UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item Low-Cost Paper-Based Assays for Multiplexed Genetic Analysis using Surface Enhanced Raman Spectroscopy(2013) Hoppmann, Eric Peter; White, Ian M; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In order to improve human health it is critical to develop low-cost sensors for chemical detection and healthcare applications. Low-cost chemical detectors can enable pervasive monitoring to identify health threats. Rapid yet accessible infectious disease diagnostics have the potential to improve patient quality of care, reduce healthcare costs and speed recovery. In both cases, when multiple targets can be detected with a single test (multiplexing), accessibility is improved through lowered costs and simplicity of operation. In this work we have investigated the practical considerations and applications of ink-jet printed paper surface enhanced Raman spectroscopy (SERS) devices. SERS enables specific simultaneous detection of numerous analytes using a single excitation source and detector. Sensitive detection is demonstrated in several real-world applications. We use a low-cost portable spectrometer for detection, further emphasizing the potential for on-site detection. These ink-jet printed devices are then used to develop a novel DNA detection assay, in which the multiplexing capabilities of SERS are combined with DNA amplification through polymerase chain reaction (PCR). In this assay, the chromatographic properties of paper are leveraged to perform discrimination within the substrate itself. As a test case, this assay is then used to perform duplex detection of the Methicillin-resistant Staphylococcus aureus (MRSA) genes mecA and femB, two genes which confer antibiotic resistance on MRSA. Finally, we explore statistical multiplexing methods to enable this assay to be applied to perform highly-multiplexed detection gene targets (5+), and demonstrate the differentiation of these samples using partial least-squares regression (PLS). By averaging the signal over a region of the SERS substrate, substrate variability was mitigated allowing effective identification and differentiation, even for the complex spectra from highly multiplexed samples which were impossible to visually analyze.Item Characterization of Electrodeposited Chitosan: an Interfacial Layer for Bio-assembly and Sensing(2009) Buckhout-White, Susan Lynn; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microfluidics and Lab-on-a-Chip devices have revolutionized the field of analytical biology. To fully optimize the potential of the microfluidic environment it is critical to be able to isolate reactions in specific locations within a channel. One solution is found using chitosan, an amine-rich biopolymer with pH responsive solubility. Induction of hydrolysis at patterned electrodes within the fluidic channel provides a means to spatially control the pH, thus enabling biochemical functionalization that is both spatially and temporally programmable. While chitosan electrodeposition has proven to be reliable at producing films, its growth characteristics are not well understood. In situ optical characterization methods of laser reflectivity, fluorescence microscopy and Raman spectroscopy have been employed to understand the growth rate inter diffusion and lateral resolution of the deposition process. These techniques have also been implemented in determining where a molecule bound to an amine site of the polymer is located within the film. Currently, electrodeposited chitosan films are primarily used for tethering of biomolecules in the recreation of metabolic pathways. Beyond just a biomolecular anchor, chitosan provides a way to incorporate inorganic nanoparticles. These composite structures enable site-specific sensors for the identification of small molecules, an important aspect to many Lab-on-a-Chip applications. New methods for creating spatially localized sites for surface enhanced Raman spectroscopy (SERS) has been developed. These methods have been optimized for particle density and SERS enhancement using TEM and Raman spectroscopy. Through optimization, a viable substrate with retained chitosan amine activity capable of integration into microfluidics has been developed.Item Tunneling and Raman Spectroscopies of the Electron-doped High-temperature Superconductors(2004-08-02) Qazilbash, Muhammad Mumtaz; Greene, Richard L; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis consists of spectroscopic studies of the electron-doped high temperature cuprate superconductors Pr2-xCexCuO4-\delta (PCCO) and Nd2-xCexCuO4-\delta (NCCO). Point contact and high barrier tunneling spectroscopies were employed to study the evolution of the superconducting gap (\Delta) with cerium doping. Point contact spectroscopy of low barrier junctions reveals that the gap changes from d-wave in under-doped PCCO to a nodeless gap in over-doped PCCO. This transition in pairing symmetry occurs just above optimal doping. High barrier tunnel junctions were prepared on optimally doped PCCO and NCCO crystals for tunneling into the ab-planes. The spectra are not consistent with either a clean s-wave gap or a clean monotonic dx2-y2 gap, and can be explained by a non-monotonic d-wave gap. A normal state gap near zero voltage bias is observed in the tunneling spectra for dopings between x = 0.13 and x = 0.19 when superconductivity is suppressed by magnetic fields larger than the upper critical fields (Hc2). The normal state gap appears to coexist with the superconducting gap. The normal state gap vanishes at a temperature close to the superconducting transition temperature for optimally doped samples. Raman spectroscopy was employed to systematically study the electronic properties of PCCO and NCCO crystals and films across the superconducting phase diagram. Polarization and doping dependence of the (2\Delta) coherence peaks in the superconducting state show a change in the superconducting gap from non-monotonic d-wave at optimal doping to either a dirty d-wave or a dirty s-wave in the over-doped samples. By analyzing coherence effects, we find that all coherent carriers in the non-superconducting state condense to form the superfluid. Carriers that are doped beyond optimal doping are incoherent and do not contribute to the coherent Raman response in the normal and superconducting states. We systematically studied the effects of temperature and magnetic field on the coherence peaks in the Raman spectra for various dopings. Compared to the optimally doped crystals, Hc2 decreases by more than an order of magnitude in the most over-doped crystal. The implications of these observations are discussed.