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Results for “Microscopy, Scanning Probe”

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At least 1,153 records · Page 64Linked to original sources
PubMed2002

Specific fluorescent tracers. Imaging and applications for photodynamic therapy.

Our main objective is to enlarge the fluorescence use in biosciences, with especially the photodynamic therapy (PDT) used for cancer treatment as one of the target applications. Meta-tetra(hydroxyphenyl)chlorin (m-THPC) is a second-generation photosensitiser, applied in photodynamic therapy. The localisation of this sensitiser as well as its induced cell death mechanisms in human breast cancer cells (MCF-7 and its resistant subline MCF-7DXR, DXR: doxorubicin) were evaluated using fluorescence microscopy. In addition, we will present two additional routes, whose aims are to create new features to respond to the PDT questioning: firstly, the synthesis of fluorescent tracers, with a particular attention to the presence of hydrophilic groups (glucosamine ring) on the basic fluorophore structure to orientate the localisation of the probe and, secondly, the use of scanning near-field optical microscopy to reach a better resolution for the fluorescence microscopy analysis.

Biological Transport↗
PubMed2004

Imaging and analysis of nanowires.

We used vapor-liquid-solid (VLS) methods to synthesize discrete single-element semiconductor nanowires and multicomposition nanowire heterostructures, and then characterized their structure and composition using high-resolution electron microscopy (HRTEM) and analytical electron microscopy techniques. Imaging nanowires requires the modification of the established HRTEM imaging procedures for bulk material to take into consideration the effects of finite nanowire width and thickness. We show that high-resolution atomic structure images of nanowires less than 6 nm in thickness have lattice "streaking" due to the finite crystal lattice in two dimensions of the nanowire structure. Diffraction pattern analysis of nanowires must also consider the effects of a finite structure producing a large reciprocal space function, and we demonstrate that the classically forbidden 1/3 [422] reflections are present in the [111] zone axis orientation of silicon nanowires due to the finite thickness and lattice plane edge effects that allow incomplete diffracted beam cancellation. If the operating conditions are not carefully considered, we found that HRTEM image delocalization becomes apparent when employing a field emission transmission electron microscope (TEM) to image nanowires and such effects have been shown to produce images of the silicon lattice structure outside of the nanowire itself. We show that pseudo low-dose imaging methods are effective in reducing nanowire structure degradation caused by electron beam irradiation. We also show that scanning TEM (STEM) with energy dispersive X-ray microanalysis (EDS) is critical in the examination of multicomponent nanowire heterostructures.

Computer Simulation↗
PubMed1999

[Dentinogenesis imperfecta. Scanning electron microscopic study and microanalysis].

BACKGROUND: Dentinogenesis imperfecta (DI) is an inherited dentine defect which affects both the primary and secondary dentitions. Shields et al. in 1973 suggested a classification of DI within three types: type I, associated with osteogenesis imperfecta (OI), type II and type III. Although the varying clinical, radiographic and histological findings in DI have been described in detail, an available method for closer examination of the abnormal dentine matrix, electron microscopy, has seldom been used. Scanning and transmission electron microscopy studies can help to understand the pathogenesis of the different types of heritable dentine defects and the diagnosis and classification of these diseases. The aim of the present study was to evaluate a case of DI using scanning electron microscopy and microanalysis. METHODS: Dentine was obtained from tooth samples from a fourteen-year-old boy affected by DI and from third molars extracted for therapeutic reasons used as controls. Samples were observed with a scanning electron microscope, scanning electron micrographs were evaluated with an image analysis program and specimens were finally observed with a scanning electron microscope equipped for micro-analysis. RESULTS AND CONCLUSIONS: The results obtained showed that the total number of dentinal tubules was significantly reduced and the presence of a dentine mineralization defect in the patient affected by DI, in comparison to the controls.

Adolescent↗
PubMed1994

Excimer laser deposition of hydroxyapatite thin films.

We have demonstrated a new and simple in situ method to fabricate adherent and dense hydroxyapatite (HA) coatings at relatively low deposition temperatures (500-600 degrees C). Under optimum processing conditions, the HA coatings possess a nominal Ca:P ratio of 1.65 and exhibit a fully crystalline single-phase structure. This deposition technique is based on the application of a pulsed excimer laser (wavelength lambda = 248 nm, pulse duration tau = 25 x 10(-9) s) to ablate a dense stoichiometric HA target. The HA target was prepared by standard ceramic coprecipitation techniques followed by cold pressing and further sintering at 1200 degrees C in air. High substrate temperatures (> or = 600 degrees C) during film deposition led to phosphorus deficient coatings because of re-evaporation of phosphorus during the deposition process. The stabilization of various calcium and phosphorus phases in the film was controlled by a number of process parameters such as substrate temperature, chamber pressure and presence of water vapour in the chamber. This is particularly advantageous for production of HA coatings, since it is known that HA decomposes at high temperatures due to the uncertainty in the starting material stoichiometry. Rutherford backscattering spectrometry, energy dispersive X-ray analysis, transmission electron microscopy, scanning electron microscopy and X-ray diffraction techniques were employed to determine the structure-processing relationships. Qualitative scratch measurements were conducted to determine the adhesion strength of the films.

Calcium↗
PubMed2003

A novel STM-assisted microwave microscope with capacitance and loss imaging capability.

We report a new technique of scanning capacitance microscopy at microwave frequencies. A near field scanning microwave microscope probe is kept at a constant height of about 1 nm above the sample with the help of scanning tunneling microscope (STM) feedback. The microwaves are incident onto the sample through a coaxial resonator that is terminated at one end with a sharp tip (the same tip is used to conduct STM), and capacitively coupled to a feedback circuit and microwave source at the other end. The feedback circuit keeps the source locked onto the resonance frequency of the resonator and outputs the frequency shift and quality factor change due to property variations of the sample. The spatial resolution due to capacitance variations is congruent with 2.5 nm. The microwave microscope is sensitive to sample sheet resistance, as demonstrated through measurements on a doped silicon sample. We develop a quantitative transmission line model treating the tip to sample interaction as a series combination of capacitance and sheet resistance in the sample.

Algorithms↗
PubMed1982

Digital image processing: a path to better pictures.

Digital image processing has been used for over a decade to provide startling improvements in the quality of photographs from deep space, satellites and low light level photography. In the last decade considerable work has gone on in major microscope labs in applying these techniques to electron micrographs. Within the last few years a number of factors have come together which allow large scale image processing techniques to be applied at reasonable costs in microscope labs everywhere. The system described here provides hardware for digitization and storage of multiple images simultaneously and multimode scan generation. System software provides easy scan control, image digitization, automatic prescale adjust on acquisition, grey scale histogram generation, grey scale manipulation, image filtering, smoothing, and random color assignment to grey levels.

Animals↗
PubMed2003

The otoliths of the antarctic teleost Trematomus bernacchii: scanning electron microscopy and X-ray diffraction studies.

The authors studied the otoliths of the Nototheniid Trematomus bernacchii with scanning electron microscopy and X-ray diffraction analysis. Results obtained reveal that three otoliths are present: a large sagitta, a lapillus and a fragile asteriscus. Their sensorial faces appear finely decorated as shown by scanning electron microscopy (SEM). The sagitta and the lapillus are aragonitic while the asteriscus is vateritic, as demonstrated by X-ray diffraction.

Animals↗
PubMed1988

Clinical applications of scanning electron microscopy and energy dispersive X-ray analysis in dermatology--an up-date.

Dermatological papers comprising scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis data published 1983 through 1986 in international journals are reviewed, as an update to our 1984 paper on Clinical applications of scanning electron microscopy and X-ray microanalysis in dermatology. The present paper not only deals with a review of recent publications in this area but also presents the application of microincineration to hair and cryosectioned freeze-dried skin specimens. Examples of the increased contrast obtained in hair cross sections are presented and a discussion on the feasibility of microincineration at analysis of hair and skin cross sections is given. Particle probe analysis (EDX: energy dispersive X-ray analysis and PMP: proton microprobe analysis) as applied to hair and skin samples are presented with stress put on the proton probe analysis. The complementarity of EDX and PMP is demonstrated and future applications are suggested.

Animals↗
PubMed1981

A cooling chain for studies of cryofixed biological specimens by scanning transmission electron microscopy and X-ray microanalysis.

A cooling chain is described which enables the transfer of frozen hydrated biological specimens (ultrathin cryosections as well as about 1 micrometer thick cultured cells) from a cryoultramicrotome into a scanning transmission electron microscope with a field emission gun. Transfer is done at 118 K, specimen temperature in the microscope is 165 K. Sublimation processes are controlled visually and by mass spectrometry. Electron micrographs and X-ray microanalytical spectra of cryofixed unstained tissue culture cells and rat liver tissue sections are described and discussed. Contamination of the specimen is much reduced by use of the cold stage.

Animals↗
PubMed2006

Lymphocytoma cutis due to pierced earrings.

We report two cases of lymphocytoma cutis caused by pierced earrings, with the results of patch tests and X-ray microanalyses on electron microscopy. We detected zinc through scanning electron microscopy from the specimen of Case 1 and gold and titanium through transmission electron microscopy from Case 2. This is the first report to demonstrate the presence of metal fragments in the lesion, which may suggest the remanence of metal for 20 years, bringing about persistent allergic reaction.

Adult↗
PubMed1996

Chemical and morphological analysis of explanted polyurethane vascular prostheses: the challenge of removing fixed adhering tissue.

During in vivo experiments to evaluate the biocompatibility and biostability of alternative biomaterials, the ideal protocol for the handling and preservation of the explanted material is often compromised in order to meet the needs of both the pathologist and the materials scientist. Explants surrounded by tissue are often fixed in formalin or glutaraldehyde to facilitate later pathological and histological analysis, but the subsequent removal of such fixed tissue from thermally sensitive and less chemically stable polymers, such as polyurethanes, poses major problems for the materials scientist, who does not wish to modify the chemical, physical or morphological characteristics of the underlying biomaterial. The present study has attempted to find a solution to this problem by exposing virgin specimens of the microporous polyurethane Vascugraft vascular prosthesis to six different cleaning conditions, all known to be effective in removing fixed tissue. These conditions included the use of 20% aqueous potassium hydroxide solution for 48 h at room temperature, 5% sodium bicarbonate solution for 5 min at the boil, and 9, 10, 11 and 12N hydrochloric acid for 48 h at room temperature. The appearance and chemical properties of the virgin and treated specimens were compared using electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, gel permeation chromatography for molecular weight and differential scanning calorimetry techniques. The use of temperatures close to the boil resulted in the formation of a translucent, rubbery material with gross changes in the microporous and microfibrous structure. The strongly acidic and alkaline conditions caused a loss in the surface carbonate group content. In addition, 12N hydrochloric acid reduced the molecular weight and urethane content. Consequently, 9N hydrochloric acid is recommended as the cleaning agent of choice for removing fixed tissue from this type of microporous polyurethane. Control experiments on virgin material should also be included in any cleaning protocol.

Adhesiveness↗
PubMed1993

Intercellular junctions and the application of microscopical techniques: the cardiac gap junction as a case model.

Intercellular junctions are fundamental to the interactions between cells. By means of these junctions, the activities of the individual cells that make up tissues are co-ordinated, enabling each tissue system to function as an integrated whole. In this review, the work of the authors on one specific type of junction--the cardiac gap junction--is presented as a case model to illustrate how the application of a range of microscopical methods, as part of a multidisciplinary approach, can help extend our understanding of cell junctions and their functions. In the heart, gap junctions form the low-resistance pathways for rapid impulse conduction and propagation, enabling synchronous stimulation of myocyte contraction. Gap junctions also form pathways for direct intercellular communication, a function of particular importance for morphogenetic signalling during development. The work discussed demonstrates some of the applications of techniques in electron microscopy, immunocytochemistry and confocal scanning laser microscopy to the understanding of the structural basis of the function of gap junctions in the normal adult heart, the developing heart and the diseased heart. Freeze-fracture electron microscopy of heart tissue prepared by rapid freezing techniques, in which excision-related structural damage to the cells is minimized or avoided, makes it possible to deduce the structure of the functioning gap junction in vivo. Gap junctions in hearts that are beating normally in the living animal until the very instant of freezing consist of connexons (transmembrane channels) organized in a quasi-crystalline arrangement, not a 'random' arrangement as proposed in the original hypothesis on the structural correlates of gap junction function. Alterations in connexon arrangement occur in response to ischaemia and hypoxia, though the relationship of these to gap-junctional permeability is indirect. To obtain probes for mapping the distribution of gap junctions in cardiac tissue, polyclonal antisera to synthetic peptides matching portions of the sequence of connexin43, the major gap-junctional protein reported in the heart, were raised. The specificity of the antisera was confirmed by dot blotting, Western blotting and by immunogold labelling of isolated gap junctions. One antiserum (that raised to residues 131-142) was found to be particularly effective as a cytochemical probe. An immunofluorescence labelling procedure for use with confocal scanning laser microscopy was developed to enable the three-dimensional precision mapping of gap junctions through thick slices of cardiac tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗