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1.
Int J Mol Sci ; 23(22)2022 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-36430353

RESUMO

Heat-up and hot-injection methods were employed to synthesize Ni nanoparticles (NPs) with narrow size distribution in the presence of hyperbranched pyridylphenylene polymer (PPP) as a stabilizing agent. It was shown that depending on the synthetic method, Ni NPs were formed either in a cross-linked polymer network or stabilized by a soluble hyperbranched polymer. Ni NPs were characterized by a combination of transmission electron microscopy (TEM), scanning TEM, thermogravimetric analysis, powder X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, and magnetic measurements. The architecture of polymer support was found to significantly effect Ni NPs characteristics and behavior. The Ni NPs demonstrated a high catalytic activity in a model Suzuki-Miyaura cross-coupling reaction. No significant drop in activity was observed upon repeated use after magnetic separation in five consecutive catalytic cycles. We believe that hyperbranched PPP can serve as universal platform for the controllable synthesis of Ni NPs, acting as highly active and stable catalysts.


Assuntos
Nanopartículas , Polímeros , Oxirredução , Catálise , Nanopartículas/química , Microscopia Eletrônica de Transmissão e Varredura
2.
Chem Commun (Camb) ; 58(88): 12274-12285, 2022 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-36260089

RESUMO

The manipulation of individual atoms has developed from visionary speculation into an established experimental science. Using focused electron irradiation in a scanning transmission electron microscope instead of a physical tip in a scanning probe microscope confers several benefits, including thermal stability of the manipulated structures, the ability to reach into bulk crystals, and the chemical identification of single atoms. However, energetic electron irradiation also presents unique challenges, with an inevitable possibility of irradiation damage. Understanding the underlying mechanisms will undoubtedly continue to play an important role to guide experiments. Great progress has been made in several materials including graphene, carbon nanotubes, and crystalline silicon in the eight years since the discovery of electron-beam manipulation, but the important challenges that remain will determine how far we can expect to progress in the near future.


Assuntos
Grafite , Nanotubos de Carbono , Microscopia Eletrônica de Transmissão e Varredura , Nanotubos de Carbono/química , Grafite/química , Silício/química
4.
Nat Methods ; 19(9): 1126-1136, 2022 09.
Artigo em Inglês | MEDLINE | ID: mdl-36064775

RESUMO

In electron cryomicroscopy (cryo-EM), molecular images of vitrified biological samples are obtained by conventional transmission microscopy (CTEM) using large underfocuses and subsequently computationally combined into a high-resolution three-dimensional structure. Here, we apply scanning transmission electron microscopy (STEM) using the integrated differential phase contrast mode also known as iDPC-STEM to two cryo-EM test specimens, keyhole limpet hemocyanin (KLH) and tobacco mosaic virus (TMV). The micrographs show complete contrast transfer to high resolution and enable the cryo-EM structure determination for KLH at 6.5 Å resolution, as well as for TMV at 3.5 Å resolution using single-particle reconstruction methods, which share identical features with maps obtained by CTEM of a previously acquired same-sized TMV data set. These data show that STEM imaging in general, and in particular the iDPC-STEM approach, can be applied to vitrified single-particle specimens to determine near-atomic resolution cryo-EM structures of biological macromolecules.


Assuntos
Microscopia Crioeletrônica , Microscopia Crioeletrônica/métodos , Microscopia Eletrônica de Transmissão e Varredura
5.
Sci Rep ; 12(1): 13462, 2022 08 05.
Artigo em Inglês | MEDLINE | ID: mdl-35931705

RESUMO

Application of scanning transmission electron microscopy (STEM) to in situ observation will be essential in the current and emerging data-driven materials science by taking STEM's high affinity with various analytical options into account. As is well known, STEM's image acquisition time needs to be further shortened to capture a targeted phenomenon in real-time as STEM's current temporal resolution is far below the conventional TEM's. However, rapid image acquisition in the millisecond per frame or faster generally causes image distortion, poor electron signals, and unidirectional blurring, which are obstacles for realizing video-rate STEM observation. Here we show an image correction framework integrating deep learning (DL)-based denoising and image distortion correction schemes optimized for STEM rapid image acquisition. By comparing a series of distortion corrected rapid scan images with corresponding regular scan speed images, the trained DL network is shown to remove not only the statistical noise but also the unidirectional blurring. This result demonstrates that rapid as well as high-quality image acquisition by STEM without hardware modification can be established by the DL. The DL-based noise filter could be applied to in-situ observation, such as dislocation activities under external stimuli, with high spatio-temporal resolution.


Assuntos
Aprendizado Profundo , Diagnóstico por Imagem , Processamento de Imagem Assistida por Computador/métodos , Microscopia Eletrônica de Transmissão e Varredura , Razão Sinal-Ruído
6.
Sci Rep ; 12(1): 12198, 2022 07 16.
Artigo em Inglês | MEDLINE | ID: mdl-35842472

RESUMO

Chromatin organization over multiple length scales plays a critical role in the regulation of transcription. Deciphering the interplay of these processes requires high-resolution, three-dimensional, quantitative imaging of chromatin structure in vitro. Herein, we introduce ChromSTEM, a method that utilizes high-angle annular dark-field imaging and tomography in scanning transmission electron microscopy combined with DNA-specific staining for electron microscopy. We utilized ChromSTEM for an in-depth quantification of 3D chromatin conformation with high spatial resolution and contrast, allowing for characterization of higher-order chromatin structure almost down to the level of the DNA base pair. Employing mass scaling analysis on ChromSTEM mass density tomograms, we observed that chromatin forms spatially well-defined higher-order domains, around 80 nm in radius. Within domains, chromatin exhibits a polymeric fractal-like behavior and a radially decreasing mass-density from the center to the periphery. Unlike other nanoimaging and analysis techniques, we demonstrate that our unique combination of this high-resolution imaging technique with polymer physics-based analysis enables us to (i) investigate the chromatin conformation within packing domains and (ii) quantify statistical descriptors of chromatin structure that are relevant to transcription. We observe that packing domains have heterogeneous morphological properties even within the same cell line, underlying the potential role of statistical chromatin packing in regulating gene expression within eukaryotic nuclei.


Assuntos
Cromatina , Cromossomos , Núcleo Celular , DNA , Microscopia Eletrônica de Transmissão e Varredura
7.
Biomacromolecules ; 23(8): 3235-3242, 2022 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-35881504

RESUMO

Electron microscopy of soft and biological materials, or "soft electron microscopy", is essential to the characterization of macromolecules. Soft microscopy is governed by enhancing contrast while maintaining low electron doses, and sample preparation and imaging methodologies are driven by the length scale of features of interest. While cryo-electron microscopy offers the highest resolution, larger structures can be characterized efficiently and with high contrast using low-voltage electron microscopy by performing scanning transmission electron microscopy in a scanning electron microscope (STEM-in-SEM). Here, STEM-in-SEM is demonstrated for a four-lobed protein assembly where the arrangement of the proteins in the construct must be examined. STEM image simulations show the theoretical contrast enhancement at SEM-level voltages for unstained structures, and experimental images with multiple STEM modes exhibit the resolution possible for negative-stained proteins. This technique can be extended to complex protein assemblies, larger structures such as cell sections, and hybrid materials, making STEM-in-SEM a valuable high-throughput imaging method.


Assuntos
Elétrons , Microscopia Crioeletrônica/métodos , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão e Varredura/métodos
8.
Histochem Cell Biol ; 158(3): 203-211, 2022 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-35829815

RESUMO

A major aim in structural cell biology is to analyze intact cells in three dimensions, visualize subcellular structures, and even localize proteins at the best possible resolution in three dimensions. Though recently developed electron microscopy tools such as electron tomography, or three-dimensional (3D) scanning electron microscopy, offer great resolution in three dimensions, the challenge is that, the better the resolution, usually the smaller the volume under investigation. Several different approaches to overcome this challenge were presented at the Microscopy Conference in Vienna in 2021. These tools include array tomography, batch tomography, or scanning transmission electron tomography, all of which can nowadays be extended toward correlative light and electron tomography, with greatly increased 3D information. Here, we review these tools, describe the underlying procedures, and discuss their advantages and limits.


Assuntos
Tomografia com Microscopia Eletrônica , Imageamento Tridimensional , Tomografia com Microscopia Eletrônica/métodos , Imageamento Tridimensional/métodos , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão e Varredura
9.
Microscopy (Oxf) ; 71(5): 302-310, 2022 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-35713554

RESUMO

Atomic-resolution electron microscopy imaging of solid-state material is a powerful method for structural analysis. Scanning transmission electron microscopy (STEM) is one of the actively used techniques to directly observe atoms in materials. However, some materials are easily damaged by the electron beam irradiation, and only noisy images are available when we decrease the electron dose to avoid beam damages. Therefore, a denoising process is necessary for precise structural analysis in low-dose STEM. In this study, we propose total variation (TV) denoising algorithm to remove quantum noise in an STEM image. We defined an entropy of STEM image that corresponds to the image contrast to determine a hyperparameter and we found that there is a hyperparameter that maximizes the entropy. We acquired atomic-resolution STEM image of CaF2 viewed along the [001] direction and executed TV denoising. The atomic columns of Ca and F are clearly visualized by the TV denoising, and atomic positions of Ca and F are determined with the error of ±1 pm and ±4 pm, respectively.


Assuntos
Algoritmos , Microscopia Eletrônica de Transmissão e Varredura
10.
Ultramicroscopy ; 239: 113562, 2022 09.
Artigo em Inglês | MEDLINE | ID: mdl-35675735

RESUMO

Preservation of analyte integrity during focused ion beam (FIB) sample preparation is a significant challenge in the scanning transmission electron microscopy (STEM) characterization of plan-view samples with sensitive surface chemistries. This can preclude the characterization of atomic arrangements, nanoscale surface coverages, and distributions and morphologies of functional molecular materials composed of surface-immobilized metal nanoparticles, clusters or coordination complexes. This work demonstrates effective protection of Pt nanoparticle (NP) morphology through a plan-view FIB lift-out and thinning procedure by encapsulating the sample surface in an Al2O3 overlayer grown by atomic layer deposition (ALD). High-angle annular dark field (HAADF)-STEM analysis was used in concert with energy dispersive X-ray spectroscopy (EDS) to identify and image sub-10 nm features attributed to Pt and to evaluate the distribution of implanted Ga+ (derived from the FIB milling beam). ALD is a mild chemical vapor deposition (CVD) technique that has the capability to generate dense, pinhole-free films with tunable compositions and properties, making this ALD-FIB procedure applicable to many sample architectures for plan-view lamella preparation and STEM analysis.


Assuntos
Nanopartículas Metálicas , Microscopia Eletrônica de Transmissão e Varredura , Espectrometria por Raios X
11.
Molecules ; 27(12)2022 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-35744947

RESUMO

The main aspects of material research: material synthesis, material structure, and material properties, are interrelated. Acquiring atomic structure information of electron beam sensitive materials by electron microscope, such as porous zeolites, organic-inorganic hybrid perovskites, metal-organic frameworks, is an important and challenging task. The difficulties in characterization of the structures will inevitably limit the optimization of their synthesis methods and further improve their performance. The emergence of integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM), a STEM characterization technique capable of obtaining images with high signal-to-noise ratio under lower doses, has made great breakthroughs in the atomic structure characterization of these materials. This article reviews the developments and applications of iDPC-STEM in electron beam sensitive materials, and provides an outlook on its capabilities and development.


Assuntos
Elétrons , Microscopia Eletrônica de Transmissão e Varredura/métodos , Microscopia de Contraste de Fase
12.
Nano Lett ; 22(12): 4677-4685, 2022 06 22.
Artigo em Inglês | MEDLINE | ID: mdl-35674452

RESUMO

Scanning transmission electron microscopy (STEM) is an indispensable tool for atomic-resolution structural analysis for a wide range of materials. The conventional analysis of STEM images is an extensive hands-on process, which limits efficient handling of high-throughput data. Here, we apply a fully convolutional network (FCN) for identification of important structural features of two-dimensional crystals. ResUNet, a type of FCN, is utilized in identifying sulfur vacancies and polymorph types of MoS2 from atomic resolution STEM images. Efficient models are achieved based on training with simulated images in the presence of different levels of noise, aberrations, and carbon contamination. The accuracy of the FCN models toward extensive experimental STEM images is comparable to that of careful hands-on analysis. Our work provides a guideline on best practices to train a deep learning model for STEM image analysis and demonstrates FCN's application for efficient processing of a large volume of STEM data.


Assuntos
Aprendizado Profundo , Processamento de Imagem Assistida por Computador/métodos , Microscopia Eletrônica de Transmissão e Varredura , Molibdênio/química
13.
ACS Nano ; 16(7): 10314-10326, 2022 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-35729795

RESUMO

High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) can be acquired together with energy dispersive X-ray (EDX) spectroscopy to give complementary information on the nanoparticles being imaged. Recent deep learning approaches show potential for accurate 3D tomographic reconstruction for these applications, but a large number of high-quality electron micrographs are usually required for supervised training, which may be difficult to collect due to the damage on the particles from the electron beam. To overcome these limitations and enable tomographic reconstruction even in low-dose sparse-view conditions, here we present an unsupervised deep learning method for HAADF-STEM-EDX tomography. Specifically, to improve the EDX image quality from low-dose condition, a HAADF-constrained unsupervised denoising approach is proposed. Additionally, to enable extreme sparse-view tomographic reconstruction, an unsupervised view enrichment scheme is proposed in the projection domain. Extensive experiments with different types of quantum dots show that the proposed method offers a high-quality reconstruction even with only three projection views recorded under low-dose conditions.


Assuntos
Aprendizado Profundo , Nanopartículas , Microscopia Eletrônica de Transmissão e Varredura/métodos , Tomografia com Microscopia Eletrônica , Tomografia Computadorizada por Raios X/métodos
14.
J Microsc ; 287(2): 93-104, 2022 08.
Artigo em Inglês | MEDLINE | ID: mdl-35638306

RESUMO

ToTEM, a multislice-based image simulation software is developed for transmission electron microscope (TEM). This software implements the following major features: (i) capability of assigning three-dimensional potentials of atom into multiple slices and precise introduction of phase shift caused by the sub-pixel atomic position, (ii) employing CUDA coding and graphical processing units (GPU) with multithreading parallel algorithm based on the powerful batch (inverse) fast Fourier transform (FFT), which is especially beneficial for image simulation of scanning transmission electron microscopy (STEM) or (integrated) differential phase contrast (I)DPC, (iii) design for efficiently generating large batch of data set of high-resolution transmission electron microscopy (HRTEM) images. Image simulation acceleration for STEM has been verified by simulating a large-scale SrTiO3 . Additionally, iDPC image of MFI-type zeolites with xylene molecules encapsulated in straight channels demonstrates the advantage of iDPC in detecting light molecules.


Assuntos
Algoritmos , Software , Simulação por Computador , Análise de Fourier , Microscopia Eletrônica de Transmissão e Varredura/métodos
15.
Talanta ; 246: 123522, 2022 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-35576757

RESUMO

Since silver ion is known for its antimicrobial function, most of the research has focused mainly on toxicity effects rather than the role of silver ion in general biology and the behind mechanism of actions of silver ion in mammalian cells. Moreover, a conventional in vitro approach to estimate the effects of silver ion on cells does not provide information about the biochemical changes and might accompany artifacts due to invasive and destructive sample preparation processes. In the present study, in-situ real time approaches were applied to evaluate the impact of silver ion (0.57, 1.34, 1.96, 2.33 mg/L) on fibroblast cells. Raman spectroscopy analysis showed that Raman peak intensities of proteins and nucleic acids significantly increased in the cells after exposure to silver ion for 21 h, especially at relatively higher levels 1.34, 1.96, and 2.33 mg/L. Raman peak at 1585 cm-1 and liquid scanning transmission electron microscopy energy-dispersive x-ray spectroscopy (STEM-EDS) analysis revealed the fate of silver ion that was taken up by the cell and reduced into metallic silver accumulating in the cell as silver nanoparticles. These results suggest cells were undergoing different activities such as enhanced metabolic activities rather than cell apoptosis or cell death. Additionally, Raman spectroscopy predicted the level of silver ion exposed to the cell at 2.11 ± 0.38 and 1.73 ± 0.26 mg/L by the PLS prediction model, compared with the results measured by inductively coupled plasma mass spectrometry (ICP-MS), 2.14 ± 0.07 and 1.87 ± 0.07 mg/L respectively, suggesting Raman spectroscopy can provide a new and fast approach to determine and measure the concentration of silver ion or probably other tested molecules treated to the cell for the future research.


Assuntos
Nanopartículas Metálicas , Prata , Animais , Fibroblastos , Íons , Mamíferos , Nanopartículas Metálicas/química , Nanopartículas Metálicas/toxicidade , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão e Varredura , Prata/química , Análise Espectral Raman , Suínos
16.
Nano Lett ; 22(10): 4137-4144, 2022 05 25.
Artigo em Inglês | MEDLINE | ID: mdl-35523204

RESUMO

Nanoscale tailoring of catalytic materials and Li-battery alternatives has elevated the importance of in situ gas-phase electron microscopy. Such advanced techniques are often performed using an environmental cell inserted into a conventional S/TEM setup, as this method facilitates concurrent electrochemical and temperature stimulations in a convenient and cost-effective manner. However, these cells are made by encapsulating gas between two insulating membranes, which introduces additional electron scattering. We have evaluated strengths and limitations of the gas-phase E-cell S/TEM technique, both experimentally and through simulations, across a variety of practical parameters. We reveal the degradation of image quality in an E-cell setup from various components and explore opportunities to improve imaging quality through intelligent choice of experimental parameters. Our results underscore the benefits of using an E-cell STEM technique, due to its versatility and excellent ability to suppress the exotic contributions from the membrane device.


Assuntos
Fontes de Energia Elétrica , Lítio , Microscopia Eletrônica , Microscopia Eletrônica de Transmissão e Varredura/métodos , Temperatura
17.
Nano Lett ; 22(9): 3628-3635, 2022 05 11.
Artigo em Inglês | MEDLINE | ID: mdl-35413204

RESUMO

Here, we demonstrate atomic-resolution scanning transmission electron microscopy (STEM) imaging of light elements in small organic molecules on graphene. We use low-dose, room-temperature, aberration-corrected STEM to image 2D monolayer and bilayer molecular crystals, followed by advanced image processing methods to create high-quality composite images from ∼102-104 individual molecules. In metalated porphyrin and phthalocyanine derivatives, these images contain an elementally sensitive contrast with up to 1.3 Å resolution─sufficient to distinguish individual carbon and nitrogen atoms. Importantly, our methods can be applied to molecules with low masses (∼0.6 kDa) and nanocrystalline domains containing just a few hundred molecules, making it possible to study systems for which large crystals cannot easily be grown. Our approach is enabled by low-background graphene substrates, which we show increase the molecules' critical dose by 2-7×. These results indicate a new route for low-dose, atomic-resolution electron microscopy imaging to solve the structures of small organic molecules.


Assuntos
Grafite , Carbono , Elétrons , Grafite/química , Microscopia Eletrônica de Transmissão e Varredura/métodos
18.
Nat Commun ; 13(1): 951, 2022 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-35177632

RESUMO

Crystallization of biomacromolecules-metal-organic frameworks (BMOFs) allows for orderly assemble of symbiotic hybrids with desirable biological and chemical functions in one voxel. The structure-activity relationship of this symbiotic crystal, however, is still blurred. Here, we directly identify the atomic-level structure of BMOFs, using the integrated differential phase contrast-scanning transmission electron microscopy, cryo-electron microscopy and x-ray absorption fine structure techniques. We discover an obvious difference in the nanoarchitecture of BMOFs under different crystallization pathways that was previously not seen. In addition, we find the nanoarchitecture significantly affects the bioactivity of the BMOFs. This work gives an important insight into the structure-activity relationship of BMOFs synthesized in different scenarios, and may act as a guide to engineer next-generation materials with excellent biological and chemical functions.


Assuntos
Estruturas Metalorgânicas/ultraestrutura , Microscopia Crioeletrônica , Cristalização , Estruturas Metalorgânicas/química , Microscopia Eletrônica de Transmissão e Varredura , Relação Estrutura-Atividade , Espectroscopia por Absorção de Raios X
19.
J Struct Biol ; 214(1): 107837, 2022 03.
Artigo em Inglês | MEDLINE | ID: mdl-35104612

RESUMO

Scanning transmission electron microscopy (STEM) is a powerful imaging technique and has been widely used in current material science research. The attempts of applying STEM (annual dark field (ADF)-STEM or annular bright field (ABF)-STEM) into biological research have been going on for decades while applications have still been limited because of the existing bottlenecks in dose efficiency and non-linearity in contrast. Recently, integrated differential phase contrast (iDPC) STEM technique emerged and achieved a linear phase contrast imaging condition, while resolving signals of light elements next to heavy ones even at low electron dose. This enables successful investigation of beam sensitive materials. Here, we investigate iDPC-STEM advantages in biology, in particular, chemically fixed and resin embedded biological tissues. By comparing results to the conventional TEM, we have found that iDPC-STEM not only shows better contrast but also resolves more structural details at molecular level, including conditions of extremely low dose and minimal heavy-atom staining. We also compare iDPC-STEM with ABF-STEM and found that contrast of iDPC-STEM is even further improved, moderately in lower frequency domains while highly with preserving high frequency biological structural details. For thick sample sections, iDPC-STEM is particularly advantageous. It avoids contrast inversion canceling effects, and by adjusting the depth of focus, fully preserves the contrast of structural details along with the sample. In addition, using depth-sectioning, iDPC-STEM enables resolving in-depth structural variation. Our results suggest that iDPC-STEM have the place and advantages within the future biological research.


Assuntos
Elétrons , Microscopia Eletrônica de Transmissão e Varredura/métodos , Microscopia de Contraste de Fase
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