High-resolution Microscopy Techniques Research Articles

Nanomolar detection of L-cysteine and Cu2+ ions based on Trehalose capped silver nanoparticles

This work describes the solvent-free solid-state synthesis of Trehalose capped silver nanoparticles (Th-AgNPs) and its L-Cysteine and Cu2+ ions sensor application. We have prepared Th-AgNPs by the solid-state method within 5 min by simple grinding. During the synthesis of AgNPs, trehalose in alkaline medium acts as reducing as well as capping agent. The Th-AgNPs were well characterized by Ultraviolet–visible (UV–vis) spectroscopy, Fourier Transform Infrared (FT-IR) Spectroscopy, X-Ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HR-TEM) techniques. FT-IR spectral studies confirmed that Trehalose –OH, groups were adsorbed on the surface of AgNPs. XRD pattern of Th-AgNPs revealed that synthesized Th-AgNPs presented good crystalline nature and face-centred cubic structure. The particles size was calculated to be 9.312 ± 0.23 nm by HR-TEM image. Interestingly, after the addition of L-Cysteine into Th-AgNPs, the particles are aggregated, followed by the decreases in SPR band absorbance at 400 nm was observed and a new peak appears at 550 nm. In contrast, the addition of Cu2+ ions led to an increase of the SPR band at 400 nm and 550 nm and the color of the solution changed to yellowish red. The reverted SPR peak shift and color changes are expected due to the deaggregation of nanoparticles, which was further confirmed by HR-TEM. Based on the changes in SPR band, the concentration of L-Cysteine and Cu2+ ions were sensed, and the limit of detection (LOD) was found to be 1.48 and 1.92 nM (LOD = 3S/m), respectively. 750-fold (2.94 × 10−4 M) of common amino acids and 300-fold (4.89 × 10−4 M) of common metal ions did not interfere with the specific detection of 0.33 μM of L-Cysteine and 1.63 μM of Cu2+ ions. We have successfully applied this system for the detection of L-Cysteine and Cu2+ ions in different environmental, biological and drug samples. Importantly, we have prepared a paper-based kit for on-site monitoring of L-Cysteine and Cu2+ ions. This new synthesis protocol and the developed paper-based kit will provide an insight in the field of material science, nanotechnology and biosensor applications.

Polymer-Based Graphene Derivatives and Microwave-Assisted Silver Nanoparticles Decoration as a Potential Antibacterial Agent.

Nanocomposites obtained by the decoration of graphene-based materials with silver nanoparticles (AgNPs) have received increasing attention owing to their antimicrobial activity. However, the complex synthetic methods for their preparation have limited practical applications. This study aims to synthesize novel NanoHybrid Systems based on graphene, polymer, and AgNPs (namely, NanoHy-GPS) through an easy microwave irradiation approach free of reductants and surfactants. The polymer plays a crucial role, as it assures the coating layer/substrate compatibility making the platform easily adaptable for a specific substrate. AgNPs’ loading (from 5% to 87%) can be tuned by the amount of Silver salt used during the microwave-assisted reaction, obtaining spherical AgNPs with average sizes of 5–12 nm homogeneously distributed on a polymer-graphene nanosystem. Interestingly, microwave irradiation partially restored the graphene sp2 network without damage of ester bonds. The structure, morphology, and chemical composition of NanoHy-GPS and its subunits were characterized by means of UV-vis spectroscopy, thermal analysis, differential light scattering (DLS), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray analysis (EDX), Atomic Force Microscopy (AFM), and High-Resolution Transmission Electron Microscopy (HRTEM) techniques. A preliminary qualitative empirical assay against the typical bacterial load on common hand-contacted surfaces has been performed to assess the antibacterial properties of NanoHy-GPS, evidencing a significative reduction of bacterial colonies spreading.

Effects of austenizing temperature, cooling rate and isothermal temperature on overall phase transformation characteristics in high carbon steel

Phase transformations in high-carbon steel has been investigated by dilatometry during continuous cooling and isothermal transformations, following austenizing at temperatures of 900 °C–1200 °C (1173–1473 K). Optical microscopy and high-resolution scanning electron microscopy techniques revealed the presence of martensite, complex bainite, pearlite and metastable retained austenite under a variety of heat treatments. Magnetic measurements proved to be a useful technique to determine the fraction of retained austenite. Quantitative image processing with ImageJ software and magnetic techniques were used to calculate phase fractions. The rate of phase transformations increased by an increase in austenizing temperature for transformations occurring during continuous cooling and isothermal transformations. A mere increase in cooling rate from 3 °C (276 K) per second to 5 °C (278 K) per second changed the relative phase fractions and hardness significantly. The hardness of isothermally cooling specimens was a strong function of temperature and microstructure. Although isothermal holding at 500–525 °C (773–798 K) resulted in a mixture of bainite and pearlite, the hardness decreased significantly by decreasing the isothermal transformation temperature from 525 °C (798 K) to 500 °C (773 K). These outcomes provide valuable guidelines for the development of novel microstructure in high carbon steel in industrial practice.

A workflow for 3D-CLEM investigating liver tissue.

Correlative light and electron microscopy (CLEM) is a method used to investigate the exact same region in both light and electron microscopy (EM) in order to add ultrastructural information to a light microscopic (usually fluorescent) signal. Workflows combining optical or fluorescent data with electron microscopic images are complex, hence there is a need to communicate detailed protocols and share tips & tricks for successful application of these methods. With the development of volume-EM techniques such as serial blockface scanning electron microscopy (SBF-SEM) and Focussed Ion Beam-SEM, correlation in three dimensions has become more efficient. Volume electron microscopy allows automated acquisition of serial section imaging data that can be reconstructed in three dimensions (3D) to provide a detailed, geometrically accurate view of cellular ultrastructure. In addition, combining volume-EM with high-resolution light microscopy (LM) techniques decreases the resolution gap between LM and EM, making retracing of a region of interest and eventual overlays more straightforward. Here, we present a workflow for 3D CLEM on mouse liver, combining high-resolution confocal microscopy with SBF-SEM. In this workflow, we have made use of two types of landmarks: (1) near infrared laser branding marks to find back the region imaged in LM in the electron microscope and (2) landmarks present in the tissue but independent of the cell or structure of interest to make overlay images of LM and EM data. Using this approach, we were able to make accurate 3D-CLEM overlays of liver tissue and correlate the fluorescent signal to the ultrastructural detail provided by the electron microscope. This workflow can be adapted for other dense cellular tissues and thus act as a guide for other three-dimensional correlative studies. LAY DESCRIPTION: As cells and tissues exist in three dimensions, microscopy techniques have been developed to image samples, in 3D, at the highest possible detail. In light microscopy, fluorescent probes are used to identify specific proteins or structures either in live samples, (providing dynamic information), or in fixed slices of tissue. A disadvantage of fluorescence microscopy is that only the labeled proteins/structures are visible, while their cellular context remains hidden. Electron microscopy is able to image biological samples at high resolution and has the advantage that all structures in the tissue are visible at nanometer (10-9 m) resolution. Disadvantages of this technique are that it is more difficult to label a single structure and that the samples must be imaged under high vacuum, so biological samples need to be fixed and embedded in a plastic resin to stay as close to their natural state as possible inside the microscope. Correlative Light and Electron Microscopy aims to combine the advantages of both light and electron microscopy on the same sample. This results in datasets where fluorescent labels can be combined with the high-resolution contextual information provided by the electron microscope. In this study we present a workflow to guide a tissue sample from the light microscope to the electron microscope and image the ultra-structure of a specific cell type in the liver. In particular we focus on the incorporation of fiducial markers during the sample preparation to help navigate through the tissue in 3D in both microscopes. One sample is followed throughout the workflow to visualize the important steps in the process, showing the final result; a dataset combining fluorescent labels with ultra-structural detail.

Superplastic deformation of Mg\u20139Li\u20132Al\u20130.5Sc alloy after grain refinement by KoBo extrusion and cyclic forging

The quaternary Mg–9Li–2Al–0.5Sc alloy (in wt%) was prepared from pure components. After homogenization, the alloy was subjected to severe plastic deformation by KoBo extrusion and cyclic forging leading to grain refinement in the range of 0.5–2 µm of hexagonal close-packed (HCP) α phase. Deformed alloys showed high ultimate tensile strength near 200 MPa and good elongation in the range 30–40% at room temperature (RT). Large elongations close to 200% were obtained during the tensile test at a temperature of 200 °C. Deformed samples showed the presence of multiple voids confirming grain boundary sliding mechanism of deformation. Twins on {10overline{1}2} planes were identified using electron backscatter diffraction analysis, being in a good agreement with the earlier observation of Mg–Li and Mg–Sc alloys. Intermetallic phases such as cubic MgSc were identified in deformed alloys mostly within HCP α phase, whereas HCP MgSc2 particles were observed within body-centered cubic (BCC) β phase. Intermetallic phases were responsible for RT strengthening of alloys and slightly lower tensile elongation during superplastic deformation. Formation of the HCP α phase was observed within the BCC β phase in tensile deformed alloys. Atomic-level nucleation of HCP phase within the β phase was identified by the use of high-resolution transmission electron microscopy technique.

Strong spin-orbit interactions in a correlated two-dimensional electron system formed in SrTiO3(001) films grown epitaxially on p−Si(001)

We observe strong spin-orbit interactions in a two-dimensional electron system formed on $\mathrm{SrTi}{\mathrm{O}}_{3}(001)$ films grown epitaxially on p-Si(001). High-resolution transmission electron microscopy and related analytical techniques reveal a sharp interface between Si and $\mathrm{SrTi}{\mathrm{O}}_{3}$. Strain mapping analysis shows in-plane strain in $\mathrm{SrTi}{\mathrm{O}}_{3}$ very close to the interface. Analysis of the low temperature magnetoconductance measurements reveals that both quantum interference and electron-electron interactions are important. The contributions of these two quantum phenomena to the temperature and magnetic field dependence of the conductance and Hall effect are separated. The electron system has carrier concentrations larger than ${10}^{14}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$, appears to be confined within \ensuremath{\sim}4 nm, and has an estimated spin-splitting energy \ensuremath{\sim}12 meV.

Strontium Calcium Phosphate Nanotubes as Bioinspired Building Blocks for Bone Regeneration.

Calcium phosphate (CaP)-based ceramics are the most investigated materials for bone repairing and regeneration. However, the clinical performance of commercial ceramics is still far from that of the native tissue, which remains as the gold standard. Thus, reproducing the structural architecture and composition of bone matrix should trigger biomimetic response in synthetic materials. Here, we propose an innovative strategy based on the use of track-etched membranes as physical confinement to produce collagen-free strontium-substituted CaP nanotubes that tend to mimic the building block of bone, i.e., the mineralized collagen fibrils. A combination of high-resolution microscopic and spectroscopic techniques revealed the underlying mechanisms driving the nanotube formation. Under confinement, poorly crystalline apatite platelets assembled into tubes that resembled the mineralized collagen fibrils in terms of diameter and structure of bioapatite. Furthermore, the synergetic effect of Sr2+ and confinement gave rise to the stabilization of amorphous strontium CaP nanotubes. The nanotubes were tested in long-term culture of osteoblasts, supporting their maturation and mineralization without eliciting any cytotoxicity. Sr2+ released from the particles reduced the differentiation and activity of osteoclasts in a Sr2+ concentration-dependent manner. Their bioactivity was evaluated in a serum-like solution, showing that the particles spatially guided the biomimetic remineralization. Further, these effects were achieved at strikingly low concentrations of Sr2+ that is crucial to avoid side effects. Overall, these results open simple and promising pathways to develop a new generation of CaP multifunctional ceramics that are active in tissue regeneration and able to simultaneously induce biomimetic remineralization and control the imbalanced osteoclast activity responsible for bone density loss.

Mechanism of CeO2 synthesized by thermal decomposition of Ce-MOF and its performance of benzene catalytic combustion

In this paper, the formation mechanism of mesoporous CeO2 synthesized by thermal decomposition of Ce-MOF and its performance of benzene catalytic combustion, as well as the structure–activity relationship between them were studied in depth. The self-assembly process and physicochemical properties of CeO2 were characterized by thermogravimetry analysis, powder X-ray diffraction, N2 adsorption/desorption, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy techniques. Characterization results show that Ce-MOF is completely decomposed into pure mesoporous CeO2 when the decomposition temperature is higher than 400 °C. At this threshold temperature, CeO2 (400) has the largest specific surface area and pore volume of 114 m2/g and 0.152 cm3/g, respectively. CeO2 (400) exhibits very high catalytic activity for benzene combustion, which can completely catalyze the degradation of benzene at 260 °C. Meanwhile, the mesoporous CeO2 (400) supported Pt nanocrystalline catalysts were prepared by high temperature solution-phase reduction method. Pt/CeO2 (400) can completely degrade benzene at about 200 °C and represents high durability and good water-resistance for benzene combustion during 100 h of continuous reaction.

Direct Observation of Li Migration into V5S8: Order to Antisite Disorder Intercalation Followed by the Topotactic-Based Conversion Reaction.

Two-dimensional transition-metal dichalcogenides hold great potential in rechargeable lithium-ion batteries. Their electrochemical properties are closely related to the structural evolutions during lithium-ion migration. Understanding these migration/reaction mechanisms is important to help improve battery performance. Herein, we report the real-time and atomic-scale observation of phase transitions during the lithiation and delithiation for V5S8 via in situ electron diffraction and high-resolution transmission electron microscopy techniques. We find that the phase transformation proceeds via a sequence of order to antisite disorder intercalation and topotactic-based conversion reaction. During the intercalation reaction, the lithium ion destroys the orderings of the interstitial V with the formation of Li/V antisite. Such a reaction is found to be reversible, i.e., the extraction of lithium from LixV5S8 leads to the recovery of V orderings. The conversion reaction involves heterogeneous nucleation of Li2S with 3-20 nm nanodomains, which maintain the crystallographic integrity with LixV5S8. These findings elucidate the complex interactions between the lithium ion and host V5S8 during ionic migration in solids, which should be helpful in understanding the relationship between phase transformation kinetics and battery performance.

Influence of MoS2-metal interface on charge injection: a comparison between various metal contacts

Achieving good contacts is vital for harnessing the fascinating properties of two-dimensional (2D) materials. However, unsatisfactory 2D material-metal interfaces remain a problem that hinders the successful application of 2D materials for fabricating nanodevices. In this study, Kelvin probe force microscopy (KPFM) and other high-resolution microscopy techniques are utilized to characterize the surface morphology and contact interface between MoS2 and common metals including Au, Ti, Pd, and Ni. Surface potential information, including the contact potential difference () and surface potential difference () of each MoS2-metal contact, is obtained. By comparing the surface potential distribution mappings with and without illumination, non-zero surface photovoltage (SPV) values and evident shift with amplitudes of 32 mV and 44 mV are observed for MoS2-Au and Ti, but not for MoS2-Pd and Ni. The Schottky barrier heights of MoS2-Au, Ti, Pd, and Ni are roughly evaluated from their I–V curves. Raman spectroscopy is also carried out to ensure more convincing results. All the results suggest that a smoother MoS2-metal interface results in better charge transport behaviors. Our analysis of the underlying mechanism and experimental findings offer a new perspective to better understand MoS2-metal contacts and underscore the fundamental importance of interface morphology for MoS2-based devices.

The zebrafish as a novel model for the in vivo study of Toxoplasma gondii replication and interaction with macrophages.

ABSTRACTToxoplasma gondii is an obligate intracellular parasite capable of invading any nucleated cell. Three main clonal lineages (type I, II, III) exist and murine models have driven the understanding of general and strain-specific immune mechanisms underlying Toxoplasma infection. However, murine models are limited for studying parasite-leukocyte interactions in vivo, and discrepancies exist between cellular immune responses observed in mouse versus human cells. Here, we developed a zebrafish infection model to study the innate immune response to Toxoplasma in vivo. By infecting the zebrafish hindbrain ventricle, and using high-resolution microscopy techniques coupled with computer vision-driven automated image analysis, we reveal that Toxoplasma invades brain cells and replicates inside a parasitophorous vacuole to which type I and III parasites recruit host cell mitochondria. We also show that type II and III strains maintain a higher infectious burden than type I strains. To understand how parasites are cleared in vivo, we further analyzed Toxoplasma-macrophage interactions using time-lapse microscopy and three-dimensional correlative light and electron microscopy (3D CLEM). Time-lapse microscopy revealed that macrophages are recruited to the infection site and play a key role in Toxoplasma control. High-resolution 3D CLEM revealed parasitophorous vacuole breakage in brain cells and macrophages in vivo, suggesting that cell-intrinsic mechanisms may be used to destroy the intracellular niche of tachyzoites. Together, our results demonstrate in vivo control of Toxoplasma by macrophages, and highlight the possibility that zebrafish may be further exploited as a novel model system for discoveries within the field of parasite immunity.This article has an associated First Person interview with the first author of the paper.

ZnWO4/SnO2@r-GO nanocomposite as an anode material for high capacity lithium ion battery

Lithium ion battery (LIB) is widely used energy storage device. Herein, we report the preparation of ZnWO4/SnO2 nanocomposite and ZnWO4/SnO2@r-GO nanocomposite via solvothermal method. The structural, elemental and morphological properties of the prepared samples are characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), high-resolution transmission electron microscopy (HR-TEM), Brunauer-Emmett-Teller (BET) measurements, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The prepared samples are tested as an anode for LIB. The ZnWO4/SnO2 (5%) nanocomposite delivers initial discharge capacity of 882 mAh g−1 at a current density of 100 mA g−1, while, the specific capacity increases with the increase of SnO2 upto 10% tested in present case. Further, ZnWO4/SnO2@r-GO nanocomposite exhibits a discharge capacity of 1486 mAh g−1 which is higher than that of ZnWO4/SnO2 nanocomposite. In addition, after 500 cycles ZnWO4/SnO2@r-GO nanocomposite exhibits 89.8% cycle life and 98% of discharge capacity retention. These results indicate that, ZnWO4/SnO2@r-GO nanocomposite is a promising anode material for LIB.

Identification of Biomarker Hyaluronan on Colon Cancer Extracellular Vesicles Using Correlative AFM and Spectroscopy.

Extracellular vesicles (EVs), naturally occurring nanosized vesicles secreted from cells, are essential for intercellular communication. They carry unique biomolecules on the surface or interior that are of great interest as biomarkers for various pathological conditions such as cancer. In this work, we use high-resolution atomic force microscopy (AFM) and spectroscopy (AFS) techniques to demonstrate differences between EVs derived from colon cancer cells and colon epithelial cells at the single-vesicle level. We observe that EV populations are significantly increased in the cancer cell media compared to the normal cell EVs. We show that both EVs display an EV marker, CD9, while EVs derived from the cancer cells are slightly higher in density. Hyaluronan (HA) is a nonsulfated glycosaminoglycan linked to malignant tumor growth according to recent reports. Interestingly, at the single-vesicle level, colon cancer EVs exhibit significantly increased HA surface densities compared to the normal EVs. Spectroscopic measurements such as Fourier transform infrared (FT-IR), circular dichroism (CD), and Raman spectroscopy unequivocally support the AFM and AFS measurements. To our knowledge, it represents the first report of detecting HA-coated EVs as a potential colon cancer biomarker. Taken together, this sensitive approach will be useful in identifying biomarkers in the early stages of detection and evaluation of cancer.

Designing a non-hazardous nano-carrier based on graphene oxide@Polyaniline-Praseodymium (III) for fabrication of the Active/Passive anti-corrosion coating

In this work, graphene oxide (GO) based nano-platforms were applied as a non-hazardous solid container with high encapsulating capacity and controllable release activity of eco-friendly inhibitor. For the first time, the adsorption and release properties of the praseodymium cations (Pr3+) on GO nanosheets functionalized with polyaniline (PANI) were investigated. The Pr3+ cations adsorption/desorption capacity of GOPANI nano-sheets was assessed by Inductively Coupled Plasma (ICP), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FE-SEM), and High-resolution transmission electron microscopy (HR-TEM) techniques. The obtained results proved that the container modified with Pr3+ cations at pH of 7, 600 ppm of adsorpt, and 1 mg/cc of adsorbent dosage provided the highest capacity of inhibitors adsorption/release rates. The adsorption capacity of the GO-PANIs reached more than 500 mg/g. Also, the modified carrier desorbed about 70 % of loaded Pr3+ cations in the corrosion simulated condition. The self-healing anti-corrosion ability of the constructed containers in an organic-inorganic hybrid coating (OIHC) was shown by electrochemical analyses results. The resistance of coating with the loaded carriers has increased about 1 order of magnitude in comparison with the neat silane. Moreover, the scratched coatings containing the inhibitor loaded GO-PANIs showed extraordinary total resistance of about 25 Kohm. cm2.

TEM Nanostructural Investigation of Ag-Conductive Filaments in Polycrystalline ZnO-Based Resistive Switching Devices.

Memristive devices based on a resistive switching mechanism are considered very promising for nonvolatile memory and unconventional computing applications, even though many details of the switching mechanisms are not yet fully understood. Here, we report a nanostructural study by means of high-resolution transmission electron microscopy and spectroscopy techniques of a Ag/ZnO/Pt memristive device. To ease the localization of the filament position for its characterization, we propose to use the guiding effect of regular perturbation arrays obtained by FIB technology to assist the filament formation. HRTEM and EDX were used to identify the composition and crystalline structure of the so-obtained conductive filaments and surrounding regions. It was determined that the conducting paths are composed mainly of monocrystalline Ag, which remains polycrystalline in some circumstances, including the zone where the switching occurs and at secondary filaments created at the grain boundaries of the polycrystalline ZnO matrix. We also observed that the ZnO matrix shows a degraded quality in the switching zone, while it remains unaltered in the rest of the memristive device.

Synthesis and structural characterization of MoS2 micropyramids

Two-dimensional (2D) materials based on molybdenum sulfide (MoS2) have shown promising applications in semiconductors, optoelectronics, and catalysis. The variety of applications implies a controlled manipulation of purity, shape, and phase of such materials. This work elaborates on the structural characterization of MoS2 micro-assemblies produced in a chemical vapor deposition (CVD) system with emphasis on the pyramidal structures formed at high temperature and low gas rate, on a silicon dioxide (SiO2) substrate. A precise control of temperature and gas rate in the CVD process prompts the growth of pyramidal and other micron-size arrangements of MoS2 layers. An integrative set of high-resolution and analytical electron microscopy techniques, in conjunction with Raman and X-ray photoelectron spectroscopy (XPS), revealed the structural features of the MoS2 microstructures. Raman and XPS confirmed the presence of MoS2 and some residual oxide phases. Ultra-high-resolution scanning electron microscopy provided direct observation of the distinctive stacking of layers forming the pyramidal microstructures. Cross section samples from selected structures were done using focused ion beam. An extent of transmission electron microscopy and Cs-corrected scanning transmission electron microscopy (Cs-corrected STEM) results is discussed. This approach allowed to understand the growth mechanism of the triangular MoS2 microstructures through spiral grow around a screw dislocation, initiated at the center of the assembly.

SrCoxZrxFe12−2xO19 and SrNixZrxFe12−2xO19 hexaferrites: A Comparison Study of AC Susceptibility, FC-ZFC and hyperfine interactions

This study compares the AC susceptibility, FC-ZFC and hyperfine interactions of Sr(CoxZrx)Fe12−2xO19 and Sr(NixZrx)Fe12−2xO19 hexaferrites (HFs) manufactured via ultrasonic route. The formation of M-type hexaferrites have been confirmed by X-ray powder diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM) techniques. Scanning electron microscopy (SEM) presented the hexagonal-platelet morphology of products. The variation in isomer shift, line width, quadrupole splitting and hyperfine magnetic field values of them have been governed by 57Fe Mössbauer spectroscopy which showed that Co2+ and Zr4+ ions located at generally octahedral and 2b sites, while Ni2+ and Zr4+ ions located at octahedral 12k and 4f2 sites. Measurements of magnetization versus temperature (M-T) and AC susceptibility versus temperature were carried out. The various synthesized HFs displayed ferrimagnetic behavior in the temperature interval of 10–325 K. Super-spin glass-like behavior was noticed at lower temperatures. Neel-Arrhenius and Vogel-Fulcher models were used to explore the experimental AC susceptibility. It was showed that a lower Co-Zr substitution content leads to strengthen the magnetic exchange interactions, however even low Ni-Zr substitution content provoke a reduction in magnetic exchange interactions.

Autofluorescent Granules of the Human Retinal Pigment Epithelium: Phenotypes, Intracellular Distribution, and Age-Related Topography.

PurposeThe human retinal pigment epithelium (RPE) accumulates granules significant for autofluorescence imaging. Knowledge of intracellular accumulation and distribution is limited. Using high-resolution microscopy techniques, we determined the total number of granules per cell, intracellular distribution, and changes related to retinal topography and age.MethodsRPE cells from the fovea, perifovea, and near-periphery of 15 human RPE flat mounts were imaged using structured illumination microscopy (SIM) and confocal fluorescence microscopy in young (≤51 years, n = 8) and older (>80 years, n = 7) donors. Using custom FIJI plugins, granules were marked with computer assistance, classified based on morphological and autofluorescence properties, and analyzed with regard to intracellular distribution, total number per cell, and granule density.ResultsA total of 193,096 granules in 450 RPE cell bodies were analyzed. Based on autofluorescence properties, size, and composition, the RPE granules exhibited nine different phenotypes (lipofuscin, two; melanolipofuscin, five; melanosomes, two), distinguishable by SIM. Overall, lipofuscin (low at the fovea but increases with eccentricity and age) and melanolipofuscin (equally distributed at all three locations with no age-related changes) were the major granule types. Melanosomes were under-represented due to suboptimal visualization of apical processes in flat mounts.ConclusionsLow lipofuscin and high melanolipofuscin content within foveal RPE cell bodies and abundant lipofuscin at the perifovea suggest a different genesis, plausibly related to the population of overlying photoreceptors (fovea, cones only; perifovea, highest rod density). This systematic analysis provides further insight into RPE cell and granule physiology and links granule load to cell autofluorescence, providing a subcellular basis for the interpretation of clinical fundus autofluorescence.

On-Surface Synthesis of Unsaturated Carbon Nanostructures with Regularly Fused Pentagon-Heptagon Pairs.

Multiple fused pentagon–heptagon pairs are frequently found as defects at the grain boundaries of the hexagonal graphene lattice and are suggested to have a fundamental influence on graphene-related materials. However, the construction of sp2-carbon skeletons with multiple regularly fused pentagon–heptagon pairs is challenging. In this work, we found that the pentagon–heptagon skeleton of azulene was rearranged during the thermal reaction of an azulene-incorporated organometallic polymer on Au(111). The resulting sp2-carbon frameworks were characterized by high-resolution scanning probe microscopy techniques and feature novel polycyclic architectures composed of multiple regularly fused pentagon–heptagon pairs. Moreover, the calculated analysis of its aromaticity revealed a peculiar polar electronic structure.

Collagen fibril abnormalities in human and mice abdominal aortic aneurysm

Vascular diseases like abdominal aortic aneurysms (AAA) are characterized by a drastic remodeling of the vessel wall, accompanied with changes in the elastin and collagen content. At the macromolecular level, the elastin fibers in AAA have been reported to undergo significant structural alterations. While the undulations (waviness) of the collagen fibers is also reduced in AAA, very little is understood about changes in the collagen fibril at the sub-fiber level in AAA as well as in other vascular pathologies. In this study we investigated structural changes in collagen fibrils in human AAA tissue extracted at the time of vascular surgery and in aorta extracted from angiotensin II (AngII) infused ApoE-/- mouse model of AAA. Collagen fibril structure was examined using transmission electron microscopy and atomic force microscopy. Images were analyzed to ascertain length and depth of D-periodicity, fibril diameter and fibril curvature. Abnormal collagen fibrils with compromised D-periodic banding were observed in the excised human tissue and in remodeled regions of AAA in AngII infused mice. These abnormal fibrils were characterized by statistically significant reduction in depths of D-periods and an increased curvature of collagen fibrils. These features were more pronounced in human AAA as compared to murine samples. Thoracic aorta from Ang II-infused mice, abdominal aorta from saline-infused mice, and abdominal aorta from non-AAA human controls did not contain abnormal collagen fibrils. The structural alterations in abnormal collagen fibrils appear similar to those reported for collagen fibrils subjected to mechanical overload or chronic inflammation in other tissues. Detection of abnormal collagen could be utilized to better understand the functional properties of the underlying extracellular matrix in vascular as well as other pathologies. STATEMENT OF SIGNIFICANCE: Several vascular diseases including abdominal aortic aneurysm (AAA) are characterized by extensive remodeling in the vessel wall. Although structural alterations in elastin fibers are well characterized in vascular diseases, very little is known about the collagen fibril structure in these diseases. We report here a comprehensive ultrastructural evaluation of the collagen fibrils in AAA, using high-resolution microscopy techniques like transmission electron microscopy (TEM) and atomic force microscopy (AFM). We elucidate how abnormal collagen fibrils with compromised D-periodicity and increased fibril curvature are present in the vascular tissue in both clinical AAA as well as in murine models. We discuss how these abnormal collagen fibrils are likely a consequence of mechanical overload accompanying AAA and could impact the functional properties of the underlying tissue.