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Browsing by Author "Sambur, Justin B., committee member"

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    Coupling electrochemistry and microfluidics for biosensor development
    (Colorado State University. Libraries, 2016) Feeny, Rachel M., author; Henry, Charles S., advisor; Van Orden, Alan, committee member; Sambur, Justin B., committee member; Kipper, Matthew J., committee member
    Biosensors are valuable analytical tools across both scientific and medical fields. Improving and miniaturizing biosensors is an area of great interest in academic, medical, and diagnostic settings. There is a constant need to improve these systems by increasing accessibility through lower costs, greater portability, and enhanced ease-of-use. Interfacing microfluidics and electrochemical methods shows great potential to address these needs. The work described in this thesis aims to address gaps in biosensor development, including increasing accessibility and improving sensing capabilities such as sensitivity, selectivity, and resolution, by combining electrochemistry and microfluidics to develop new tools for use in a range of biosensor systems. The primary focus of this research was to couple electrochemical detection methods with microfluidic devices for bioanalytical applications. Two main topics are reported. The first is a fluid transport mechanism employing the gas permeability of poly(dimethylsiloxane) (PDMS). Degassed PDMS pumps provide a simple, portable, inexpensive method to generate controlled fluid flow in a microfluidic device to transport a sample to electrodes for electrochemical detection. The second topic reported does not aim to address cost or portability of the system, but rather focuses on improving the capabilities of electrode arrays as chemical imaging platforms. In this work, a platinum microelectrode system was developed for biomarker detection, primarily nitric oxide and norepinephrine. Microfluidic devices interfaced directly with the electrodes provided precise control of fluid delivery to the sensors enabling both localized control of chemical concentrations as well as selective chemical stimulation of living tissue. The microelectrodes, when arranged in a high-density array, provided a platform capable of achieving electrochemical biomarker detection and imaging from live tissue slices with high spatiotemporal resolution. Both technologies described required the effective interfacing of microfluidic devices with electrochemical sensors to generate biomarker detection platforms. Custom microfluidic systems were developed to directly integrate biological samples into the platforms, including dried serum spots on a filter paper matrix and live ex vivo murine adrenal slices embedded in agarose. To achieve reproducible biomarker detection in complex biological matrices, electrochemical cleaning methods were developed and utilized for electrode maintenance. All of the tools described in this thesis were designed to address specific applications, but were also intended to be translatable to other systems. The degassed PDMS pump could be used as a fluid transport mechanism for other microfluidic devices, improving the simplicity and portability of systems that could otherwise be limited by external pumping equipment. Similarly, the strategies described for interfacing microfluidic devices with the reported electrode arrays and platinum microelectrodes could be applied to other silicon microchips to accomplish precise control of fluid delivery to the electrodes. The technology developed to generate an electrochemical imaging platform could be further pursued to achieve a high level of chemical selectivity by employing alternative waveforms, such as fast scan cyclic voltammetry, or electrode modifications to better elucidate the role of chemical gradients in biological systems. All of these tools, when applied to other bioanalytical platforms, could continue to advance the field of biomarker detection using microfluidic systems.
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    Investigations of low-temperature reaction pathways in solid-state reactions
    (Colorado State University. Libraries, 2024) Tran, Gia Thinh, author; Neilson, James R., advisor; Prieto, Amy L., committee member; Sambur, Justin B., committee member; Chen, Hua, committee member
    Advances in our technology are limited by our knowledge of functional materials, and access to new, possibly better, functional materials is limited by our synthesis methods. This dissertation discusses different synthesis methods for a variety of solid state materials. At the core of this thesis are metathesis reactions i.e. double displacement reactions. Metathesis reactions allow for control over product selectivity and reaction kinetics with choice of the spectating ions. We demonstrate these characteristics with different spectating ions in metathesis and cometathesis (e.g., combining 2 halides) reactions. LaMnO3 was chosen to probe the product selectivity of anion cometathesis towards specific off-stoichiometries of LaMnO3. The metathesis reaction for BiFeO3 illustrates that prediction of thermodynamic selectivity is important, but reaction kinetics remain important as well. Kinetic studies of metathesis reactions that form YMnO3 demonstrate the importance of crystalline intermediates to modulate the reaction rates. The complexity of solid-state kinetics their kinetic regimes within a reaction can be identified through synchrotron X-ray diffraction. We attempted to synthesize LiMoO2 as precursors for the proposed phase LaMoO3. We demonstrate our considerations on the synthesis challenges and offer gained insights into alternative Mo-based systems (nitrides). Aside from metathesis reactions, we employ learned concepts to flux reactions to influence the chemical potential of N2. Synthesis of Li-Fe-O-N and Li-Mn-O-N phases was attempted under the hypothesis that alkali halide salt mixtures solubilize nitrogen and pin nitrogen's chemical potential to prevent N2 formation. Cs2SbCl6 was chosen as a single crystal target to gain clearer insights into the electronic structure. Single crystals were synthesized via hydrothermal synthesis, but preliminary conductivity measurements suggest that Cs2SbCl6 has a photoconductance below our limit detection.
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    ItemOpen Access
    The development of portable electrochemical sensors for environmental and clinical analysis
    (Colorado State University. Libraries, 2020) Kava, Alyssa A., author; Henry, Charles S., advisor; Shores, Matthew P., committee member; Sambur, Justin B., committee member; Dandy, David S., committee member
    The ability to perform chemical and biochemical analysis at the point-of-need (PON) has become increasingly sought. PON sensing is critical in both environmental and clinical monitoring applications to reduce cost and time of analysis and achieve early detection of potentially harmful pollution and health indicators. Electroanalysis is very well suited to PON sensing applications with miniaturized instrumentation available, fast analysis times, high sensitivity, low detection limits and the ability to be interfaced with both conventional and paper-based microfluidics (μPADs). The primary focus of this thesis is to improve electrochemical sensors for PON applications by: 1) reducing the number of liquid handling steps required by the end user, 2) further development of better performing disposable electrode materials and 3) the proper integration of electrodes with disposable microfluidic paper-based devices. The first half of this thesis, Chapter 2 through Chapter 4, focuses on the development of a new functionality in μPADs coupled with high quality boron doped diamond paste electrodes (BDDPESs). The electrochemical PAD (ePAD) is referred to as the Janus-ePAD after the two- faced Greek god. The Janus-ePAD developed in Chapter 2 takes advantage of the ability to store reagents within porous paper matrices. In the Janus-ePAD, reagents were stored in two separate channels connected by a sample inlet to adjust the sample pH and perform multiplexed electrochemical detection at two analytes' optimal pH conditions. Therefore, the device is able to carry out several liquid handling and operator steps in situ, further simplifying electrochemical PON sensing. In Chapter 3, fundamental electrochemical characteristics of the BDDPEs are then studied in order to improve their electroanalytical utility, providing a guide to the use of this new composite electrode material. Then, in Chapter 4, a second generation Janus-ePAD is developed to overcome several problems typically encountered in ePADs, namely, slow flow rates and analysis times and lowered electrochemical detection sensitivities due to the paper-electrode interface. Both of these problems are addressed by developing a multi-layer Janus-ePAD that consists of a wax-patterned paper layer taped to a transparency film layer, generating microfluidic channel in the gap between the two layers. Passive fluid transport is still achieved within the channel gap via capillary action but at much faster flow rates decreasing analysis time by over 20 times compared to a one-layer Janus- ePAD. The paper-electrode interface is removed by placing screen-printed carbon electrodes (SPCEs) on the transparency film layer, providing increased reproducibility and bulk solution sensitivity. The second main focus of this thesis is the development of better performing electrode materials that retain the simplicity and disposability required for on-site electroanalysis. In Chapter 5, this goal is accomplished by the development of a novel SPCE composition using glassy carbon (GC) microparticles as the active electrode component and a conductive commercial ink as the binder component of this composite electrode material. The GC-SPE is then applied to the detection of the toxic heavy metals Cd and Pb using anodic stripping voltammetry (ASV). The use of GC microparticles as opposed to the widely used graphite powders in the bulk SPCE formulation allows for the GC-SPE to sensitively and quantitatively detect Cd and Pb at environmentally relevant levels without the need for any post-fabrication modification which is typically required for graphite based SPCEs. Following the development of the GC-SPE in Chapter 5, in Chapter 6, a systematic study was carried out to understand the relationship between SPCE composition, or carbon particle type, and electrochemical performance with the goal of improving the electrochemical performance of these single-use, mass producible, inexpensive and disposable electrode materials in their native, or unmodified state. Significantly, it was found that SPCE composition can be optimized and tuned to provide electrochemical sensing performance on par with other types of carbon composites historically believed to outperform SPCEs. The work contained within this thesis achieves the goal of developing better performing PON electrochemical sensing motifs while retaining maximum simplicity of fabrication and operation of ePADs and SPCEs. Through automation of liquid handling steps using a paper-based device, further simplification of sensitive multiplexed electrochemical detection was achieved. The fundamental understanding of the electrochemical performance of SPCEs allowed for further applications without extensive post-fabrication modifications which have historically hindered their translation from academic to real-world settings. The work presented herein can be used to guide further development of electrochemical PON sensors for a variety of environmental and clinical applications.