Advancing High-Resolution Imaging of Virus Assemblies in Liquid and Ice

Interest in liquid-electron microscopy (liquid-EM) has skyrocketed in recent years as scientists can now observe real-time processes at the nanoscale. It ...

Pennsylvania State University

Tetrapod-shaped ZnO nanocrystals exhibit exceptional optoelectronic properties, including intense ultraviolet photoluminescence emission, that make them attractive for applications that include lasers, sensors, and photocatalysts. However, synthetic methods that produce ZnO tetrapods typically include high-temperature vapor-deposition approaches that do not readily achieve characteristic dimensions of less than 100 nm or colloidal methods that require added metal dopants, which modify the inherent properties of ZnO. Here, we report a robust, modified solution-phase synthetic protocol for generating colloidal ZnO tetrapods that does not require the use of metal dopants. The ZnO tetrapod arm lengths can be tuned from 10 to 25 nm by adjusting the amount of Zn reagent used in the reaction. Subsequent seeded-growth produced even larger colloidal ZnO tetrapods with 62 nm arms. Photoluminescence (PL) measurements confirm that the tetrapods are of high crystalline quality, and the ultraviolet PL emission wavelengths that are observed fall between those of previously reported metal-doped colloidal ZnO tetrapods, which exhibit dopant-induced red- or blue-shifts. Furthermore, the reaction strategy can be modified to produce cobalt-substituted ZnO, offering a chemical pathway to tetrapod-shaped Zn1-xCoxO nanocrystals. 

Colloidal ZnO and Zn(1-x)Co(x)O tetrapod nanocrystals with tunable arm lengths.

The high-pressure reactivity of caged olefinic carbons and polyatomic aromatic hydrocarbons (PAHs) are of interest because of their ability to produce unique C-H networks with varying geometries and bonding environments. Here, we have selected triptycene to explore the creation of pores via high-pressure polymerization. Triptycene has internal free volume on a molecular scale that arises due to its paddle wheel-like structure, formed via fusion of three benzene rings via sp-hybridized bridgehead carbon sites. At 25 GPa and 298 K, triptycene polymerizes to yield an amorphous hydrogenated carbon, with FTIR indicating an sp C-H content of approximately 40%. Vibrational spectroscopy conclusively demonstrates that triptycene polymerizes via cycloaddition reactions at the aromatic sites via a ring opening mechanism. The bridgehead carbons remain intact after polymerization, indicating the rigid backbone of the triptycene precursor is retained in the polymer, as well as molecular-level (∼1-3 Å) internal free volume. High resolution transmission electron microscopy, combined with dark field imaging, indicates the presence of ∼10 nm voids in the polymer, which we attribute to either polymeric clustering or a hierarchical tertiary porous network. Creation of a polymerized network that retains internal voids via high-pressure polymerization is attributed to the presence and retention of the bridgehead carbons.

High-Pressure Reactivity of Triptycene Probed by Raman Spectroscopy.

The solid-electrolyte interphase (SEI) is pivotal in stabilizing lithium metal anodes for rechargeable batteries. However, the SEI is constantly reforming and consuming electrolyte with cycling. The rational design of a stable SEI is plagued by the failure to control its structure and stability. Here we report a molecular-level SEI design using a reactive polymer composite, which effectively suppresses electrolyte consumption in the formation and maintenance of the SEI. The SEI layer consists of a polymeric lithium salt, lithium fluoride nanoparticles and graphene oxide sheets, as evidenced by cryo-transmission electron microscopy, atomic force microscopy and surface-sensitive spectroscopies. This structure is different from that of a conventional electrolyte-derived SEI and has excellent passivation properties, homogeneity and mechanical strength. The use of the polymer-inorganic SEI enables high-efficiency Li deposition and stable cycling of 4 V Li|LiNiCoMnO cells under lean electrolyte, limited Li excess and high capacity conditions. The same approach was also applied to design stable SEI layers for sodium and zinc anodes.

Polymer-inorganic solid-electrolyte interphase for stable lithium metal batteries under lean electrolyte conditions.

Liquid-phase electron microscopy (LP-EM) is an exciting new area in the materials imaging field, providing unprecedented views of molecular processes. Time-resolved insights from LP-EM studies are a strong complement to the remarkable results achievable with other high-resolution techniques. Here, the opportunities to expand LP-EM technology beyond 2D temporal assessments and into the 3D regime are described. The results show new structures and dynamic insights of human viruses contained in minute volumes of liquid while acquired in a rapid timeframe. To develop this strategy, adeno-associated virus (AAV) is used as a model system. AAV is a well-known gene therapy vehicle with current applications involving drug delivery and vaccine development for COVID-19. Improving the understanding of the physical properties of biological entities in a liquid state, as maintained in the human body, has broad societal implications for human health and disease.

High-Resolution Imaging of Human Viruses in Liquid Droplets.

Liquid-electron microscopy (EM), the room-temperature correlate to cryo-EM, is a rapidly growing field providing high-resolution insights of macromolecules in solution. Here, we describe how liquid-EM experiments can incorporate automated tools to propel the field to new heights. We demonstrate fresh workflows for specimen preparation, data collection, and computing processes to assess biological structures in liquid. Adeno-associated virus (AAV) and the SARS-CoV-2 nucleocapsid (N) were used as model systems to highlight the technical advances. These complexes were selected based on their major differences in size and natural symmetry. AAV is a highly symmetric, icosahedral assembly with a particle diameter of ~25 nm. At the other end of the spectrum, N protein is an asymmetric monomer or dimer with dimensions of approximately 5–7 nm, depending upon its oligomerization state. Equally important, both AAV and N protein are popular subjects in biomedical research due to their high value in vaccine development and therapeutic efforts against COVID-19. Overall, we demonstrate how automated practices in liquid-EM can be used to decode molecules of interest for human health and disease.

Automated Tools to Advance High-Resolution Imaging in Liquid.

Low-frequency shear and breathing modes are important Raman signatures of two-dimensional (2D) materials, providing information on the number of layers and insights into interlayer interactions. We elucidate the nature of low-frequency modes in a 2D polar metal-2D Ga covalently bonded to a SiC substrate, using a first-principles Green's function-based approach. The low-frequency Raman modes are dominated by surface resonance modes, consisting primarily of out-of-phase shear modes in Ga, coupled to SiC phonons. Breathing modes are strongly coupled to the substrate and do not give rise to peaks in the phonon spectra. The highest-frequency shear mode blue-shifts significantly with increasing thickness, reflecting both an increase in the number of Ga layers and an increase in the effective interlayer force constant. The surface resonance modes evolve into localized 2D Ga modes as the phonon momentum increases. The predicted low-frequency modes are consistent with Raman measurements on 2D polar Ga.

Jennifer L. Gray

Materials Research Institute

Pennsylvania State University

Advancing High-Resolution Imaging of Virus Assemblies in Liquid and Ice

Jennifer L. Gray

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Materials Research Institute

Pennsylvania State University

Advancing High-Resolution Imaging of Virus Assemblies in Liquid and Ice

Materials Research Institute