Convective assembly of 2D lattices of virus-like particles visualized by in-situ grazing-incidence small-angle X-ray scattering

Delayed In Vivo Encapsulation of Enzymes Alters the Catalytic Activity of Virus-Like Particle Nanoreactors

Encapsulation of enzymes inside protein cage structures, mimicking protein-based organelle structures found in nature, has great potential for the development of new catalytic materials with enhanced properties. In vitro and in vivo methodologies have been developed for the encapsulation of enzymes within protein cage structures of several types, particularly virus-like particles (VLPs), with the ability to retain the activity of the encapsulated enzymes. Here, we examine the in vivo encapsulation of enzymes within the bacteriophage P22 derived VLP and show that some enzymes may require a delay in encapsulation to allow proper folding and maturation before they can be encapsulated inside P22 as fully active enzymes. Using a sequential expression strategy, where enzyme cargoes are first expressed, allowed to fold, and later encapsulated by the expression of the P22 coat protein, altered enzymatic activities are obtained in comparison to enzymes encapsulated in P22 VLPs using a simultaneous coexpression strategy. The strategy and results discussed here highlight important considerations for researchers investigating the encapsulation of enzymes inside confined reaction environments via in vivo routes and provide a potential solution for those that have been unable to produce active enzymes upon encapsulation.

Small Angle X-ray Scattering for Nanoparticle Research

X-ray scattering is a structural characterization tool that has impacted diverse fields of study. It is unique in its ability to examine materials in real time and under realistic sample environments, enabling researchers to understand morphology at nanometer and angstrom length scales using complementary small and wide angle X-ray scattering (SAXS, WAXS), respectively. Herein, we focus on the use of SAXS to examine nanoscale particulate systems. We provide a theoretical foundation for X-ray scattering, considering both form factor and structure factor, as well as the use of correlation functions, which may be used to determine a particle's size, size distribution, shape, and organization into hierarchical structures. The theory is expanded upon with contemporary use cases. Both transmission and reflection (grazing incidence) geometries are addressed, as well as the combination of SAXS with other X-ray and non-X-ray characterization tools. We conclude with an examination of several key areas of research where X-ray scattering has played a pivotal role, including in situ nanoparticle synthesis, nanoparticle assembly, and operando studies of catalysts and energy storage materials. Throughout this review we highlight the unique capabilities of X-ray scattering for structural characterization of materials in their native environment.

Crystallization, structural diversity and anisotropy effects in 2D arrays of icosahedral viruses

We investigate two-dimensional (2D) assembly of the icosahedral turnip yellow mosaic virus (TYMV) under cationic lipid monolayers at the aqueous solution–vapor interface. The 2D crystallization of TYMV has been achieved by enhancing electrostatically induced interfacial adsorption, an approach recently demonstrated for another virus. In situ X-ray scattering reveals two close-packed 2D crystalline phases of TYMV that are distinct from the previously reported hexagonal and centered square (√2 × √2) arrays of TYMV. One of the newly observed phases arises from either a dimeric double-square (2 × 1) or tetrameric square (2 × 2) unit cell. The other is a rhombic crystal with a lattice angle of 80°. The two observed crystal phases are substantially less dense (by over 10%) than a 2D lattice of TYMV could be according to its known size and shape, indicating that local anisotropic interparticle interactions play a key role in stabilizing these crystals. TYMV's anisotropy attributes and numerical analysis of 2D arrays of virus-shaped particles are used to derive a model for the rhombic crystal in which the particle orientation is consistent with the electrostatic lipid–TYMV attraction and the interparticle contacts exhibit steric complementarity. The interplay between particle anisotropy and packing is contrasted between the rhombic crystal model and the square (√2 × √2) crystal. This study highlights how the high symmetry and subtle asphericity of icosahedral particles enrich the variety and complexity of ordered 2D structures that can be generated through self-assembly.

From atoms to layers: in situ gold cluster growth kinetics during sputter deposition

The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction of morphological real space parameters, such as cluster size and shape, correlation distance, layer porosity and surface coverage, directly from reciprocal space scattering data. This approach enables a large variety of future investigations of the influence of different process parameters on the thin metal film morphology. Furthermore, our study allows for deducing the wetting behavior of gold cluster films on solid substrates and provides a better understanding of the growth kinetics in general, which is essential for optimization of manufacturing parameters, saving energy and resources.

Revealing the interfacial self-assembly pathway of large-scale, highly-ordered, nanoparticle/polymer monolayer arrays at an air/water interface

The pathway of interfacial self-assembly of large-scale, highly ordered 2D nanoparticle/polymer monolayer or bilayer arrays from a toluene solution at an air/water interface was investigated using grazing-incidence small-angle scattering at a synchrotron source. Interfacial-assembly of the ordered nanoparticle/polymer array was found to occur through two stages: formation of an incipient randomly close-packed interfacial monolayer followed by compression of the monolayer to form a close-packed lattice driven by solvent evaporation from the polymer. Because the nanoparticles are hydrophobic, they localize exclusively to the polymer-air interface during self-assembly, creating a through thickness asymmetric film as confirmed by X-ray reflectivity. The interfacial self-assembly approach can be extended to form binary NP/polymer arrays. It is anticipated that by understanding the interfacial self-assembly pathway, this simple evaporative procedure could be conducted as a continuous process amenable to large area nanoparticle-based manufacturing needed for emerging energy technologies.

The dedicated high-resolution grazing-incidence X-ray scattering beamline 8-ID-E at the Advanced Photon Source

As an increasingly important structural-characterization technique, grazing-incidence X-ray scattering (GIXS) has found wide applications for in situ and real-time studies of nanostructures and nanocomposites at surfaces and interfaces. A dedicated beamline has been designed, constructed and optimized at beamline 8-ID-E at the Advanced Photon Source for high-resolution and coherent GIXS experiments. The effectiveness and applicability of the beamline and the scattering techniques have been demonstrated by a host of experiments including reflectivity, grazing-incidence static and kinetic scattering, and coherent surface X-ray photon correlation spectroscopy. The applicable systems that can be studied at 8-ID-E include liquid surfaces and nanostructured thin films.

Controlled deposition of structured polymer films: chemical and rheological factors in chitosan film formation

The technique of "spread coating" has been used to create thin films from solutions of deacetylated and butyl-modified chitosan polymer, and the effect of deposition rate on film thickness has been characterized. Results show that films of controlled thickness can be reproducibly produced and that hydrophobic modification of the polymer can extend the range over which a linear response between film thickness and deposition rate is achieved. Viscometry and fluorescence spectroscopy were also employed to characterize the micellar characteristics of solutions of both deacetylated and butyl-modified chitosan polymer. Although both deacetylated and butyl-modified chitosan solutions were found to have inter- and intramolecular interactions, as well as hydrophobic domains able to incorporate fluorophores, deacetylated chitosan was found to be more interconnected via intermolecular interactions at higher concentrations. These results are important as having the ability to understand how the introduction of hydrophobic modification, a technique shown to introduce solution-based micelle structure and micellar aggregates that support enzyme immobilization, affects film thickness and morphology of spread coated thin films will aid the long-term development and deployment of chitosan-based biofuel cell electrodes.