Single‐Particle Cryo‐EM and 3D Reconstruction of Hybrid Nanoparticles with Electron‐Dense Components

Single‐particle cryo‐electron microscopy (cryo‐EM), accompanied with 3D reconstruction, is a broadly applicable tool for the structural characterization of macromolecules and nanoparticles. Recently, the cryo‐EM field has pushed the limits of this technique to higher resolutions and samples of smaller molecular mass, however, some samples still present hurdles to this technique. Hybrid particles with electron‐dense components, which have been studied using single‐particle cryo‐EM yet with limited success in 3D reconstruction due to the interference caused by electron‐dense elements, constitute one group of such challenging samples. To process such hybrid particles, a masking method is developed in this work to adaptively remove pixels arising from electron‐dense portions in individual projection images while maintaining maximal biomass signals for subsequent 2D alignment, 3D reconstruction, and iterative refinements. As demonstrated by the success in 3D reconstruction of an octahedron DNA/gold hybrid particle, which has been previously published without a 3D reconstruction, the devised strategy that combines adaptive masking and standard single‐particle 3D reconstruction approach has overcome the hurdle of electron‐dense elements interference, and is generally applicable to cryo‐EM structural characterization of most, if not all, hybrid nanomaterials with electron‐dense components.     

Bismuthene Metallurgy: Transformation of Bismuth Particles to Ultrahigh‐Aspect‐Ratio 2D Microsheets

Ultrathin bismuth exhibits promising performance for topological insulators due to its narrow band gap and intrinsic strong spin–orbit coupling, as well as for energy‐related applications because of its electronic and mechanical properties. However, large‐scale production of 2D sheets via liquid‐phase exfoliation as an established large‐scale method is restricted by the strong interaction between bismuth layers. Here, a sonication method is utilized to produce ultrahigh‐aspect‐ratio bismuthene microsheets. The studies on the mechanism excludes the exfoliation of the layered bulk bismuth and formation of the microsheets is attributed to the melting of spherical particles (r = 1.5 µm) at a high temperature—generated under the ultrasonic tip—followed by a recrystallization step producing uniformly‐shaped ultrathin microsheets (A = 0.5–2 µm², t: ≈2 nm). Notably, although the preparation is performed in oxygenated aqueous solution, the sheets are not oxidized, and they are stable under ambient conditions for at least 1 month. The microsheets are used to construct a vapor sensor using electrochemical impedance spectroscopy as detection technique. The device is highly selective, and it shows long‐term stability. Overall, this project exhibits a reproducible method for large‐scale preparation of ultrathin bismuthene microsheets in a benign environment, demonstrating opportunities to realize devices based on bismuthene.     

Cryo‐EM‐On‐a‐Chip: Custom‐Designed Substrates for the 3D Analysis of Macromolecules

The fight against human disease requires a multidisciplinary scientific approach. Applying tools from seemingly unrelated areas, such as materials science and molecular biology, researchers can overcome long‐standing challenges to improve knowledge of molecular pathologies. Here, custom‐designed substrates composed of silicon nitride (SiN) are used to study the 3D attributes of tumor suppressor proteins that function in DNA repair events. New on‐chip preparation strategies enable the isolation of native protein complexes from human cancer cells. Combined techniques of cryo‐electron microscopy (EM) and molecular modeling reveal a new modified form of the p53 tumor suppressor present in aggressive glioblastoma multiforme cancer cells. Taken together, the findings provide a radical new design for cryo‐EM substrates to evaluate the structures of disease‐related macromolecules.     

3D Nanoprinted Plastic Kinoform X‐Ray Optics

High‐performance focusing of X‐rays requires the realization of very challenging 3D geometries with nanoscale features, sub‐millimeter‐scale apertures, and high aspect ratios. A particularly difficult structure is the profile of an ideal zone plate called a kinoform, which is manufactured in nonideal approximated patterns, nonetheless requires complicated multistep fabrication processes. Here, 3D fabrication of high‐performance kinoforms with unprecedented aspect ratios out of low‐loss plastics using femtosecond two‐photon 3D nanoprinting is presented. A thorough characterization of the 3D‐printed kinoforms using direct soft X‐ray imaging and ptychography demonstrates superior performance with an efficiency reaching up to 20%. An extended concept is proposed for on‐chip integration of various X‐ray optics toward high‐fidelity control of X‐ray wavefronts and ultimate efficiencies even for harder X‐rays. Initial results establish new, advanced focusing optics for both synchrotron and laboratory sources for a large variety of X‐ray techniques and applications ranging from materials science to medicine.     

A Cut‐and‐Paste Approach to 3D Graphene‐Oxide‐Based Architectures

Properly cut sheets can be converted into complex 3D structures by three basic operations including folding, bending, and pasting to render new functions. Folding and bending are extensively employed in crumpling, origami, and pop‐up fabrications for 3D structures. Pasting joins different parts of a material together, and can create new geometries that are fundamentally unattainable by folding and bending. However, it has been much less explored, likely due to limited choice of weldable thin film materials and residue‐free glues. Here it is shown that graphene oxide (GO) paper is one such suitable material. Stacked GO sheets can be readily loosened up and even redispersed in water, which upon drying, restack to form solid structures. Therefore, water can be utilized to heal local damage, glue separated pieces, and release internal stress in bent GO papers to fix their shapes. Complex and dynamic 3D GO architectures can thus be fabricated by a cut‐and‐paste approach, which is also applicable to GO‐based hybrid with carbon nanotubes or clay sheets.     

3D‐Printed Scanning‐Probe Microscopes with Integrated Optical Actuation and Read‐Out

Scanning‐probe microscopy (SPM) is the method of choice for high‐resolution imaging of surfaces in science and industry. However, SPM systems are still considered as rather complex and costly scientific instruments, realized by delicate combinations of microscopic cantilevers, nanoscopic tips, and macroscopic read‐out units that require high‐precision alignment prior to use. This study introduces a concept of ultra‐compact SPM engines that combine cantilevers, tips, and a wide variety of actuator and read‐out elements into one single monolithic structure. The devices are fabricated by multiphoton laser lithography as it is a particularly flexible and accurate additive nanofabrication technique. The resulting SPM engines are operated by optical actuation and read‐out without manual alignment of individual components. The viability of the concept is demonstrated in a series of experiments that range from atomic‐force microscopy engines offering atomic step height resolution, their operation in fluids, and to 3D printed scanning near‐field optical microscopy. The presented approach is amenable to wafer‐scale mass fabrication of SPM arrays and capable to unlock a wide range of novel applications that are inaccessible by current approaches to build SPMs.     

Semi‐analytical analysis for multi‐directional functionally graded plates: 3‐D elasticity solutions

Semi‐analytical 3‐D elasticity solutions are presented for orthotropic multi‐directional functionally graded plates using the differential quadrature method (DQM) based on the state‐space formalism. Material properties are assumed to vary not only through the thickness but also in the in‐plane directions following an exponential law. The graded in‐plane domain is solved numerically via the DQM, while exact solutions are sought for the thickness domain using the state‐space method. Convergence studies are performed, and the present hybrid semi‐analytical method is validated by comparing numerical results with the exact solutions for a conventional unidirectional functionally graded plate. Finally, effects of material gradient indices on the displacement and stress fields of the plates are investigated and discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Keyhole‐3D phase contrast magnetic resonance angiography: A time‐resolved reconstruction method

In this study, we studied the keyhole imaging technique to 3D Phase‐contrast magnetic resonance angiography (PC MRA) to improve its temporal resolution. Previously, our research group has already studied the 2D PC MRA combined with keyhole technique, and evaluated the applicability. For keyhole‐3D PC MRA, the keyhole factor was used from 12.5% to 50% of the full k‐space. With keyhole factors above 50%, the images were similar to the original image and the vessels in the brain were well observed. We believe the keyhole‐3D PC MRA will give some advantages for improving the temporal resolution of MR systems.     

Assembly and Self‐Assembly of Nanomembrane Materials—From 2D to 3D

Nanoscience and nanotechnology offer great opportunities and challenges in both fundamental research and practical applications, which require precise control of building blocks with micro/nanoscale resolution in both individual and mass‐production ways. The recent and intensive nanotechnology development gives birth to a new focus on nanomembrane materials, which are defined as structures with thickness limited to about one to several hundred nanometers and with much larger (typically at least two orders of magnitude larger, or even macroscopic scale) lateral dimensions. Nanomembranes can be readily processed in an accurate manner and integrated into functional devices and systems. In this Review, a nanotechnology perspective of nanomembranes is provided, with examples of science and applications in semiconductor, metal, insulator, polymer, and composite materials. Assisted assembly of nanomembranes leads to wrinkled/buckled geometries for flexible electronics and stacked structures for applications in photonics and thermoelectrics. Inspired by kirigami/origami, self‐assembled 3D structures are constructed via strain engineering. Many advanced materials have begun to be explored in the format of nanomembranes and extend to biomimetic and 2D materials for various applications. Nanomembranes, as a new type of nanomaterials, allow nanotechnology in a controllable and precise way for practical applications and promise great potential for future nanorelated products.