88 Matching Results

Search Results

Advanced search parameters have been applied.

A Quenchofluorometric Study of Polycyclic Aromatic Hydrocarbons in Molecularly Organized Media

Description: Detection, identification and separation of polycyclic aromatic compounds in environmental samples are of extreme importance since many of these compounds are well known for their potential carcinogenic and/or mutagenic activities. Selective quenching of molecular fluorescence can be utilized effectively to analyze mixtures containing different polycyclic aromatic hydrocarbons. Molecularly organized assemblies are used widely in detection and separation of these compounds mainly because of less toxicity and enhanced solubilization capabilities associated with these media. Feasibility of using nitromethane and the alkylpyridinium cation as selective fluorescence quenching agents for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is critically examined in several molecularly organized micellar solvent media. Fluorescence quenching is used to probe the structural features in mixed micelles containing the various combinations of anionic, cationic, nonionic and zwitterionic surfactants. Experimental results provide valuable information regarding molecular interactions between the dissimilar surfactants.
Date: May 1998
Creator: Pandey, Siddharth
Partner: UNT Libraries

Advanced microinstrumentation for rapid DNA sequencing and large DNA fragment separation

Description: Our efforts to develop novel technology for a rapid DNA sequencer and large fragment analysis system based upon gel electrophoresis are described. We are using microfabrication technology to build dense arrays of high speed micro electrophoresis lanes that will ultimately increase the sequencing rate of DNA by at least 100 times the rate of current sequencers. We have demonstrated high resolution DNA fragment separation needed for sequencing in polyacrylamide microgels formed in glass microchannels. We have built prototype arrays of microchannels having up to 48 channels. Significant progress has also been made in developing a sensitive fluorescence detection system based upon a confocal microscope design that will enable the diagnostics and detection of DNA fragments in ultrathin microchannel gels. Development of a rapid DNA sequencer and fragment analysis system will have a major impact on future DNA instrumentation used in clinical, molecular and forensic analysis of DNA fragments.
Date: January 25, 1995
Creator: Balch, J.; Davidson, J.; Brewer, L.; Gingrich, J.; Koo, J.; Mariella, R. et al.
Partner: UNT Libraries Government Documents Department

Detection of lead in soil with excimer laser fragmentation fluorescence spectroscopy (ELFFS)

Description: Excimer laser fragmentation fluorescence spectroscopy (ELFFS) is used to monitor lead in soil sample and investigate laser-solid interactions. Pure lead nitrate salt and soil doped with lead nitrate are photolyzed with 193 nm light from an ArF excimer at fluences from 0.4 to 4 J/cm{sup 2}. Lead emission is observed at 357.2, 364.0, 368.3, 373.9 and 405.8 nm. Time-resolved data show the decay time of the lead emission at 405.8 nm grows with increasing fluence, and a plasma is formed above fluences of 2 J/cm{sup 2}, where a strong continuum emission interferes with the analyte signal. Fluences below this threshold allow us to achieve a detection limit of approximately 200 ppm in soil.
Date: March 1, 2004
Creator: Choi, J.H.; Damm, C.J.; O'Donovan, N.J.; Sawyer, R.F.; Koshland, C.P. & Lucas, D.
Partner: UNT Libraries Government Documents Department

Near-field single molecule spectroscopy

Description: The high spatial resolution and sensitivity of near-field fluorescence microscopy allows one to study spectroscopic and dynamical properties of individual molecules at room temperature. Time-resolved experiments which probe the dynamical behavior of single molecules are discussed. Ground rules for applying near-field spectroscopy and the effect of the aluminum coated near-field probe on spectroscopic measurements are presented.
Date: February 1, 1995
Creator: Xie, X.S. & Dunn, R.C.
Partner: UNT Libraries Government Documents Department

Directly labeled fluorescent DNA probes for chromosome mapping

Description: A new strategy is briefly described for employing nucleic acid probes that are directly labeled with fluorochromes in fluorescence in situ hybridization techniques. These probes will permit the detection, quantitation, and high-precision spatial analysis of multiple DNA sequences along a single chromosome using video-enhanced fluorescence microscopy and digital image processing and analysis. Potential advantages of direct labeled DNA probes for fluorescence in situ hybridization far surpass currently available, indirect DNA probe labeling techniques in ease of use, versatility, and increased signal- to-noise ratio.
Date: December 31, 1995
Creator: Marrone, B.L.; Deaven, L.L.; Chen, D.J.; Park, Min S.; MacInnes, M.A.; Salzman, G.C. et al.
Partner: UNT Libraries Government Documents Department

Laser physics research for KrF lasers - fluorescence suppression measurments. Final report

Description: This final report describes the work performed for Los Alamos National Laboratory (LANL) to measure the wavelength-dependent KrF fluorescence suppression as a function of intracavity flux. To our knowledge, this is the first time the wavelength-dependent suppresssion has been measured for KrF.
Date: October 1, 1991
Partner: UNT Libraries Government Documents Department

Optical properties of fluids in microfabricated channels

Description: Microfabricated channels are widely thought to be the key to realizing chemical analysis on a microscopic scale. Chemical and biological information in the microchannels is often probed with optical techniques such as fluorescence, Raman and absorption spectroscopy. However, the optical effects of a microchannel are not well characterized. For example, it is important to understand the optics of the channel in order to optimize optical coupling efficiency. The authors consider various designs for enhancing the sensitivity of fluorescence detection in a microchannel.
Date: March 1, 1997
Creator: French, T.; Gourley, P.L. & McDonald, A.E.
Partner: UNT Libraries Government Documents Department

The self-supporting disc: A specimen geometry exhibiting low secondary characteristic fluorescence

Description: Secondary characteristic fluorescence, when expressed relative to the primary intensity of the fluorescing element, can be written as the product of three factors, which represent the probabilities of the various processes that govern the magnitude of fluorescence and thus have values between zero and one. Two of these factors are characteristic of the material being analyzed. The factor C{sub X}{sup Y} is the likelihood that the primary x ray of Y is absorbed by the element X if it is absorbed in the fluoresced volume of the specimen. The factor P{sub X} is the probability that element X, having absorbed the primary x ray, emits the secondary x ray of interest. The third factor is the likelihood that the primary x ray is absorbed in the fluoresced volume, and is denoted {Omega}{sub eff}/4{pi}. For critical microanalysis studies, thin-flake specimens are most desirable, especially if the size of individual flakes is small relative to the scale, {approximately}10 {mu}m, over which the primary x rays are typically absorbed. However, a specimen comprised of small flakes may be impractical for many studies. Such a geometry may not indicate the relative positions and orientations of important microstructural features. The lack of sampling volume may also inhibit microanalysis of a specific feature of the microstructure, such as an interface, which may not be represented within the small specimen volume. For such analyses, a specimen geometry that leaves the specimen intact, yet minimizes secondary fluorescence by virtue of having a small geometric factor, may be preferable. Because the geometric factor depends only on the absorption properties of the secondary x ray, a rule-of-thumb maximum secondary fluorescence of an elemental line can be calculated by assuming an extreme microanalysis situation: when the entire disc is composed of the fluoresced element.
Date: June 1, 1995
Creator: Anderson, I.M.; Bentley, J. & Carter, C.B.
Partner: UNT Libraries Government Documents Department

Preliminary evaluation of resinite recovery from Illinois coal. Technical report, December 1, 1994--February 28, 1995

Description: Resinite is a naturally occurring substance found in coal and derived from original plant resins. It is ubiquitous in North American coals. It makes up one to four percent by volume of most Illinois coals. It has been commercially exploited in the western USA for use in adhesives, varnishes and thermal setting inks. The overall objective of this project is to compare the properties of the resinite contained in Illinois Basin coals to resinite being commercially exploited in the western United States, and to recover the resinite from Illinois coals by microbubble column floatation techniques. This project is relevant to priority 1.4A identified in ICCI/RFP93-1. The significance of this study is that it has the potential to show the way to recover a valuable chemical, resinite, from coal using only physical processing techniques. The value of the resinite at $1.00/kg or $0.50/lb makes it about fifty times more valuable than steam coal. The removal of resinite from coal does not decrease the value of the remaining coal in any way. The unique aspects are that: (1) it is the first examination of the resinite recovery potential of Illinois coal, (2) it integrates the latest characterization techniques such as density gradient centrifugation, microspectrofluorometry, and gas chromatography-mass spectrometry, and (3) it uses microbubble column flotation to determine the resinite recovery potential. During this quarter samples were obtained, information from both the databases of both the Illinois State Geological Survey (ISGS) and the Pennsylvania State University (PSU) was obtained and evaluated, and IBCSP samples from the Herrin No. 6, the Springfield No. 5 and the Colchester No. 2 seams were analyzed petrographically and the resinites in these samples were characterized by fluorescence spectral analysis.
Date: December 31, 1995
Creator: Crelling, J.C.
Partner: UNT Libraries Government Documents Department

Dispersion functions and factors that determine resolution for DNA sequencing by gel electrophoresis

Description: The number of bases that can be read in a single run by a DNA sequencing instrument that detects fluorophore labeled DNA arriving at a ``finish-line`` located a fixed distance from the starting wells is influenced by numerous parameters. Strategies for improving the length-of-read of a DNA sequencer can be based on quantitative models of the separation of DNA by gel electrophoresis. The dispersion function of the electrophoretic system--the relationship between molecular contour length and time of arrival at the detector--is useful in characterizing the performance of a DNA sequencer. We adapted analytical representations of dispersion functions, originally developed for snapshot imaging of DNA gels, (samples electrophoresed for constant time), to finish-line imaging, and demonstrated that a logistic-type function with non-integral exponent is required to describe the experimental data. We use this dispersion function to determine the resolution length and resolving power of a LI-COR DNA sequencing system and a custom built capillary gel electrophoresis system, and discuss the factors that presently limit the number of bases that can be determined reliably in a single sequencing run.
Date: April 1, 1996
Creator: Sutherland, J.C.; Reynolds, K.J. & Fisk, D.J.
Partner: UNT Libraries Government Documents Department

Fabrication of High Performance Microlenses for an Integrated Capillary Channel Electrochromatograph with Fluorescence Detection

Description: We describe the microfabrication of an extremely compact optical system as a key element in an integrated capillary channel electrochromatograph with fluorescence detection. The optical system consists of a vertical cavity surface-emitting laser (VCSEL), two high performance microlenses and a commercial photodetector. The microlenses are multilevel diffractive optics patterned by electron beam lithography and etched by reactive ion etching in fused silica. The design uses substrate-mode propagation within the fused silica substrate. Two generations of optical subsystems are described. The first generation design has a 6 mm optical length and is integrated directly onto the capillary channel-containing substrate. The second generation design separates the optical system onto its own substrate module and the optical path length is further compressed to 3.5 mm. The first generation design has been tested using direct fluorescence detection with a 750 nm VCSEL pumping a 10{sup {minus}4}M solution of CY-7 dye. The observed signal-to-noise ratio of better than 100:1 demonstrates that the background signal from scattered pump light is low despite the compact size of the optical system and is adequate for system sensitivity requirements.
Date: July 7, 1999
Creator: Wendt, J.R.; Warren, M.E.; Sweatt, W.C.; Bailey, C.G.; Matzke, C.M.; Arnold, D.W. et al.
Partner: UNT Libraries Government Documents Department

Structure of mix in a rayleigh-taylor unstable fuild cell

Description: Laser-induced fluorescence is used to image the central plane of the mix region of two immiscible liquids subject to the Rayleigh-Taylor instability. The familiar bubbles and spikes display a complex internal structure. This small-scale structure creates a large contact area whose density is constant in time. The size of the mixing zone, defined in a new way, grows with coefficient ab >= 0.054.
Date: September 2, 1997
Creator: Schneider, M.B.; Dimonte, G. & Remington, B.A.
Partner: UNT Libraries Government Documents Department

Photoinduced degradation of PAHs in the presence of ozone

Description: Polycyclic Aromatic Hydrocarbons (PAH) are formed from both anthropogenic and natural sources. In order to assess the environmental impact caused by the surface-adsorbed PAHs, the chemical lifetimes of these compounds in the atmosphere must be determined. Although ozone is known to be a primary reactant in the chemical transformation of surface-adsorbed PAHs in the atmosphere, the kinetics of these reactions have not been investigated in detail. In addition to the experimental difficulties that arise in using an oxygen-ozone stream while monitoring the PAH with fluorescence, complications in analyzing the kinetic mechanism also exist. It is difficult to determine whether the ozone or oxygen initially quenches the excited state of PAH. Ozone could enhance the degradation rate by simply reacting with a product derived from the excited state of PAH and oxygen. The focus of this study is to demonstrate the use of fluorescence spectroscopy in monitoring the degradation of PAH adsorbed on a three dimensional particle in the presence of gaseous ozone free from the interference of oxygen. More specifically, the experimental procedure will involve the generation of an ozone-nitrogen gas stream to be used in the investigation of dark and photochemical reactions between ozone and naphthalene. The absence of oxygen in the system will allow for the accurate monitoring of PAH fluorescence decay due solely to ozone quenching. It will also aid in the determination of the reaction mechanism. This is the first time that the direct interaction of ozone with an excited state of PAH has been demonstrated.
Date: December 31, 1995
Creator: Schutt, W.S.; Li, Y. & Sigman, M.E.
Partner: UNT Libraries Government Documents Department

Development of fluorescence lifetime diagnostic. Project accomplishments summary (Attachment 1), Revision 1

Description: Fiber-optic-based sensors are excellent candidates for detecting the presence and monitoring the levels of degradation products in stockpiled weapons. Specifically, fluorescence-based sensors are extremely sensitive, can have high specificity for compounds of interest, and are electrically inert. In addition to their applications in the enhanced surveillance program, fiber optic sensors are important for remote sensing, environmental remediation, and medical diagnostics. Optiphase Inc. has developed inexpensive technology for extremely precise measurement of phase shifts of interferometric optical and electrical signals. The company was interested in applying this capability in the rapidly expanding field of fluorescence lifetime spectroscopy, but lacked the expertise and resources associated with fluorescence chemistry and instrumentation. LLNL`s fiber-optic sensor group had significant expertise in these areas, but had previously concentrated its efforts on the chemistry, sensitivity, and selectivity of fluorescence amplitude-based sensors. Stability is a well known issue with this type of sensor whereas lifetime-based sensors exhibit excellent stability, a critical factor for the efficacy of sensors employed in the long-term monitoring of stockpiled weapons. Cooperation with the company afforded LLNL access to enabling, proprietary technology which could simplify and accelerate the transition to the next level of Enhanced Surveillance Program (ESP) sensor sophistication, namely fluorescence lifetime based sensors.
Date: February 18, 1998
Partner: UNT Libraries Government Documents Department

Surfactant loss control in chemical flooding: Spectroscopic and calorimetric study of adsorption and precipitation on reservoir minerals. Quarterly technical progress report. October 1, 1994--December 31, 1994

Description: The aim of this research is to elucidate the mechanisms underling adsorption and surface precipitation of flooding surfactants on reservoir minerals. The adsorption and desorption behaviors of tetradecyltrimethyl ammonium chloride (TTAC) and pentadecylethoxylated nonylphenol (NP-15) mixtures as reported earlier were rather complex and to better understand the interactions involved fluorescence spectroscopy and ultrafiltration were used during this report period to probe the microstructure of the adsorbed layer and to determine individual surfactant monomer concentration respectively. It was observed that pyrene was solubilized in mixed aggregates (hemimicelles) of a 1:1 TTAC:NP-15 mixture at the alumina-water interface over a wider concentration range than for TTAC alone. It was also observed that the adsorbed aggregate of a 1:1 TTAC:NP-15 mixture is as hydrophobic as the mixed micelle in solution. This is contrary to what was observed for the adsorption of TTAC alone: pyrene was preferentially solubilized in the TTAC micelles rather than the adsorbed aggregate. The preference of pyrene for the mixed adsorbed aggregates over individual aggregates is relevant to the application of surfactant mixtures in enhanced oil recovery and solubilization. The adsorption/desorption behavior of surfactants is directly related to the monomer concentration of the surfactant, hence it is important to monitor changes in monomer concentration during the adsorption and desorption processes. Ultrafiltration techniques were used to monitor the monomer concentration in solution and at the interface to determine the partitioning of the surfactants to the solid-liquid interface.
Date: March 1, 1995
Creator: Somasundaran, P.
Partner: UNT Libraries Government Documents Department

Application of fluorescent antibody and enzyme-linked immunosorbent assays for TCE and PAH degrading bacteria

Description: Historically, methods used to identify methanotrophic and polyaromatic hydrocarbon-degrading (PAH) bacteria in environmental samples have been inadequate because isolation and identification procedures are time-consuming and often fail to separate specific bacteria from other environmental microorganisms. Methanotrophic bacteria have been isolated and characterized from TCE-contaminated soils (Bowman et al. 1993; Fliermans et al., 1988). Fliermans et al., (1988) and others demonstrated that cultures enriched with methane and propane could cometabolically degrade a wide variety of chlorinated aliphatic hydrocarbons including ethylene; 1,2-cisdichloroethylene (c-DCE); 1,2-trans-dichloroethylene (t-DCE); vinyl chloride (VC); toluene; phenol and cresol. Characterization of select microorganisms in the natural setting is important for the evaluation of bioremediation potential and its effectiveness. This realization has necessitated techniques that are selective, sensitive and easily applicable to soils, sediments, and groundwater (Fliermans, et al., 1994). Additionally these techniques can identify and quantify microbial types in situ in real time
Date: July 1, 1996
Creator: Brigmon, R.L.; Franck, M.; Brey, J.; Scott, D.; Lanclos, K. & Fliermans, C.
Partner: UNT Libraries Government Documents Department

Fluorescence spectroscopy of single molecules at room temperature and its applications

Description: We performed fluorescence spectroscopy of single and pairs of dye molecules on a surface at room temperature. Near field scanning optical microscope (NSOM) and far field scanning optical microscope with multi-color excitation/detection capability were built. The instrument is capable of optical imaging with 100nm resolution and has the sensitivity necessary for single molecule detection. A variety of dynamic events which cannot be observed from an ensemble of molecules is revealed when the molecules are probed one at a time. They include (1) spectral jumps correlated with dark states, (2) individually resolved quantum jumps to and from the meta-stable triplet state, (3) rotational jumps due to desorption/readsorption events of single molecules on the surface. For these studies, a computer controlled optical system which automatically and rapidly locates and performs spectroscopic measurements on single molecules was developed. We also studied the interaction between closely spaced pairs of molecules. In particular, fluorescence resonance energy transfer between a single resonant pair of donor and acceptor molecules was measured. Photodestruction dynamics of the donor or acceptor were used to determine the presence and efficiency of energy transfer Dual molecule spectroscopy was extended to a non-resonant pair of molecules to obtain high resolution differential distance information. By combining NSOM and dual color scheme, we studied the co-localization of parasite proteins and host proteins on a human red blood cell membrane infected with malaria. These dual-molecule techniques can be used to measure distances, relative orientations, and changes in distances/orientations of biological macromolecules with very good spatial, angular and temporal resolutions, hence opening new capabilities in the study of such systems.
Date: December 1, 1996
Creator: Ha, Taekjip
Partner: UNT Libraries Government Documents Department

Developing optical traps for ultra-sensitive analysis

Description: The authors describe the coupling of a magneto-optical trap to a mass separator for the ultra-sensitive detection of selected radioactive species. As a proof of principle test, they have demonstrated the trapping of {approximately} 6 million {sup 82} Rb (t{sub 1/2} = 75 s) atoms using an ion implantation and heated foil release method for introducing the sample into a trapping cell with minimal gas loading. Gamma-ray counting techniques were used to determine the efficiencies of each step in the process. By far the weakest step in the process is the efficiency of the optical trap itself (0.3%). Further improvements in the quality of the nonstick dryfilm coating on the inside of the trapping cell and the possible use of larger diameter laser beams are indicated. In the presence of a large background of scattered light, this initial work achieved a detection sensitivity of {approximately} 4,000 trapped atoms. Improved detection schemes using a pulsed trap and gated photon detection method are outlined. Application of this technology to the areas of environmental monitoring and nuclear proliferation are foreseen.
Date: September 1, 1998
Creator: Zhao, X.; Vieira, D.J.; Guckert, R. & Crane, S.
Partner: UNT Libraries Government Documents Department

X-ray Raman scattering in H-BN observed by soft x-ray fluorescence spectroscopy

Description: Raman scattering of soft x-rays is observed in h-BN using monochromatic soft x-rays just below the B K absorption edge. The inelastic features are visible below threshold, track with the excitation energy, go through a resonance as the excitation is tuned to the B ls core exciton energy, and finally evolve into normal fluorescence as the excitation is raised above the energy needed to excite the B ls electron into the conduction band. The inelastic energy loss is identified as an excitation of valence {sigma} electrons into the {pi}* valence exciton state; at resonance and above, {pi} {minus} {pi}* transitions are also observed. At resonance, a sideband on the elastic peak Ls observed, which gives evidence of additional electronic and phonon loss processes. Very similar results have also been observed for B{sub 2}O{sub 3}.
Date: March 1, 1995
Creator: Jia, J.J.; Callcott, T.A.; Carlisle, J.A.; Terminello, L.J.; Asfaw, A.; Ederer, D.L. et al.
Partner: UNT Libraries Government Documents Department

Resonant soft x-ray fluorescence studies of novel materials

Description: The authors are using resonant soft x-ray fluorescence at the Advanced Light Source to probe the electronic and geometric structure of novel materials. In the resonant process, a core electron is excited by a photon whose energy is near the core binding energy. In this energy regime the absorption and emission processes are coupled, and this coupling manifests itself in several ways. In boron nitride (BN), the resonant emission spectra reflect the influence of a ``spectator`` electron in an unoccupied excitonic state. The resonant emission can be used to distinguish between the various bulk phases of BN, and can also be used to probe the electronic structure of a monolayer of BN buried in a bulk environment, where it is inaccessible to electron spectroscopies. For highly-oriented pyrolytic graphite (HOPG) a coherent absorption-emission process takes place in the resonant regime, whereby crystalline momentum is conserved between the core excited electron and the valence hole which remains after emission.
Date: February 8, 1995
Creator: Carlisle, J.A.; Terminello, L.J.; Hudson, E.A.; Shirley, E.L.; Jia, J.J.; Callcott, T.A. et al.
Partner: UNT Libraries Government Documents Department