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.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Bringing New Chemistry to Guanosine Hydrogels(2020) Xiao, Songjun; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Molecular self-assembly is a powerful method to construct functional materials such as supramolecular hydrogels. Hydrogels contain mostly water but show solid-like rheology. Nucleosides and nucleotides contain rich recognition information, which opens up opportunities for gelator design. Hydrogels derived from these natural products have seen a resurgence in the past decade due to the high biodegradability and biocompatibility. Guanosine (G 1) and its analogs are powerful supramolecular hydrogelators. The structural basis for most guanosine hydrogels is G4•M+ quartet with K+ being the best metal to stabilize such a structure. These hydrogen-bonded macrocycles further stack to form 1D G-quadruplex that traps water to give hydrogels. Guanosine hydrogels have been used for applications such as bioactive molecule trap and release, environmental remediation, sensing and cell culture. While the H-bonded G-quadruplex is critical for gelation, G 1 can be synthetically modified to introduce new functions. The work presented here is focused on G-quartet hydrogels made from synthetic guanosine analogs. Guanosine analogs containing sulfur on 8- and 5ʹ-position are purified and their hydrogelation properties in water were examined. The resulting hydrogels can potentially be applied to environmental remediation. Substitution of 5ʹ-OH in G 1 into a hydrazine group in HG 2 significantly improves the hydrogelation properties. The resulting HG 2 KCl hydrogel can be used to non-covalently bind anionic dyes and covalently trap toxic electrophiles such as acrolein. A binary mixture of G 1 and HAG 15 forms a stable hydrogel with KCl. The hydroxamic acid group in HAG 15 serves as a pH-switchable group that can be applied as a carboxylic acid substitute in hydrogelator design. Furthermore, the hydrogel serves as a supramolecular siderophore and binds Fe3+ to generate patterns on the gel surface. The surface can be erased with a reducing agent and rewritten with Fe3+.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 INTEGRATED SINGLE-PHOTON SENSING AND PROCESSING PLATFORM IN STANDARD CMOS(2013) Nouri, Babak; Abshire, Pamela A; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Practical implementation of large SPAD-based sensor arrays in the standard CMOS process has been fraught with challenges due to the many performance trade-offs existing at both the device and the system level [1]. At the device level the performance challenge stems from the suboptimal optical characteristics associated with the standard CMOS fabrication process. The challenge at the system level is the development of monolithic readout architecture capable of supporting the large volume of dynamic traffic, associated with multiple single-photon pixels, without limiting the dynamic range and throughput of the sensor. Due to trade-offs in both functionality and performance, no general solution currently exists for an integrated single-photon sensor in standard CMOS single photon sensing and multi-photon resolution. The research described herein is directed towards the development of a versatile high performance integrated SPAD sensor in the standard CMOS process. Towards this purpose a SPAD device with elongated junction geometry and a perimeter field gate that features a large detection area and a highly reduced dark noise has been presented and characterized. Additionally, a novel front-end system for optimizing the dynamic range and after-pulsing noise of the pixel has been developed. The pixel is also equipped with an output interface with an adjustable pulse width response. In order to further enhance the effective dynamic range of the pixel a theoretical model for accurate dead time related loss compensation has been developed and verified. This thesis also introduces a new paradigm for electrical generation and encoding of the SPAD array response that supports fully digital operation at the pixel level while enabling dynamic discrete time amplitude encoding of the array response. Thus offering a first ever system solution to simultaneously exploit both the dynamic nature and the digital profile of the SPAD response. The array interface, comprising of multiple digital inputs capacitively coupled onto a shared quasi-floating sense node, in conjunction with the integrated digital decoding and readout electronics represents the first ever solid state single-photon sensor capable of both photon counting and photon number resolution. The viability of the readout architecture is demonstrated through simulations and preliminary proof of concept measurements.Item Design, Fabrication and Testing of Micronozzles for Gas Sensing Applications(2006-04-03) Li, Sheng; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Real-time identification and quantitative analysis of volatile and semi-volatile chemical vapors are critical for environmental monitoring. Currently available portable instruments lack the sensitivity for routine air quality monitoring, so preconcentrators are employed as front-ends for miniaturized chemical sensors. However, commonly used techniques for sensitivity enhancement have a time constant associated with adsorption/desorption or permeation of gas molecules being concentrated. Little work has been reported on fast-response concentrating techniques for gas sensing applications. This research is devoted to the development of a fast-response microfluidic gas concentrating device with appropriate flow dynamic shapes and pressure gradients based on the separation nozzle method. It is capable of concentrating heavy gas molecules diluted in light ones when they are flowing at high speeds, thus maintaining the measurement system response time. This is promising for developing real-time preconcentrators to improve the sensitivity of miniature chemical sensors. In the initial phase of this work, linear test structures were used to characterize viscous effects in microfluidic devices. Unit processes were developed to fabricate encapsulated micronozzles with through-hole inlets and outlets. The mass flow efficiency of the test structures was measured to be in the range of 0.36-0.81, increasing with rising Reynolds number as a result of the decreasing influence of boundary layers. Single-stage gas concentration devices were designed and fabricated on the basis of the test structures. A gas separation experimental setup and a mass spectrometric analysis apparatus were developed to evaluate the performance of the devices. Analytical and finite element analyses were conducted to better understand and verify the experimental results. As a proof-of-concept, gas separation experiments with two different inert gas mixtures were carried out in conjunction with mass spectrometric analysis. More than two-fold enrichment of SF6 molecules with a response time on the order of 0.01 ms was demonstrated through the device. The effects of design parameters and operating conditions on the separation factor were determined experimentally and compared to the numerical simulation results. This study forms the basis for developing a cascade of the single-stage elements envisioned as a preconcentrator for miniature chemical sensors to realize real-time environmental monitoring.