Single DNA molecule patterning for high-throughput epigenetic mapping

We present a method for profiling the 5-methyl cytosine distribution on single DNA molecules. Our method combines soft-lithography and molecular elongation to form ordered arrays estimated to contain more than 250 000 individual DNA molecules immobilized on a solid substrate. The methylation state of the DNA is detected and mapped by binding of fluorescently labeled methyl-CpG binding domain peptides to the elongated dsDNA molecules and imaging of their distribution. The stretched molecules are fixed in their extended configuration by adsorption onto the substrate so analysis can be performed with high spatial resolution and signal averaging. We further prove this technique allows imaging of DNA molecules with different methylation states.     

Microstructural evolution and micromechanical properties of gamma-irradiated Au ball bonds

The effect of gamma radiation on the mechanical and structural properties of gold ball bonds was investigated. Gold wires from thermosonic wire bonding were exposed to gamma rays from a Cobalt-60 source at a low dose (5 Gy). The load–depth curve of nanoindentation for the irradiated gold wire bond has an apparent staircase shape during loading compared to the as-received sample. The hardness of the specimens calculated from the nanoindentation shows an increase in value from 0.91 to 1.09 GPa for specimens after exposure. The reduced elastic modulus for irradiated specimens significantly increased as well, with values from 75.18 to 98.55 GPa. The change in intrinsic properties due to gamma radiation was investigated using dual-focused ion beam and high-resolution transmission electron microscope analysis. The dual-focused ion beam and high-resolution transmission electron microscope images confirmed the changes in grain structure and the presence of dislocations. The scanning electron microscope micrographs of focused ion beam cross sections showed that the grain structure of the gold became elongated and smaller after exposure to gamma rays. Meanwhile, high-resolution transmission electron microscopy provided evidence that gamma radiation induced dislocation of the atomic arrangement.     

A Novel Hydrothermal Synthesis of Single Crystalline PbS Nanorods and Their Characterization

1.IntroductionDuring the past decade,one-dimensional(1D)nanos-tructures,such as nanorods,nanowires,nanobelts andnanotubes,have attracted increasing attentions due totheir novel electrical,optical and magnetic properties,and their potential applications in nanoscale eletronics,photonics and functional materials[1~3].Great effortshave been made to prepare1D semiconductor nanostruc-tures such as Si nanowires[4],ZnO nanorods[5]and GaNnanowires[6].At the same time,chalcogenide nanostruc-tures su…     

DNA nanopositioning and alignment by electron-beam-induced surface chemical patterning

Nanopositioning and alignment of arrays of DNA molecules on a surface by combination of high-resolution prepatterning and standard macroscopic deposition is presented. Direct electron beam exposure of a graphite substrate activated by amino groups neutralizes locally the surface charge, preventing the DNA adhesion during the consequent deposition. Because of the high resolution of the electron beam writing process, precise active patches can be created directly on the functionalized surface. Narrow (50 nm) stripe patterns produce both positioning and alignment acting as electrostatic traps for the DNA molecules. The approach is demonstrated using triple- and double-stranded DNA of medium length (350 nm). High yield of alignment and regular arrangement of the deposited molecules are achieved in a simple way within large areas.     

DNA origami-based nanoribbons: assembly, length distribution, and twist

A variety of polymerization methods for the assembly of elongated nanoribbons from rectangular DNA origami structures are investigated. The most efficient method utilizes single-stranded DNA oligonucleotides to bridge an intermolecular scaffold seam between origami monomers. This approach allows the fabrication of origami ribbons with lengths of several micrometers, which can be used for long-range ordered arrangement of proteins. It is quantitatively shown that the length distribution of origami ribbons obtained with this technique follows the theoretical prediction for a simple linear polymerization reaction. The design of flat single layer origami structures with constant crossover spacing inevitably results in local underwinding of the DNA helix, which leads to a global twist of the origami structures that also translates to the nanoribbons.     

Nanostructured tellurium semiconductor: from nanoparticles to nanorods

Selective fabrication of single crystalline tellurium nanorods of various lengths and spherical nanoparticles can be easily achieved by a simple hydrothermal reduction method. The product was characterised by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction and energy-dispersive X-ray spectroscopy techniques. It was found that when the concentration of orthotelluric acid gradually increased from 4 to 10, 20, 30 and 50?mM with other conditions controlled, the morphology of the tellurium nanocrystals gradually changed from long nanorod to shorter nanorods and eventually became spherical. Based on the experimental results, the morphology control mechanism of tellurium nanocrytals was well reasoned.     

Casting of Gold Nanoparticles with High Aspect Ratios inside DNA Molds

DNA nanostructures provide a powerful platform for the programmable assembly of nanomaterials. Here this approach is extended to synthesize rod‐like gold nanoparticles in a full DNA controlled manner. The approach is based on DNA molds containing elongated cavities. Gold is deposited inside the molds using a seeded‐growth procedure. By carefully exploring the growth parameters it is shown that gold nanostructures with aspect ratios of up to 7 can be grown from single seeds. The highly anisotropic growth is in this case controlled only by the rather soft and porous DNA walls. The optimized seeded growth procedure provides a robust and simple routine to achieve continuous gold nanostructures using DNA templating.     

Synthesis of GaN nanowires by CVD method: effect of reaction temperature

GaN nanowires are fabricated on Si substrates by ammoniating Ga₂O₃/NiCl₂ thin films using chemical vapour deposition method. The influence of reaction temperature on microstructure, morphology and optical properties of GaN nanowires is characterised by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrophotometer, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The results demonstrate that the GaN nanowires are single crystalline and exhibit hexagonal wurtzite symmetry. The best crystalline quality was achieved for an reaction temperature of 1150°C for 15?min. The growth process follows vapour–liquid–solid mechanism and Ni plays an important role as the nucleation point and as a catalyst.     

Growth of high quality ZnO nanowires on graphene

We report growth of the ZnO nanowires on graphene/SiO2/Si substrates using a chemical vapor deposition method. The length of nanowires varies from 1 microm to 10 microm with increasing the growth time from 30 min to 90 min. X-ray diffraction and high-resolution transmission electron microscopy investigations predict the high structural quality of the c-axis grown single crystalline ZnO nanowires. Temperature dependent photoluminescence spectra from the nanowires reveal excellent optical quality and excitonic behavior in the single crystalline ZnO nanowires. A well-resolved free exciton emission at 3.375 eV, indicates high crystalline quality nanowires and a strong PL peak at 3.370 eV is assigned to neutral-donor bound excitons (D0X).     

Near-field optical imaging of flagellar filaments of salmonella in water with optical feedback control

We report on the high-resolution observation of biological samples in water with a collection-mode near-field optical microscope (c-mode NOM) operating under optical feedback control. With rapidly decreasing evanescent field power used as the feedback signal, for the first time to our knowledge, an image of straight-type flagellar filaments of salmonella in water has been obtained. The estimated diameter of a single filament is around 55 nm with a pixel size of 10 nm. A comparison with its nominal value of 25 nm obtained from electron microscope observations under high vacuum confirms that our c-mode NOM performs high-resolution imaging in water.     

Facile synthesis, optical and photoconductive properties of novel ZnO nanocones

Large-scale, uniform ZnO nanocones with tips about 200 nm and length about 50 μm have been synthesized by a facile hydrothermal method. The morphology and structures were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HR-TEM). The effects of reaction time and PEG-400 on the morphology of ZnO nanostructures were investigated, also an oriented attachment mechanism has been briefly proposed. The optical properties were investigated by lasing confocal microscope and photoluminescence spectrum, a strong near band edge emission peak centered at 387 nm from the ZnO nanocones was observed in photoluminescence spectrum. Finally, we have fabricated UV photodetector based on single ZnO nanocone, which present good switching properties by turning the UV light on and off.     

Facile synthesis of nanocrystalline zinc ferrite via a self-propagating combustion method

Macroporous nanocrystalline zinc ferrite with single spinel-phase was prepared by a facile self-propagating combustion method using zinc nitrate, iron nitrate and glycine. The as-prepared ZnFe₂O₄ were characterized by X-ray diffraction (XRD) analysis, N₂ adsorption, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectrum (EDS). The magnetic properties of the prepared ZnFe₂O₄ were also studied.     

Semiconductor nanocrystal quantum dots on single crystal semiconductor substrates: high resolution transmission electron microscopy

We report on high-resolution transmission electron microscope structural studies of InAs colloidal semiconductor nanocrystal quantum dots (NCQDs) on ultrathin GaAs (001) semiconductor single-crystal substrates. We employ a benign method for preparing electron transparent specimens that is suitable for the study of such fragile samples. The image contrast comprises contributions from electron scattering from both the NCs and the GaAs substrate. Long-term electron exposure studies reveal different damage mechanisms operative in the nanocrystals and the substrate.     

水热法制备氧化锌阵列及其形貌控制

低温条件下, 采用水热法, 通过控制前驱溶液的pH值, 在预先镀有ZnO纳米膜的导电玻璃衬底上制备了形貌各异的ZnO阵列, 用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)和紫外-可见分光光度计等分析手段对ZnO纳米棒的结构和形貌进行了表征. 同时还对不同形貌阵列的形成机理进行探讨. 结果表明, 所制ZnO纳米棒为单晶, 沿c轴择优生长. 在pH值为10.5左右时, 能得到取向性好、直径均匀(d~nm)的ZnO纳米棒阵列. 光学测试表明, 在可见光区透光度超过80%, 禁带宽度约为3.25eV.     

Preparation of sheet like polycrystalline NiFe2O4 nanostructure with PVA matrices and their properties

Sheet-like nickel ferrite (NiFe₂O₄) has been synthesised with PVA matrices using co-precipitation technique. The sheet is formed from the oriented aggregation of single crystalline NiFe₂O₄ nanoparticles with PVA as the structure directing template. The synthesised materials are characterised based on X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The XRD results show that the nanocrystal contains single phase spinel structure of Fd3m space group. The existence of PVA with nanoparticles has been confirmed by FTIR spectra. The room temperature ferromagnetic property is exhibited by the as synthesised sample with high saturation magnetisation.     

向日葵髓芯的微结构与力学性能

向日葵髓芯是一种天然的高分子泡沫材料。文中通过扫描电子显微镜(SEM)和光学显微镜,研究了一种具有复合结构的向日葵髓芯的胞体形态结构,并结合胞体可能的堆砌模式,得出这种天然泡沫体的单元胞体的立体形状基本上是十四面体。探讨了胞体形状对泡沫材料的压缩变形机制,以及压缩杨氏模量和压缩屈服强度的影响,并对其原因作了进一步的分析。研究结果表明,胞体形状的变化,即由比较规则的十四面体逐渐变为伸长的十四面体,是引起泡沫材料在拉长方向的压缩杨氏模量比其它大3~4倍,压缩屈服强度大2倍以上的主要原因。     

A method of studying dislocation core structures by high-resolution electron microscopy

A method to study the crystal defects at atomic level by high-resolution electron microscopy (HREM) is introduced. The image taken with a field-emission high-resolution electron microscope and not directly reflecting the examined crystal structure can be transformed into the structure image by means of image deconvolution in combination with dynamical scattering effect correction. The principle of image deconvolution and the procedure of technique are briefly introduced. The results of applications on the epilayer of Si_0.76Ge_0.24/Si are given. It is shown that atoms in the dislocation core structures have been distinguished individually in the deconvoluted images and the point resolution of images can be improved up to the information limit of the field-emission high-resolution electron microscope.     

Recrystallization of the ODS superalloy PM-1000

The primary recrystallization of a 1 0 0-fiber textured coarse-grained oxide dispersion strengthened nickel-based superalloy (PM-1000) has been investigated by high-resolution electron backscatter diffraction. The annealing behavior of this alloy is quite complex. Even at high annealing temperatures (e.g. 1200 °C), recrystallization is only partial. The microstructure of this superalloy in the annealed state consists of a blurred subgrain structure, coarse grains with sizes of about 10–20 μm at the pre-existing grain boundaries and a significant fraction of small crystals in the interior of the recovered grains. These small grains are elongated and display anisotropic growth. In the present paper we present a detailed explanation for this peculiar microstructure. Particular focus is placed on the origin of the new grains in the recovered structure in a [1 0 0]-oriented grain.     

Hydrothermal synthesis of layered sodium manganese oxide nanowires and their electrochemical performance

A new method for preparing black birnessite nanowires is introduced. Layer-structured manganese oxide nanowires were synthesized by a facile hydrothermal method, and using both NaMnO4 and CH3CH2OH as the precursors in a concentrated NaOH solution. The structure, composition, appearance and electrochemical performance of the product were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy diffraction (ED), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA) and constant current charge/discharge. The XRD patterns showed a single phase corresponding to a crystalline birnessite-based manganese oxide. TEM studies suggested their wire-like structures. The TGA measurement demonstrated that they possessed an excellent thermal stability up to 400 degrees C. In the potential window of 2.0-4.3 V, the product exhibited excellent cyclic stability and rapid charge-discharge performance.     

Electrochemical template synthesis of large-scale uniform copper selenides nanowire arrays

Ordered Cu₃Se₂ nanowire arrays have been prepared by electrochemical template synthesis based on anodic alumina membranes at room temperature. After annealing in argon ambient at 300 °C for 1 h, Cu₂Se nanowire arrays were obtained by structural change. Field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) results show that single crystal copper selenides nanowires with a high filling rate are dense, smooth, and uniform in large area. The effects of several electrodeposition parameters on high-filling, stoichiometric and single crystal copper selenides were discussed.