The infection course of Mycobacterium tuberculosis is highly dynamic and comprises sequential stages that require damaging and crossing of several membranes to enable the translocation of the ...bacteria into the cytosol or their escape from the host. Many important breakthroughs such as the restriction of mycobacteria by the autophagy pathway and the recruitment of sophisticated host repair machineries to the Mycobacterium‐containing vacuole have been gained in the Dictyostelium discoideum/M. marinum system. Despite the availability of well‐established light and advanced electron microscopy techniques in this system, a correlative approach integrating both methods with near‐native ultrastructural preservation is currently lacking. This is most likely due to the low ability of D. discoideum to adhere to surfaces, which results in cell loss even after fixation. To address this problem, we improved the adhesion of cells and developed a straightforward and convenient workflow for 3D‐correlative light and electron microscopy. This approach includes high‐pressure freezing, which is an excellent technique for preserving membranes. Thus, our method allows to monitor the ultrastructural aspects of vacuole escape which is of central importance for the survival and dissemination of bacterial pathogens.
A sophisticated setup for achieving high‐resolution light microscopy of cells on sapphire discs was established.
An innovative workflow for correlative light and electron microscopy of infected Dictyostelium discoideum integrating high‐pressure freezing and TEM tomography was developed.
With this methodology, ruptured and intact mycobacteria‐containing vacuoles can be visualised in remarkable detail.
The ternary Co/SiOx/N-C catalyst is synthesized by a facile method and characterized by the 3D tomography technique, which is considered as oxygen electrocatalysts for rechargeable Zn-air batteries.
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•The utilization of biomass through simple and low-cost procedures is provided.•Well-dispersed cobalt nanoparticles are synthesized on the SiOx/N-C framework.•The structure has been characterized through 3D TEM tomography.•The framework enhances the catalytic activity and stability of the Co systems.•The Zn-air battery with a CR900 air catalyst shows cycling durability for 400 h.
Well-dispersed cobalt nanoparticles (NPs) are synthesized on a silicon oxide/nitrogen-doped carbon framework derived from sustainable bamboo leaves through in situ pyrolysis of cobalt silicate/nitrogen-doped carbon. The three-dimensional (3D) transmission electron microscopy (TEM) tomography technique reveals the detailed distribution of Co NPs on the framework. The framework ensures a fine distribution, provides an interconnected conductive network, and improves the catalytic activity and stability of the ternary Co catalysts. Consequently, the optimized CR900 electrocatalyst exhibits superior electrochemical activity, including a low overpotential of 263 mV at 10 mA cm−2 and a half-wave potential of 0.81 V for OER and ORR, respectively. Furthermore, the Zn-air battery with the CR900 catalyst displays a maximum power density of 138.2 mW cm−2 and prominent cycling durability after 400 h. Furthermore, we provide insights into the scalable synthetic strategy of metal or alloy-based catalysts towards high-performance rechargeable metal-air batteries.
Production of biocompatible and stable porous materials, e.g., boron nitride, exhibiting tunable and enhanced porosity is a prerequisite if they are to be employed to address challenges such as drug ...delivery, molecular separations, or catalysis. However, there is currently very limited understanding of the formation mechanisms of porous boron nitride and the parameters controlling its porosity, which ultimately prevents exploiting the material’s full potential. Herein, we produce boron nitride with high and tunable surface area and micro/mesoporosity via a facile template-free method using multiple readily available N-containing precursors with different thermal decomposition patterns. The gases are gradually released, creating hierarchical pores, high surface areas (>1900 m2/g), and micropore volumes. We use 3D tomography techniques to reconstruct the pore structure, allowing direct visualization of the mesopore network. Additional imaging and analytical tools are employed to characterize the materials from the micro- down to the nanoscale. The CO2 uptake of the materials rivals or surpasses those of commercial benchmarks or other boron nitride materials reported to date (up to 4 times higher), even after pelletizing. Overall, the approach provides a scalable route to porous boron nitride production as well as fundamental insights into the material’s formation, which can be used to design a variety of boron nitride structures.
A versatile method is presented to form dendrimer superstructures by exploiting coacervate-core micelles as a template to confine and organize the hyperbranched macromolecules. First, complex ...coacervate-core micelles are formed from negative–neutral block copolymers and positively charged polyamidoamine dendrimers. The dendrimers inside the micellar core are then covalently cross-linked with each other upon addition of glutaraldehyde. After removal of the block copolymer from the assembly by increasing the salt concentration, consecutively, the formed Schiff bases cross-linking the dendrimers are reduced to amines, followed by a final dialysis step. This leads to well-defined covalently cross-linked nanostructures, coined dendroids, with a size of around 30 nm in diameter and a molecular weight of approximately 2.5 MDa. By incorporating dendrimer-encapsulated gold nanoparticles (AuDENs) into the micelle template strategy, the aggregation number of dendrimers inside the dendroids is determined by counting the nanoparticles in TEM micrographs. Furthermore, TEM performed at different tilt angles and AFM analysis corroborate formation of stable, covalently linked three-dimensional structures. Reconstruction of the TEM tilt series results in a tomogram further illustrating the 3D distribution of the gold nanoparticles, and hence the individual dendrimers, in the nanostructure. These dendroids appear to have a hard, poorly compressible core and a relatively soft outside. The versatility of the hierarchical building up of the supermolecules is illustrated by the controlled and synchronous incorporation of empty dendrimers and AuDENs into a single hybrid dendroid structure. The presented strategy allows for the preparation of a variety of classes of supermolecules, depending on the type of micellar-core macromolecule, e.g., dendrimer, cross-linker, and nanoparticles, used. Considering the broad interest in dendrimers as well as micelles in a plethora of research areas, e.g., (targeted) drug delivery, biomedical imaging, theragnostics, and catalysis, there is a great potential for dendroids and related classes of covalently linked macromolecules, viz., supermolecules.
Viburnum tinus is an evergreen shrub that is native to the Mediterranean region but cultivated widely in Europe and around the world. It produces ripe metallic blue fruits throughout winter 1. ...Despite its limited fleshy pulp 2, its high lipid content 3 makes it a valuable resource to the small birds 4 that act as its seed-dispersers 5. Here, we find that the metallic blue appearance of the fruits is produced by globular lipid inclusions arranged in a disordered multilayer structure. This structure is embedded in the cell walls of the epicarp and underlaid with a dark layer of anthocyanin pigments. The presence of such large, organized lipid aggregates in plant cell walls represents a new mechanism for structural coloration and may serve as an honest signal of nutritional content.
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•V. tinus fruits produce blue color by interference of light with a nanostructure•The reflective periodic structure is a globule array embedded within the cell wall•The fruits are fatty and the embedded contrast phase in the cell wall is lipid•The constituents of this bright, chromatic signal indicate it is an honest signal
Middleton et al. report that the metallic blue appearance of Viburnum tinus fruits relies on a layered nanostructure of lipid globules in the epidermal cell wall. As this lipid-based structural coloration correlates with a high fat content, it is proposed that this represents an honest signal of nutritional value.
Characterization of the three-dimensional (3D) structure in directed self-assembly (DSA) of block copolymers is crucial for understanding the complex relationships between the guiding template and ...the resulting polymer structure so DSA could be successfully implemented for advanced lithography applications. Here, we combined scanning transmission electron microscopy (STEM) tomography and coarse-grain simulations to probe the 3D structure of P2VP-b-PS-b-P2VP assembled on prepatterned templates using solvent vapor annealing. The templates consisted of nonpreferential background and raised guiding stripes that had PS-preferential top surfaces and P2VP-preferential sidewalls. The full 3D characterization allowed us to quantify the shape of the polymer domains and the interface between domains as a function of depth in the film and template geometry and offered important insights that were not accessible with 2D metrology. Sidewall guiding was advantageous in promoting the alignment and lowering the roughness of the P2VP domains over the sidewalls, but incommensurate confinement from the increased topography could cause roughness and intermittent dislocations in domains over the background region at the bottom of the film. The 3D characterization of bridge structures between domains over the background and breaks within domains on guiding lines sheds light on possible origins of common DSA defects. The positional fluctuations of the PS/P2VP interface between domains showed a depth-dependent behavior, with high levels of fluctuations near both the free surface of the film and the substrate and lower fluctuation levels in the middle of the film. This research demonstrates how 3D characterization offers a better understanding of DSA processes, leading to better design and fabrication of directing templates.
•Three dimensional observations on GEMS grains in CP-IDPs by TEM-tomography.•High textual similarity with products of condensation experiments (core-shell particles and Mg/Si binary ...distributions).•We concluded GEMS grains are condensates.
GEMS (Glass with Embedded Metal and Sulfides) grains found in interplanetary dust particles are considered one of the most primitive materials in the Solar System, yet questions remain on how they formed. It has been suggested that GEMS grains are products of radiation processing and amorphization of sulfide and silicate mineral grains in the interstellar medium. Alternatively, GEMS grains are proposed to be disequilibrium condensation products in late-stage protosolar disks. We examined the 3D distributions of elements and inclusions within GEMS grains using TEM (transmission electron microscopic)-tomography to better constrain their possible formation processes. We found some core–shell particles composed of metals and amorphous silicates and observed a binary distribution of Mg/Si in amorphous silicates of GEMS grains. These properties are highly similar to the features of experimental condensation products. Furthermore, the location of sulfides only on the surface of GEMS and their larger sizes than metals are also consistent with the condensation experiments, where sulfides formed by sulfidation of metal grains with S-bearing gas species. Textures showing aggregation and possible coalescence of primary grains were also observed. Therefore, we conclude that GEMS grains are condensates from gas at high temperatures and some of them were aggregated.
Within a cell, vesicles play a crucial role in the transport of membrane material and proteins to a given target membrane, and thus regulate a variety of cellular functions. Vesicular transport ...occurs by means of, among others, endocytosis, where cargoes are taken up by the cell and are processed further upon vesicular trafficking, i.e. transported back to the plasma membrane via recycling endosomes or the degraded by fusion of the vesicles with lysosomes. During evolution, a variety of vesicles with individual functions arose, with some of them building up highly specialised subcellular compartments. In this study, we have analysed the biosynthesis of a new vesicular compartment present in the valve cells of Drosophila melanogaster. We show that the compartment is formed by invaginations of the plasma membrane and grows via re-routing of the recycling endosomal pathway. This is achieved by inactivation of other membrane-consuming pathways and a plasma membrane-like molecular signature of the compartment in these highly specialised heart cells.
Directed self-assembly (DSA) of block copolymers (BCPs) can achieve perfectly aligned structures at thermodynamic equilibrium, but the self-assembling morphology can become kinetically trapped in ...defective states. Understanding and optimizing the kinetic pathway toward domain alignment is crucial for enhancing process throughput and lowering defectivity to levels required for semiconductor manufacturing, but there is a dearth of experimental, three-dimensional studies of the kinetic pathways in DSA. Here, we combined arrested annealing and TEM tomography to probe the kinetics and structural evolution in the chemoepitaxy DSA of PS-b-PMMA with density multiplication. During the initial stages of annealing, BCP domains developed independently at first, with aligned structures at the template interface and randomly oriented domains at the top surface. As the grains coarsened, the assembly became cooperative throughout the film thickness, and a metastable stitch morphology was formed, representing a kinetic barrier. The stitch morphology had a three-dimensional structure consisting of both perpendicular and parallel lamellae. On the basis of the mechanistic information, we studied the effect of key design parameters on the kinetics and evolution of structures in DSA. Three types of structural evolutions were observed at different film thicknesses: (1) immediate alignment and fast assembly when thickness < L 0 (L 0 = BCP natural periodicity); (2) formation of stitch morphology for 1.25–1.45L 0; (3) fingerprint formation when thickness >1.64L 0. We found that the DSA kinetics can be significantly improved by avoiding the formation of the metastable stitch morphology. Increasing template topography also enhanced the kinetics by increasing the PMMA guiding surface area. A combination of 0.75L 0 BCP thickness and 0.50L 0 template topography achieved perfect alignment over 100 times faster than the baseline process. This research demonstrates that an improved understanding of the evolution of structures during DSA can significantly improve the DSA process.
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