bluuebunny/crossref_metadata_2025_split huggingface dataset:
Colloidal gold markers and probes for routine application in microscopy
Authors: Goodman S. L. , Hodges G. M. , Trejdosiewicz L. K. , Livingston D. C. 
Published: August 2011

SUMMARYColloidal gold can be used as an electron‐dense cytochemical probe for direct or indirect labelling techniques. Gold markers can be prepared in a size range of 5–150 nm, and show size‐dependent shape characteristics and absorption spectra. Size and shape distribution increases with mean particle diameter, with appreciable overlapping between populations of different mean size. Using radio isotope‐binding assays, spectrophotometric analysis and an innovative rapid microtitration technique, the effect of pH, ionic strength and protein concentration on gold‐protein interaction has been studied. Efficient adsorption of protein to gold occurs at, or near, the pI of the protein. The amount of protein needed to effect stabilization is both a function of pH and of ionic strength, but does not reflect the amount of protein binding for all proteins. There is evidence for multilamellar adsorption of proteins to gold, which is discussed in context of the bioactivity, and stability of the probe. A working protocol for the routine reproducible manufacture of protein‐gold probes is given, making use of the microtitration assay.
Study of supported ruthenium catalysts by STEM
Authors: Pennycook S. J. 
Published: August 2011

SUMMARYA VG Microscopes' HB5 STEM has been used to study supported ruthenium catalysts provided by ICI Ltd. They consist of small ruthenium particles 3–10 nm in diameter and have been imaged using a variety of detectors. The signal combining strongest contrast from the particles with minimum contrast variations due to diffraction effects is from a high angle annular detector. The detector is particularly useful with crystalline supports. For microanalysis purposes, X‐ray spectra, electron energy loss spectra, and microdiffraction patterns have been recorded and together show conclusively that even the smallest particles are hexagonal ruthenium metal.
The measurement of atomic number and composition in an SEM using backscattered detectors
Authors: Ball M. D. , McCartney D. G. 
Published: August 2011

SUMMARYThe atomic number dependence of electron backscattering can be used as the basis of a microanalysis technique. The operating procedures and condition for quantitative measurements of specimen atomic number are outlined and an expression relating the accuracy of composition to the atomic number sensitivity has been derived. Some measurements of the spatial resolution of backscattered electron microanalysis are also presented and compared with the resolution of X‐ray microanalysis.Although the range of application of this technique is limited, where it can be applied it has the following advantages: (i) higher spatial resolution than X‐ray microanalysis for bulk specimens; (ii) very rapid measurement; (iii) can be applied to compounds of low atomic number elements, (e.g. borides, carbides, nitrides, etc.); (iv) specimen preparation is often relatively straightforward.
Quantitative studies of the autofluorescence derived from neuronal lipofuscin
Authors: Dowson J. H. , Harris S. J. 
Published: August 2011

SUMMARYThe degree of accumulation of neuronal lipofuscin in the human brain can indicate the age of some neurones, may be correlated with certain disease processes and can be affected by drugs. The estimation of the volume of neuronal lipofuscin has usually employed relatively unreliable methods such as counting techniques or visual ratings, while the present paper describes and illustrates a method for measuring the intensity of the autofluorescence derived from neuronal lipofuscin. The relationship between autofluorescence intensity and amount of lipofuscin is discussed.
The etching behaviour of silicon carbide compacts
Authors: Jepps N. W. , Page T. F. 
Published: August 2011

SUMMARYA series of microstructural investigations has been undertaken in order to explore the reliability of particular etches in revealing microstructural detail in silicon carbide compacts. A series of specimens has been etched and examined following complete prior microstructural characterization by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X‐ray diffractometry techniques. In particular, the sensitivity of both a molten salt (KOH/KNO3) etch and a commonly‐used oxidizing electrolytic ‘colour’ etch to crystal purity, crystallographic orientation and polytypic structure has been established. The molten salt etch was found to be sensitive to grain boundaries and stacking disorder while the electrolytic etch was found to be primarily sensitive to local purity and crystallographic orientation. Neither etch appeared intrinsically polytype sensitive. Specifically, for the ‘colour’ etch, the p‐ or n‐type character of impure regions appears critical in controlling etching behaviour; p‐type impurities inhibiting, and n‐type impurities enhancing, oxidation. The need to interpret etching behaviour in a manner consistent with the results obtained by a variety of other microstructural techniques will be emphasized.
Factors affecting the ion‐beam thinning characteristics of ceramics
Authors: Salehpoor B. , Marquis P. M. 
Published: August 2011

SUMMARYA study of the factors that affect thinning rates and damage processes during the ion‐beam thinning of ceramics has been undertaken. The results of these studies are reported and related to the conditions necessary for the preparation of uniform damage free specimens. Particular emphasis is placed on the variations in specimen stoichiometry that can occur during ion‐beam thinning. It is shown that under certain conditions the positively charged ion‐beam can induce charged interstitial migration into the bulk of the sample. The extent to which this effect, atomic bonding, crystal orientation and beam conditions can produce non‐uniform samples is discussed.
Microstructure dependence of the creep and creep‐fracture behaviour of ceramic materials
Authors: Wilshire B. 
Published: August 2011

SUMMARYThe microstructure dependence of the creep and creep‐fracture properties of ceramics is illustrated with particular reference to the behaviour of magnesia, lime and silicon nitride materials. From a consideration of the various models proposed to account for deformation and fracture under high temperature creep conditions, a consistent interpretation can be provided for the diverse behaviour recorded for different ceramics as a result of variations in crystal structure, composition and phase distribution.
The characterization of surfaces of technical ceramics used in the synthetic fibres industry by microscopy
Authors: Gallant P. E. , Merigold R. J. 
Published: August 2011

SUMMARYIn the manufacture of synthetic fibres such as nylon and Terylene, ceramic surfaces are used to guide and control the threadlines. Successful operation is critically dependent on correct friction between the threadline and the surface it contacts; this is achieved by control of surface topography. Microscopy, particularly the SEM, has played an important role in understanding the characteristics of different surfaces, control of manufacture of the surfaces, development of new surfaces and processes, and the elucidation of plant problems. Examples of these applications are illustrated and discussed.
Energy dispersive X‐ray microanalysis of air dried casein micelles from bovine milk
Authors: O'Brien Timothy L. , Baumrucker Craig R. 
Published: August 2011

SUMMARYSecretory proteins (casein micelles) were air dried prior to elemental analysis either without treatment, following glutaraldehyde fixation and dialysis, or following dialysis against distilled water. Samples were then examined by energy dispersive X‐ray microanalysis in a scanning transmission electron microscope (STEM). Untreated samples and samples dialysed against distilled water retain colloidal (bound) elements as compared to glutaraldehyde treated samples. Contamination of air dried casein micelles by ionic constituents in the non‐protein aqueous phase was observed in the untreated sample and in the glutaraldehyde treated sample. Dialysis of casein micelles against distilled water reduced contamination from the aqueous phase without diminishing the apparent concentrations of colloidal elements.
Measuring line length with the Quantimet 720 image analysing computer
Authors: Gaskell S. A. , Pearse A. D. 
Published: August 2011

SUMMARYThe line mode of the Quantimet 720 image editor used in conjunction with the MS3 computer to measure lengths of sloping or curved lines gives considerably inaccurate results. Depending on the degree of accuracy required, two methods are proposed for improving these results.
Point‐projection imaging of macromolecular contours
Authors: Panitz J. A. 
Published: August 2011

SUMMARYA point‐projection microscope is described which uses an electric field of several volts per nanometre to generate ions from a layer of benzene condensed in high vacuum on to the apex of a cryogenically cooled field‐emitter tip. Clusters of ferritin (a spherical protein molecule) embedded in the layer, have been imaged by exposing their contours during controlled field‐desorption. Image contrast is high. A magnification of 2 times 105 has been achieved at a spatial resolution estimated to be better than 3 nm. Three‐dimensional reconstructions of cluster morphology from a series of molecular contours are in qualitative agreement with transmission‐electron micrographs of the ferritin covered emitter apex. Reproducibility of the cluster contours, and TEM images of the apex before and after imaging suggest that the imaging procedure is nondestructive.
A new fixation procedure for preserving the ultrastructure of marine invertebrate tissues
Authors: Eisenman Edward A. , Alfert Max 
Published: August 2011

SUMMARYAddition of 0·05% OsO4 to a conventional glutaraldehyde fixative for the first 10 min of fixation was found to improve greatly the preservation of ultrastructure in the eggs of Urechis caupo. Several workers have since confirmed this result in other marine invertebrate tissues. Specific protocols and techniques are given. We believe that the OsO4 rapidly renders the plasma membranes of cells freely permeable to glutaraldehyde, allowing faster penetration of this fixative. This method should be applicable to a wide variety of tissues that are difficult to fix.
Freeze‐substitution and isothermal freeze‐fixation studies to elucidate the pattern of ice formation in smooth muscle at 252 K (‐21°C)
Authors: Hunt C. J. , Taylor M. J. , Pegg D. E. 
Published: August 2011

SUMMARYTaenia coli muscle was cooled to 252 K in the presence of the cryoprotectant dimethyl‐sulphoxide, at cooling rates known to reduce viability by significantly different amounts. The reduction in viability was known to be related to ice formation. Freeze‐substitution and isothermal freeze‐fixation studies were carried out to determine the distribution of ice within the muscle at this temperature. Freeze‐substitution using ethylene glycol was unsuccessful but a new method, using high concentrations of the cryoprotectant as the substituting solvent, was able to maintain ice configurations at this relatively high substitution temperature.The results of freeze‐substitution in dimethylsulphoxide were confirmed by isothermal freeze‐fixation when both techniques were conducted under identical cooling conditions. The results indicated that the functional differences produced by cooling muscle at either 0·3 K min−1 or 2 K min−1 were related to the distribution of the ice phase within the tissue.
Low temperature scanning electron microscopy of fungal material
Authors: Beckett A. , Porter R. , Read N. D. 
Published: August 2011

SUMMARYA preliminary evaluation has been made of different preparatory techniques used for the scanning electron microscope with regard to their application to a number of fungal specimens. A brief description of the use of the Emscope sputter cryo apparatus for the preparation of frozen‐hydrated specimens is given and the results obtained with this equipment are compared with those obtained by critical point‐drying and freeze‐drying. Perithecia from 11‐day‐old cultures of Sordaria humana, germinating conidia of Erysiphe graminis f.sp. hordei and uredosori and intercellular hyphae of Uromyces fabae were examined. In all cases the frozen‐hydrated specimens consistently showed the best preservation; particularly with regard to their external morphology, internal morphology, cell exudates and in relation to dimensional changes.
Freeze‐fracture electron microscopic analysis of solutions of biological molecules
Authors: Gulik A. , Aggerbeck L. P. , Dedieu J. C. , Gulik‐Krzywicki T. 
Published: August 2011

SUMMARYFreeze‐fracture electron microscopy was used to study the morphology of proteins in solution. The sizes of the particles appearing on the fractured surfaces, replicated with tungsten‐tantalum, were measured in a direction perpendicular to the shadowing angle. The distributions of the measured particle sizes could be correlated with the known shape and dimensions for each protein. It is concluded that freeze‐fracture electron microscopy is a useful technique to study the morphology of biological molecules in solution, particularly hydrophobic proteins which may be difficult to study by other microscopic techniques.
Some experiences in the use of a polymeric cryoprotectant in the freezing of plant tissue
Authors: Wilson A. J. , Robards A. W. 
Published: August 2011

SUMMARYRecently it has been suggested that polymeric cryoprotectants might be usefully employed for reducing ice crystal size during ultrastructural and analytical studies of frozen biological tissues. Furthermore, it was reported that they have little physiological effect and cause negligible structural changes in the tissue.Our experiences with one such polymer, polyvinyl pyrrolidone (PVP), in the cryopreservation of mature plant roots prepared for electron microscopy, have led us to conclude that preservation deep into the structure of this tissue is not improved. Even short periods of exposure of tissue to polymer cause rapid withdrawal of water from vacuolated cells of plant roots, resulting in shrinkage and collapse.Low temperature techniques have confirmed that little if any improvement in the reduction of ice crystal size results if the root is first treated with PVP.
A simple airlock system for hoar frost free specimen exchange in freeze‐etch vacuum plants
Authors: Niedermeyer W. 
Published: August 2011

SUMMARYThis paper describes a simple airlock system which allows hoar frost free quick specimen exchange on freeze‐fracture machines. The time needed for one preparation is reduced to about 15–20 min. The described modifications improve vacuum conditions and reduce the total water content within the recipient to less than 20% of the total residual gases. These conditions also enhance the topographic resolution of the specimen under research.
Freeze‐fracturing at low temperatures: I. A device for fracturing biological specimens at 77–10 K under high vacuum
Authors: Niedermeyer W. 
Published: August 2011

SUMMARYStandard freeze‐etching or freeze‐cleaving is performed at 173 K in a vacuum of 133 μPa or at 77 K under liquid nitrogen with subsequent transfer of the specimen into a vacuum chamber. It has been suggested that the frequent poor resolution of morphological details, the poor complementarity of innermembrane protein particles and the semi‐crystalline substructures in biomembranes are caused by structural distortion or plastic deformation due to sheer forces which occur even at 77 K during fracturing or cleaving. In addition, water contamination and radiant heat damage occurring during replication introduce artefacts to the structural record. These artefacts could be avoided or reduced by lowering the temperature at which fracturing or cleaving and shadowing is carried out, to about 10 K. Therefore, a device for cleaving biological specimens at 15–10 K under high vacuum was constructed. To allow the use of existing equipment, the device was built into a standard Balzers 301 vacuum unit, where the specimen transfer is done via an airlock system which allows hoar frost contamination free transport of the specimen holder onto the specimen table.To reduce or prevent the condensation of water and other residual gases in the vacuum onto the freshly cleaved specimen surface at 10 K, the specimen is surrounded by two cooled surfaces of 6 and 20 K. All condensable gases outside those shielding shrouds will condense on these surfaces before reaching the specimen. This makes it possible to work at a high vacuum of 3 μPa outside the cooled shrouds, which can be reached with standard turbomolecular pumps. The actual vacuum within the cooled shrouds is estimated to be approximately 13 nPa. Residual gas analysis before and during replication reveals equal conditions to ultra high vacuum systems.An analysis of the yeast cell paracrystalline plasmalemma structure shows that the topographic resolution of the crystalline arrays has been improved by working at 12 K. However, plastic deformation still occurs under these conditions. This observation points to the possibility that what is described as plastic deformation, for at least some membrane proteins, may be a loss of resilience at low temperatures.
Replica production for scanning electron microscopy: a test of materials suitable for use in field settings
Authors: Scott Eugenie C. 
Published: August 2011

SUMMARYSeven dental impression materials were tested in combination with five epoxy resins for the purpose of producing positive replicas suitable for use with the scanning electron microscope. Goals of the project were that the materials and procedures could be used in vivo, on high or low relief surfaces, involve a minimum of equipment, and produce high fidelity replicas. The combination of the dental impression material Xantopren with the resin Stycast 1266 was superior to all others tested at magnifications up to x 600.The Stycast also has the additional advantage of not requiring a heat cure, which further minimizes equipment in the field.
Age dependence of collagen fibril and subfibril diameters revealed by transverse freeze‐fracture and ‐etching technique
Authors: Itoh T. , Klein L. , Geil P. H. 
Published: August 2011

SUMMARYCollagenous tissues taken from tail tendons and cornea of freshly killed rats and rabbits, respectively, were fractured transversely and longitudinally at 80 K without any chemical pretreatment. The tissues were subsequently etched at 195 K for 30 min under a vacuum in the 130 μPa range. Carbon‐platinum replicas of the tissues were examined by transmission electron microscopy. It is demonstrated that the collagen fibrils are very closely packed and are composed of subfibrils whose size may vary with each tissue. Fibrils and subfibrils grow in diameter during growth and maturation but their size remains unchanged during the ageing process. The subfibril is suggested to be the growing unit in the collagen fibril based on the observation that the ratio of the diameter of fibril to subfibril does not change through growth, maturation and ageing. The ratio is approximately 10 for rat tail tendon and 5 for rabbit cornea and ear cartilage, suggesting the tissues from the two animals contain on the order of 100 and 25 subfibrils per fibril, respectively. It is proposed that the usual chemical fixation and dehydration processes used in conventional electron microscopy cause significant shrinkage in the diameters of subfibrils and fibrils.
Monolayer freeze‐fracture autoradiography: origins and directions
Authors: Fisher Knute A. 
Published: August 2011

SUMMARYMonolayer freeze‐fracture autoradiography (MONOFARG) is a product of two earlier methods: freeze‐fracture autoradiography (FARG) and cell monolayer freeze‐fracture. MONOFARG incorporates many of the basic principles and cytochemical goals of FARG while exploiting the technical advantages of monolayer freeze‐fracturing. The latter method offers the opportunity to process freeze‐dried ‘half’ membranes at room temperature. Although the feasibility of MONOFARG has been shown for qualitative analyses of split membranes, its quantitative feasibility for transmembrane and in‐plane analyses has just begun to be documented. An example of one aspect of that documentation is included in this report. The distribution of 125I‐FITC‐Concanavalin‐A in the plane of split plasma membranes, human erythrocyte extracellular fracture faces, was examined and found to be homogeneous. The relevance of this finding to recently described double labelled membrane splitting experiments is discussed. The future of MONOFARG appears promising, especially in the application of the technique to biologically significant questions.
Optimum conditions for cryoquenching of small tissue blocks in liquid coolants
Authors: Elder H. Y. , Gray C. C. , Jardine A. G. , Chapman J. N. , Biddlecombe W. H. 
Published: August 2011

SUMMARYThree approaches were taken with the aim of defining the optimum conditions for rapid cryopreservation in liquid quenchants. In a theoretical approach, two mathematical models were used. The first is of value in defining the absolute maximum rates of cooling which could be achieved at various depths in the tissues. The second highlights the poor thermal properties of liquid coolants and therefore emphasizes the essential requirement for vigorous quenchant mixing and rapid specimen entry.Experimental work with thermocouples showed that fastest cooling rates occur at the leading edge of the object entering coolant. Of five liquid quenchants investigated, cooling rates were in the order, propane> Freon 22> Freon 12> liquid nitrogen slush> liquid nitrogen. Other considerations, however, may affect the choice of quenchant. For a given quenchant, cooling rate is maximal near the equilibrium freezing point. The consequences of quenching in the presence of thermal gradients either within the coolant or in the gas layer above it are shown. Cooling rate was found to be approximately proportional to entry velocity at least up to ∼2 m s−1 in our system.Stereological analysis of rapidly quenched, freeze‐substituted tissue samples, of geometry which imposed an approximately unidirectional heat flow, revealed four zones: (i) a narrow surface layer (∼10 μm) of low image contrast and apparent absence of ice crystals; (ii) a zone of enhanced contrast with ice crystals whose size increased rapidly with depth from the surface (the ‘slope’); (iii) a sharply defined zone (the ‘ridge’) of maximum ice crystal size beyond which there is (iv) an extensive ‘plateau’ with smaller ice crystals and no marked increase in size with depth. The ‘ridge’ of maximal ice‐crystal damage was consistently found but varied considerably in depth from the surface (∼25–120 μm) between samples. The existence of the deeper plateau region of relatively uniform ice‐crystal‐size may be of significance in X‐ray microanalytical studies of physiological processes at some depth from the sample surface.In terms of our present understanding of the quenching process, the conditions for optimal cryofixation of small tissue samples are listed.