Microscopy and Microanalysis最新文献

Ten years ago, the term "resolution revolution" was used for the first time to describe how cryogenic electron microscopy (cryo-EM) marked the beginning of a new era in the field of structural biology, enabling the investigation of previously unsolvable protein targets. The success of cryo-EM was recognized with the 2017 Chemistry Nobel Prize and has become a widely used method for the structural characterization of biological macromolecules, quickly catching up to x-ray crystallography. Bioenergetics is the division of biochemistry that studies the mechanisms of energy conversion in living organisms, strongly focused on the molecular machines (enzymes) that carry out these processes in cells. As bioenergetic enzymes can be arranged in complexes characterized by conformational heterogeneity/flexibility, they represent challenging targets for structural investigation by crystallography. Over the last decade, cryo-EM has therefore become a powerful tool to investigate the structure and function of bioenergetic complexes; here, we provide an overview of the main achievements enabled by the technique. We first summarize the features of cryo-EM and compare them to x-ray crystallography, and then, we present the exciting discoveries brought about by cryo-EM, particularly but not exclusively focusing on the oxidative phosphorylation system, which is a crucial energy-converting mechanism in humans.

Intensities in high-resolution phase-contrast images from electron microscopes build up discretely in time by detecting single electrons. A wave description of pulse-like coherent-inelastic interaction of an electron with matter implies a time-dependent coexistence of coherent partial waves. Their superposition forms a wave package by phase decoherence of 0.5 - 1 radian with Heisenbergs energy uncertainty ΔEH = ħ/2 Δt-1 matching the energy loss ΔE of a coherent-inelastic interaction and sets the interaction time Δt. In these circumstances, the product of Planck's constant and the speed of light hc is given by the product of the expression for temporal coherence λ2/Δλ and the energy loss ΔE. Experimentally, the self-coherence length was measured by detecting the energy-dependent localization of scattered, plane matter waves in surface proximity exploiting the Goos-Hänchen shift. Chromatic-aberration Cc-corrected electron microscopy on boron nitride (BN) proves that the coherent crystal illumination and phase contrast are lost if the self-coherence length shrinks below the size of the crystal unit cell at ΔE > 200 eV. In perspective, the interaction time of any matter wave compares with the lifetime of a virtual particle of any elemental interaction, suggesting the present concept of coherent-inelastic interactions of matter waves might be generalizable.

Characterizing threading dislocations (TDs) in gallium nitride (GaN) semiconductors is crucial for ensuring the reliability of semiconductor devices. The current research addresses this issue by combining two techniques using a scanning electron microscope, namely electron channeling contrast imaging (ECCI) and high-resolution electron backscattered diffraction (HR-EBSD). It is a comparative study of these techniques to underscore how they perform in the evaluation of TD densities in GaN epitaxial layers. Experiments reveal that the dislocation line vectors mostly deviate from the growth direction of the film, i.e., ∦ [0001], followed by edge-type dislocations (dislocation lines || [0001]) with insignificant screw character. Furthermore, TDs from the dislocation clusters are characterized as edge- and (edge + mixed)-type TDs. By combining ECCI counting of dislocations and HR-EBSD description of geometrically necessary dislocation density type, it is possible to measure the total TD density and provide the proportion of pure (edge and screw) and mixed TDs. It has also been observed from the analyses of residual elastic strain fields and lattice rotations that it is not possible to identify individual dislocations for the spatial resolution of 50 nm in HR-EBSD. Nevertheless, ECCI and HR-EBSD can be complementarily used to count and characterize the TDs.

In this study, we explore the dynamics of grain boundaries in nanocrystalline carbon monolayers, focusing on their variation with electron beam energy and electron dose rate in a spherical and chromatic aberration-corrected transmission electron microscope. We demonstrate that a clean surface, a high-dose rate, and a 60 keV electron beam are essential for precise local control over the dynamics of grain boundaries. The structure of these linear defects has been evaluated using neural network-generated polygon mapping.

The challenge of imaging low-density objects in an electron microscope without causing beam damage is significant in modern transmission electron microscopy. This is especially true for life science imaging, where the sample, rather than the instrument, still determines the resolution limit. Here, we explore whether we have to accept this or can progress further in this area. To do this, we use numerical simulations to see how much information we can obtain from a weak phase object at different electron doses. Starting from a model with four phase values, we compare Zernike phase contrast with measuring diffracted intensity under multiple random phase illuminations to solve the inverse problem. Our simulations have shown that diffraction-based methods perform better than the Zernike method, as we have found and addressed a normalization issue that, in some other studies, led to an overly optimistic representation of the Zernike setup. We further validated this using more realistic 2D objects and found that random phase illuminated diffraction can be up to five times more efficient than an ideal Zernike implementation. These findings suggest that diffraction-based methods could be a promising approach for imaging beam-sensitive materials and that current low-dose imaging methods are not yet at the quantum limit.

Leeches are widely used as model organisms in scientific studies and medical treatments. Medical leeches are hematophagous parasites that usually feed on the blood of their hosts. Some leeches show deformities, usually after feeding. This causes both medical and economic losses as it reduces the effectiveness of leeches in cultivation and medical treatment. The aim of this study was to investigate the effects of morphological deformations after feeding in Hirudo verbana, Carena 1820 (Annelida, Hirudinea), an important species in medical leech treatments. For this purpose, both histopathological and scanning electron microscopy examinations of starved and fed leeches were performed. The causes of deformities in medical leeches were found to be due to overfeeding, which caused cracks on the intestinal surface and therefore deterioration of the tissues. It is also thought that the immunological agents in the fed blood destroyed the medical leech tissue in these regions. In addition, it was determined that the cellular structure of the shaped blood elements stored in the cavity after feeding was preserved for a long time (months) without deterioration. It is certain that revealing the mechanism by which this occurs will inspire the preservation of blood for a long time in blood transfusion.

The pluripotency-related T-box family transcription factor TBX3 maintains mESC self-renewal and plays a key role in the development of several tissues, including the heart, mammary glands, limbs, and lungs. However, the role of TBX3 during porcine preimplantation embryo development remains unclear. In our research, TBX3 was knocked down by injecting dsRNA to explore the function of TBX3. TBX3 expression gradually increases during early embryonic development. TBX3 knockdown resulted in decreased in the rate of four-cell and blastocyst. Depletion of TBX3 decreased the level of H3K9Ac/H3K27Ac and decreased ZGA gene expression at the four-cell stage. Furthermore, TBX3 knockdown led to a decrease in ZSACN4 protein level, DNMT1 and intracellular 5mc levels were increased, and then induced telomeres shorten and DNA damaged. Additionally, TBX3 knockdown significantly decreased histone acetylation and pluripotency genes NANOG/OCT4 expression in blastocysts. TBX3 knockdown induced apoptosis in blastocysts. Taken together, TBX3 regulate histone acetylation and play important roles in zygotic genome activation and early embryonic development in pigs.

To identify the origin of high intensities of BO2- signals on grain boundaries (GBs) in boron (B) mapping using secondary-ion mass spectrometry (SIMS), atom probe tomography analysis was performed on high-brightness GBs in the steel with the addition of B. Homogeneous segregation of B atoms as a solid solution, rather than continuous GB precipitation of fine boride, was observed at the GBs. The amounts of B segregation varied between the GBs. An estimation of the incident angle of the GB from the sample surface in each GB indicated that the high-brightness GBs always have smaller incident angles than the median angle under the assumption of random GB orientation, resulting in an increase in the GB area in the SIMS analyzed region. The product of the actual B segregation amount and area increase factor roughly corresponded to the apparent B intensity of the GB in B-mapping with SIMS. The high brightness in the B-mapping originated mainly from small incident angles of GB from the sample surface in the steel. The incident angle of the GB plane must be considered for quantification of GB segregation of B in the SIMS analysis.

2D elemental imaging techniques such as micro-X-ray fluorescence (micro-XRF) and micro-particle-induced X-ray emission (micro-PIXE) play a critical role in elemental mapping across diverse fields such as biology, geology, materials science, and engineering. However, surface irregularities often introduce shadow effects, hindering accurate spectrometric analysis. Knowing the topography information is essential for addressing this issue. Here, we propose integrating a global least squares algorithm for reconstructing the 3D surface topography in micro-PIXE analysis which is applicable in other similar techniques based on X-ray microscopy. This algorithm utilizes two independent gradient components, distorted by noise, to calculate the gradient vector from X-ray data acquired by an annular quad-segment spectrometer. We demonstrate the capability of this approach on a real homogeneous sample, yielding 3D elemental surface topography. This noniterative code provides surface reconstructions which in turn could find application to enhance the correction of spatial elemental distributions across heterogeneous sample types.