Doctor of Philosophy, Case Western Reserve University, 2024, Chemical Engineering

Lowering energy-related CO2 emissions of the U.S. requires the implementation of renewable energy sources to generate electricity. These sources, e.g. solar and wind power, are intermittent in their output, necessitating some form of grid-scale energy storage. Redox flow batteries, particularly hybrid flow batteries based on zinc (Zn), are a highly attractive solution due to their high energy density, scalability, earth-abundance of Zn, and usage of safer aqueous electrolytes as opposed to flammable organics. However, Zn has notable problems such as forming dendrites during high-rate deposition and spontaneous corrosion in acidic and alkaline electrolytes leading to substantial self-discharge of a battery over time. To address these issues, significant research has been conducted on electrolyte additives that can suppress dendrite formation and prevent corrosion, but many of these conventional additives also polarize the electrode and harm battery energy-efficiency. In the present work, a novel additive, benzyldimethylhexadecylammonium chloride (BDAC), is shown to markedly suppress Zn corrosion (battery self-discharge) rate in a pH = 3 ZnSO4 medium without harming (i.e., by minimizing overpotential losses) the high-rate deposition or stripping performance of Zn. Cyclic voltammetry (CV) measurements show BDAC induces hysteresis, where the electrode can either exhibit passivity or electrochemical activity at a given electrode potential depending on the scan direction. The hysteresis is a result of complex surface adsorption and deactivation behavior of BDAC on Zn. An additive adsorption-deactivation model is proposed which captures above behavior and shows that, at low current densities (i.e. low BDAC deactivation rates), the electrode surface tends towards full additive coverage while, at higher deposition or stripping rates (i.e. rapid BDAC deactivation), the electrode surface tends towards a coverage depending on the additive's adsorption and deactivatio (open full item for complete abstract)

Committee: Rohan Akolkar (Committee Chair); Robert Warburton (Committee Member); Jesse Wainright (Committee Member); Alp Sehirlioglu (Committee Member) Subjects: Chemical Engineering

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

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, 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, 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

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

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

Doctor of Philosophy (PhD), Wright State University, 2017, Environmental Sciences PhD

The goal of this research was to study the electrochemical behavior of tri-nuclear clusters of molybdenum and tungsten. In addition, the feasibility of using these clusters as catalysts for the purpose of oxidizing ethanol was investigated. Four tri-nuclear cluster compounds were studied: hexa-µ2-acetatotriaquadi-µ3-oxotrimolybdenum (IV, IV, IV) trifluoromethanesulfonate [Mo3O2(O2CCH3)6(H2O)3](CF3SO3)2, hexa-µ2-acetatotriaquadi-µ3-oxodimolybdenum (IV, IV) tungsten (IV) trifluoromethanesulfonate [Mo2W2O2(O2CCH3)6(H2O)3](CF3SO3)2, hexa-µ2-acetatotriaquadi-µ3-oxomolybdenum (IV) ditungsten (IV, IV) trifluoromethanesulfonate [MoW2O2(O2CCH3)6(H2O)3](CF3SO3)2, and hexa-µ2-acetatotriaquadi-µ3-oxotritungsten (IV, IV, IV) trifluoromethanesulfonate [W3O2(O2CCH3)6(H2O)3](CF3SO3)2. Data was gathered from experimental results with cyclic voltammetry for the four tri-nuclear clusters. Initially, an ionic liquid, EMIBF4 (1-ethyl-3-methylimidazolium tetrafluoroborate), was used as the solvent. Subsequent solvents for use with these clusters were investigated, including ACN (acetonitrile) and NMF (N-methylformamide). The secondary solvent system settled on was the DMSO-TBAHFP solvent system. Each tri-nuclear cluster displayed a reversible redox reaction and one or more irreversible reduction reactions. The redox peak potentials were found to be Ep,a: -0.44V and Ep,c: -0.42V for Mo3, Ep,a: -0.32V and Ep,c: -0.43V for Mo2W, Ep,a: -0.31 V and Ep,c: -0.44 V for MoW2, and Ep,a: -0.42 and Ep,c: -0.46 for the W3 tri-nuclear cluster. The irreversible reduction reactions for each tri-nuclear cluster were observed at Ep,c(2): -0.74 for Mo3, Ep,c(2): -1.15 for Mo2W, Ep,c(2): -1.14 for MoW2, and Ep,c(2): -0.84 for the W3 tri-nuclear cluster. The diffusion coefficients in DMSO were determined to be DMo3 = 9.105E-06 cm2s-1, DMo2W = 1.743E-05 cm2s-1, DMoW2 = 1.764E-05 cm2s-1, and DW3 = 1.991E-05 cm2s-1. Exploring the electrocatalytic capability of these compounds was another effort made, by a (open full item for complete abstract)

Committee: Vladimir Katovic Ph.D. (Advisor); Jay Johnson Ph.D. (Advisor); Suzanne Lunsford Ph.D. (Committee Member); William Heineman Ph.D. (Committee Member); Christopher Barton Ph.D. (Committee Member); Doyle Watts Ph.D. (Committee Member) Subjects: Alternative Energy; Chemistry; Environmental Science; Materials Science

Doctor of Philosophy, Case Western Reserve University, 2015, EECS - Electrical Engineering

This project has developed two integrated microsystems fabricated in a 0.35-µm two-poly four-metal CMOS process for high-fidelity sensing and manipulation of brain neurochemistry. In particular, first, a system-on-chip (SoC) has been developed for neurochemical pattern generation in vivo. This SoC uniquely integrates electrical stimulation with embedded timing management for generation of neurochemical patterns and 400V/s fast-scan cyclic voltammetry (FSCV) sensing at a carbon-fiber microelectrode (CFM), for subsequent assessment of fidelity in the generated profiles, and manages a novel switched-electrode scheme that eliminates the possibility of large stimulus artifacts adversely affecting electrochemistry. The SoC also leverages the discontinuous sampling inherent in FSCV to reduce the sensing power consumption by 87.5% to 9.3µW from 2.5V using a duty-cycled, 3rd-order, continuous-time, delta-sigma modulator (CT-ΔΣM) with an input-referred noise current of 78pArms (dc – 5 kHz) within an input current range of ±950nA. Utilizing a transfer function that relates electrical stimulation of dopamine axons traversing the medial forebrain bundle (MFB) to evoked extracellular dopamine dynamics in the dorsal striatum of the forebrain, the correlation coefficient between predicted and measured dopamine temporal profiles was found to be 0.95 in an anesthetized rat. Next, the second SoC has been developed for closed-loop regulation of brain dopamine. This SoC uniquely integrates neurochemical sensing, on-the-fly chemometrics, and feedback-controlled electrical microstimulation to mimic a “neurochemical thermostat” by maintaining brain levels of electrically evoked dopamine between two user-set thresholds. The SoC incorporates a 90µW, custom-designed, digital signal processing (DSP) unit for real-time processing of neurochemical data obtained by 400V/s FSCV at a CFM. Specifically, the DSP unit executes a chemometrics algorithm based upon principal component regression (PCR) t (open full item for complete abstract)

Committee: Pedram Mohseni (Advisor); Swarup Bhunia (Committee Member); Soumyajit Mandal (Committee Member); Paul Garris (Committee Member) Subjects: Electrical Engineering

Master of Science (M.S.), University of Dayton, 2014, Chemical Engineering

Claims made by literature use models that do not account for mass transport that is likely to affect the cyclic voltammetric response of nanostructured electrodes. This response is generally assumed to be electrocatalytic in nature. Recent research has suggested that mass transfer must have a combined effect on the increased current reported in cyclic voltammetry, however, no model exists that sheds light on these effects. As nanostructured electrodes have become standard for numerous applications, it would be to the benefit of these applications that a more fundamental understanding exists. Fundamental transport is applied to semi-infinite and thin-layer diffusion regions to estimate the corresponding diffusivities. The derivation parallels the previous work by Nicholson and thin layer diffusion theorized by Streeter. The model fits voltammetric data from common redox reactions whose bulk diffusivities and electron rate transfer parameters are readily accepted in literature. The results estimate an effective thin layer diffusivity lower than the bulk diffusivity due to the nature of hindered pore diffusion. The diffusion model more accurately describes the diffusion conditions that occur as a result of nanomodified electrode structures, and can be used to optimize an electrode structure to maximize its electrochemical efficiency.

Committee: Kevin Myers D.Sc., P.E. (Committee Member); Charles Browning Ph.D. (Committee Member); Sarwan Sandhu Ph.D. (Committee Member); Paul Eloe Ph.D. (Committee Member) Subjects: Chemical Engineering; Materials Science; Mathematics

Master of Science (MS), Wright State University, 2011, Chemistry

Specially constructed carbon paste electrodes were coated with 10 mM cetyltrimethylammonium halide (CTAX) solutions, bromide and chloride being the counter anions. These surfactant modified electrodes were used to detect the catecholamine neurotransmitter dopamine using cyclic voltammetry. The coated electrodes gave reproducible quasi-reversible behavior for the analyte dopamine over a range of concentrations from 1 mM to 200 mM. When combined in solution with common interferents ascorbic acid (1 mM) and uric acid (300 μM), all cathodic and anodic current peaks maintained resolution at the biological pH of 7.4. When the coating solutions were below the critical micelle concentration (0.5 mM), reduced anodic peak current was observed. Throughout multiple experiments, no discernible difference in performance between cetyltrimethylammonium bromide and cetyltrimethylammonium chloride was found.

Committee: Suzanne Lunsford PhD (Committee Chair); Audrey McGowin PhD (Committee Member); Ioana Pavel Sizemore PhD (Committee Member) Subjects: Chemistry

Master of Science (MS), Wright State University, 2009, Chemistry

The central focus is the development and implementation of a research/lab module for first year chemistry courses. Electrochemical techniques are utilized to study oxidation and reduction reactions of neurotransmitters with a poly(2,2'-Bithiophene) modified electrode. The goal is to excite students about chemistry and encourage them to continue studies in Science, Technology, Engineering, and Mathematics (STEM) during their undergraduate education. The lab module was created for Project REEL (Research Experiences to Enhance Learning) and will be illustrated with results typically obtained by students. The experiment is inquiry-based, which includes challenging questions students have to do collaboration and research to answer, as opposed to a traditional step-by-step lab. The effectiveness of the lab is assessed with pre/post-tests and a survey response. Analysis of the pre/post-test scores indicates the students' content gain was high. Overall, the students responded positively to their experience with this innovative lab module.

Committee: Suzanne Lunsford PhD (Advisor); Kenneth Turnbull PhD (Committee Member); Daniel Bombick PhD (Committee Member) Subjects: Chemistry; Education

PhD, University of Cincinnati, 2012, Arts and Sciences: Chemistry

The need for sensors that can be used to selectively detect analytes in the presence of direct interferences cannot be over emphasized. Thus, the first part of this dissertation focuses on spectroelectrochemically sensing tris (2,2 bipyridyl) ruthenium (II) dichloride hexahydrate ([Ru(bpy)3]2+)- a model analyte, in low ionic strength samples containing other ‘multiple ions'. Spectroelectrochemical sensors used in this research are rugged and highly selective to the analyte of interest and possess three modes of selectivity in one device. First, the analyte partitions into a charge-selective film which is coated on an indium tin oxide (ITO) optically transparent electrode. At the electrode surface, reversible electrochemistry at a specific potential window for the analyte is initiated resulting in one redox form absorbing light at a specific wavelength and the other form non-absorbing. The amount of analyte trapped in the film is measured by attenuated total reflection absorbance spectroscopy for optical detection. In the course of this study, the extent of ion-exchange competition occurring between the analyte and ions of supporting electrolyte and how this competition ultimately affects the sensor's signal was determined. The spectroelectrochemical sensor's high point is its selectivity and this property was proven in detecting [Ru(bpy)3]2+ in natural (Hanford, WA well water and Bothell, WA river water) and treated water (Cincinnati, OH tap water) samples. Calibration curves were obtained for [Ru(bpy)3]2+ in well, river and tap water with detection limits of 108, 139 and 264 nM, respectively. A standard addition method was employed to determine the concentration of [Ru(bpy)3]2+ spiked in the Hanford well water. The unknown concentration of [Ru(bpy)3]2+ determined by spectroelectrochemical experiments was 0.39 ¿¿¿¿ 0.03 ¿¿¿¿M versus the actual concentration of 0.40 ¿¿¿¿M. Overall, the results from the spectroelectrochemistry with the water samples were very promisin (open full item for complete abstract)

Committee: William Heineman PhD (Committee Chair); Neil Ayres PhD (Committee Member); Joseph Caruso PhD (Committee Member) Subjects: Chemistry

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, Miami University, 2008, Chemistry and Biochemistry

Hydrogen and methanol fuel cells are important energy devices. The need for energy has pressed a tremendous drive towards development of smaller and more efficient fuel cells. There are certain limitations in the fundamental fuel cell reactions. For example, the use of platinum (Pt) nanoparticles as fuel cell catalyst poses serious carbon monoxide (CO) poisoning problem. Slow kinetics of oxygen reduction reaction (ORR) at cathode of a fuel cell also limits the efficiency of fuel cells. In addition, there is little control over the size and distribution of catalyst nanoparticles. For decades, size and distribution dependent catalytic activity of nanoparticles has been the subject of active research. Though numerous studies have been conducted in past to elucidate the effect of size and distribution of nanoparticles towards its activity, the results are inconclusive. In most studies there is no control of particle size and distribution. It is therefore important to design a new system where the metal nanoparticles are fabricated on conductive solid support with uniform size and distribution, so that the role of particle size and distribution towards fundamental fuel cell reactions can be unambiguously addressed. In order to achieve these objectives, a diblock copolymer template method is employed during this dissertation work. Uniformly distributed Au and Pt nanoparticles were synthesized to study the solution CO and methanol electrooxidation as well as ORR. Synthesis of core-shell metal nanoparticles with Pt shell and Au or Cu core is also reported. Utilizing the core-shell metal nanoparticles, the activity of Pt layer may be enhanced for fuel cell reactions in addition to achieving the reduction in Pt usage. The reduction in the use of Pt as the fuel cell catalyst has an enormous impact towards economic viability of fuel cells for commercialization.

Committee: Shouzhong Zou PhD (Advisor); Gilbert E. Pacey PhD (Committee Chair); Andre J. Sommer PhD (Committee Member); Hong Wang PhD (Committee Member); Shashi B. Lalvani PhD (Committee Member) Subjects: Chemistry; Materials Science