Influence of nanostructure composition on its morphometric characterization by different techniques

Morphometric characterization of nanoparticles is crucial to determine their biological effects and to obtain a formulation pattern. Determining the best technique requires knowledge of the particles being analyzed, the intended application of the particles, and the limitations of the techniques being considered. The aim of this article was to present transmission (TEM) and scanning (SEM) electron microscopy protocols for the analysis of two different nanostructures, namely polymeric nanoemulsion and poly(lactic‐co‐glycolic acid) (PLGA) nanoparticles, and to compare these results with conventional dynamic light scattering (DLS) measurements. The mean hydrodynamic diameter, the polydispersity index, and zeta potential of the nanostructures of polymeric nanoemulsion were 370.5 ± 0.8 nm, 0.133 ± 0.01, and ?36.1 ± 0.15 mV, respectively, and for PLGA nanoparticles were 246.79 ± 5.03 nm, 0.096 ± 0.025, and ?4.94 ± 0.86 mV, respectively. TEM analysis of polymeric nanoemulsion revealed a mean diameter of 374 ± 117 nm. SEM analysis showed a mean diameter of 368 ± 69 nm prior to gold coating and 448 ± 70 nm after gold coating. PLGA nanoparticles had a diameter of 131 ± 41.18 nm in TEM and 193 ± 101 nm in SEM. Morphologically, in TEM analysis, the polymeric nanoemulsions were spherical, with variable electron density, very few showing an electron‐dense core and others an electron‐dense surface. PLGA nanoparticles were round, with an electron‐lucent core and electron‐dense surface. In SEM, polymeric nanoemulsions were also spherical with a rough surface, and PLGA nanoparticles were round with a smooth surface. The results show that the “gold standards” for morphometric characterization of polymeric nanoemulsion and PLGA nanoparticles were, respectively, SEM without gold coating and TEM with negative staining. Microsc. Res. Tech. 77:691–696, 2014. © 2014 Wiley Periodicals, Inc.     

基于腔内原位探测的空间冷原子微波钟

原子钟作为目前最精密的计时仪器,在国民经济和国家安全各领域发挥着重要作用。 在地球轨道卫星上运行高精度原 子钟,可以在地球大范围内开展高精度时间同步与比对。 不同于以往通过抛射冷原子团两次经过微波腔实现 Ramsey 微波作用 的空间冷原子钟,提出了一种新型的基于腔内原位探测的空间冷原子微波钟方案,在同一微波谐振腔内先后完成铷 87 原子的 激光冷却、原子微波相互作用、冷原子探测等过程。 该方案可以更好的利用微重力环境提高钟周期中原子与微波相互作用时间 的占空比,从而有效减小 Dick 效应对原子钟性能的影响。 介绍了冷原子微波钟系统设计与工作原理,给出了微重力环境下性 能分析和预期指标,最后展示了冷原子微波钟地面测试中获得的大约为 1. 35×10 -12 τ -1/ 2 的频率稳定度,初步展示了新型空间冷 原子钟方案的可行性。     

Imperative role of electron microscopy in toxicity assessment: A review

Electron microscope (EM) was developed in 1931 and since then microscopical examination of both the biological and non-biological samples has been revolutionized. Modifications in electron microscopy techniques, such as scanning EM and transmission EM, have widened their applicability in the various sectors such as understanding of drug toxicity, development of mechanism, criminal site investigation, and characterization of the nano-molecule. The present review summarizes its role in important aspects such as toxicity assessment and disease diagnosis in special reference to SARS-COV2. In the biological system, EM studies have elucidated the impact of toxicants at the ultra-structural level in various tissue in conformity to physiological alterations. Thus, EM can be concluded as an important tool in toxicity assessment and disease prognosis.     

Electron energy loss spectroscopy for analysis of inhaled ultrafine particles in rat lungs

Epidemiologic studies have associated cardiovascular morbidity and mortality with ambient particulate air pollution. Particles smaller than 100 nm in diameter (ultrafine particles) are present in the urban atmosphere in very high numbers yet at very low mass concentration. Organs beyond the lungs are considered as targets for inhaled ultrafine particles, whereby the route of particle translocation deeper into the lungs is unclear. Five rats were exposed to aerosols of ultrafine titanium dioxide particles of a count median diameter of 22 nm (geometric standard deviation, GSD 1.7) for 1 hour. The lungs were fixed by intravascular perfusion of fixatives immediately thereafter. TiO(2) particles in probes of the aerosol as well as in systematic tissue samples were analyzed with a LEO 912 transmission electron microscope equipped with an energy filter for elemental microanalysis. The characteristic energy loss spectra were obtained by fast spectrum acquisition. Aerosol particles as well as those in the lung tissue were unambiguously identified by electron energy loss spectroscopy. Particles were mainly found as small clusters with a rounded shape. Seven percent of the particles in the lung tissue had a needle-like shape. The size distribution of the cluster profiles in the tissue had a count median diameter of 29 nm (GSD 1.7), which indicates no severe clustering or reshaping of the originally inhaled particles. Electron energy loss spectroscopy and related analytical methods were found to be suitable to identify and localize ultrafine titanium dioxide particles within chemically fixed and resin-embedded lung tissue.     

A model of the deciliation process caused by Mycoplasma fermentans strain incognitus on respiratory epithelium

The aim of this study was to investigate by light microscopy as well as by scanning and transmission electron microscopy the deciliation process which takes place on the respiratory epithelium of tracheal explants after experimental infection with Mycoplasma fermentans strain incognitus. Time-point photography allowed distinguishing five phases which occurred during the infection on the epithelial cell surface: (1) Attachment of M. fermentans to the cilia causing clumping of the cilia tips; (2) matting of cilia into bundles; (3) formation of abnormally shaped and shorter cilia; (4) collapse of cilia onto the epithelial cell surface; and (5) widespread loss of cilia. Based on the photographic images, a schematic model of the deciliation process was developed. Various potential factors contributing to the cilia destruction are discussed, including the release of mycoplasmal toxins, the physical presence of a high number of M. fermentans cells attached to the cilia, and the depletion of culture medium components by the mycoplasmas. This model of M. fermentans strain incognitus infection of respiratory epithelium is important for understanding mycoplasmal pathogenicity on a comparative level.     

Study of temperature factors in cubic crystals by high-voltage electron diffraction

The critical voltages for systematic reflections and splits of Kikuchi lines were measured using a high-voltage electron microscope to investigate the atomic temperature factors in cubic crystals. The split of the Kikuchi line at the intersection with the forbidden 222 Kikuchi line as well as the critical voltage of the 333 reflection for Si and Ge decreased steeply with temperature. The temperature dependence showed that the anharmonic contribution to the atomic-temperature factor for Si and Ge is extremely weak in the temperature range 300 ～ 1078 K. On the contrary, the B factors obtained from the measured critical voltages for Al, Cu, and Fe varied nonlinearly with temperature, suggesting the importance of the anharmonic effect in the vibration of atoms. The observed temperature dependence of the critical voltages for the metals were compared with calculations based on harmonic, quasi-harmonic, and anharmonic approximations. The quasi-harmonic approximation that takes into account the thermal expansion modification reproduces well the observed values for Fe but not those for Al and Cu. The effect of intrinsic anharmonic vibration should be considered for reproducing the results for Al and Cu. Fitting the measured critical voltages with the calculated ones, we estimated the values for coefficients of the isolated atom potentials. The results are in good agreement with those obtained by neutron and X-ray diffraction.     

3-D morphological characterization of the liver parenchyma by atomic force microscopy and by scanning electron microscopy

A comparative study of atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging of the healthy human liver parenchyma was carried out to determine the similarities and the differences. In this study, we compared the fine hepatic structures as observed by SEM and AFM. Although AFM revealed such typical hepatic structures as bile canaliculi and hepatocytes, it also showed the location of the nucleus and chromatin granules in rough relief structure, which was not visible by SEM. By contrast, SEM visualized other structures, such as microvilli, the central vein, and collagenous fibers, none of which was visualized by AFM. For better orientation and confirmation of most of the structures imaged by SEM and AFM, Congo Red-stained specimens were also examined. Amyloid deposits in the Disse's spaces were shown especially clearly in these images. The differences between the SEM and AFM images reflected the characteristics of the detection systems and methods used for sample preparation. Our results reveal that more detailed information on hepatic morphology is obtained by exploiting the advantages of both SEM and AFM.     

New developments in the characterization of dislocation loops from LACBED patterns

The characterization of the Burgers vector of dislocations from large‐angle convergent‐beam electron diffraction (LACBED) patterns is now a well‐established method. The method has already been applied to relatively large and isolated dislocation loops in semiconductors. Nevertheless, some severe experimental difficulties are encountered with small dislocation loops. By using a 2 µm selected‐area aperture and a carbon contamination point to mark the loop of interest, we were able to characterize both the plane and the Burgers vector of dislocation loops of a few tens of nanometres in size present in Al‐Cu‐Mg alloys.     

Fabrication of a versatile substrate for finding samples on the nanometer scale

With increasing interest in nanometer scale studies, a common research issue is the need to use different analytical systems with a universal substrate to relocate objects on the nanometer scale. Our paper addresses this need. Using the delicate milling capability of a focused ion beam (FIB) system, a region of interest (ROI) on a sample is labelled via a milled reference grid. FIB technology allows for milling and deposition of material at the sub 20-nm level, in a similar user environment as a standard scanning electron microscope (SEM). Presently commercially available transmission electron microscope (TEM) grids have spacings on the order 100 μm on average; this technique can extend this dimension down to the submicrometre level. With a grid on the order of a few micrometres optical, FIBs, TEMs, scanning electron microscopes (SEMs), and atomic force microscopes (AFM) are able to image the ROI, without special chemical processes or conductive coatings required. To demonstrate, Au nanoparticles of ∼ 25 nm in size were placed on a commercial Formvar^®- and carbon-coated TEM grid and later milled with a grid pattern. Demonstration of this technique is also extended to bulk glass substrates for the purpose of sample location. This process is explained and demonstrated using all of the aforementioned analytical techniques.     

Image matching between experimental and simulated high‐resolution electron micrographs of sapphire on the orientation

The effects of imaging parameters have been studied on their roles of the severe mismatches between experimental and simulated high‐resolution transmission electron micrographs of sapphire along the direction. Image simulation and convergent‐beam electron diffraction techniques have been performed on misalignments of the electron beam and the crystal specimen. Based on this study, we have introduced an approach to achieve reliable simulation for experimental images of sapphire on the projection by the use of iterative digital image matching.     

TEM study of chirality in MoS2 nanotubes

The dark-field diffraction contrast of helical nanotubes (NTs) is shown to be asymmetric when an NT is tilted at appropriate angle with respect to the incident electron beam. This phenomenon was used for the chirality determination of multi-shell NTs observed in MoS₂ layered compound. Both kinds of NT — helical and non-helical — were found. In the case of helical NTs only right-hand chirality was observed.     

A comparison of two models for the characteristic X-ray fluorescence correction in thin foil analysis

It is shown that Philibert & Tixier's calculation for the contribution of characteristic fluorescence in thin foil X-ray microanalysis is in error. The calculation of Nockolds et al. for this contribution is shown to be correct.     

Influence of weave structures on the tribological properties of hybrid Kevlar/PTFE fabric composites

The existing research of the woven fabric self-lubricating liner mainly focus on the tribological performance improvements and the service life raised by changing different fiber type combinations, adding additive modification, and performing fiber surface modification. As fabric composites, the weave structures play an important role in the mechanical and tribological performances of the liners. However, hardly any literature is available on the friction and wear behavior of such composites with different weave structures. In this paper, three weave structures (plain, twill 1/3 and satin 8/5) of hybrid Kevlar/PTFE fabric composites are selected and pin-on-flat linear reciprocating wear studies are done on a CETR tester under different pressures and different frequencies. The relationship between the tensile strength and the wear performance are studied. The morphologies of the worn surfaces under the typical test conditions are analyzed by means of scanning electron microscopy (SEM). The analysis results show that at 10 MPa, satin 8/5 performs the best in friction-reduction and antiwear performance, and plain is the worst. At 30 MPa, however, the antiwear performance is reversed and satin 8/5 does not even complete the 2 h wear test at 16 Hz. There is no clear evidence proving that the tensile strength has an influence on the wear performance. So the different tribological performance of the three weave structures of fabric composites may be attributed to the different PTFE proportions in the fabric surface and the different wear mechanisms. The fabric composites are divided into three regions: the lubrication region, the reinforced region and the bonding region. The major mechanisms are fatigue wear and the shear effects of the friction force in the lubrication region. In the reinforced region fiber-matrix de-bonding and fiber breakage are involved. The proposed research proposes a regional wear model and further indicates the wear process and the wear mechanism of fabric composites.