Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
5 results
Search Results
Item SEROTONIN SENSOR-INTEGRATED IN VITRO SYSTEMS AS RESEARCH TOOLS TO ADDRESS THE GUT BRAIN AXIS(2022) Chapin, Ashley Augustiny; Ghodssi, Reza; Bentley, William E; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The gut-brain-axis (GBA) is a bi-directional communication system between the gastrointestinal (GI) enteric nervous system and the central nervous system, capable of complex crosstalk between the gut and the brain to maintain GI homeostasis and influence mood and higher cognitive functions. Under healthy conditions, this communication is beneficial for regulating immune function, proper peristaltic motion, and hormone release related to hunger and feeding behaviors. However, GBA communication can cause co-morbid occurrence of both GI and neural disorders. For instance, chronic inflammatory conditions of the gut, such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), often present with symptoms of depression and anxiety. Clinical studies, animal models, and molecular research techniques have implicated serotonin (5-HT) as a key signaling molecule to both regulate GI functions and stimulate enteric nerves. These studies are limited by the inability to study sub-mucosal 5-HT on the basolateral side of the epithelium, wheremost of the 5-HT is released and acts on nerves endings. The ability to measure 5-HT release patterns in this area, at native spatial and temporal scales, within an in vitro culture of the gut epithelium, would allow researchers to distinguish 5-HT release patterns stimulated by different GI luminal conditions associated with health and disease, to better understand how these stimuli affect the brain. In this dissertation, electrochemical sensors are fabricated within two types of in vitro platforms to measure 5-HT at physiological scales (sub-micromolar concentrations). The goal of this design is to facilitate the direct detection of 5-HT released from cells cultured in the platform to improve both spatial and temporal access to basolaterally-secreted molecules and provide continuous, automated measurements over experimental time scales. 5-HT sensors fabricated on both porous and smooth cell culture substrates are demonstrated, achieving sensitivities of ~1 – 10 μA/μM and limits of detection of ~100 nM. Electrochemical characterization allow understanding of 5-HT adsorption kinetics, which was modeled to track and predict sensor fouling over continuous measurements. These sensor-integrated substrates were packaged in 3D printed structures, which allowed rapid fabrication of custom designs and were shown to be biocompatible and support growth of RIN14B cells, a model 5-HT-secreting cell line. Finally, cell-secreted 5-HT was detected at ~100 – 500 nM, corresponding to ~4 pmol 5-HT / 105 cells. Ultimately, slow adsorption kinetics prevented direct detection of 5-HT from cells cultured directly on top of the sensors, but the thorough characterization of the platform demonstrated here lays significant groundwork for future optimization of the sensing protocol.Item Optical and Thermal Systems for Automation of Point-of-Care Assays(2018) Goertz, John; White, Ian M; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Modern medicine has detailed 70,000 different diagnoses; the 21st century challenge is bringing those diagnoses to over 7 billion people. This phenomenal feat requires precision biosensing strategies that minimize necessary training and manual effort while maximizing portability and affordability. Microfluidic strategies, both fabricated chips and paper-based devices, held the promise to facilitate point-of-care diagnostics but have been inadequate for many applications due to the trade-off between bulky pumps or limited control and complexity. This dissertation details novel strategies that control the progression of biochemical reactions with high functionality, portability, and ease-of-use. First, I will describe an amplified signaling reaction that leverages both positive and negative feedback loops to achieve optically-regulated control. This assay, termed “Peroxidyme-Amplified Radical Chain Reaction” enables naked-eye detection of catalytic reporter DNA structures at concentrations across five orders of magnitude down to 100 pM while eliminating the need for manual addition of hydrogen peroxide common to other such detection reactions. Next, I will describe the development of a platform for thermal regulation of generic reactions. To address the need for a broadly capable automation platform that provides equal utility in the lab and field alike, we recently developed “phase-change partitions”. In our system, purified waxes segregate reagents until incremental heating melts the partitions one by one, causing the now-liquid alkane to float and allowing the desired reagents to interact with the sample on demand. This tight control over reaction progression enabled us to construct hands-free detection systems for isothermal DNA amplification, heavy metal contamination, and antibiotic resistance profiling. My work has demonstrated a broadly capable suite of assay control systems with the potential to enable simple, inexpensive automation of a broad array of chemical and biological analysis across human medicine, environmental surveillance, and industrial chemical synthesis.Item MICROFLUIDIC ASSAY PERFORMANCE ENHANCEMENT USING POROUS VOLUMETRIC DETECTION ELEMENTS FOR IMPEDEMETRIC AND OPTICAL SENSING(2016) Wiederoder, Michael; DeVoe, Don L; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microfluidic technologies have great potential to help create automated, cost-effective, portable devices for rapid point of care (POC) diagnostics in diverse patient settings. Unfortunately commercialization is currently constrained by the materials, reagents, and instrumentation required and detection element performance. While most microfluidic studies utilize planar detection elements, this dissertation demonstrates the utility of porous volumetric detection elements to improve detection sensitivity and reduce assay times. Impedemetric immunoassays were performed utilizing silver enhanced gold nanoparticle immunoconjugates (AuIgGs) and porous polymer monolith or silica bead bed detection elements within a thermoplastic microchannel. For a direct assay with 10 µm spaced electrodes the detection limit was 0.13 fM AuIgG with a 3 log dynamic range. The same assay was performed with electrode spacing of 15, 40, and 100 µm with no significant difference between configurations. For a sandwich assay the detection limit was10 ng/mL with a 4 log dynamic range. While most impedemetric assays rely on expensive high resolution electrodes to enhance planar senor performance, this study demonstrates the employment of porous volumetric detection elements to achieve similar performance using lower resolution electrodes and shorter incubation times. Optical immunoassays were performed using porous volumetric capture elements perfused with refractive index matching solutions to limit light scattering and enhance signal. First, fluorescence signal enhancement was demonstrated with a porous polymer monolith within a silica capillary. Next, transmission enhancement of a direct assay was demonstrated by infusing aqueous sucrose solutions through silica bead beds with captured silver enhanced AuIgGs yielding a detection limit of 0.1 ng/mL and a 5 log dynamic range. Finally, ex situ functionalized porous silica monolith segments were integrated into thermoplastic channels for a reflectance based sandwich assay yielding a detection limit of 1 ng/mL and a 5 log dynamic range. The simple techniques for optical signal enhancement and ex situ element integration enable development of sensitive, multiplexed microfluidic sensors. Collectively the demonstrated experiments validate the use of porous volumetric detection elements to enhance impedemetric and optical microfluidic assays. The techniques rely on commercial reagents, materials compatible with manufacturing, and measurement instrumentation adaptable to POC diagnostics.Item Thermoplastic microfluidic technologies for portable and disposable bioanalytical and diagnostic platforms(2015) Rahmanian, Omid David; DeVoe, Don L; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Portable and cost-effective medical diagnostic technologies that require minimal external infrastructure for their operation are highly desirable for on-field military operations, defense against acts of bioterrorism, and infectious disease screening in resource-limited environments. Miniaturized Total Analysis Systems (µTAS) have the potential to fulfill this un-met need via low-cost, portable, and disposable point-of-care (POC) diagnostic devices. Inherent advantages of µTAS systems can be utilized to transform diagnostic technologies that currently require significant investment in centralized laboratories and highly trained personnel into automated, integrated, and miniaturized platforms. This dissertation addresses the development of microfabrication techniques and resulting component technologies that are realized in low-cost thermoplastic substrates. A thermoplastic microfabrication technique termed orogenic microfabrication, based on a non-reversible solvent-assisted swelling mechanism, is developed to provide unique capabilities for microscale and nanoscale patterning in rigid thermoplastics with minimal infrastructure. Orogenic microfabrication is compatible with multiple masking techniques including photolithography, chemical surface modification, contact and noncontact spotting, and inkjet deposition techniques, with each masking method offering unique influence on resulting orogenic structures that can be applied to microfluidic and µTAS systems. Direct ink masking is further explored as a low-cost rapid prototyping tool for fabrication of simple microfluidic devices where channel formation and bonding are combined into a single step, resulting in fully enclosed microfluidic channels within 30 minutes. Chemical surface passivation by UV-ozone treatment is utilized in combination with orogenic swelling and thermocompression bonding to develop single-use burst valves with tunable burst pressures. In addition to assisting in on-chip fluid manipulation, the normally closed burst valves enable on-chip reagent packaging and hermetic sealing of bioactive material in lyophilized format, and can be used for delivery of stored reagents for a range of disposable point-of-care assays. On-chip integrated micropumps are also developed, using simple fabrication process compatible with conventional thermoplastic fabrication techniques such as direct micromilling or injection molding. Direct displacement of liquid reagents using screw-assisted pumping can be operated either automatically or manually, with on-demand delivery of liquid reagents in a wide range of flow rates typically used in microfluidic applications. Collectively, the technologies developed in this dissertation may be applied to the future development of simple, disposable, and portable diagnostic devices that have the potential to be operated without off-chip instrumentation. On-chip storage of buffers and reagents in either dry or liquid format, and on-demand delivery of liquid reagents is packaged in a miniaturized, portable, and automated platform that can be operated in resource-constrained settings by practitioners with minimal expertise.Item CMOS IMAGE SENSORS FOR LAB-ON-A-CHIP MICROSYSTEM DESIGN(2011) Sander, David; Abshire, Pamela; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The work described herein serves as a foundation for the development of CMOS imaging in lab-on-a-chip microsystems. Lab-on-a-chip (LOC) systems attempt to emulate the functionality of a cell biology lab by incorporating multiple sensing modalidites into a single microscale system. LOC are applicable to drug development, implantable sensors, cell-based bio-chemical detectors and radiation detectors. The common theme across these systems is achieving performance under severe resource constraints including noise, bandwidth, power and size. The contributions of this work are in the areas of two core lab-on-a-chip imaging functions: object detection and optical measurements.