caused by a solid-solid phase transition (gel-to-crystal) typical for all main classes of lipid substances - phospholipids, triglycerides, diglycerides, alkanes, etc. We discovered that this transition leads to spontaneous formation of a network of nanopores, spreading across the entire lipid structure. These nanopores are spontaneously impregnated (flooded) by water when appropriate surfactants are present, thus fracturing the lipid structure at a nano-scale. As a result, spontaneous disintegration of the lipid into nanoparticles or formation of doubl…
Morphology of gold nanoparticles determined by full-curve fitting of the light absorption spectrum. Comparison with X-ray scattering and electron microscopy data
Surface enhanced Raman scattering (SERS) is optically sensitive and chemically specific to detect single molecule spectroscopic signatures. Facilitating this capability in optically-trapped nanoparticles at low laser power remains a significant challenge. In this letter, we show single molecule SERS signatures in reversible assemblies of trapped plasmonic nanoparticles using a single laser excitation (633 nm). Importantly, this trap is facilitated by the thermoplasmonic field of a single gold nanoparticle dropcasted on a glass surface. We employ bi-analyte SERS technique to ascertain the singl…
We study translational and rotational diffusion of anisotropic gold nanoparticles (NPs) dispersed in the bulk of a nematic liquid crystal fluid host. Experimental data reveal strong anisotropy of translational diffusion with respect to the uniform far-field director, which is dependent on shape and surface functionalization of colloids as well as on their ground-state alignment. For example, elongated NPs aligned parallel to the far-field director translationally diffuse more rapidly along the director whereas diffusion of NPs oriented normal to the director is faster in the direction perpendi…
Gold nanoparticles (AuNPs) are increasingly used for their thermoplasmonic properties, i.e. their ability to convert light into heat upon plasmon resonance. However, measuring temperature gradients generated at the microscale by assemblies of AuNPs remains challenging, especially when they are randomly distributed in three dimensions. Here, we introduce a label-free thermometry approach, combining optical wavefront microscopy and numerical simulations, to infer the heating power dissipated by a three-dimensional model system consisting in emulsion microdroplets loaded with AuNPs. This approach…
We demonstrate that highly-ordered two-dimensional crystals of ligand-capped gold nanoparticles display a local photo-mechanical stiffness as high as that of solids such as graphite. In out-of equilibrium electron diffraction experiments, a strong temperature jump is induced in a thin film with a femtosecond laser pulse. The initial electronic excitation transfers energy to the underlying structural degrees of freedom, with a rate generally proportional to the stiffness of the material. With femtosecond small-angle electron diffraction, we observe the temporal evolution of the diffraction feat…
