UMD Theses and Dissertations
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Item NOVEL GRAPHENE HETEROSTRUCTURES FOR SENSITIVE ENVIRONMENTAL AND BIOLOGICAL SENSING(2024) Pedowitz, Michael Donald; Daniels, Kevin; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The COVID-19 pandemic has underscored the need for rapid, mobile, and adaptable sensing platforms to respond swiftly to pandemic-level emergencies. Additionally, smog and volatile organic compounds (VOCs), which posed significant health risks during last year’s wildfires, highlight the critical need for environmental air quality monitoring. Graphene, with its high sensitivity and fast response times, shows promise as a powerful sensing platform. However, it faces challenges related to low selectivity and the complexities of device fabrication using conventional chemical vapor-deposited graphene grown on metal foil, which requires exfoliation and transfer to suitable substrates.This dissertation explores the use of epitaxial graphene, which is graphene grown from the sublimation of silicon from silicon carbide, and forming heterostructures with legacy functional materials, such as transition metal oxides and selective capture probes like antibodies and aptamers to develop rapid, ultrasensitive, and selective sensors to address critical environmental and public health challenges. Epitaxial graphene provides a single-crystal, lithography-compatible graphene substrate that retains the desirable electronic properties of graphene without the drawbacks associated with transferred materials. This work focuses on creating heterostructures using traditional functional materials, such as manganese dioxide and antibodies, to develop high-quality, selective sensors for both biological and environmental applications. The practical applications of these sensors are demonstrated and validated using techniques such as Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and electrical characterization. Additionally, detailed material analysis on producing these heterostructures is provided, emphasizing their ability to be modified without damaging the underlying graphene surface. This highlights epitaxial graphene's robust and versatile nature and its potential for creating high-quality devices with relatively simple designs. Finally, these biosensors are applied to alternate antibody-antigen systems, including influenza, to enhance disease-tracking capabilities. We also explore advanced functional materials, such as protease-peptide systems, which enable the creation of on-chip chemistry systems previously unattainable with current material systems.Item INTEGRATED THRESHOLD-ACTIVATED FEEDBACK MICROSYSTEM FOR REAL-TIME CHARACTERIZATION, SENSING AND TREATMENT OF BACTERIAL BIOFILMS(2016) Subramanian, Sowmya; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biofilms are the primary cause of clinical bacterial infections and are impervious to typical amounts of antibiotics, necessitating very high doses for treatment. Therefore, it is highly desirable to develop new alternate methods of treatment that can complement or replace existing approaches using significantly lower doses of antibiotics. Current standards for studying biofilms are based on end-point studies that are invasive and destroy the biofilm during characterization. This dissertation presents the development of a novel real-time sensing and treatment technology to aid in the non-invasive characterization, monitoring and treatment of bacterial biofilms. The technology is demonstrated through the use of a high-throughput bifurcation based microfluidic reactor that enables simulation of flow conditions similar to indwelling medical devices. The integrated microsystem developed in this work incorporates the advantages of previous in vitro platforms while attempting to overcome some of their limitations. Biofilm formation is extremely sensitive to various growth parameters that cause large variability in biofilms between repeated experiments. In this work we investigate the use of microfluidic bifurcations for the reduction in biofilm growth variance. The microfluidic flow cell designed here spatially sections a single biofilm into multiple channels using microfluidic flow bifurcation. Biofilms grown in the bifurcated device were evaluated and verified for reduced biofilm growth variance using standard techniques like confocal microscopy. This uniformity in biofilm growth allows for reliable comparison and evaluation of new treatments with integrated controls on a single device. Biofilm partitioning was demonstrated using the bifurcation device by exposing three of the four channels to various treatments. We studied a novel bacterial biofilm treatment independent of traditional antibiotics using only small molecule inhibitors of bacterial quorum sensing (analogs) in combination with low electric fields. Studies using the bifurcation-based microfluidic flow cell integrated with real-time transduction methods and macro-scale end-point testing of the combination treatment showed a significant decrease in biomass compared to the untreated controls and well-known treatments such as antibiotics. To understand the possible mechanism of action of electric field-based treatments, fundamental treatment efficacy studies focusing on the effect of the energy of the applied electrical signal were performed. It was shown that the total energy and not the type of the applied electrical signal affects the effectiveness of the treatment. The linear dependence of the treatment efficacy on the applied electrical energy was also demonstrated. The integrated bifurcation-based microfluidic platform is the first microsystem that enables biofilm growth with reduced variance, as well as continuous real-time threshold-activated feedback monitoring and treatment using low electric fields. The sensors detect biofilm growth by monitoring the change in impedance across the interdigitated electrodes. Using the measured impedance change and user inputs provided through a convenient and simple graphical interface, a custom-built MATLAB control module intelligently switches the system into and out of treatment mode. Using this self-governing microsystem, in situ biofilm treatment based on the principles of the bioelectric effect was demonstrated by exposing two of the channels of the integrated bifurcation device to low doses of antibiotics.Item Design and Implementation of Microfluidic Systems for Bacterial Biofilm Monitoring and Manipulation(2014) Meyer, Mariana; Ghodssi, Reza; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bacterial biofilms - pathogenic matrices formed through bacterial communication and subsequent extracellular matrix secretion - characterize the majority of clinical bacterial infections. Biofilms exhibit increased resistance to conventional antibiotics, necessitating development of alternative treatments. Standard microbiological methods for studying biofilms often rely on in vitro systems with involved instrumentation for biofilm quantification, or destroy the biofilm in the process of characterization. Additionally, biofilm formation is sensitive to many growth parameters, and can exhibit a large degree of variability between repeated experiments. This dissertation presents the development of systems designed to address these challenges through integration of continuous biofilm monitoring in a microfluidic platform, and through creation of a microfluidic platform for multiple assays performed on one biofilm formed in a single channel. The microsystems developed in this work provide building blocks for developing controlled, high throughput testbeds for development and evaluation of drugs targeting bacterial biofilms. The first platform developed relied on optical density monitoring as a means for evaluating biofilm formation. This method was noninvasive, as it used an external light source and array of photodiodes to evaluate biofilms by the amount of light transmitted through the microfluidic channel where they were grown. The optical density biofilm measurement method and microfluidic platform were used to evaluate the dependence of biofilm formation on quorum sensing, an autoinducer-mediated intercellular communication process. This system was also used in the first demonstration of biofilm inhibition and reduction by two different autoinducer-2 analogs. The second microfluidic system developed addressed the challenge of variability in biofilm formation. Biofilms formed in a single microfluidic channel were partitioned by hydraulically actuated valves into three separate segments, which were then treated as representatives of the original biofilm in further experiments. A novel photoresist passivation process was developed in order to create the multi-depth channels needed to accommodate both valve actuation and biofilm formation. Biofilms grown in the device were uniform throughout, providing reliable experimental controls within the system. Biofilm partitioning was demonstrated by exposing three segments of one biofilm to varying detergent concentrations.Item INKJET PRINTED PAPER SURFACE ENHANCED RAMAN SPECTROSCOPY DEVICES FOR TRACE CHEMICAL ANALYSIS(2013) Yu, Wei Wen; White, Ian M; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The needs of an ever growing human population are fueling demands for better and cheaper sensors for the early detection of harmful chemicals, pathogens and diseases markers from a variety of sources such as food, water, bodily fluids and contaminated surfaces. To address this, recent innovations utilize Microelectromechanical Systems (MEMS) technology to integrate multiple laboratory functions onto millimeter-sized chips to form Micro Total Analysis Systems (µTAS) or Lab-on-chip (LOC) devices. While sophisticated and powerful, the use of these devices for chemical and biological sensing is limited by complicated fabrication processes, high cost and robustness of the sensors. In this work we have developed a simple and inexpensive but exceptionally sensitive portable chemical and biological sensing platform through the innovative use of paper combined with Surface Enhanced Raman spectroscopy (SERS). Paper is functionalized with plasmonic nanostructures to transform it into a SERS substrate, while the natural properties of paper are leveraged for sample collection, cleanup, and analyte concentration in user-friendly formats such as wipes, dipsticks, and filters. The use of simple deposition methods such as inkjet printing for sensor fabrication combined with paper as the construction material means that sensors can be made at a very low cost. Additionally, the ability to be printed on demand eliminates issues with sensor shelf-life, while the absence of mechanical components makes these paper sensors much more robust than conventional sensors. In this work, practical applications of paper SERS sensors for the detection of food contaminants, narcotics, pesticides and other chemicals at trace levels are presented. Paper SERS sensors, by virtue of their low cost, simplicity of fabrication, high sensitivity and ease of use, promises to make chemical and biological sensing more accessible to the common user.