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Browsing by Subject "biosensors"

Now showing 1 - 2 of 2
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    Development of giant magnetoresistive biosensors and systems for early disease detection
    (2018-02) Klein, Todd
    Giant magnetoresistance (GMR) biosensors have been used with great success for the detection of a variety of biomarkers. Linear GMR biosensors were first proposed in 1998 and have been used since then. The major scientific contribution of this dissertation is to go beyond the previously published models for the linear GMR biosensor and provide analysis of practical design decisions that occur during sensor fabrication. I highlight the central role played by GMR free layer stray field near the sensor edge and present a numerical calculation to guide future linear GMR biosensor design. In addition, I explain how I proposed and demonstrated a novel, non-linear, domain-wall based GMR biosensor, in an effort to detect single molecules. I also describe my contributions to an effort to understand and build upon a previous experimental result using a large area sensor with multidomain switching. The major technological contribution described in this dissertation is the development of a GMR biosensing system that can potentially contribute to the early detection of ovarian cancer and serve as a platform for detecting a wide variety of other biomarkers. System integration included spintronic and nanomagnetic materials engineering, design of a coil with a ferrite core, electrical engineering, analog and digital signal processing, firmware programming, user interface programming on both a PC and an Android smartphone, communications over both USB and Bluetooth, and mechanical design. Hand-held and bench-top systems of this GMR bionsensor were both developed. Both versions use the same sensors, electrical hardware, firmware, and software, but differ mechanically and in the number of sensors available per assay. The bench-top version was completed first and used to demonstrate high sensitivity multiplex detection of ovarian cancer biomarkers CA-125, HE-4, and IL-6, with limits of detection below 10 pg/mL. The hand-held version was then completed and used with a preliminary biotin-streptavidin demonstration. Further development of the hand-held system involves integrating microfluidics.
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    Leveraging Linear Polymer Affinity Agents and Surface-enhanced Raman Scattering for the Detection of Food Contaminants
    (2022-04) Rodriguez, Rebeca
    This thesis focuses on leveraging linear polymer affinity agents and surface- enhanced Raman scattering (SERS) for the detection of food contaminants. First, I discuss the different sensing techniques and methodology that exist for food contamination detection: UV-visible spectroscopy, immuno- and lateral flow assays, liquid and gas chromatography, field-effect transistors, and SERS. I address the need for relatively facile and inexpensive multiplex detection and how linear polymer affinity agents can address these needs. The first experimental work focuses on optimization of SERS substrates for biosensing applications and initial work with anchored polymer chain lengths for the detection of the food allergen and protein soybean agglutinin with a glycopolymer. I then focus on optimization of linear polymer affinity agents for the detection of mycotoxins, which are small molecule food toxins that are naturally produced by fungi. I determined that attachment order, attachment chemistry, and polymer chain length all play a role in small molecule sensing. These optimization studies led me to be able to do multiplex detection of two small molecule toxins with linear polymer affinity agents and formulate conclusions on how polymers and small molecules bind through hydrogen bonding. I did this by combining SERS experimental studies and computational modeling of these small molecules to label what vibrational modes are being observed in the multiplexed spectra. In an effort to use linear polymer affinity agents for another class of food contaminants, bacteria, we work to optimize and use a linear glycopolymer for the detection of Listeria monocytogenes. Although the previous work with small molecules concluded that small to mid-length polymers performed best for capture and detection, this work has shown that longer polymer chain lengths work best to promote binding between polymer and Listeria. This gives insight on how to move forward with linear polymer affinity-enabled detection of different classes of food contaminants and pathogens. Overall, this work demonstrates optimization of SERS sensing to achieve limits of detection comparable to current detection methods with a simpler and more flexible signal transduction mechanism, providing an opportunity for future applications to multiplex at low-cost.