Nanoscale characterization of gold nanoparticles created by in situ reduction at a polymeric surface

Transmission Electron Microscopy is used as a quantitative method to measure the shapes, sizes and volumes of gold nanoparticles created at a polymeric surface by three different in situ synthesis methods. The atomic number contrast (Z‐contrast) imaging technique reveals nanoparticles which are formed on the surface of the polymer. However, with certain reducing agents, the gold nanoparticles are additionally found up to 20 nm below the polymer surface. In addition, plan‐view high‐angle annular dark‐field scanning transmission electron microscopy images were statistically analyzed on one sample to measure the volume, height and effective diameter of the gold nanoparticles and their size distributions. Depth analysis from high‐angle annular dark‐field scanning transmission electron microscopy micrographs also gives information on the dominant shape of the nanoparticles.     

High resolution SEM imaging of gold nanoparticles in cells and tissues

The growing demand of gold nanoparticles in medical applications increases the need for simple and efficient characterization methods of the interaction between the nanoparticles and biological systems. Due to its nanometre resolution, modern scanning electron microscopy (SEM) offers straightforward visualization of metallic nanoparticles down to a few nanometre size, almost without any special preparation step. However, visualization of biological materials in SEM requires complicated preparation procedure, which is typically finished by metal coating needed to decrease charging artefacts and quick radiation damage of biomaterials in the course of SEM imaging. The finest conductive metal coating available is usually composed of a few nanometre size clusters, which are almost identical to the metal nanoparticles employed in medical applications. Therefore, SEM monitoring of metal nanoparticles within cells and tissues is incompatible with the conventional preparation methods. In this work, we show that charging artefacts related to non‐conductive biological specimen can be successfully eliminated by placing the uncoated biological sample on a conductive substrate. By growing the cells on glass pre‐coated with a chromium layer, we were able to observe the uptake of 10 nm gold nanoparticles inside uncoated and unstained macrophages and keratinocytes cells. Imaging in back scattered electrons allowed observation of gold nanoparticles located inside the cells, while imaging in secondary electron gave information on gold nanoparticles located on the surface of the cells. By mounting a skin cross‐section on an improved conductive holder, consisting of a silicon substrate coated with copper, we were able to observe penetration of gold nanoparticles of only 5 nm size through the skin barrier in an uncoated skin tissue. The described method offers a convenient modification in preparation procedure for biological samples to be analyzed in SEM. The method provides high conductivity without application of surface coating and requires less time and a reduced use of toxic chemicals.     

A Brief Discussion About Image Quality and SEM Methods for Quantitative Fractography of Polymer Composites

The methodology for fracture analysis of polymeric composites with scanning electron microscopes (SEM) is still under discussion. Many authors prefer to use sputter coating with a conductive material instead of applying low‐voltage (LV) or variable‐pressure (VP) methods, which preserves the original surfaces. The present work examines the effects of sputter coating with 25 nm of gold on the topography of carbon‐epoxy composites fracture surfaces, using an atomic force microscope. Also, the influence of SEM imaging parameters on fractal measurements is evaluated for the VP‐SEM and LV‐SEM methods. It was observed that topographic measurements were not significantly affected by the gold coating at tested scale. Moreover, changes on SEM setup leads to nonlinear outcome on texture parameters, such as fractal dimension and entropy values. For VP‐SEM or LV‐SEM, fractal dimension and entropy values did not present any evident relation with image quality parameters, but the resolution must be optimized with imaging setup, accompanied by charge neutralization. SCANNING 35: 196‐204, 2013. © 2012 Wiley Periodicals, Inc.     

Cryogenic transmission electron microscopy study: preparation of vesicular dispersions by quenching microemulsions

We previously showed that long‐lived nanoemulsions, seeming initially vesicular, might be prepared simply by diluting and cooling (quenching) warm microemulsions with n‐hexadecane with precooled water. In this paper, we confirm that these systems are vesicular dispersions when fresh, and they can be made with similar structures and compositional dependence using alkanes with chain lengths ranging from octane to hexadecane. The nanostructures of fresh nanoemulsions are imaged with cryogenic transmission electron microscopy (cryo‐TEM). We confirm that water‐continuous microemulsions give simple dispersions of vesicles (sometimes unilamellar), typically less than 100 nm in diameter; these systems can avoid separation for over 2 months. Selected samples were also prepared using halogenated alkanes to create additional contrast in the cryo‐TEM, allowing us to confirm that the oil is located in the observed vesicular structures.     

Controlled Synthesis and Optical Properties of Pure Gold Nanoparticles

Abstract

Gold nanoparticles were synthesized by laser ablation of a gold metallic disc at wavelengths of 532 nm and 355 nm with 7 ns pulse duration in the pure water. The colloidal gold nanoparticles were characterized by ultraviolet-visible absorption spectroscopy, transmission electron microscopy, and fluorescence spectrometry. The presence of a surface plasmon resonance peak around ～ 524 nm indicates the formation of gold nanoparticles. The formation efficiencies of gold nanoparticles in colloids were found to increase when ablating the gold metallic disc with a laser having a longer wavelength. The size distributions of the gold nanoparticles thus produced were measured by transmission electron microscopy. A reduction in mean diameter of the particles was observed with a decrease in the laser wavelength under the irradiation at a high fluence of 25 mJ/pulse. The fluorescence spectroscopy demonstrated that these gold nanoparticles are fluorescent, showing a strong blue emission intensity at 458 nm.     

Electron Beam Induced Growth of Silver Nanoparticles

An electron beam inducing method for sprouting large quantities of silver nanoparticles on the surface of silver chloride particles is reported. The electron beam driven process was characterized by time‐dependent scanning electron microscope (SEM) and energy dispersive spectrum (EDS), allowing for observing several key intermediates in and characteristics of the growth process. Theoretical calculation coupled with experimental observation demonstrated that the growth of silver nanoparticles was mostly related to the current density of electron beam. Decomposition of the silver chloride on the surface of sample was under electron beam irradiation resulted in silver nanoparticles and chlorine. This phenomenon could be useful in developing a novel mechanism for preparation of nanostructures and proposing a reference to avoid image distortion during the characterization of silver compounds under SEM. SCANNING 35: 69‐74, 2013. © 2012 Wiley Periodicals, Inc.     

The Preparation and Tribological Investigation of Ni–P Amorphous Alloy Nanoparticles

Amorphous Ni–P alloy nanoparticles were synthesized by chemical reduction of nickel acetate in water reacted with sodium hypophosphite under stirring. The nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Results of XRD and TEM showed that nanoparticles have an average diameter 100 nm. And XPS analysis indicated that part of the surface of Ni–P amorphous alloy nanoparticles was oxidized. The tribological properties of the prepared Ni–P nanoparticles as an additive in lithium grease were evaluated with a four-ball friction and wear tester. The worn surfaces of the lubricated GCr15 steel were analyzed by means of XPS and scanning electron microscopy (SEM). The lubricating mechanisms were discussed on the basis of XPS and SEM analyses of the worn steel surfaces. The results show that these nanoparticles as a grease additive can effectively enhance the friction-reduction and antiwear ability of lithium grease. Tribochemical reactions were involved for steel–steel frictional pair lubricated with the lithium grease containing amorphous Ni–P alloy nanoparticles, with the formation of a boundary lubricating and protecting film composed of additives of lithium grease and tribochemical reaction products (iron phosphate, iron oxides, nickel oxide, nickel, etc.) of the lubricants. This contributes to improve the tribological properties of the lithium grease.     

Traditional coating techniques in scanning electron microscopy compared to uncoated charge compensator technology: Looking at human blood fibrin networks with the ZEISS ULTRA Plus FEG‐SEM

Scanning electron microscopy (SEM) studies surface morphology. Biological material needs to be coated to render the material conductive, and gold coating is traditionally used, although other coating material like carbon and ruthenium vapors may also be used. With modern SEM technology (e.g., ZEISS ULTRA Plus FEG‐SEM), we are able to work at very low kilovolts and also view fine surface structure in much better detail than with previous older technology. Some machines also allow for the study of uncoated material, although this is usually not done with biological material. This study focuses on surface clarity by comparing gold, ruthenium vapor, and carbon coating techniques for biological material. Human fibrin networks are used as example. Uncoated specimens are also viewed with a ZEISS ULTRA Plus FEG‐SEM because of its unique nitrogen charge compensator, and here, the first micrographs for uncoated human fibrin networks versus carbon, gold, and ruthenium coating are shown. We conclude that gold coating for biological material is not preferable with the latest SEM machines, as this method forms gold islands on top of the biological material and therefore produces a false surface morphology. Microsc. Res. Tech., 2011. © 2010 Wiley‐Liss, Inc.     

Structure analysis of sputter-coated and ion-beam sputter-coated films: a comparative study

Gold, platinum and tungsten films were deposited by low energy input (7 mA, 450 V), or high deposition rate (80 mA, 1500 V), diode sputter coating and by ion beam sputter coating. Film structures on Formvar coated grids and on the surface of coated erythrocytes, resin embedded, sectioned, and recorded at high magnification in a TEM were compared using computer-assisted measurements and analysis of film thickness and grain size. The average grain size of the thinnest gold and platinum films was relatively independent of the mode or rate of deposition but as the film thickness increased, significant differences in grain size and film structure were observed. Thick platinum or gold films deposited by low energy input sputter coating contained large grain size and electron transparent cracks; however, more even films with narrower cracks but larger grain size were produced at high deposition rates. Ion beam sputter coated gold had relatively large grain size in 10 nm thick films, but beyond this thickness the grains coalesced to form a continuous film. Platinum films deposited by ion beam sputter coating were even and free of electron transparent cracks and had a very small grain size (1–2 nm), which was relatively independent of the film thickness. Tungsten deposition either by low energy input or ion beam sputter coating resulted in fine grained even films which were free of electron transparent cracks. Such films remained granular in substructure and had a grain size of about 1 nm which was relatively independent of film thickness. Tungsten films produced at high deposition rates were of poorer quality. We conclude that thick diode sputter coated platinum and gold films are best deposited at high deposition rates provided the specimens are not heat sensitive, the improvement in film structure being more significant than the slight increase in grain size. Thick diode or ion beam sputter coated gold films should be suitable for low resolution SEM, and thin discontinuous gold films for medium resolution SEM. Diode sputter coated platinum should be suitable for medium resolution SEM and ion beam sputter coated platinum for medium and some high resolution SEM. 1–5 nm thick tungsten films, deposited by low energy input or ion beam sputter coating should be suitable for high resolution SEM, particularly where contrast is of less importance than resolution.     

Topography and thickness of air-dried human platelets measured by correlative transmission and scanning electron microscopy.

Human platelets rapidly air-dried on carbon-coated grids were examined by transmission and scanning electron microscopy. Whole cell mounts were photographed in a transmission electron microscope (TEM), coated with gold, and then examined in a scanning electron microscope (SEM). The thickness of the cytoplasm towards the centre of the cells was estimated to be 20-40 nm, and the rim of dense material surrounding the cells was 40 nm thick. Some dense bodies stood out as much as 100 nm above the dried cytoplasm. These measurements are important for evaluating cytoplasmic volume during microprobe analyses of air-dried platelet preparations.     

Use of sputter coating to prepare whole mounts of cytoskeletons for transmission and high-resolution scanning and scanning transmission electron microscopy

This paper describes the use of sputter coating to prepare detergent-extracted cytoskeletons for observation by scanning (SEM), scanning transmission (STEM), inverted contrast STEM, and transmission (TEM) electron microscopy. Sputtered coats of 1–2 nm of platinum or tungsten provide both an adequate secondary electron signal for SEM and good contrast for STEM and TEM. At the same time, the grain size of the coating is sufficiently fine to be just at (platinum) or below (tungsten) the limit of resolution for SEM and STEM. In TEM, the granular structure of platinum coats is resolved, and platinum decoration artifacts are observed on the surface of structures. The platinum is deposited as small islands with a periodic distribution that may reveal information about the underlying molecular structure. This method produces samples that are similar in appearance to replicas prepared by low-angle rotary shadowing with platinum and carbon. However, the sputter-coating method is easier to use; more widely available to investigators; and compatible with SEM, STEM, and TEM. It may also be combined with immunogold and other labeling methods. While TEM provides the highest resolution images of sputter-coated cytoskeletons, it also damages the specimens owing to heating in the beam. In SEM and STEM cytoskeletons are stable and the resolution is adequate to resolve individual microfilaments. The best single method for visualizing cytoskeletons is inverted contrast STEM, which images both the metal-coated cytoskeletal structures and electron-dense material within the nucleus and cytoplasm as white against a dark background. STEM and TEM were both suitable for visualizing colloidal gold particles in immunolabeled samples.     

High-resolution scanning electron microscopy of immunogold-labelled cells by the use of thin plasma coating of osmium

The feasibility of plasma coating of a thin osmium layer for high‐resolution immuno‐scanning electron microscopy of cell surfaces was tested, using Drosophila embryonic motor neurones as a model system. The neuro‐muscular preparations were fixed with formaldehyde and labelled with a neurone‐specific antibody and 10 or 5 nm colloidal gold‐conjugated secondary antibodies. The specimens were post‐fixed with osmium tetroxide and freeze‐dried. Then they were coated with a 1–2 nm thick layer of osmium using a hollow cathode plasma coater. The thin and continuous coating of amorphous osmium gave good signals of gold particles and fine surface structures of neurites in backscattered electron images simultaneously. This method makes it possible to visualize the antigen distribution and the three‐dimensionally complex surface structures of cellular processes with a resolution of several nanometres.     

3D‐quantum interferometer using silicon microring‐embedded gold grating circuit

A 3D (three‐dimensional) quantum interferometer consisting of a silicon microring circuit proposed. The interferometer based on the electron spin cloud projections generated by microring‐embedded gold grating. The electron cloud oscillations result from the excitation of the gold grating at the center of the silicon microring by the dark soliton pulse of 1.50 μm center wavelength. The electron cloud spin‐down, spin‐up automatically formed in the two axes (x, y, respectively) and propagated along the z‐axis. In this proposal, the sensing mechanism of the circuit is manipulated by varying the reflector gold lengths of the sensing arm. The electron cloud spin coupled and changed by changing the gold lengths. The sensitivity measurement of the 3D quantum interferometer for three gold layer lengths of 100 nm, 500 nm, and 1,000 nm is (47.62 nm fs^?1, ±0.4762 fs^?1, ±0.01 nm^?1), (238.10 nm fs^?1, ±0.4762 fs^?1, ±0.002 nm^?1), (476.20 nm fs^?1, ±0.4762 fs^?1, ±0.001 nm^?1), respectively. The used circuit parameters are the real ones that can be fabricated by the currently available technology. Moreover, the silicon micro ring circuit acts as a plasmonic antenna, which can apply for wireless quantum communication. The electron cloud spin projection space–time control can apply for quantum cellular automata.     

Correlative scanning electron and confocal microscopy imaging of labeled cells coated by indium‐tin‐oxide

Confocal microscopy imaging of cells allows to visualize the presence of specific antigens by using fluorescent tags or fluorescent proteins, with resolution of few hundreds of nanometers, providing their localization in a large field‐of‐view and the understanding of their cellular function. Conversely, in scanning electron microscopy (SEM), the surface morphology of cells is imaged down to nanometer scale using secondary electrons. Combining both imaging techniques have brought to the correlative light and electron microscopy, contributing to investigate the existing relationships between biological surface structures and functions. Furthermore, in SEM, backscattered electrons (BSE) can image local compositional differences, like those due to nanosized gold particles labeling cellular surface antigens. To perform SEM imaging of cells, they could be grown on conducting substrates, but obtaining images of limited quality. Alternatively, they could be rendered electrically conductive, coating them with a thin metal layer. However, when BSE are collected to detect gold‐labeled surface antigens, heavy metals cannot be used as coating material, as they would mask the BSE signal produced by the markers. Cell surface could be then coated with a thin layer of chromium, but this results in a loss of conductivity due to the fast chromium oxidation, if the samples come in contact with air. In order to overcome these major limitations, a thin layer of indium‐tin‐oxide was deposited by ion‐sputtering on gold‐decorated HeLa cells and neurons. Indium‐tin‐oxide was able to provide stable electrical conductivity and preservation of the BSE signal coming from the gold‐conjugated markers. Microsc. Res. Tech. 78:433–443, 2015. © 2015 Wiley Periodicals, Inc.     

STEM study of Li4Ti5O12 anode material modified with Ag nanoparticles

Comprehensive scanning transmission electron microscopy (STEM) analysis of Li₄Ti₅O₁₂ (LTO) powder modified by deposited Ag nanoparticles was performed. Nanocomposite powders with Ag content of 1 wt.%, 4 wt.%, 10 wt.% were fabricated in a chemical process from suspensions of Ag and LTO. Apart from the STEM results, the presence of pure silver on the surface of the ceramic powder was confirmed by XRD and XPS analyses. The silver particles deposited on the LTO particles were characterized using the EDS mapping technique. The quantified results of the EDS mapping showed a relatively homogenous distribution of silver nanoparticles on the powder surface for every metal content. The mean diameter of the nanoparticles deposited on the LTO powder was about 4 nm in all cases. An increase in the Ag content during chemical surface modification did not cause changes in the microstructure. Focusing on an analysis of the metallic nanoparticles on the ceramic powder, electron tomography was used as an investigative technique. A very precise analysis of three‐dimensional nanostructures is desirable for a comprehensive analysis of complex materials. The quantified analysis of the Ag nanoparticles visualized using electron tomography confirmed the results of the size measurements taken from the two‐dimensional EDS maps.     

Rapid detection of microorganisms with nanoparticles and electron microscopy

Rapid detection of microorganisms is highly desirable. A procedure has been developed based on interactions between gold nanoparticles and proteins of microorganisms (Escherichia coli, Rhodococcus rhodochrous, and Candida sp.) followed by scanning electron microscopy (SEM). The nanoparticle-cell interaction was confirmed by ultraviolet resonance Raman spectroscopy (UVRS) in the SEM focus. Cell suspensions in a buffer were interacted with gold nanoparticles (<10 nm in diameter) prepared from tetrachloroauric acid and sodium borohydride. Possible interference of elevated salt concentrations was eliminated by dialysis in deionized water. Small (10 microL) aliquots of cell-nanoparticle suspensions were dried on a silicon wafer and photographed under an SEM. Characteristic bacterial or yeast cell images in the micrographs indicated the actual presence of microorganisms in the suspension examined. This was further confirmed by UV resonance Raman spectroscopy.     

Synthesis and tribological behaviour of oleic acid‐capped lanthanum borate/graphene oxide nanocomposites

The lanthanum borate/graphene oxide (LB/GO) nanocomposites were obtained by GO decorated by LB using an eco‐friendly hydrothermal method. For improving the oil solubility of the LB/GO nanocomposites, the oleic acid (OA)‐capped LB/GO (OA–LB/GO) nanocomposites were achieved. The as‐prepared nanocomposites were determined by a series of characterisations such as Fourier transform‐infrared spectroscopy (FT‐IR), X‐ray powder diffraction (XRD), Raman, UV‐vis, transmission electron microscopy (TEM) and SEM. The results indicated that most of LB nanoparticles with the size of 50–100 nm were well loaded on the surface of GO nanosheets. In addition, the tribological properties of the as‐prepared nanocomposites were tested by a four‐ball friction machine. The results demonstrated that the OA–LB/GO nanocomposites were of good anti‐wear ability and excellent load‐carrying capacity. Copyright © 2016 John Wiley & Sons, Ltd.     

Particle size analysis: 90Y and 99mTc‐labelled colloids

Colloidal particle size is an important characteristic to consider when choosing a radiopharmaceutical for diagnosis and therapeutic purposes in nuclear medicine. Photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM) were used to determine the particle‐size distribution of ⁹⁰Y‐ and ^99mTc‐labelled antimony trisulfide (Sb₂S₃) and tin colloids (Sn‐colloid). ⁹⁰Y‐Sb₂S₃ and ^99mTc‐Sb₂S₃ were found to have a diameter of 28.92 ± 0.14 and 35.61 ± 0.11 nm, respectively, by PCS. By TEM, ⁹⁰Y‐Sb₂S₃ particles were measured to be 14.33 ± 0.09 nm. ⁹⁰Y‐labelled Sn colloid were found to exist with a d_v(max1) of 805 nm and a d_v(max2) of 2590 nm, by PCS, whereas ^99mTc‐Sn colloid was shown to have more than 80% of radioactive particles of approximately 910 nm by PCS. For ⁹⁰Y‐labelled Sb₂S₃ and Sn colloid, a comparison of TEM and PCS indicates that these techniques found significantly different mean diameters. TEM has an excellent resolution necessary for radiocolloid particle‐sizing analysis, and it is a desirable size‐measuring technique because it is more reliable than PCS.     

Preparation and tribological properties of surface‐modified ZnS nanoparticles

Surface‐modified ZnS nanoparticles have been fabricated, and the morphologies and crystalline structures of the powder have been characterised by transmission electron microscopy, X‐ray diffraction and Fourier transformation infrared spectrum. The tribological properties of the surface‐modified ZnS (SM‐ZnS) nanoparticles as an additive in PEG400 were evaluated with a four‐ball tester. It was found that the as‐prepared SM‐ZnS nanoparticles had a very narrow size distribution, with the average diameter about 5–10 nm. The SM‐ZnS nanoparticles as the additive led to an obvious improvement in the anti‐wear and friction‐reduction properties of the synthetic PEG400. Analysis indicated that a boundary film was formed during the friction process. Copyright © 2014 John Wiley & Sons, Ltd.     

Dimensions of active cytochrome c oxidase in reconstituted liposomes using a gold ball shadow width standard: a freeze-etch electron microscopy study

The preparation and characterization of a distribution of gold balls on a thin, flat carbon film is described. The relation of the platinum carbon shadow width distribution means to a gold ball size is reported. Freeze-etched cytochrome oxidase vesicles and gold ball calibration grids were simultaneously shadowed with platinum/carbon. The shadow width distribution of the cytochrome oxidase located in and spanning the membrane was measured. The membrane fracture face edge and cross-fractured bilayer membrane edge were also measured. Dimensions of the cytochrome oxidase were found to be 5·8 ± 0·3 nm in diameter parallel to the membrane and 8·2 ± 0·3 nm long across the membrane. The bilayer membrane dimensions were 3·0 ± 0·3 nm for the half bilayer and 5·8 ± 0·3 nm for the cross-fractured bilayer membrane edge thickness. The length of the cytochrome oxidase was observed to span the bilayer membrane. Previous X-ray diffraction measurements on similar hydrated liquid crystalline artificial membranes were found to be in good agreement with the freeze-etched results. Membrane widths from thin-sectioned cytochrome oxidase vesicles were measured and found to be 5·8–5·9 nm in non-post-stained sections. Post-staining with uranyl acetate and/or lead citrate was shown to increase this average thickness. The technique of freeze-etching electron microscopy in conjunction with the gold ball shadow width calibration experiment has been shown to provide accurate and precise measurements of membranes and a functional intramembrane protein in a hydrated non-crystalline sample.