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R W Linton

Publications and source records attributed to R W Linton.

13 recordsLinked to original sources
PubMed1992

The role of secondary ion mass spectrometry (SIMS) in biological microanalysis: technique comparisons and prospects.

The virtues and limitations of SIMS ion microscopy are compared with other spectroscopic techniques applicable to biological microanalysis, with a special emphasis on techniques for elemental localization in biological tissue (electron, X-ray, laser, nuclear, ion microprobes). Principal advantages of SIMS include high detection sensitivity, high depth resolution, isotope specificity, and possibilities for three-dimensional imaging. Current limitations, especially in comparison to X-ray microanalysis, center on lateral spatial resolution and quantification. Recent SIMS instrumentation advances involving field emission liquid metal ion sources and laser post-ionization will help to minimize these limitations in the future. The molecular surface analysis capabilities of static SIMS, especially with the new developments in commercial time-of-flight spectrometers, are promising for application to biomimetic, biomaterials, and biological tissue or cell surfaces. However, the direct microchemical imaging of biomolecules in tissue samples using SIMS will be hindered by limited concentrations, small analytical volumes, and the inefficiencies of converting surface molecules to structurally significant gas phase ions. Indirect detection using elemental or isotopically tagged molecules, however, shows considerable promise for molecular imaging studies using SIMS ion microscopy.

Forecasting↗
PubMed1984

Ultrastructural comparison of ion beam and radiofrequency plasma etching effects on biological tissue sections.

Three dry etching techniques (Ar+ ion beam, O2+ ion beam, O2 radiofrequency electrodeless discharge) were compared with respect to preferential etching and damage to the ultrastructure of glutaraldehyde-fixed Epon-embedded frog skeletal muscle sections. SEM and TEM studies were performed on both unstained and stained (osmium tetroxide, uranyl acetate) sections. Etching effects were observed to differ for the various ion beam or plasma etching techniques. Whereas selective retention of electron dense structures (e.g. Z lines, nuclear heterochromatin) was observed for oxygen plasma etching, preferential etching of these components was observed using O2+ ion beam bombardment. Selectively etched Z lines and etch-resistant nucleoli were observed for both reactive (O2+) and inert (Ar+) ion beam sputtering after sufficiently high ion doses. The above suggest that selective etching under keV ion beam irradiation is related more to physical sputtering processes (momentum transfer) than to the chemical reactivity of the incident ion. Heavy metal post-fixation and staining had no qualitative effect on the nature of the selective etching phenomena. The above findings are significant in that they potentially influence both electron and ion microprobe measurements of etched biological specimens.

Animals↗
PubMed1984

New techniques for imaging and analyzing lung tissue.

The recent technological revolution in the field of imaging techniques has provided pathologists and toxicologists with an expanding repertoire of analytical techniques for studying the interaction between the lung and the various exogenous materials to which it is exposed. Analytical problems requiring elemental sensitivity or specificity beyond the range of that offered by conventional scanning electron microscopy and energy dispersive X-ray analysis are particularly appropriate for the application of these newer techniques. Electron energy loss spectrometry, Auger electron spectroscopy, secondary ion mass spectrometry, and laser microprobe mass analysis each offer unique advantages in this regard, but also possess their own limitations and disadvantages. Diffraction techniques provide crystalline structural information available through no other means. Bulk chemical techniques provide useful cross-checks on the data obtained by microanalytical approaches. It is the purpose of this review to summarize the methodology of these techniques, acknowledge situations in which they have been used in addressing problems in pulmonary toxicology, and comment on the relative advantages and disadvantages of each approach. It is necessary for an investigator to weigh each of these factors when deciding which technique is best suited for any given analytical problem; often it is useful to employ a combination of two or more of the techniques discussed. It is anticipated that there will be increasing utilization of these technologies for problems in pulmonary toxicology in the decades to come.

Environmental Pollutants↗
PubMed1983

Acute toxicity of lead particulates on pulmonary alveolar macrophages. Ultrastructural and microanalytical studies.

Although it is well established that respiratory uptake of lead-containing particles plays a substantial role in the epidemiology of plumbism, relatively little is known about the role of the pulmonary alveolar macrophage in lead poisoning. An in vitro system was designed to investigate the effects of lead oxide particles of respirable size on the rabbit alveolar macrophage. The studies were concerned with the intracellular solubility of PbO and Pb3O4 and changes in fine structure attributable to lead toxicity. The distribution of phagocytosed lead and its intracellular reprecipitation complexes was established by electron microprobe analysis and secondary ion mass spectroscopy in conjunction with transmission electron microscopy, scanning electron microscopy, scanning transmission electron microscopy, and backscatter imaging. It was found that Pb3O4, PbO and PbO-coated particles were ingested by the rabbit alveolar macrophages and that each of these lead oxide compounds produced similar damage to the fine structure of the cell. Swelling of the mitochondria, nuclear membrane, and endoplasmic reticulum was common, as well as were characteristic reprecipitation complexes of lead, phosphorous, and calcium within the nuclear heterochromatin and cytoplasm of the cell. The precipitation complexes were not seen in cells incubated with the particles if phagocytosis was blocked by 0.22-microns, membrane filters. It was concluded that phagocytosis of these lead oxide particles was necessary to produce the cytopathic changes. It is suggested that solubilization of lead from the ingested particles in phagosomes of macrophages results in the liberation of intracellular lead with the resultant formation of reprecipitation complexes.

Animals↗
PubMed1982

Ion beam etching effects in biological microanalysis.

Oxygen ion beam sputter etching used in SIMS has been shown to produce morphologic effects which have similarities and differences in comparison to rf plasma etching of biological specimens. For example, selective retention of nuclear and plasma membranes is observed in both cases, however, heterochromatin is preferentially sputtered by O2+ bombardment in SIMS and preferentially preserved during O2 plasma etching. Sputter yield variations resulting from structural microheterogeneity are illustrated (e.g. etch-resistant nucleoli in preferentially etched nuclei), including their impact upon ion image formation in an ion microanalyzer. These image artifacts must be evaluated before secondary ion images revealing subcellular organelles can be related quantitatively to elemental localization in cells or tissues. To minimize gross surface roughness effects such as cone formation induced by ion bombardment, ion imaging studies of thin sections using low primary ion doses are indicated.

Animals↗
PubMed1980

Ion microanalysis of cells.

The application of ion microanalysis (IMA) to the chemical characterization of freeze-fixed, freeze-dried cells is reviewed. Particular emphasis is given to pathological studies involving the determination of the chemical composition of isolated cells (e.g. rabbit alveolar macrophages--RAMs) exposed in vitro to toxic species (e.g. Pb3O4 particles). Ion microscopic results indicated that lead from Pb3O4 migrated into the RAMs and subsequently formed phosphorous-containing compounds. Quantitative comparisons of the relative concentrations of physiologic elements in Pb3O4-treated versus control RAMs also were made using ion microanalytical techniques. The Pb3O4 results illustrate that the three-dimensional analysis capabilities of the IMA may be exploited for the in situ observation of the penetration of xenobiotic agents into cell interiors and their subsequent intracellular chemistry. The potential advantages of ion microanalysis for the characterization of cells include high elemental sensitivity (including low atomic number elements and diffusible ions), broad elemental coverage, three dimensional analysis, and isotopic information. The major limitations include non-idealities of the ion sputtering process, the constraints on the lateral resolution available to identify subcellular features, and the difficulties inherent in the determination of absolute elemental concentrations.

Animals↗
PubMed1976

Surface predominance of trace elements in airborne particles.

A number of minor and trace elements including Be, C, Ca, Cr, K, Li, Mn, Na, P, Pb, S, Tl, V, and Zn present in coal fly ash are found to be preferentially concentrated on the particle surfaces. Environmentally effective concentrations of these elements are thus much higher than indicated by conventional bulk analyses.

Air Pollutants↗