Theses and Dissertations from UMD
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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 give thesis/dissertation in DRUM
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Item Surface enhanced Raman spectroscopy technologies and techniques for on-site quantification of chemical and biological analytes(2017) Restaino, Stephen Mario; White, Ian M; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The rapid advancement in mobile devices has illustrated the widening technological gap in health and environmental sensing. Unfortunately, the time and financial burdens imposed by the current central lab model prohibit regular sensing of crucial biological and ecological elements, which can lead to delayed responses and exacerbated conditions. Current portable diagnostic solutions lack the necessary sensitivity or multiplexing potential to address the ever-expanding library of biomarkers. An emerging solution known as surface enhanced Raman spectroscopy (SERS) can provide the sensitivity of current techniques, but with drastically improved multiplexing density. Many existing SERS applications however, require multiple processing steps to introduce samples to the enhancement surface. Practical application of SERS to diagnostics and environmental samples requires more convenient materials and methods to support the broad array of conditions in on-site sensing. In this work, three new methods to apply SERS to portable sensing systems are developed. Specifically, a new SERS diagnostic is presented that details the first implementation of SERS for real-time PCR; we accomplished multiplexed detection of MRSA genes to specifically identify species and drug resistance. Second, we developed a new flexible SERS sponge based on PDMS that provides unprecedented control over sample handling and can readily concentration organic analytes. Finally, we present a novel raster scanning protocol to address the persistent reproducibility issues that has slowed commercialization of new SERS devices. Together, these three techniques advance the development SERS as a practical and portable solution for on-site diagnostics and environmental sensing.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 An Optofluidic Surface Enhanced Raman Spectroscopy Microsystem for Sensitive Detection of Chemical and Biological molecules(2013) Hossein Yazdi, Soroush; White, Ian M; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As the human population grows, there is an increasing demand for early detection of a variety of analytes in different fields. This demand mainly includes early and sensitive detection of pathogens, disease biomarkers, pesticides, food contaminants, and explosives. To address this, lab-on-a-chip (LOC) technology has emerged as a tool to improve portability, automation and sensitivity of sensors by taking advantage of integrated laboratory functions on a miniaturized chip. It is agreed that LOC has the potential to make various sensing modules practical for real- world applications. In this work, we have developed a highly sensitive, portable, and automated optofluidic surface enhanced Raman spectroscopy (SERS) microsystem for chemical and biological detection. SERS is a powerful molecular identification technique that combines laser spectroscopy with optical properties of metal nanoparticles. Optofluidic SERS is defined as the synergistic use of microfluidic functions to improve the performance of SERS. By leveraging microfluidic functions, the optofluidic SERS microsystem mixes and concentrates the sample and nanoparticles resulting in an improved performance as compared to conventional open microfluidic SERS systems. The device requires low sample volume and has multiplexed detection capabilities. Moreover, it is suitable for on-site detection of analytes in the field because of its improved automation and portability due to the integrated fiber optics. The final device consists of two regions of packed silica beads inside microchannels for biomolecular interaction as well as sample concentration for SERS measurements. Additionally, an on-chip micromixer and fiber optics are integrated into the device. Optical fibers aligned to the detection zone make the biosensor alignment-free, which greatly improves automation. Practical applications for the detection of real-world analytes (e.g., pesticides, fungicides, food contaminants, and DNA sequences) are demonstrated utilizing our optofluidic SERS microsystem. Detection of biological samples could be extended to proteins and proteolytic enzymes through displacement assays. Consequently, the integration of microfluidic functions, including a microporous reaction zone, a nanoparticle concentration zone, and a micromixer, combined with the use of integrated fiber optics and portable spectrometers, make our microsystem suitable for on-site detection of analytes at trace levels.Item Bio-templated Substrates for Biosensor Applications(2013) Fu, Angela Li-Hui; Kofinas, Peter; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanopatterning of materials is of particular interest for applications in biosensors, microfluidics, and drug delivery devices. In biosensor applications there is a need for rapid, low cost, and durable system for detection. This dissertation aims to investigate methods to pattern nanostructured surfaces using virus particles as templates. The virus species used in these experiments is a cysteine modified tobacco mosaic virus. The first project utilized the lamellar microphase separation of a block copolymer to pattern the virus particles. Although microphase separation of the poly(styrene-b-2-vinylpyridine) (PS-P2VP) into lamellae was confirmed, specificity of the viruses to the gold doped block of the polymer could not be achieved. Single virus particles lay across multiple lamellae and aggregated in side-to-side and head-to-tail arrangements. The second project studied the effect of a surfactant on virus assembly onto a gold chip. The experiments included placing a gold chip in virus solutions with varying triton concentrations (0-0.15%), then plating the virus particles with a metal. Results showed that as the triton concentration in the virus solution increases, the virus density on the surface decreases. The gold coated virus particles were applied to Surface Enhanced Raman Spectroscopy (SERS) detection in the final project. SERS is of interest for biosensor applications due to its rapid detection, low cost, portability, and label-free characteristics. In recent years, it has shown signal enhancement using gold, silver, and copper nanoparticles in solutions and on roughened surfaces. The gold plated virus surfaces were tested as SERS substrates using R6G dye as the analyte. An enhancement factor (EF) of 10^4 was seen in these samples versus the non-SERS substrate. This corresponded to the sample with 0.05% triton in the virus solution which showed the most intersection points between the virus particles and the most uniform coverage of the viruses on the surface. This value is lower than that of previous studies; however, future work may be performed to optimize conditions to achieve the highest signal possible.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.