The scanning ion-conductance microscope

A scanning ion-conductance microscope (SICM) has been developed that can image the topography of nonconducting surfaces that are covered with electrolytes. The probe of the SICM is an electrolyte-filled micropipette. The flow of ions through the opening of the pipette is blocked at short distances between the probe and the surface, thus, limiting the ion conductance. A feedback mechanism can be used to maintain a given conductance and in turn determine the distance to the surface. The SICM can also sample and image the local ion currents above the surfaces. To illustrate its potential for imaging ion currents through channels in membranes, a topographic image of a membrane filter with 0.80-micrometer pores and an image of the ion currents flowing through such pores are presented.     

Two-photon laser scanning fluorescence microscopy

Molecular excitation by the simultaneous absorption of two photons provides intrinsic three-dimensional resolution in laser scanning fluorescence microscopy. The excitation of fluorophores having single-photon absorption in the ultraviolet with a stream of strongly focused subpicosecond pulses of red laser light has made possible fluorescence images of living cells and other microscopic objects. The fluorescence emission increased quadratically with the excitation intensity so that fluorescence and photo-bleaching were confined to the vicinity of the focal plane as expected for cooperative two-photon excitation. This technique also provides unprecedented capabilities for three-dimensional, spatially resolved photochemistry, particularly photolytic release of caged effector molecules.     

High-resolution scanning x-ray diffraction microscopy

Coherent diffractive imaging (CDI) and scanning transmission x-ray microscopy (STXM) are two popular microscopy techniques that have evolved quite independently. CDI promises to reach resolutions below 10 nanometers, but the reconstruction procedures put stringent requirements on data quality and sample preparation. In contrast, STXM features straightforward data analysis, but its resolution is limited by the spot size on the specimen. We demonstrate a ptychographic imaging method that bridges the gap between CDI and STXM by measuring complete diffraction patterns at each point of a STXM scan. The high penetration power of x-rays in combination with the high spatial resolution will allow investigation of a wide range of complex mesoscopic life and material science specimens, such as embedded semiconductor devices or cellular networks.     

High-speed scanning in human memory

When subjects judge whether a test symbol is contained in a short memorized sequence of symbols, their mean reaction-time increases linearly with the length of the sequence. The linearity and slope of the function imply the existence of an internal serial-comparison process whose average rate is between 25 and 30 symbols per second.     

A scanning micropipette molecule microscope

A movable quartz micropipette, whose tip is sealed with a polymer plug, is used as a liquid-vacuum interface to a mass spectrometer. A light microscope allows observation of, and positioning of, the micropipette tip on the surface of a sample mounted in a perfusion chamber. This forms the basis of an instrument which enables one to study, in vitro, the localization of transepithelial transport of water and other molecules. Some preliminary results from the use of this instrument are presented.     

应用LSCM和SEM鉴定银杏花粉的倍性

以经秋水仙碱诱导获得的银杏大花粉为材料,以未经处理的正常银杏花粉为对照,利用扫描电子显微镜和激光扫描共聚焦显微镜分别观察2种花粉表面形态,并分析对比其细胞内的DNA相对荧光量与银杏大花粉核内染色体倍性关系,为正确检出银杏二倍体花粉奠定重要工作基础。研究结果表明,此方法用于花粉粒的倍性鉴定科学准确,所需试验样本少,实用性强,在植物花粉倍性鉴定中有着较好的应用前景。      

昆虫材料扫描电镜样品制备技术

在昆虫材料的扫描电镜样品制备中,组织固定是极其重要的环节.由于昆虫体壁均有一定程度的骨化,具有阻止外界物质侵入的作用,使得固定液不容易浸透昆虫体内组织器官,且昆虫体内液体含量较高,因此利用常规前固定方法（即用2％～3％的戊二醛固定）难以保持昆虫材料的原有形态.本研究通过改变固定液的配制方法,即在3％戊二醛中加入氯化钠及吐温-80,比较了桃蛀螟幼虫经过微波固定、常规固定和自然干燥标本处理后,在扫描电镜下的观察效果.结果发现：在微波和固定液共同处理下,昆虫材料扫描电镜样品皱缩程度显著降低,有益于观察昆虫体表的超微结构.研究结果可为昆虫扫描电镜材料的制备提供技术参考.     

Picosecond resolution in scanning tunneling microscopy

A method has been developed for performing fast time-resolved experiments with a scanning tunneling microscope. The method uses the intrinsic nonlinearity in the microscope's current versus voltage characteristics to resolve optically generated transient signals on picosecond time scales. The ability to combine the spatial resolution of tunneling microscopy with the time resolution of ultrafast optics yields a powerful tool for the investigation of dynamic phenomena on the atomic scale.     

英语视读能力的培养与训练

学习英语,少不了听、说、读、写,核心视读、意群视读、搜寻视读、纵式阅读是提高英语阅读能力的有效方法。英语视读能力的培养与训练应循序渐进。     

Is a scanning ion microscope feasible?

Atomic collisions of high-energy heavy ions produce large yields of x-rays. The small de Broglie wavelength of massive ions leads to an estimate of 0.2 angstrom for the resolution of a microscope utilizing nitrogen ions with energies of 14 million electron volts. Estimates of the yield of x-rays relative to molecular radiation damage of the bases in DNA are made.     

Infrared scanning images: an archeological application

Aerial infrared scanner images of an area near the Little Colorado River in north-central Arizona disclosed the existence of scattered clusters of parallel linear features in the ashfall area of Sunset Crater. The features are not obvious in conventional aerial photographs, and only one cluster could be recognized on the ground. Soil and pollen analyses reveal that they are prehistoric agricultural plots.     

Sensitive 4 pi detector for scanning radiochromatograms

In an effort to obtain improved sensitivity in scanning unidimensional radiochromatograms of compounds labeled with weak beta-emitters, a detecting system was devised which simultaneously scans the upper and lower surfaces of the chromatogram. The instrument embodies substantial improvements based on the operation of a prototype.     

A scanning x-ray microscope using synchrotron radiation

Focused synchrotron radiation collimated by means of a pinhole has been used to construct a scanning x-ray microscope capable of making stereoscopic element-discriminating pictures of relatively thick specimens in an atmospheric environment.     

Capillary tube scanning applied to cell growth kinetics

We have developed an optical scanning instrument which may become a valuable aid in a variety of cell studies. Cell multiplication can be readily monitored with the instrument. By varying the chemical environment in which the cells are tested, questions of research and clinical interest may be quickly and conveniently answered. It appears possible to investigate the chemotherapeutic value of experimental agents, and to scan the sensitivity of a given population of neoplastic cells to a variety of chemotherapeutic agents at several concentrations. The optical scanning system may also be used to investigate certain metabolic pathways of cells in tissue culture, to determine drug resistance, and to assess the effects of medium composition on cell growth. Our studies of BrdU resistance in mouse lymphoma cells were done primarily to demonstrate the potential of this optical scanning method, and we do not intend to continue the cytokinetic studies at present. We trust that others will be stimulated to investigate further applications of this instrumental approach to problems in cell biology.     

Molecular structure of DNA by scanning tunneling microscopy

Uncoated DNA molecules marked with an activated tris(l-aziridinyl) phosphine oxide (TAPO) solution were deposited on gold substrates and imaged in air with the use of a high-resolution scanning tunneling microscope (STM). Constant-current and gap-modulated STM images show clear evidence of the helicity of the DNA structure: pitch periodicity ranges from 25 to 35 angstroms, whereas the average diameter is 20 angstroms. Molecular structure within a single helix turn was also observed.     

Endothelial projections as revealed by scanning electron microscopy

Scanning electron micrographs of the endothelium of the pulmonary artery reveal that the entire surface is covered by a meshwork of irregular projections which vastly increase the surface area. The size and density of the projections suggest that they may function to direct an eddying flow of plasma along the endothelial surface.     

Macrophage membranes viewed through a scanning electron microscope

When rabbit peritoneal macrophages were cultured in serum and Tyrode medium, numerous membranous structures varying in size and transparency were observed to cover the surface in complex cascading patterns. Modifications in the methods of fixation and drying probably accounted for the new perspective of macrophage surfaces gained in this study.     

Single molecules observed by near-field scanning optical microscopy

Individual carbocyanine dye molecules in a sub-monolayer spread have been imaged with near-field scanning optical microscopy. Molecules can be repeatedly detected and spatially localized (to approximately lambda/50 where lambda is the wavelength of light) with a sensitivity of at least 0.005 molecules/(Hz)(1/2) and the orientation of each molecular dipole can be determined. This information is exploited to map the electric field distribution in the near-field aperture with molecular spatial resolution.     

Skin replication procedure for the scanning electron microscope

Ani improved method for preparing polyethylene replicas of skin from silicone rubber molds was developed for examination in the scanning electron microscope. Electro micrographs of the replicas compare favorably to those of fixed tissues from the same animal. Because of the great depth of field of the scanning electron microscope, both loosely attached epidermal cells and the background epidermal surface can be seen simultaneously in sharp focus, thus providing, a more complete picture of the topography of skin.