Doctor of Philosophy, The Ohio State University, 2005, Chemistry

Nitroazobenzene (NAB) diazonium salts were reduced with cyclic voltammetry scans to derivatize pyrolyzed photoresist (PPF) surfaces. This process resulted in covalently bonded NAB on the PPF surface, as shown by XPS and Raman spectroscopy. Junction top contacts were fabricated by using various deposition conditions and metal layers including titanium, copper, aluminum, silver and gold. Junction low voltage resistance, current density and properties of aging molecular junctions will be discussed, along with their role in electron injection for NAB. The PPF/NAB/Ti/Au junctions are examples of monolayer molecular electronic devices with covalent bonding between the contacts and the molecular layer. Electron transfer through the molecular layer was found to be a strong function of molecular structure as well as molecular thickness. The pressure in the electron beam chamber during metal deposition was found to have a large effect on junction resistance in titanium junctions, and to a lesser extent with copper junctions. Both high and low oxide junctions are discussed with titanium being the most commonly used metal. Electronic and Raman characterization of different metal top contact molecular junctions was performed. Raman intensity ratios were used to characterize reduction of the NAB molecular layer with different metal top contacts. XPS characterization was used to show the surface bonding between the molecule and metal contact, as well as oxide characterization in the junction metal contact. Depth profiling using Argon ion sputtering was used to determine depth-resolved composition inside fabricated molecular junctions. Five different metals were used with PPF/NAB(3.7nm). Aluminum junctions were shown to have low conductivity, and high resistance compared to other metals. Titanium junctions deposited at high oxide conditions exhibited semiconductor properties with asymmetric i/V curves that included hysteresis and rectification. At lower deposition pressures, Ti, Cu (open full item for complete abstract)

Committee: Richard McCreery (Advisor) Subjects:

Doctor of Philosophy, Case Western Reserve University, 2011, Chemical Engineering

Kinetic parameters that describe the operating efficiency and rate of a reaction are revealed in situ by applying normal pulse voltammetry to normally operating proton exchange membrane fuel cells. The Tafel slope for the oxygen reduction reaction is directly extracted from the steady state chronoamperometric response. Conditioning potential, temperature, and relative humidity are varied independently to observe their effect on the Tafel slope. Aqueous ex situ techniques commonly used to collect kinetic data only mimic the conditions within fuel cell and are unable to capture true operating processes, especially the effects of relative humidity. The observed Tafel slopes are 47-62 mV/decade for oxide covered platinum indicating a smaller activation overpotential than that for oxide free platinum with Tafel slopes of 91-119 mV/decade in initial studies. High temperature operation at 120°C showed no kinetic or mechanistic benefit compared to fuel cell operation at 80°C. If high efficiency is desired, the fuel cell should be operated in a potential range where oxide is present on the platinum surface. A novel technique is presented using pulse voltammetry measure platinum oxide coverage in situ on PEMFC electrodes. A linear logarithmic rate was noticed for oxide conditioning times longer than 1 second. Extended testing of relative humidity effects at 80 °C, combined with electrochemical active surface area measurements to normalize the oxide growth, showed a growth rate of 28 μC cm-2 (log s)-1 and also provided the ability to monitor platinum dissolution from the electrode. Concepts from both these projects are assimilated to develop novel pulse voltammetry waveforms that are applied in situ on normally operating proton exchange membrane fuel cells to reveal Tafel kinetics with control of adsorbed oxide on platinum. The results show that the Tafel slope decreases with increasing platinum oxide coverage on the electrode. The oxidation of higher order polyols such as gl (open full item for complete abstract)

Committee: Thomas Zawodzinski Jr. (Advisor); Jay Mann Jr. (Committee Chair); Mohan Sankaran (Committee Member); David Schiraldi (Committee Member) Subjects: Alternative Energy; Analytical Chemistry; Chemical Engineering; Energy; Engineering; Mechanical Engineering

Doctor of Philosophy, Miami University, 2024, Chemistry and Biochemistry

Carbon is a highly versatile material which can form different bonding structures each with very specific properties. High sp3 hybridized carbon like diamond and diamond-like carbon (DLC) are characterized by high hardness, chemical inertness, and thermal stability. These properties are utilized in many industries as protective coatings, abrasives, and insulators. Although diamond and DLCs are semiconductors with limited electrical conductivity, dopants incorporated into their structures facilitate electron transfer. Combining the acquired electrical conductivity with the inherent material properties expands upon the viable applications. Although they share similar properties due to their bonding structures, diamond and DLCs differ in various ways, including their manufacturing process, surface morphology, and electrical properties. Recently, boron doped diamond (BDD) and tetrahedral amorphous carbon (ta-C) have gained popularity as electrochemical sensors, each with advantages and disadvantages. They exhibit excellent electrochemical properties with wider potential windows and low background currents. Although recent advances in diamond growth have reduced temperature and pressure conditions, substrates still reach temperatures over 750°C. BDD is characterized by a rough polycrystalline structure, adding to the intricacies of electrochemical detection. Meanwhile, ta-C thin films are coated onto substrates in a vacuum system with substrate temperatures remaining below 100°C. Doped ta-C is characterized by a very smooth surface with low friction, but the electrochemical properties are not as well studies. In this project, we explore the electrochemical properties of BDD and doped ta-C. A nanoparticle modification was used to increase the sensitivity of BDD to hydrogen peroxide (H2O2), an important biomolecule in the inflammation process and in cellular signaling. H2O2 is also implicated as a molecule which participates in oxidative stress, possibly leading to n (open full item for complete abstract)

Committee: Cory Rusinek (Advisor); Niel Danielson (Committee Chair); Rock Mancini (Committee Member); Eric Sikma (Committee Member); Catherine Almquist (Committee Member) Subjects: Chemistry; Materials Science

PhD, University of Cincinnati, 2024, Arts and Sciences: Chemistry

Real-time monitoring of neurotransmitters is of great importance because of the roles these neurochemicals play in vital bodily functions. Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes (CFMEs) has advanced our understanding of neurotransmitter dynamics as a prominent electroanalytical technique. Innate biocompatibility, functionalization, etc. make carbon an attractive electrode substrate; unfortunately, decades of research have rarely branched away from dopamine due to poor CFME morphology tunability and reliance on adsorption interactions. Here, we developed tunable carbon-based microelectrode surfaces through geometry manipulation and surface chemical doping for enhanced neurochemical interfacial interactions. Chapter 1 provides a critical perspective on the future of carbon-based neurochemical detection with a summary of novel FSCV electrode materials used to date; we identified three challenges FSCV detection faces and routes to address these challenges through novel carbon electrodes. Challenge one involves unobserved events caused by diminished temporal resolution. Chapters 2-5 addressed this issue by introducing porous structures to CFMEs or surface roughness to graphene oxide microelectrodes (GFMEs) for improved electrochemical reversibility. Chapter 2 uses nanoporous carbon nanofibers electrodeposited onto CFME frameworks. These microelectrodes improve dopamine sensitivity and electron transfer kinetics, but low pore dimensions fail to trap dopamine generating negligible changes in temporal resolution. Chapter 3 uses biomass syntheses of macroporous carbon demonstrating the first instance of the use of biomass-derived porous carbons for implantable electrode applications. Macroporous framework-modified CFMEs provide increased surface defects and pores large enough to momentarily trap dopamine for improved electrochemical reversibility, sensitivity, and frequency independence. Chapter 4 uses copolymer wetspinning to synthesize u (open full item for complete abstract)

Committee: Ashley Ross Ph.D. (Committee Chair); Ryan White Ph.D. (Committee Member); Noe Alvarez Ph.D. (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2023, Arts and Sciences: Chemistry

Lead contamination of drinking water is a concern to all living in old cities where lead pipes and soldering are still present. Electrochemical methods are simple, in-expensive, and thus are promising for analysis of this type of contamination. Howev-er, a major inconvenience with detection of metal ions is the need to acidify the solu-tion. Otherwise, the measurements are usually misrepresentative because of hy-drolysis and metal hydroxide precipitation. Presence of anions like CO32- and PO43- in tap water also leads to Pb precipitation. Membrane electrolysis with an anion-exchange membrane can be used to substi-tute the need for adding acid to the sample. The protons needed to acidify the solu-tion are generated as a result of electrochemical water oxidation. This allows for the precise control of the pH and conductivity and replaces classic reagent sample prep-aration. In such set up, the cathode and anode are separated by the anion-exchange membrane to prevent proton oxidation at the anode. Applying +4.5 V to the electro-lytic cell for 30 min would result in a rapid increase in acidity in the anodic com-partment (pH 2), which is sufficient to transform most of Pb species in the soluble format. At the same time, due to anomalously high mobility of protons, the conduc-tivity of solution would significantly increase. Pb was detected using anodic stripping square wave voltammetry. The calibration graph for Pb quantification in acidified tap water was linear in the range of 24.0 – 400 nM (5 – 83 µg/L) that includes the target values of 48 nM (10 µg/L) and 72 nM (15 µg/L) suggested by the World Health Organization and the Environmental Pro-tection Agency respectively. To automize Pb detection and transform the membrane electrolysis cell into an au-tomated device, the configuration for Pb voltammetric analysis was integrated in the membrane electrolysis set up.

Committee: Noe Alvarez Ph.D. (Committee Chair); Ryan White Ph.D. (Committee Member); Ashley Ross Ph.D. (Committee Member) Subjects: Analytical Chemistry

MS, University of Cincinnati, 2023, Arts and Sciences: Chemistry

Neuroinflammation, oxidative stress, and glutamatergic excitotoxicity are prevalent in several neurological disorders including stroke, substance abuse, and neurodegenerative diseases. Chemical compounds and biomolecules which can ameliorate those conditions are gaining interest for new treatments. Despite many advances in understanding brain anatomy and physiology, the underlying neuropathological mechanisms behind ischemic stroke are still poorly understood. The purine nucleosides adenosine and guanosine have been shown to exhibit neuroprotective behavior in both in vivo and ex vivo models of ischemia. However, real-time detection of guanosine sub-second signaling dynamics in the brain is not understood. Various techniques have been developed for the detection of guanosine in vivo and in in vitro. We have used fast-scan cyclic voltammetry (FSCV), a novel electrochemical technique for real-time detection of the neurochemical release in sub-second timescales at carbon-fiber microelectrodes (CFME). Previously our lab has observed a significant increase in the concentration of guanosine during ischemia with the help of FSCV, showing a neuroprotective effect in ischemia. Despite prior studies, it is still unknown how guanosine released during ischemia is impacted as the function of ischemic severity. Here, we have developed an ex vivo oxygen-glucose deprivation model to investigate the guanosine signaling changes as a function of ischemic severity. Characterization of three different ischemic conditions was studied: normoxia, mild ischemia, and severe ischemia with the help of an optically dissolved oxygen sensor. triphenyl tetrazolium chloride assay and immunohistochemical staining were used to validate these ischemic conditions. Overall, we have successfully developed and maintained three different ex vivo experimental ischemic condition.

Committee: Ashley Ross Ph.D. (Committee Chair); Ryan White Ph.D. (Committee Member); Anthony Grillo Ph.D. (Committee Member) Subjects: Analytical Chemistry

PhD, University of Cincinnati, 2023, Arts and Sciences: Chemistry

The importance of the gut-brain axis has become increasingly apparent, insights into the neurotransmission along this axis could provide crucial information into roles along the gut-brain-immune axis. Physiologic culture methods of ex vivo tissue slice models are imperative to assess physiological function ex vivo. Microfluidics has been adapted to improve the physiological environment of current culture methods. In this thesis I have detailed microfluidic improvements to analytical detection methods, single organ slice culture devices and multi-organ communication devices. The first chapter details the importance of the gut-brain axis and the communication pathways along this connection. Detection methods for this multi-organ communication are also detailed in the first chapter. Wrapping up this chapter the need to expand our ex vivo culture platforms currently in the field is discussed. In the second chapter, I detail a microfluidic electrochemical flow cell to improve the current experimental procedure. The T-channel device design followed by a long microfluidic channel facilitate full mixing of solutions before the electrode surface. Flow rates can be varied to allow for a full concentration curve to be performed from a single stock analyte solution. This device reduces human error drastically in the experiment and decreases time and cost due to the microfluidic nature of the device. Chapter three describes a culture platform for ex vivo intestinal slices that recreates the physiological oxygen gradient that occurs in the intestine. Flow rates of oxygenated and deoxygenated media can be varied to allow for strategic delivery to different sized slices. The delivery of this gradient was proven to remain steady over the course of an hour. This device also provides an open culture platform for easy coupling with external detection methods such as fast scan cyclic voltammetry and microscopy techniques. Chapter four details a multi-organ (open full item for complete abstract)

Committee: Ashley Ross Ph.D. (Committee Chair); Ryan White Ph.D. (Committee Member); In-Kwon Kim Ph.D. (Committee Member); Leyla Esfandiari Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, Case Western Reserve University, 2023, Chemical Engineering

Nuclear energy is a reliable, clean source of electricity that does not produce greenhouse gases and can be relied on for baseload energy generation. In the United States, the major bottleneck to expansion of nuclear power is the management of nuclear material, including the byproducts of nuclear fission, as well as the main fuel component, uranium, throughout its lifetime. One of the solutions to mitigating risks associated with the waste from nuclear power generation, i.e., used nuclear fuel (UNF), is to separate the longest- lived fission products, the actinides. Actinides can be separated from the bulk of UNF through electrodeposition in molten salt. The electrodeposition of americium, a pertinent actinide in UNF, is not well understood. This work synthesizes AmCl3 within LiCl-KCl to investigate the two-step reduction scheme of Am. A diffusion−reaction model is proposed to explain the kinetically-limited deposition reaction. Simulations agree well with experimental voltammetry collected in AmCl3-LiCl-KCl at 500°C. In addition, the Coulombic efficiency of the Am deposition reaction is studied via a two-step chronoamperometry experiment. The low Coulombic efficiency results are discussed through the framework of the diffusion−reaction model. Uranium contamination into aqueous environments is known to create a complex transport problem due to the inherent complexity of uranium chemistry. Factors such as pH, ligands in solution, presence of surfaces (e.g., minerals, metal oxides), presence of 24 oxidizing or reducing agents and ionic strength affect the speciation of uranium and its mobility in the environment. Adsorption of uranium onto surfaces is one naturally occurring phenomenon that impedes its mobility, and is often accompanied by charge transfer reactions. This phenomenon is also harnessed as an intentional tool for remediation, where polarized surfaces are exposed to bodies of water that have uranium to reduce and adsorb uranium species. This work prese (open full item for complete abstract)

Committee: Christine Duval (Advisor); Rohan Akolkar (Committee Member); Krista Hawthorne (Committee Member); Robert Savinell (Committee Member); Mark De Guire (Committee Member) Subjects: Chemical Engineering; Energy; Nuclear Chemistry

Doctor of Philosophy, Case Western Reserve University, 0, Chemical Engineering

Organic compounds containing nitroxide radicals such as 4–hydroxy–2,2,6,6–tetramethylpiperidine–1–oxyl (4–hydroxy–TEMPO) are redox–active and are of interest for potential applications in redox flow batteries. The mechanisms governing charge–transfer reactions of such compounds are not well understood. Specifically, the anodic charge transfer coefficient (α_a) corresponding to the electro–oxidation of 4–hydroxy–TEMPO in an aqueous and non–aqueous electrolyte is ~0.9, i.e., α_a deviates considerably from the expected value (0.5) for a symmetric single–step one–electron transfer redox reaction. To explain this observation, a two–step oxidation mechanism is proposed wherein the nitroxide–containing species undergo fast charge transfer at an electrode surface followed by slow rate–limiting desorption of the adsorbed oxidized species. Numerical simulations are reported to characterize how the proposed two–step mechanism manifests in transient cyclic voltammetry behavior of the 4–hydroxy–TEMPO oxidation reaction, and good agreement with experiments is noted. In the present contribution, supporting evidence is provided for the aforementioned mechanism. In situ surface–enhanced Raman spectroscopy is employed to confirm the presence of surface–adsorbed species at a Au electrode during electro–oxidation of 4–hydroxy–TEMPO. Furthermore, chronopotentiometry is used to track the gradual re–equilibration of the electrode–electrolyte interface following the electro–oxidation of 4–hydroxy–TEMPO. Analysis of the chronopotentiometry data further suggests the presence of adsorbed species. Electrochemical cycling and spectroscopic evidence are presented to investigate the passivating effect of surface films that form following the electro–oxidation of 4–hydroxy–TEMPO.

Committee: Rohan Akolkar (Committee Chair); Lydia Kisley (Committee Member); Burcu Gurkan (Committee Member); Robert Savinell (Committee Member) Subjects: Chemical Engineering

PhD, University of Cincinnati, 2022, Arts and Sciences: Chemistry

Carbon nanotubes (CNTs) have exceptional electrical and mechanical properties that make them ideal materials for electrochemical sensors, including fast electron transfer rate, large aspect ratio, electrical conductance, and corrosion resistance. The individual properties can be taken advantage of by using bulk CNT devices. In this research, I have designed three different bulk assemblies of CNTs for their use as sensors for determining lead in drinking water and ammonia gas in the air. An inkjet printing recipe was formulated to print a multi-walled carbon nanotube (MWCNT) electrode optimized for detecting Pb2+ using the square wave anodic stripping voltammetry technique. The printed MWCNT electrode demonstrated a limit of detection of 1.0 ppb Pb2+ in a drinking water sample without the need for sample preparation. A gold modified CNT fiber cross-section electrode was designed for the sensitive detection of trace Pb2+ and to explore the impact water quality parameters have on the square wave stripping voltammetry technique. Six standard water parameters: pH, conductivity, free chlorine, alkalinity, temperature, and copper, both in simulated and local drinking water samples. A MWCNT film electrode was constructed using a highly ordered CNT forest array. The MWCNT film was functionalized using a facile in-situ polymerization of polyaniline (PANI) and optimized as a chemiresistive NH3 sensor. The polymerization at the CNT surface formed a porous nanostructure of PANI, a conducting polymer whose inherent resistance is sensitive to NH3. The PANI-CNT nanocomposite demonstrated detections down to ppb NH3 levels with fast response and recovery times.

Committee: Noe Alvarez Ph.D. (Committee Member); Ryan White Ph.D. (Committee Member); Ashley Ross Ph.D. (Committee Member) Subjects: Analytical Chemistry

PhD, University of Cincinnati, 2021, Arts and Sciences: Chemistry

Fast scan cyclic voltammetry (FSCV) has been used for monitoring neurotransmitters real-time in vivo and in vitro over the last several decades and carbon fiber microelectrodes are the standard working electrode to monitor electroactive neurotransmitters. Carbon is an excellent electrode surface because it can be easily modified to change the chemical structure, topology, functionalization, defects, and 3D shape. This dissertation aims to develop novel carbon-based microelectrode surfaces to study fundamental electrode-analyte interactions to inform the development of ultrasensitive electrochemical sensors. Chapter 1 covers the importance of neurotransmitter detection, neurochemical detection methods, and novel carbon nanomaterial design for FSCV detection. Chapter 2, 3 and 4 study the relationship between the carbon microelectrode's surface structure and their electrochemical behavior. More specifically, Chapter 2 explores the effects of plasma treatment on surface roughness and functionalization of carbon-fiber microelectrodes to enhance purine detection. Chapter 3 introduces different functional groups on carbon fiber and measures their impact on ATP detection with FSCV and Chapter 4 explores the mechanism of fouling resistance by correlating changes in defect sites to degree of fouling resistance. Chapter 5 introduces the concept of incorporating metal nanoparticles on carbon microelectrodes to enhance the sensitivity and catalytic properties for ATP detection. Chapter 6 describes a brand-new material for neurochemical detection: graphene microfibers. Finally, Chapter 7 covers challenges and future directions using graphene to fabricate electrode sensors and addresses the development of improved sensitivity of detection. Overall, my dissertation explores fundamental electrochemical studies on the surface and chemical structures of carbon microelectrodes for neurotransmitter detection. The fundamental studies introduce nanoparticles and graphene-based mate (open full item for complete abstract)

Committee: Ashley Ross Ph.D. (Committee Chair); Ryan White (Committee Member); Noe Alvarez Ph.D. (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2021, Arts and Sciences: Chemistry

Guanosine is a crucial molecule within the central nervous system known to play a role in neuromodulation and protection in the instance of chemical or physical damage to the brain. Neurochemical release is a dynamic process, necessitating an analytical method that can capture rapid and subsecond signaling events. Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes is an electrochemical technique enabling detection of rapidly released electroactive compounds. In this dissertation, I have detailed an FSCV technique for the quantitation and characterization of dynamic guanosine events within living brain tissue. In the first chapter, I describe the chemistry and neurobiology of guanosine, covering its role within the central nervous system, the metabolic pathways of guanosine and its regulation, and its receptors and transporters. I also describe extant and popular detection techniques for guanosine and its sister compound adenosine. In Chapter 2, I describe the guanosine FSCV waveform I developed for my first graduate project. Here, I go into detail regarding the full characterization of this waveform and present a proof-of-concept for in-tissue detection of guanosine. In the following chapter, I present an additional FSCV waveform allowing for the codetection of both guanosine and adenosine. This waveform is a modified version of the adenosine waveform which enables simultaneous detection of the purine ribonucleosides. This waveform could prove useful in the future for codetection of the ribonucleosides, as earlier studies have suggested an intricate interaction between guanosine and adenosine with important downstream modulatory effects. In the fourth chapter, I use the guanosine waveform to detect endogenous, spontaneous guanosine transients ex vivo. Guanosine events were recorded during a control period and in response to a drug and neurochemical injury. This study marks the first ever recordings of subsecond, dynamic guanosine events in the brain (open full item for complete abstract)

Committee: Ashley Ross Ph.D. (Committee Chair); Ryan White (Committee Member); Mark Baccei Ph.D. (Committee Member); Noe Alvarez Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy in Engineering, University of Toledo, 2021, Engineering

Reactive oxygen species (ROS) are constantly generated in human cells. The most found ROS are superoxide (O2•−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). These ROS are considered either constructive or destructive species depending on their level in live cells. A proper level of ROS provides several benefits, such as control of blood pressure, elimination of bacteria, and interruption of virus activity. However, the overproduction of ROS as a result of a weak antioxidant mechanism in cells turns ROS into destructive species. Tissue damage and cell death are some of the major detrimental effects of ROS. Cancer, skin aging, diabetes, heart disease, tumors, and several neurodegenerative diseases are examples of fatal conditions related to tissue damage and cells death from uncontrolled concentrations of ROS. Among all ROS, hydroxyl radicals (•OH) are the most reactive and dangerous ones, with a short lifetime of nanoseconds. Thus, the ability to detect and measure the concentration of •OH in real time could provide a crucial piece of information to understand the role that ROS play on the development of those fatal diseases. As a result, this thesis focuses on the development of an electrochemical sensor for the detection of hydroxyl free radicals. To do so, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to analyze the interaction between the electrochemical sensor and •OH. In order to detect •OH, the electrochemical sensor required the use of a sensing element. Since cerium oxide (CeOx) is a well-known scavenger of hydroxyl free radicals, this was used as the sensing element of the device. In order to provide the sensor with both sensitivity and selectivity, our research focused on the development of nanocomposites containing both cerium oxide nanoparticles (CeNPs) and a highly conductive material, such as graphene oxide (GO) or highly conductive carbon. First, we developed a composite-based electrochemic (open full item for complete abstract)

Committee: Dong-Shik Kim (Advisor); Ana C. Alba-Rubio (Advisor); Steve Kim (Committee Member); Maria Coleman (Committee Member); Youngwoo Seo (Committee Member) Subjects: Chemical Engineering; Chemistry

Doctor of Philosophy, University of Akron, 2020, Chemistry

This work explores the effects of ac waveform heated microelectrodes on the detection of bacterial and redox analytes. By applying ac waveform to a microelectrode, a “hot zone” can be created in solution, while the bulk solution remains unheated.1,2 This causes a temperature gradient in solution, and electrothermal flow (ETF) force is generated. ETF force helps to direct solution toward the electrode surface, increasing the sensitivity.3 Dielectrophoresis (DEP) force is also created with the generation of a non uniform electric field by the applied ac waveform. DEP force acts on uncharged particles and causes motion toward or away from the electrode.4,5 ETF and DEP forces are exploited in this work in order to more sensitively detect analytes. ETF and DEP forces generated by heating an electrode with ac waveform were first used to decrease the detection limit of Ag NP-covered Escherichia coli (E. coli) bacteria. While the bacteria experience a DEP force away from the electrode, Ag NPs experience DEP force toward the electrode, and when enough NPs are bound to the bacteria, the overall force is toward the electrode surface. Thus, DEP and ETF forces pull the bacteria toward the electrode where the bound NPs are oxidized on the electrode surface, indicating the collision. Ag NP-covered E. coli were detected at as low of a concentration of 1.5 x 10^6 colony forming units (CFU)/mL on a microelectrode in a period of three minutes, improving a previously reported detection limit on a larger electrode when bacteria moved solely by diffusion by two orders of magnitude.6 A microfluidic chip for the purpose of biosensing was also fabricated. Further, ac heated microelectrodes were used in the sensing of redox couples, ferricyanide/ferrocyanide and iron (II)/iron (III). Heating electrodes via application of high frequency ac waveform was used in conjunction with Square-Wave Voltammetry (SWV) in order to develop a me (open full item for complete abstract)

Committee: Aliaksei Boika (Committee Member); Leah Shriver (Committee Member); Chrys Wesdemiotis (Committee Member); Michael Konopka (Committee Member); Rajeev Gupta (Committee Member) Subjects: Chemistry

Master of Science in Chemistry, Youngstown State University, 2019, Department of Chemistry

Solid state hydrogen storage is seen as the ultimate answer in realizing the hydrogen economy and minimizing our overdependence on nonrenewable fossil fuels. The use of fossil fuels has contributed negatively towards climate change, leading to a lot of future uncertainties. Alkali metal borohydrides, especially lithium borohydride, with desirable H2 storage properties such dry air stability and high gravimetric and volumetric storage densities of 18.5 wt% and 121 kg/m3, respectively, are proving to be some of the most important solid state hydrogen storage materials. However, their current cost of production is very high considering that most borohydrides are synthesized from sodium borohydride, which in turn is made from sodium hydride, NaH, and trimethyl borate, B(OCH3)3. NaH, which is a product of an energetic process, namely hydrogenation following electrodeposition of the metal from a molten salt, acts as the source of H- required for the formation of the borohydride ion. In this work, electrochemical transfer of H- from a Pd foil, which is considered less energetic than NaH, was investigated. Hydrogen gas at a pressure of about 1 atm was passed through the Pd foil, which was used as the working electrode in an electrochemical cell containing 0.1 M LiClO4 and 4.4 M B(OCH3)3 in CH3CN as the electrolyte. Using a potentiostat, a voltammetric experiment with 3 cycles at 50 mV/s was performed with and without hydrogen application. A potentiostatic experiment was conducted by holding the Pd foil at -2.75 V vs Ag/AgClO4 and run for 10.6 hours. Analysis of a portion of the electrolyte using IR and NMR spectrometry showed the presence of borohydride. A two compartment cell with Nafion as the separator of the electrode reagents was used to increase the yield.

Committee: Clovis Linkous PhD (Advisor); Sherri Lovelace-Cameron PhD (Committee Member); Timothy Wagner PhD (Committee Member) Subjects: Chemistry; Energy; Materials Science

Master of Science, The Ohio State University, 2019, Chemistry

Since its discovery in 1979, the solid electrolyte interface (SEI) has drawn attention due to its importance for efficient battery performance. Despite its significance, there is still some ambiguity with regards to how certain electrolytes form a protective interface to aid Li+ intercalation whilst others irreversibly degrade the anode structure. One of the most debated examples is the “EC-PC disparity” towards the graphite anode, where ethylene carbonate (EC) results in protective SEI formation whilst propylene carbonate (PC) leads to destructive graphite exfoliation. This study focuses on the correlation between the concentration of the Li+ salt, LiPF6 dissolved in PC and the growth of SEI on graphite. In-situ and in-operando electrochemical scanning tunneling microscope (STM) observation of the basal plane of highly oriented pyrolytic graphite (HOPG) is performed in 1 M, 2.5 M and 3 M LiPF6 dissolved in propylene carbonate (PC) in sequence to cyclic voltammetry (CV) and potential hold experiments. This technique allows the study of the topographic evolution of the basal plane and edge sites on HOPG with changes in the potential, as a result of solvent co-intercalation, reduction, graphite exfoliation and SEI formation. STM images obtained whilst holding the potential at selected values, gives an insight into the nature of SEI formation, in connection to the extent of regeneration of the graphite surface. It is found that below 0.9 V vs Li, solvent decomposition, followed by extensive graphite exfoliation takes place in the 1 M and to a lesser degree in 2.5 M LiPF6 electrolyte solutions. However, in the 3 M salt solution, graphite exfoliation is scarce and SEI formation is observed at potentials as high as 1.1 V vs Li, which clearly indicates a concentration dependent SEI formation on graphite. CV experiments conducted in parallel to EC-STM, provide further confirmation. The HOPG is cycled between 3 to 0.005 V vs Li in all three salt concentrations within Swa (open full item for complete abstract)

Committee: Anne Co Dr. (Advisor); Zachary Schultz Dr. (Committee Member) Subjects: Chemistry

Master of Science, Miami University, 2019, Chemical, Paper and Biomedical Engineering

A quick and easy method for determining concentrations of 17-α-Ethinyl Estradiol is through the use of an electrochemical method utilizing disposable screen-printed carbon electrodes. The electrochemical behavior of 17-α-Ethinyl Estradiol was investigated by cyclic voltammetry. The oxidation reaction occurs on the screen-printed carbon electrode and the linear response of 17-α-Ethinyl Estradiol is obtained for the concentration range of 3×10-5 M (8900 μg/L) to 3×10-6 M (890 μg/L) with an achieved sensitivity of 0.1714 μA/μM. The experimentally determined detection limit of this electrode is measured to be 2×10-7 M (59.2 μg/L). The repeatability of this method, (Relative Standard Deviation) %, was conducted on concentrations of 1×10-5 M (2368.3 μg/L) and 3×10-6 M (890 μg/L) with respective RSD% values of 5.11% and 13.72% (n=5). The performance of different pH values (from pH 4-10) for 17-α-Ethinyl Estradiol was also investigated. It was determined that pH 6.8 gives the best electrochemical behavior. Selectivity of this method is validated and screen-printed carbon electrodes are able to detect 17-α-Ethinyl Estradiol with the presence of interferences. The proposed method for determines 17-α-Ethinyl Estradiol is simple and fast.

Committee: Lei Kerr (Advisor); Shashi Lalvani (Advisor); Hang Ren (Committee Member) Subjects: Chemical Engineering

PhD, University of Cincinnati, 2019, Arts and Sciences: Chemistry

Monitoring signaling communication pathways in the brain have considerable attracted attention because of the well-known disparities that exist describing brain function. This is an effect of a lack of analytical tools able to perform with the required sensitivity, specificity, spatiotemporal resolution. Moreover, brain processes are diverse and naturally complex, and the development of these tools need to be tunable to specific requirements. This work here focuses on the development of strategies to tailor the use of electrochemical, aptamer-based (E-AB) sensors with the required sensitivity, specificity, and temporal resolution to monitor gliotransmission processes, with particular attention to ATP release. The first part emphasizes the use of the specificity, sensitivity, and stability of the E-AB sensing approach. Specifically, Chapter 2 introduces the interface between E-AB sensors with hydrogels with the ultimate goal of protecting RNA-based E-AB sensors against exogenous entities such as ribonucleases. The biocompatibility of the hydrogel with encapsulated ribonuclease inhibitor promotes the protection of an aminoglycoside-binding RNA E-AB sensor up to 6 hours, enabling full sensor function in nuclease-rich environments without prior sample preparation or modification. The use of collagen as a biocompatible membrane represents a general approach to compatibly interface E-AB sensors with complex biological samples. Similarly, Chapter 3 further expands the applicability of the interface between collagen membranes and E-AB sensors to study ATP release from astrocyte cells. Here, we propose a 3D tissue culture combined with E-AB sensors as a model to study gliotransmitter release. In general, the specificity provided by microscale E-AB sensors coupled with the 3D astrocyte cell culture approach not only allow unequivocal in vitro neuroactive molecules measurements but also it has the potential to be translatable to in vivo studies of the brain. T (open full item for complete abstract)

Committee: Ryan White Ph.D. (Committee Chair); Noe Alvarez Ph.D. (Committee Member); William Heineman Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy in Clinical-Bioanalytical Chemistry, Cleveland State University, 2017, College of Sciences and Health Professions

Peroxynitrite (ONOO-, PON) plays a crucial role in several cardiovascular dysfunctions and other diseases triggered by oxidative stress. PON is a strong oxidizing agent produced from the diffusion-controlled reaction between nitric oxide radical and superoxide anion-radical. It is also a member of the reactive oxygen-nitrogen species family, which attacks vital components inside the body and initiates deleterious effects via direct and indirect interactions. PON reacts directly with lipids, DNA, and proteins, whereas indirectly, it acts as an initiator of radical-chain reactions. In this work, we have explored various interfaces of manganese-oxide-decorated graphene/hemin and selenium-containing compound for PON detection and quantification. The combination of manganese oxide nanoparticles with the graphene/hemin matrix has allowed for more hemin molecules to be adsorbed on the final composite matrix. As a result, the adsorbed hemin has enhanced the catalytic activity of the final composite and improved the sensitivity towards PON detection. In the same context, a selenium-containing compound (aniline-selenide) has been synthesized and grafted on the electrode surface using the chemistry of diazonium salt. The aniline-selenide-modified electrode showed an increase of approximately 40 times the catalytic current as the aniline-modified electrode. Throughout this project, the preparation methods of the electroactive nanomaterials were described in detail. Moreover, the characterizations of the prepared-materials have been investigated by various physicochemical methods using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet/visible measurements (UV/Vis), and X-ray photoelectron spectroscopy (XPS). This study showed the importance of using selenium and manganese interfaces as sensitive platforms for PON detection. It also provides the initial stage to extend the use of these interfaces to ultramicroelectrodes sensors for use (open full item for complete abstract)

Committee: Mekki Bayachou Ph.D. (Committee Chair); Aimin Zhou Ph.D. (Committee Member); John Turner Ph.D. (Committee Member); W. Christopher Boyd Ph.D. (Committee Member); Petru S. Fodor Ph.D. (Committee Member) Subjects: Chemistry

MS, University of Cincinnati, 2017, Engineering and Applied Science: Computer Engineering

The occurrence of pediatric septic shock is a major health concern in the United States. Children are often susceptible to contract sepsis due to microbial invasion, and there have been 42,000 cases of septic shock annually with an approximate 10% mortality rate [1]. Pediatric patients going through septic shock often exhibit critically low levels of zinc (Zn), which is an important trace element required for normal functioning of hormones, certain enzymes, and transcription-related factors [2]. Thus, it has been proposed to use oral supplementation of Zn as a therapeutic strategy to treat critically ill patients [3]. In order to protect patients, it is necessary to closely monitor Zn concentration levels in blood serum due to the risk of heavy metal toxicity. If Zn concentration levels are not maintained near physiologically normal levels, heavy metal toxicity can cause major problems for the patient and malpractice concerns for the doctor. Current methods of monitoring Zn concentration involve taking a blood sample and sending it to an external laboratory for processing. The two primary methods for measuring Zn concentration are Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Mass Spectroscopy (ICP-MS), which have turnaround times ranging from a few hours to a few days. This timeframe is inadequate for monitoring patients undergoing oral Zn supplementation, as it would be too late to take counter-measures to reverse over-supplementation by the time results are received from the external laboratory. The limitations of current measurement methods have impeded the use of oral zinc supplementation in clinical experiments that could save many lives. This impetus has prompted the development of a device for measuring Zn concentration in blood serum in a rapid manner. A Point-of-Care (POC) device to overcome these obstacles has been in the works by students at the iiUniversity of Cincinnati for several years. The device involves a th (open full item for complete abstract)

Committee: Fred Beyette Ph.D. (Committee Chair); Carla Purdy Ph.D. (Committee Member); Philip Wilsey Ph.D. (Committee Member) Subjects: Computer Engineering