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PubMed1994

X-ray microanalysis with the environmental scanning electron microscope: interpretation of data obtained under different atmospheric conditions.

X-ray microanalysis of non-biological and biological specimens was carried out in an environmental scanning electron microscope (ESEM) over a range of atmospheric conditions. Introduction of water vapour into the specimen chamber lead to direct X-ray contribution from oxygen atoms, an increase in extraneous background (causing reduced P/B ratios of other elements), X-ray absorption (also reducing P/B ratios) and broadening (skirting) of the electron beam. Similar results were obtained after introduction of an argon atmosphere. These effects were reduced under conditions of minimal chamber atmospheric pressure and maximal accelerating voltage. Because of beam skirting, quantitative X-ray microanalysis of biological specimens in a water vapour atmosphere was only valid where the sample was spread over a wide area (leading to mean elemental values for the whole preparation). Unless appropriate correction factors or changes in instrumentation can be implemented, quantitative analysis of wet specimens in ESEM cannot be applied to discrete specimens or to limited areas within a mixed sample.

Anabaena↗
PubMed1977

Zinc distribution in injured myocardium. EMMA-4 examinations of dogs' hearts after coronary ligation.

Electron microscopic X-ray microanalysis and atomic absorption spectrophotometry were used to determine changes in zinc concentration after myocardial ischemic injury by coronary ligature in dogs. The zinc concentration increased in the damaged myocardium especially in specific intracellular locations identified by means of the microprobe. It was concluded that the selective zinc augmentation was related to proliferative and biosynthetic reactive processes in the myocardium.

Animals↗
PubMed1991

Ultrastructure and microanalyses of the protoscolex hooks of Echinococcus granulosus.

The rostellar distal cytoplasm of Echinococcus granulosus protoscoleces is characterized by extensive basal membrane infolding, prominent hemidesmosomes and is subtended by a lamina reticularis with microfibrils of approximately 10 nm diameter that occasionally show a 55 nm banding periodicity. The rostellar hooks, in 2 rows, each have a blade, guard and handle region and possess a central amorphous pulp, a middle microfibrillar medulla with microfibrils of approximately 4 nm diameter, and a complex outer cortex in all but the proximal region of the guard and the base of the handle. In these regions additional material, of similar electron density to the medulla, but lacking the fibrillar substructure, occurs and gives the areas a lobed appearance. Energy-dispersive X-ray microanalysis of whole hooks demonstrated the presence of sulphur and trace quantities of phosphorus. X-ray near-edge absorption spectra resembled those of cystine, feather and hair and showed the sulphur to be predominantly in the form of disulphide linkages. X-ray diffraction patterns of whole hook preparations revealed 2 diffuse rings with equatorial spacings of 7.99 A and 15.22 A, thus differing from vertebrate keratins.

Animals↗
PubMed1998

The efficiency of X-ray production at low energies.

The absolute efficiency of X-ray production has been determined for the K-lines of Al, Si and Cu; for the L-lines of Fe, Co, Cu, Ge and As; and for the M-lines of Hf, Ir, Pt, Au and Bi, using overvoltage ratios in the range 1-10. These emissions, with the exception of the Cu K, have critical excitation energies below 2.6 keV and are therefore typical of the lines used for X-ray microanalysis at low beam energies. For K-lines it is found that the experimental results are in good agreement with a Bethe, or a Casnati, crosssection model. For the L- and M-lines a Monte Carlo technique has been used to find an effective X-ray generation cross-section for each of the elements. The functional forms of these cross-sections are found to be in general agreement with proposed theoretical models.

Electron Probe Microanalysis↗
PubMed1987

The photoelectron x-ray microscope, a possible tool for analytical soft x-ray microscopy.

In the soft x-ray region, different techniques have been recently developed which can give images of biological objects at an intermediate resolution between optical and electron microscopes. At these wavelengths, very little sample preparation is required because the image contrast is directly dependent upon the chemical composition of the sample itself and on the x-ray wavelength. X-ray microscopy can be extended to absorption microanalysis with a similar resolution, provided that the basic microscope can work through a large range of wavelengths. The photoelectron x-ray microscope that we are developing at LURE satisfies this condition. Its principle is to make a contact x-ray image of the object on a plane photocathode and then, to magnify the secondary electron image, into which it is converted, by means of an emission electron microscope. In the present state of the art, the expectable detection limit, for element maps of 0.1 micron resolution, would be near 1% in concentration.

Electron Probe Microanalysis↗
PubMed1998

The role of proteins in the nucleation and formation of calcium-containing deposits on biomaterial surfaces.

In experiments in vivo using diffusion chambers, the morphology and composition of calcium-containing deposits on natural and artificial biomaterials that had no direct contact with cells were studied using scanning electron microscopy with energy dispersion X-ray microanalysis. It was revealed that the formation of a protein layer containing protein-calcium complexes is the key event in biomaterial calcification. A mechanism of formation of a calcium-containing protein matrix that creates the conditions for supersaturation of the crystal-forming medium over critical value has been proposed. The formation of nuclei of insoluble calcium phosphate starts predominantly deep in an adsorbed protein layer enriched by calcium ions.

Biocompatible Materials↗
PubMed1986

Interface corrosion in amalgam-to-amalgam and amalgam-to-nonprecious metal crown couplings.

This study examined the contact surface area in the coupling of a class II amalgam restoration with another class II amalgam restoration or with a stainless steel or nickel-chrome crown in 1% NaCl solution. The characterization of interfaces was carried out by using SEM and EDX microanalysis. The results indicate that the coupling of an amalgam-stainless steel crown and an amalgam-inconel crown in NaCl solution forms a deposit on the crown surfaces. This deposit contains all the constituents of corrodible phases of amalgam, including Zn. If amalgam restorations in adjoining teeth are contemplated, non-Zn-containing amalgam alloys of the same composition should be considered.

Chemical Phenomena↗
PubMed1982

A low x-ray background low temperature specimen stage for biological microanalysis in the TEM.

The side entry specimen stage described in this paper is a development of a specimen stage for use at room temperature in the JEOL JEM 100 and 200 series transmission electron microscopes. The earlier specimen stage was designed to ensure that the extraneous instrumental contribution to thin specimen X-ray spectra is both small and quantifiable. As well as having a low X-ray background the new stage will also maintain the specimen at temperatures sufficiently low (down to 100 K) to minimize the loss of organic material due to electron irradiation. A new anticontaminator which provides a clean low temperature environment for the specimen stage is also described.

Cold Temperature↗
PubMed1991

Electron probe X-ray microanalysis of intracellular element concentrations in cryosections in the presence of changes in cell volume.

The interpretation of element concentration data for X-ray microanalyses of biological tissues, which are subjected to some experimental treatment, can be complicated by changes in cell volume and total cell dry matter induced by the treatment. We have examined the manner in which such changes would affect the values measured in frozen-dried cryosections of soft tissues, and how they may be taken into account in the interpretation of the results. The element content (mass per unit dry weight) measured by the peak-to-continuum or Hall method is independent of changes in cell volume, but is sensitive to a change in the local dry mass. Conversely, intracellular concentrations in terms of mass per unit volume, as determined by the peripheral or internal standard technique, are dependent on volume changes but independent of dry mass. The estimated dry weight fraction is affected by changes in both volume and dry mass. The results obtained from both quantification methods can therefore provide information on the combination of changes in cellular element levels, volume and total dry mass that may occur following the experimental treatment. In a study of the late effect of the drug cisplatin on electrolyte concentrations in kidney proximal tubules, both quantification methods have been used to obtain wet weight and dry weight concentrations. By applying the above considerations, the analytical results have been interpreted as a combination of changes in element levels and a shrinkage of the tubule cells. Cell shrinkage was confirmed by morphometric analysis of tubular cross-sections.

Animals↗
PubMed2003

Application of quantitative analytical electron microscopy to the mineral content of insect cuticle.

Quantification of calcium in the cuticle of the fly larva Exeretonevra angustifrons was undertaken at the micron scale using wavelength dispersive X-ray microanalysis, analytical standards, and a full matrix correction. Calcium and phosphorus were found to be present in the exoskeleton in a ratio that indicates amorphous calcium phosphate. This was confirmed through electron diffraction of the calcium-containing tissue. Due to the pragmatic difficulties of measuring light elements, it is not uncommon in the field of entomology to neglect the use of matrix corrections when performing microanalysis of bulk insect specimens. To determine, firstly, whether such a strategy affects the outcome and secondly, which matrix correction is preferable, phi-rho (z) and ZAF matrix corrections were contrasted with each other and without matrix correction. The best estimate of the mineral phase was found to be given by using the phi-rho (z) correction. When no correction was made, the ratio of Ca to P fell outside the range for amorphous calcium phosphate, possibly leading to flawed interpretation of the mineral form when used on its own.

Animals↗
PubMed1984

Subcellular distribution of potassium in striated muscles.

Microanalytical experiments have been performed to answer the question whether the main cellular cation, K+, follows the water distribution in the striated muscle cell or whether K+ follows the distribution of negative fixed charges (beta- and gamma-carboxyl groups of aspartic and glutamic acid residues). Subcellular localization of K and/or of the K surrogates Rb, Cs, and Tl has been investigated by the following methods: Chemical precipitation of K with tetraphenylborate. Autoradiography of alkali-metals and Tl in air-dried and frozen-hydrated preparations. TEM visualization of electron dense Cs and Tl in sections of freeze-dried and plastic embedded muscle. X-ray microanalysis of air-dried myofibrils and muscle cryosections. The experiments consistently show that K, Rb, Cs, and Tl do not follow the water distribution but are mainly accumulated in the A band, especially in the marginal regions, and at Z lines. The same sites preferentially accumulate Cs or uranyl cations when sections of freeze-dried, embedded muscle are exposed to these electron microscopic stains. It is concluded that the detected uneven distribution of K, Rb, Cs, and Tl in muscle is neither a freeze-drying artifact nor an embedding artifact and may result from a weak ion binding to the beta- and gamma-carboxyl groups of cellular proteins.

Animals↗
PubMed2005

Toxicity of selenite in the unicellular green alga Chlamydomonas reinhardtii: comparison between effects at the population and sub-cellular level.

The toxicity of selenium in aquatic ecosystems is mainly linked to its uptake and biotransformation by micro-organisms, and its subsequent transfer upwards into the food chain. Thus, organisms at low trophic level, such as algae, play a crucial role. The aim of our study was to investigate the biological effects of selenite on Chlamydomonas reinhardtii, both at the sub-cellular level (effect on ultrastructure) and at the population level (effect on growth). The cells were grown under batch culture conditions in well-defined media and exposed to waterborne selenite at concentrations up to 500 microM; i.e. up to lethal conditions. Based on the relationship between Se concentration and cell density achieved after a 96 h exposure period, an EC(50) of 80 microM with a 95% confidence interval ranging between 64 and 98 microM was derived. No adaptation mechanisms were observed: the same toxicity was quantified for algae pre-contaminated with Se. The inhibition of growth was linked to impairments observed at the sub-cellular level. The intensity of the ultrastructural damages caused by selenite exposure depended on the level and duration of exposure. Observations by TEM suggested chloroplasts as the first target of selenite cytotoxicity, with effects on the stroma, thylakoids and pyrenoids. At higher concentrations, we could observe an increase in the number and volume of starch grains. For cells collected at 96 h, electron-dense granules were observed. Energy-dispersive X-ray microanalysis revealed that these granules contained selenium and were also rich in calcium and phosphorus. This study confirms that the direct toxicity of selenite on the phytoplankton biomass is not likely to take place at concentrations found in the environment. At higher concentrations, the link between effects at the sub-cellular and population levels, the over-accumulation of starch, and the formation of dense granules containing selenium are reported for the first time in the literature for a phytoplankton species after exposure to selenite.

Animals↗
PubMed2003

Cytochemical localization of calcium and X-ray microanalysis of Catharanthus roseus L. infected with phytoplasmas.

The potassium pyroantimonate (KPA) Ca(2+) precipitation technique, X-ray microanalysis and Electron Energy Loss Spectroscopy carried out by transmission electron microscopy were used to analyze the Ca(2+) distribution in Catharanthus roseus L. leaves infected with phytoplasmas belonging to different taxonomic groups, and in phytoplasma cells. The analysis revealed that the distribution of Ca(2+) was different in healthy and diseased plants (where the KPA deposits were numerous) and no differences were observed in the tissues of the three types of infected C. roseus L. Since no KPA precipitates were visible in the phloem and on phytoplasma cells, it is likely that Ca(2+) ions are not directly involved in phytoplasma replication, but, in infected cells is a response to the pathogen indicative of a higher Ca(2+) in the plasmalemma.

Antimony↗
PubMed1987

Scanning electron microscopic analysis of intraocular ossification in advanced retinal disease.

Chicken eyes from congenic blind (rd/rd) animals showing early, intermediate, and final stages of ossification, similar to the phthisis bulbi condition in man, were examined using scanning and transmission electron microscopy as well as light microscopy and X-ray microanalysis. Early stages of ossification were devoid of mineralized calcium apatite while intermediate and end stages of the disorder contained large amounts of calcium and phosphorus. This process resulted in metaplastic bone formation. An intact Bruch's membrane appeared to separate the choroid from the degenerated pigment epithelium and the developing bone suggesting that its possible origin was metaplasia of the retinal pigment epithelium and the degenerated sensory retina. The end-stage ossification resulted in "phthisic bone" formation which completely filled the vitreous cavity in a manner very similar to the human condition of phthisis bulbi.

Animals↗
PubMed2000

Modified drug release from inert matrix tablets prepared from formulations of identical composition but different organisations.

This paper develops for the first time a concept to modify the release rate of a fixed formulation by changing only the organisation of the mix used to prepare the tablets (ordered mixing). To estimate the influence of the organisation of binary mixes, several mixes of ethylcellulose and niflumic acid of the same composition but different organisation were compacted. The tablet surfaces were examined by energy dispersive X-ray microanalysis before the release experiments. Finally, the cross-sections of the remaining matrix were examined by scanning electronic microscopy. Excipient-excipient and excipient-drug interactions are the major factors influencing the drug release rate from the tablets. In the case of interacting materials, the initial release behaviour depends on the tablet surface presented to the dissolution media. The dissolution properties of the tablets are governed by the percolating material. When the inert excipient is percolating, the release rate increases linearly with the excipient/drug size ratio, whereas when the drug is the only material percolating through the system, its release rate is independent of the size ratio. When both materials are percolating through the system, the release rate is independent of the component particle sizes.

Cellulose↗
PubMed1995

Calcium concretions in the pineal gland of aged rats: an ultrastructural and microanalytical study of their biogenesis.

The genesis of calcium concretions in aged rats was studied by means of transmission and scanning electron microscopy. The potassium pyroantimonate method, combined with X-ray microanalysis, allowed us to study the distribution of cations and calcium. Notable accumulations of calcium (associated with phosphorus) were localized in vesicles, vacuoles, lipid droplets, lipopigments, and mitochondria of dark pinealocytes. The results obtained in the present investigation suggest that these organelles are involved in the genesis of the concretions. The presence of sulfur indicates the existence of an organic matrix. We propose that genesis takes place in dark pinealocytes, which contain more calcium than light pinealocytes. Mineralization foci are sometimes associated with cellular debris and enlarge by further apposition of material. Two types of concretions, as determined by electron microscopy and confirmed by electron diffraction, could be observed: the "amorphous" type with concentric layers and the crystalline type with needle-shaped crystals. Once formed, the concretions reach the extracellular space and the cell breaks down. Possible extracellular calcification is suggested in the extracellular calcium-rich floculent material. The mineralization process is interpreted as being an age-related phenomenon and mainly a consequence of the degeneration of pinealocytes.

Aging↗
PubMed1991

Accumulation of phosphate-containing granules in the nucleoid area of Pseudomonas aeruginosa.

Many electron-dense granules were found in the nucleoid area of Pseudomonas aeruginosa strain K by electron microscopy with the technique of the freeze-substitution method. These granules contained phosphorus and calcium as determined by X-ray microanalysis. The size and the numbers of the granules decreased when the bacteria was cultured in the medium from which phosphate-containing compounds were depleted. From these observations we concluded that the granule was a phosphate-containing granule and possibly a polyphosphate granule. The excellent preservation of the fine structures by the freeze-substitution technique enables us to show very small polyphosphate granules in the nucleoid area of the bacterial cells which cannot be revealed by the conventional chemical fixation method. As we could not see the granules in other bacteria cultured in nutrient medium such as Serratia, Escherichia, Bacillus and Vibrios, the accumulation of the phosphate granules in Ps. aeruginosa might be a unique character of this bacteria and might be related to the growing capability of this bacteria in extremely low nutrient supply.

Cytoplasmic Granules↗
PubMed1984

Energy-dispersive X-ray microanalysis and scanning electron microscopy of developing and mature cat enamel.

Calcium and phosphorus distribution in forming, maturing and mature enamel of cat teeth and the microstructures manifest in all these were examined in fractured enamel from the dentine-enamel junction toward the enamel surface. concentrations of both Ca and P increased gradually from the forming enamel, through the maturing enamel and into the mature enamel. The innermost layer, adjacent to the dentine-enamel junction showed the greatest and the superficial layer the lowest concentration of Ca. Still the mature enamel of the erupted tooth was not yet completely mineralized and Ca and P concentrations only slightly higher than those in maturing enamel. Molar Ca:P ratio of each enamel stage was lower than that of pure crystalline hydroxyapatite. Simultaneously-performed SEM observations revealed microstructural changes in the enamel: in the forming-front layer of the forming enamel, the enamel was a rough, immature structure but began to show more compact, tighter structures as concentrations of Ca and P altered. The results suggest that the enamel organ exercises intense cellular control over increases of Ca and P concentration during the formation and maturation stages of amelogenesis.

Amelogenesis↗