Structural Characterization of Nanoparticle-Supported Lipid Bilayer Arrays by Grazing Incidence X-ray and Neutron Scattering

Engineering curvature: block copolymer lithography for the fabrication of curved lipid membranes and their impact on protein-membrane interactions

Studying biological membranes is essential for understanding key cellular processes such as signal transduction and ion transport, which have significant implications for developing advanced therapies for diseases like cancer and cardiovascular disorders. However, the structural complexity of these membranes presents challenges for detailed analysis, necessitating advanced techniques that are often incompatible with in-cell studies. As a result, current research has shifted toward fabricating artificial membranes that closely mimic their natural counterparts. A critical limitation remains in replicating the natural curvature of biological membranes that restricts the effectiveness of existing flat in vitro models. In response, this study introduces block copolymer (BCP) lithography as a method for creating nanostructured surfaces that induce controllable local membrane curvature. Lipid bilayer formation was confirmed using atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D). Subsequent investigations into clathrin assembly lymphoid myeloid-leukemia (CALM) protein interactions with curved membranes revealed a preferential binding to curved surfaces, characterized by a more homogeneous protein distribution compared to flat membranes. These findings enhance our understanding of membrane-protein interactions and cellular processes, opening up potential applications in drug delivery and biosensing.

Tuning the Morphology of Spray-Coated Biohybrid Beta-lactoglobulin:TiBALDh Films with pH for Water-Based and Nanostructured Titania

The whey protein beta-lactoglobulin (β-lg) is used as a biotemplate for the water-based synthesis of nanostructured and foam-like titania films based on its variation in supramolecular structure when denatured at different pH values. Acting as a matrix, β-lg is mixed with the water-soluble titania precursor Ti(IV) bis(ammonium lactate)dihydroxide (TiBALDh) to promote biotemplated titania precipitation. Since TiBALDh is in chemical equilibrium with anatase titania nanoparticles and Ti(IV)-lactate complexes, and this equilibrium shifts with varying pH, the influence of the pH value on the final film morphology becomes essential. This work investigates this influence for three pH values: pH 7, pH 5, i.e., close to the isoelectric point of β-lg, and pH 2. Spray coating, a method of industrial relevance, is used to fabricate biohybrid β-lg:TiBALDh foam-like films. The obtained films are calcined to combust biotemplate β-lg and achieve nanostructured titania films. To understand the influence of pH on the film morphology, grazing-incidence small-angle and wide-angle X-ray scattering (GISAXS/GIWAXS) and grazing-incidence small-angle neutron scattering (GISANS), in combination with scanning electron microscopy (SEM), are applied to both the biohybrid and biotemplated titania films. With these techniques, information about domain sizes, porosity, and crystal structure is obtained with high statistical significance. Fourier-transform infrared spectroscopy (FTIR) probes the interaction of TiBALDh and β-lg on the molecular level as a function of pH. The results underline pH as a suitable tool for tuning the morphology in biotemplated titania films.

Comparative Kinetics of Supported Lipid Bilayer Formation on Silica Coated Vertically Oriented Highly Curved Nanowires and Planar Silica Surfaces

Supported lipid bilayers (SLBs), formed via lipid vesicle adsorption on highly curved silica surfaces, are widely used in biosensor applications and as models for curved cell membranes. However, SLB formation is often hindered on convex structures with radii comparable to the vesicles. In this study, lightguiding semiconductor nanowires (NWs), engineered for fluorescence signal enhancement, were used to compare the kinetics of SLB formation on vertically oriented NWs and planar silica surfaces. Time resolved fluorescence microscopy with single-molecule sensitivity revealed that while vesicle adsorption rates were similar on both surfaces lateral expansion of the SLB was up to three times faster on NWs than on the planar control. This accelerated expansion is attributed to lower energy penalties when SLBs spread along the cylindrical NWs compared with a planar surface, accompanied by accelerated SLB expansion driven by the merging of the SLB with excess lipids from vesicles accumulated on the NWs.

Unravelling the interactions between small molecules and liposomal bilayers via molecular dynamics and thermodynamic modelling

Lipid-based drug delivery systems hold immense promise in addressing critical medical needs, from cancer and neurodegenerative diseases to infectious diseases. By encapsulating active pharmaceutical ingredients - ranging from small molecule drugs to proteins and nucleic acids - these nanocarriers enhance treatment efficacy and safety. However, their commercial success faces hurdles, such as the lack of a systematic design approach and the issues related to scalability and reproducibility. This work aims to provide insights into the drug-phospholipid interaction by combining molecular dynamic simulations and thermodynamic modelling techniques. In particular, we have made a connection between the structural properties of the drug-phospholipid system and the physicochemical performance of the drug-loaded liposomal nanoformulations. We have considered two prototypical drugs, felodipine (FEL) and naproxen (NPX), and one model hydrogenated soy phosphatidylcholine (HSPC) bilayer membrane. Molecular dynamic simulations revealed which regions within the phospholipid bilayers are most and least favoured by the drug molecules. NPX tends to reside at the water-phospholipid interface and is characterized by a lower free energy barrier for bilayer membrane permeation. Meanwhile, FEL prefers to sit within the hydrophobic tails of the phospholipids and is characterized by a higher free energy barrier for membrane permeation. Flory-Huggins thermodynamic modelling, small angle X-ray scattering, dynamic light scattering, TEM, and drug release studies of these liposomal nanoformulations confirmed this drug-phospholipid structural difference. The naproxen-phospholipid system has a lower free energy barrier for permeation, higher drug miscibility with the bilayer, larger liposomal nanoparticle size, and faster drug release in the aqueous medium than felodipine. We suggest that this combination of molecular dynamics and thermodynamics approach may offer a new tool for designing and developing lipid-based nanocarriers for unmet medical applications.

Oversaturating Liquid Interfaces with Nanoparticle-Surfactants

Assemblies of nanoparticles at liquid interfaces hold promise as dynamic "active" systems when there are convenient methods to drive the system out of equilibrium via crowding. To this end, we show that oversaturated assemblies of charged nanoparticles can be realized and held in that state with an external electric field. Upon removal of the field, strong interparticle repulsive forces cause a high in-plane electrostatic pressure that is released in an explosive emulsification. We quantify the packing of the assembly as it is driven into the oversaturated state under an applied electric field. Physiochemical conditions substantially affect the intensity of the induced explosive emulsification, underscoring the crucial role of interparticle electrostatic repulsion.

Neutron reflectometry as a powerful tool to elucidate membrane interactions of drug delivery systems

The last couple of decades have seen an explosion of novel colloidal drug delivery systems, which have been demonstrated to increase drug efficacy, reduce side-effects, and provide various other advantages for both small-molecule and biomacromolecular drugs. The interactions of delivery systems with biomembranes are increasingly recognized to play a key role for efficient eradication of pathogens and cancer cells, as well as for intracellular delivery of protein and nucleic acid drugs. In parallel, there has been a broadening of methodologies for investigating such systems. For example, advanced microscopy, mass-spectroscopic "omic"-techniques, as well as small-angle X-ray and neutron scattering techniques, which only a few years ago were largely restricted to rather specialized areas within basic research, are currently seeing increased interest from researchers within wide application fields. In the present discussion, focus is placed on the use of neutron reflectometry to investigate membrane interactions of colloidal drug delivery systems. Although the technique is still less extensively employed for investigations of drug delivery systems than, e.g., X-ray scattering, such studies may provide key mechanistic information regarding membrane binding, re-modelling, translocation, and permeation, of key importance for efficacy and toxicity of antimicrobial, cancer, and other therapeutics. In the following, examples of this are discussed and gaps/opportunities in the research field identified.

Decoding the Self-Assembly Plasmonic Interface Structure in a PbS Colloidal Quantum Dot Solid for a Photodetector

Hybrid plasmonic nanostructures have gained enormous attention in a variety of optoelectronic devices due to their surface plasmon resonance properties. Self-assembled hybrid metal/quantum dot (QD) architectures offer a means of coupling the properties of plasmonics and QDs to photodetectors, thereby modifying their functionality. The arrangement and localization of hybrid nanostructures have an impact on exciton trapping and light harvesting. Here, we present a hybrid structure consisting of self-assembled gold nanospheres (Au NSs) embedded in a solid matrix of PbS QDs for mapping the interface structures and the motion of charge carriers. Grazing-incidence small-angle X-ray scattering is utilized to analyze the localization and spacing of the Au NSs within the hybrid structure. Furthermore, by correlating the morphology of the Au NSs in the hybrid structure with the corresponding differences observed in the performance of photodetectors, we are able to determine the impact of interface charge carrier dynamics in the coupling structure. From the perspective of architecture, our study provides insights into the performance improvement of optoelectronic devices.

Plasmonic Scattering Imaging of Surface-Bonded Nanoparticles at the Solution-Solid Interface

Imaging nanoscale objects at interfaces is essential for revealing surface-tuned mechanisms in chemistry, physics, and life science. Plasmonic-based imaging, a label-free and surface-sensitive technique, has been widely used for studying the chemical and biological behavior of nanoscale objects at interfaces. However, direct imaging of surface-bonded nanoscale objects remains challenging due to uneven image backgrounds. Here, we present a new surface-bonded nanoscale object detection microscopy that eliminates strong background interference by reconstructing accurate scattering patterns at different positions. Our method effectively functions at low signal-to-background ratios, allowing for optical scattering detection of surface-bonded polystyrene nanoparticles and severe acute respiratory syndrome coronavirus 2 pseudovirus. It is also compatible with other imaging configurations, such as bright-field imaging. This technique complements existing methods for dynamic scattering imaging and broadens the applications of plasmonic imaging techniques for high-throughput sensing of surface-bonded nanoscale objects, enhancing our understanding of the properties, composition, and morphology of nanoparticles and surfaces at the nanoscale.

Fully Aqueous Self-Assembly of a Gold-Nanoparticle-Based Pathogen Sensor

Surface plasmon resonance (SPR) is a very sensitive measure of biomolecular interactions but is generally too expensive for routine analysis of clinical samples. Here we demonstrate the simplified formation of virus-detecting gold nanoparticle (AuNP) assemblies on glass using only aqueous buffers at room temperature. The AuNP assembled on silanized glass and displayed a distinctive absorbance peak due to the localized SPR (LSPR) response of the AuNPs. Next, assembly of a protein engineering scaffold was followed using LSPR and a sensitive neutron reflectometry approach, which measured the formation and structure of the biological layer on the spherical AuNP. Finally, the assembly and function of an artificial flu sensor layer consisting of an in vitro-selected single-chain antibody (scFv)-membrane protein fusion was followed using the LSPR response of AuNPs within glass capillaries. In vitro selection avoids the need for separate animal-derived antibodies and allows for the rapid production of low-cost sensor proteins. This work demonstrates a simple approach to forming oriented arrays of protein sensors on nanostructured surfaces that uses (i) an easily assembled AuNP silane layer, (ii) self-assembly of an oriented protein layer on AuNPs, and (iii) simple highly specific artificial receptor proteins.