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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Single-molecule fluorescence microscopy studies of fluorescent probes in thin films and on nanoparticle surfaces

Lu, Yin 30 March 2011 (has links)
Single-molecule (SM) fluorescence spectroscopy has become a useful and important experimental approach for investigating the optical properties of chemical systems. In this thesis, four subprojects in the field of SM fluorescence spectroscopy are presented in which SM spectroscopy has provided invaluable experimental insight into the systems of interest.<p> In the first project, the photophysical properties of Calcium-Green 1 (CG-1), a calcium-ion indicator, were studied at both the ensemble and SM levels. CG-1 is non-fluorescent in the absence of Ca2+ and becomes strongly fluorescent when bound to Ca2+. In the ensemble measurements, the absorption and fluorescence spectra were collected under various Ca2+ concentrations. In addition, the fluorescence lifetime of CG-2 was also studied as a function of [Ca2+]. From SM measurements, the photobleaching time and fluorescence intensity distributions of CG-1 were studied both in the presence and in absence of Ca2+. The results were compared with those obtained for the dual-fluorophoric variant, Calcium-Green 2 (CG-2), whose photophysical properties have been investigated by previous researchers. The experimental results reveal that CG-1 can exist in two different forms: a highly-quenched form due to the occurrence of photoinduced electron transfer (PET) in the absence of Ca2+, and a strongly fluorescent form when bound to Ca2+.<p> The second project is a continuation of a previous study on CG-2. In the dual-chromophore CG-2 system, energy transfer between chromophores is controlled by the orientation and spatial separation between chromophores. Dual polarization fluorescence microscopy was used to determine the relative conformation of the two fluorophores in the emissive form of CG-2. Distributions of fluorescence polarization of individual CG-2 molecules were collected for both Ca2+-free and Ca2+-saturated conditions. The experimental polarization results were compared to those calculated from a simple geometric model based on randomly-orientated fluorescent dimers. The results show good agreement with previous calculations of the molecular conformation of CG-2. This indicates that the dual polarization imaging approach has significant potential as a general tool for characterizing chromophore orientation in coupled-fluorophore systems.<p> In the third project, Nile Red (NR), a solvatochromic lipid stain, was incorporated into phase separated Langmuir-Blodgett (LB) films composed of arachidic acid (AA) and perfluorotetradecanoic acid (PA). According to previous studies by atomic force microscopy (AFM), two types of separated domains are formed in the LB films: micron-sized hexagonal discontinuous domains that are exclusively comprised of AA, and the surrounding continuous domains which are enriched in PA. The photophysical properties of NR were characterized in the two physically and chemically distinct domains via bulk and SM fluorescence measurements. In addition to fluorescence microscopy, fluorescence confocal spectromicroscopy was also applied in the ensemble measurements to determine the spectral properties of NR in different sub-environments. Experimental results indicated that a small sub-population of dye molecules localize on the perfluorinated regions of the sample, but this sub-population is spectroscopically indistinguishable from that associated with the hydrogenated domains. Contrast in images was primarily due to preferential accumulation of the hydrophobic dye on the hydrophobic regions of the LB films.<p> In the final project, the fluorescence quenching behavior of a strongly fluorescent probe Alexa Fluor 514 (AF514) was investigated when it was covalently bound to gold metal protected clusters (AuMPC) with negligible plasmon bands. The fluorescence emission of the dye-AuMPCs system was characterized at different dye/Au MPC loading ratios with a combination of steady state and time-resolved ensemble spectroscopic measurements. It was found that the extent of fluorescence quenching in the system was small. After correction of inner filter effects, the results from bulk measurement demonstrate that the weak quenching is due to static quenching of the dye by the AuMPCs. SM measurements provided further support for the bulk measurements, with the fluorescence intensity of coupled AF514 molecules being comparable with that of unconjugated molecules. The photobleaching of the dye-AuMPC conjugates took place as a series of consecutive photobleaching events, without additional blinking dynamics within the time resolution of the experiment. These results suggest that the fluorophores on the AuMPCs are either entirely quenched, or remaining unquenched, as is consistent with the ensemble measurements.
42

CONFOCAL LASER SCANNING MICROSCOPY AS A TOOL FOR THE INVESTIGATION OF TETRACYCLINE FLUORESCENCE IN ARCHAEOLOGICALHUMAN BONE

Maggiano, Corey 09 January 2006 (has links)
Fluorochromes such as tetracycline have been used to label bone for histomorphometric analysis, measuring bone formation, growth, maintenance, and pathology. More recently, similar fluorescence has been observed in ancient human bone. Attributed to tetracycline (TC) exposure, this phenomenon could affect various aspects of health during life and/or preservation of remains postmortem. Standard epifluorescence microscopy is the most common tool employed in the analysis of these labels. Though valuable, this technique is limited by its inability to penetrate bone three-dimensionally and its inclusion of out-of-focus light, possibly disrupting accurate analysis. Confocal Laser Scanning Microscopy (CLSM) has been demonstrated as a valuable tool for three-dimensional histology. Its application to the study of compact bone fluorescence has been lacking, especially in archaeological and forensic sciences. In the following two papers, modern TC-controlled bone is compared to well preserved archaeological bone recovered from the Dakhleh Oasis, Egypt, using both standard wide-field and more modern confocal techniques for imaging and analysis. Spectral analysis via CLSM shows that both modern and ancient fluorescent labels in bone share the exact same fluorescence emission peak at 525 nm. Differences in the shape of the spectral curve and photobleaching characteristics are discussed. In addition, CLSM's high-resolution two- and three-dimensional imaging capabilities (in polarized light, scattered light, and fluorescence light) are found to increase the flexibility and creativity of investigations into the occurrence of tetracycline labels in archaeological bone and could have added benefits for modern medical and anatomical experimentation. / M.S. / Department of Biology / Arts and Sciences / Biology
43

Single molecule mechanical testing

Lillehei, Peter Thomas 05 1900 (has links)
No description available.
44

Visualizing the Structural Basis of Genome Silencing

Fussner, Eden Margaret 19 June 2014 (has links)
Eukaryotic genomes must be folded and compacted to fit within the restricted volume of the nucleus. This folding, and the subsequent organization of the genome, reflects both the transcription profile of the cell and of the specific cell type. A dispersed, mesh-like chromatin configuration, for example, is characteristic of a pluripotent stem cell. Here we show that the acquisition of the pluripotent state during somatic cell reprogramming is coincident with the disruption of compact heterochromatin domains. Using Electron Spectroscopic Imaging (ESI), I made the surprising observation that the heterochromatin domains of the induced pluripotent and of the parental somatic cell contained 10 nm chromatin fibres. Since ESI generates projection images, the precise three-dimensional organization of all chromatin fibres within these domains could not be elucidated. To circumvent this limitation, I developed an electron microscopy technique that combines ESI with tomography. Using this approach, I found that both heterochromatin domains and the surrounding euchromatin of murine pluripotent cells, fibroblasts, and somatic tissues are in fact organized entirely as 10 nm chromatin fibres. This challenges the current paradigm that most, if not all, of the genome exists as 30 nm and higher-order chromatin fibre assemblies. Rather than transitions between 10 nm and 30 nm fibres, I propose that the organization and thus the regulation of the genome is achieved by the bending and folding of 10 nm chromatin fibres into discrete domains in a cell type-specific manner.
45

Visualizing the Structural Basis of Genome Silencing

Fussner, Eden Margaret 19 June 2014 (has links)
Eukaryotic genomes must be folded and compacted to fit within the restricted volume of the nucleus. This folding, and the subsequent organization of the genome, reflects both the transcription profile of the cell and of the specific cell type. A dispersed, mesh-like chromatin configuration, for example, is characteristic of a pluripotent stem cell. Here we show that the acquisition of the pluripotent state during somatic cell reprogramming is coincident with the disruption of compact heterochromatin domains. Using Electron Spectroscopic Imaging (ESI), I made the surprising observation that the heterochromatin domains of the induced pluripotent and of the parental somatic cell contained 10 nm chromatin fibres. Since ESI generates projection images, the precise three-dimensional organization of all chromatin fibres within these domains could not be elucidated. To circumvent this limitation, I developed an electron microscopy technique that combines ESI with tomography. Using this approach, I found that both heterochromatin domains and the surrounding euchromatin of murine pluripotent cells, fibroblasts, and somatic tissues are in fact organized entirely as 10 nm chromatin fibres. This challenges the current paradigm that most, if not all, of the genome exists as 30 nm and higher-order chromatin fibre assemblies. Rather than transitions between 10 nm and 30 nm fibres, I propose that the organization and thus the regulation of the genome is achieved by the bending and folding of 10 nm chromatin fibres into discrete domains in a cell type-specific manner.
46

Study of magnetic and multiferroic oxides by scanning force microscope

Chuang, Tien-Ming 28 August 2008 (has links)
Not available / text
47

Magnetic studies of colossal magnetoresistance materials and FePt nanocrystals

Hyun, Changbae, 1974- 28 August 2008 (has links)
This dissertation introduces scanning probe microscopy (SPM) and describes the construction and design of a home built low temperature magnetic force microscope (MFM). Then the magnetic coatings on atomic force microscope cantilevers with a focused ion beam (FIB) will be explained. This technique allows the convenient deposition of complex or expensive materials such as CoCrPt. With the MFM tip coated by FIB, the ferromagnetic domain structure of a La[subscript 0.67]Ca[subscript 0.33]MnO₃ film is studied as a function of an in-plane magnetic field below room temperature. Next I will discuss the use of chemically-synthesized FePt nanocrystals as a good candidate for high density storage media. This nanocrystal film showed sintering problems during the annealing process, which is essential to make FePt a hard ferromagnet. A silica overcoating method was used to prevent nanocrystal sintering, which allowed the MFM study of films made from these nanocrystals. I will also discuss resistance measurements of the FePt nanocrystals.
48

Scanning optical microscopy of semiconductor devices

McCabe, Eithne January 1987 (has links)
A new method to display low contrast OBIC images has been used to highlight defects in semiconductor devices. In addition an exciting novel method to obtain spatial information on the distribution of defects at the silicon/silicon-dioxide interface in metal oxide semiconductor devices has been found. This method can examine many defects which cause serious problems for device manufacturers including the effect of radiation damage on device performance. Other non-destructive techniques which can complement OBIC imaging are explored including photoluminescence and infrared transmission imaging. Additional research is proposed for the future. This research in conjunction with the research in this thesis would allow a comprehensive and powerful examination approach of both static and dynamic conditions of semiconductor devices.
49

Spatial resolution in STEM EDX microanalysis

Kerr, R. T. January 1985 (has links)
No description available.
50

High-resolution structured illumination solid immersion fluorescence microscopy

Wang, Lin January 2010 (has links)
The use of aplanatic solid immersion lenses (ASILs) made of high refractive index optical glasses provides a route to wide-field high-resolution optical microscopy. Structured illumination microscopy (SIM) can double the spatial bandwidth of a microscope to achieve high-resolution imaging. This research aims to investigate the combination of the ASILs and SIM in fluorescence microscopy, which we call structured illumination solid immersion fluorescence microscopy (SISIM), to pursue a microscopic system with very large numerical aperture and high lateral resolution. The first stage of the research shows the development of solid immersion fluorescence microscopy (SIF) employing an ASIL allows us to obtain a fluorescence microscope with effective numerical aperture of 1.85. The aberration issues, especially chromatic aberration, that need to be circumvented are analysed by both optical simulation and experimental verification. The near-field imaging property is also discussed and demonstrated. Then the SIM using a diffraction grating to generate structured illumination pattern via two-beam interference is developed. Finally, the SISIM system is constructed by combining the structured illumination with the SIF, and an effective numerical aperture of 3 has been obtained. Future developments of the SISIM system to make it achieve higher resolution and suit routine use are proposed. SISIM is a promising high-resolution microscopic technique with extensive potential applications in cell biology.

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