Surface-enhanced Raman scattering measurement from a lipid bilayer encapsulating a single decahedral nanoparticle mediated by an optical trap

Structure Analysis of Amyloid Aggregates at Lipid Bilayers by Supercritical Angle Raman Microscopy

The amyloid-β peptide is correlated with Alzheimer's disease and is assumed to cause toxicity by its interaction with the neuron membrane. A custom-made microscope objective based on the supercritical angle technique was developed by our group, which allows investigation of interfacial events by performing surface-sensitive and low-invasive spectroscopy. Applied to Raman spectroscopy, this technique was used to collect information about the structure of polypeptides that interact with a supported lipid bilayer. Notably, the conformation used by amyloid-β(1-40) and amyloid-β(1-42) when interacting directly with or next to the supported lipid bilayer was characterized. We observed two distinct secondary structures, α-helix and β-sheet, which were exhibited by the peptide. These two structures were detected simultaneously. The propensity of the peptide to fold into these structures seemed dependent on both their number of amino acids and their proximity with the supported lipid bilayer. The α-helix structure was observed for amyloid-β(1-42) fragments that were closer to the lipid bilayer. Peptides that were located further away from the bilayer favored the β-sheet structure. Amyloid-β(1-40) was less prone to adopt the α-helix secondary structure.

Nanovesicles Versus Nanoparticle-Supported Lipid Bilayers: Massive Differences in Bilayer Structures and in Diffusivities of Lipid Molecules and Nanoconfined Water

We carry out molecular dynamics (MD) simulations to compare the equilibrium architecture and properties of nanoparticle-supported lipid bilayers (NPSLBLs) with the free vesicles of similar dimensions. Three key differences emerge. First, we witness that for a free vesicle, a much larger number of lipid molecules occupy the outer layer as compared to the inner layer; on the other hand, for the NPSLBL the number of lipid molecules occupying the inner and outer layers is identical. Second, we witness that the diffusivities of the lipid molecules occupying both the inner and the outer layers of the free vesicles are identical, whereas for the NPSLBLs the diffusivity of the lipid molecules in the outer layer is more than twice the diffusivity of the lipid molecules in the inner layer. Finally, the NPSLBLs entrap nanoscopic thin water film between the inner lipid layer and the NP and the diffusivity of this water film is nearly 1 order of magnitude smaller than the diffusivity of the bulk water; on the other hand, the water inside the free vesicles has a diffusivity that is only slightly lower than that of the bulk water. Our findings, possibly the first probing the atomistic details of the NPSLBLs, are anticipated to shed light on the properties of this important nanomaterial with applications in a large number of disciplines ranging from drug and gene delivery to characterizing curvature-sensitive molecules.

Lipid Bilayer-Enabled Synthesis of Waxberry-like Core-Fluidic Satellite Nanoparticles: Toward Ultrasensitive Surface-Enhanced Raman Scattering Tags for Bioimaging

Herein, we presented waxberry-like core-satellite (C-S) nanoparticles (NPs) prepared by an in situ growth of satellite gold NPs on spherical phospholipid bilayer-coated gold cores. The fluidic lipid bilayer cross-linker was reported for the first time, which imparted several novel morphological and optical properties to the C-S NPs. First, it regulated the anisotropic growth of the satellite NPs into vertically oriented nanorods on the core NP surface. Thus, an interesting waxberry-like nanostructure could be obtained, which was different from the conventional raspberry-like C-S structures decorated with spherical satellite NPs. Second, the satellite NPs were "soft-landed" on the lipid bilayer and could move on the core NP surface under certain conditions. The movement induced tunable plasmonic features in the C-S NPs. Furthermore, the fluidic lipid bilayer was capable of not only holding an abundance of reporter molecules but also delivering them to the hotspots at the junctions between the core and satellite NPs, which made the C-S NPs an excellent candidate for preparing ultrasensitive surface-enhanced Raman scattering (SERS) tags. The bioimaging capabilities of the C-S NP-based SERS tags were successfully demonstrated in living cells and mice. The developed SERS tags hold great potential for bioanalysis and medical diagnostics.

Imaging the chemical activity of single nanoparticles with optical microscopy

Chemical activity of single nanoparticles can be imaged and determined by monitoring the optical signal of each individual during chemical reactions with advanced optical microscopes. It allows for clarifying the functional heterogeneity among individuals, and for uncovering the microscopic reaction mechanisms and kinetics that could otherwise be averaged out in ensemble measurements.

Light Scattering By Optically-Trapped Vesicles Affords Unprecedented Temporal Resolution Of Lipid-Raft Dynamics

A spectroscopic technique is presented that is able to identify rapid changes in the bending modulus and fluidity of vesicle lipid bilayers on the micrometer scale, and distinguish between the presence and absence of heterogeneities in lipid-packing order. Individual unilamellar vesicles have been isolated using laser tweezers and, by measuring the intensity modulation of elastic back-scattered light, changes in the biophysical properties of lipid bilayers were revealed. Our approach offers unprecedented temporal resolution and, uniquely, physical transformations of lipid bilayers can be monitored on a length scale of micrometers. As an example, the deformation of a membrane bilayer following the gel-to-fluid phase transition in a pure phospholipid vesicle was observed to take place across an interval of 54 ± 5 ms corresponding to an estimated full-width of only ~1 m°C. Dynamic heterogeneities in packing order were detected in mixed-lipid bilayers. Using a ternary mixture of lipids, the modulated-intensity profile of elastic back-scattered light from an optically-trapped vesicle revealed an abrupt change in the bending modulus of the bilayer which could be associated with the dissolution of ordered microdomains (i.e., lipid rafts). This occurred across an interval of 30 ± 5 ms (equivalent to ~1 m°C).