Greg M. Swain - US grants

DESCRIPTION (provided by applicant): The proposed research will fabricate, evaluate and develop diamond and hydrogenated carbon fiber microelectrodes for use in the measurement and detection of electroactive neurotransmitters, related metabolites and other bioanalytes. These new, low oxide and chemically stable microelectrodes have the potential to significantly impact in vitro and in vivo neuroelectrochemical measurements because they solve several problems/complications often encountered with common sp2 carbon fiber microelectrodes. These problems/complications exist because of the presence of electroactive and ionizable surface carbon-oxygen functionalities. Boron-doped microcrystalline and nitrogen-incorporated nanocrystalline diamond films conformally deposited on 20-100 micron diameter W and Mo fibers, and hydrogen plasma treated carbon fibers (pitch and pan-based, 10-40 micron diameter) will be the microelectrodes investigated. These electrode materials offer advantages compared to commonly used sp2 carbon electrodes including a lower voltammetric and amperometric background current; no background voltammetnc features associated with electroactive surface carbon-oxygen functionalities; no variations in the response sensitivity for charged solution analytes due to the absence of ionizable carbon-oxygen functionalities; resistance to fouling due to the nonpolar, hydrogen-terminated surface; low limits of detection; and improved response precision and stability.The goals of the research are (i) to prepare and comprehensively characterize the microelectrodes, (ii) to demonstrate their efficacy for the measurement of neurotransmitters, metabolites and bioanalytes, (iii) to verify that the low oxide surfaces solve the problems/complications that exist in fast scan voltammetric measurements when oxygen functionalized electrodes are used, (iv) to develop a detailed understanding of the electrode reaction kinetics and mechanisms at the hydrogen-terminated surfaces and (v) to apply the electrodes in FIA-EC, LC-EC and CE-EC assays with the objective of significantly improving the analytical detection figures of merit.

DESCRIPTION (provided by applicant): The proposed research (continuation of GM65958-01) seeks (i) to continue development of the diamond microelectrode for in vitro chronoamperometric measurements of neurotransmitter release and for use in microcapillary separation techniques coupled with electrochemical detection for the analysis of catecholamine neurotransmitters and metabolites in biological fluids, and (ii) to apply these tools to the study of sympathetic neural control mechanisms of arteries and veins in hypertension. Hypertension is a major health problem in the U.S. Those suffering from chronic high blood pressure are at high risk for organ damage and cardiovascular disease. Although the risk factors are known and treatments have been developed to alleviate symptoms, little is known about the underlying biological pathways and mechanisms. A goal of our research program is to gain a better understanding of how the sympathetic nervous system influences the development and maintenance of hypertension, and what effect chronic hypertension has on the cardiovascular system function and resistance to disease. Specific aims for the research include the following. Specific Aim 1: There are differences between sympathetic neural control of arteries and veins. These differences include the neurotransmitters released, receptors and mechanisms controlling release, and termination of the actions of the neurotransmitters. We seek to understand how these processes are altered in hypertension. Specific Aim 2: Endothelin-1 (ET-1) activity is increased in DOCA-salt hypertensive rats. It is also known that sympathetic activity is elevated in these animals and that ET-1 may be involved in changing sympathetic function in hypertension. We seek to understand the mechanism of ET-1 activity and how it can modulate NE release from sympathetic nerves. We also seek to understand if ET-1 can modulate ATP release from sympathetic nerves supplying mesenteric arteries and if this response is altered in hypertension.

ABSTRACT
CHE-0616730
Swain/Michigan State

This research project funded by the Analytical and Surface Chemistry program seeks to investigate the electrical, electrochemical and optical properties of boron-doped diamond thin films with the goal of developing a new type of optically transparent electrode that can be used for transmission spectroelectrochemical measurements in both the UV/Visible and infrared regions of the electromagnetic spectrum. Professor Greg M. Swain and his group at Michigan State University are studying several different electrode architectures, including free-standing films and thin films deposited on transparent substrates like quartz and silicon. They seek to develop a low frequency IR (< 1000 cm-1) spectroelectrochemical method that can be used to study redox-linked metal-ligand modes in metalloproteins and enzymes. Recent advances in protein film voltammetry along with spectroelectrochemical measurements using IR-transparent diamond electrodes will be employed to gain insight into the mechanistic details of radical-producing metalloproteins and enzymes. Redox-linked metal-substrate and metal-cofactor normal modes will be probed by electrochemical difference spectroelectrochemical techniques with the goal of understanding how these structural changes correlate with biological function. The focus initially is on method development using well-characterized inorganic/organic redox systems and soluble redox proteins (e.g., myoglobin), but will be extended to representatives of the metalloradical enzyme class (e.g., cytochrome c oxidase (CcO)).

A second task involves coupling an optically transparent diamond electrode in the UV/Vis with microchip capillary electrophoresis to enable multiple detection strategies (electrochemical, UV/Vis absorbance, and fluorescence) on the same device. The possibility of multiple detection schemes will facilitate high-throughput analysis and improved sample characterization. Demonstrating the method for the analysis of the sympathetic nervous system neurotransmitters norepinephrine (NE) and adenosine triphosphate (ATP), and their metabolites, is the goal. If successful, the method will be used to provide new insight into neural control mechanisms in hypertension. The chemical problems being addressed are at the interface between chemistry and biology; therefore, the undergraduate and graduate students working on the project will receive broad training in materials science, electrochemistry, separation science, optical spectroscopy, redox protein chemistry, and neurochemistry as it relates to the disease state, hypertension.

Professor Greg M. Swain of Michigan State University is supported by the Analytical and Surface Chemistry Program in the Division of Chemistry to study the physical, chemical, electrical, optical and electrochemical properties of optically transparent diamond and diamond-like carbon thin-film electrodes and explore their application in UV/Vis and IR transmission spectroelectrochemical measurements. The electrochemical properties of the electrodes will be tailored through control of their deposition conditions, and characterized by conductivity-probe atomic force microscopy, scanning electrochemical microscopy, and other surface characterization techniques. Transmission spectroelectrochemical methods in the UV/Vis and IR will be used to investigate the electrode reaction mechanism of redox-active neuropharmacological agents, and low frequency IR spectroelectrochemical method will be used for the study of redox-linked metal-ligand modes in metalloproteins and enzymes. Graduate and undergraduate students will be trained in analytical chemistry, electrochemistry, materials science, optical spectroscopy, and spectroelectrochemistry. Students from underrepresented minorities will be involved in this research through the local NOBCChE chapter.

DESCRIPTION (provided by applicant): Electrochemical methods with diamond microelectrodes will be used to investigate neuronal signaling pathways in the gut wall. These methods provide a direct measure of local concentration changes of electroactive neurotransmitters near the sites of release and action with high temporal resolution. Enteric neurons contain and release many neurotransmitters and some of these can be detected by electrochemical methods, in particular, serotonin (5-HT) and nitric oxide (NO). The extension of these techniques to the study of the peripheral nervous system constitutes an interesting and significant development. Many functional GI disorders, such as disturbances in motility, absorption/secretion and sensation that do not have an identifiable pathophysiological basis, are thought to be related to dysfunction in neurogenic signaling mechanisms. The proposed research will improve our understanding of the normal motility and secretory activities of the GI tract during postnatal maturation of the intestine. These studies will lead to the discovery of age specific pathophysiologic changes in neuronal signaling responsible for functional gut disorders that lead to disease. To this end, we will apply electrochemical methods of analysis with a diamond microelectrode, to investigate two functional questions: (i) can the excitatory neurotransmitter serotonin (5-HT) and the inhibitory neurotransmitter nitric oxide (NO) be measured in the small intestine and colon of test animals and can the associated neuropharmacology controlling release and clearance be understood, and (ii) how do the 5-HT and NO signaling pathways change with postnatal maturation of the ENS? Our goal is to identify the mechanisms controlling release and clearance of 5-HT and NO in the gut wall. We will conduct these studies in vitro in the myenteric and submucosal plexuses of the small intestine (ileum and duodenum) and colon of guinea pigs and a new SERT-KO rat animal model. We also propose to expand the scope of the studies to include dopamine (DA) and norepinephrine (NE) released in the myenteric plexus. These studies, which have significant relevance for pediatric health, will be performed as a function of test animal (guinea pig) age in order to learn about the postnatal ENS development. A better understanding of neural signaling pathways in GI health and disease can be gained through measurements of local neurotransmitter concentrations in the gut wall with high spatial and temporal resolution. PUBLIC HEALTH RELEVANCE: The research will investigate the postnatal development of neuronal signaling in the gut wall that controls muscular function. This will be accomplished through in vitro electrochemical measurements of neurotransmitter concentration changes made near the sites of release and action. These studies will provide new insights into potential pathophysiological changes responsible for pediatric GI motility disturbances that would persist into adulthood and would be responsible for the prevalence of functional GI disorders in the United States.

With this award from the Chemistry Research Instrumentation and Facilities: Multi-user (CRIF:MU) program, Professor John McCracken and colleagues Gary Blanchard, Robert Ofoli, Greg Swain and David Weliky from Michigan State University will acquire a series of components to build a rapid acquisition, picosecond fluorescence lifetime and anisotropy imaging system. The award will enhance research training and education at all levels, especially in areas of study such as (a) fluorescence lifetime and anisotropy imaging of lipid structures, (b) optical and electrochemical characterization of biomimetic nanostructured interfaces, (c) chemically modified electrodes for studies of graphene and thin carbon films, and (d) imaging of membrane perturbations induced by viral fusion peptides and proteins.

A rapid acquisition, picosecond fluorescence lifetime and anisotropy imaging system is important to the study of a broad range of structurally heterogeneous and fluid interfaces such as those in biological membranes. These experiments provide novel information on molecular motion and energy transfer, and specifically how these properties vary with the physical condition and chemical composition of the interface. This instrumentation will support not only research activities but also research training to graduate and undergraduate students at Michigan State University and nearby institutions such as Saginaw Valley State University. The instrument will also support international interactions with the University of Warsaw, University of Bath and Shaanxi Normal University as well as activities with local high school students.

This National Science Foundation award from the Division of Chemistry (CHE) supports a Research Experience for Undergraduate (REU) site led by Professors Greg M. Swain and Robert L. LaDuca both at Michigan State University. In this project, students are learning how sustainable practices impact all fields of chemistry and how these practices cut across different disciplines of science and engineering. The research experience will provide them with the skills needed to carry out chemical research or chemical processes in an environmentally-conscientious manner. The overall objectives of the project are therefore, (i) to involve undergraduate students in graduate-level research in sustainable chemistry, (ii) to provide a positive mentoring experience for undergraduates, (iii) to better prepare undergraduate students for graduate school, (iv) to motivate undergraduate students to consider pursuing an academic career, and (v) to recruit undergraduate students for graduate school at MSU. Student interns will also participate in outreach activities that will provide high school and middle school students with educational benefits and the interns with valuable experience in communicating scientific information and mentoring. The impact will be even broader when interns communicate their positive experience with others at their own institutions. The activities will teach the student interns, who will be part of the next generation workforce, how chemical research is conducted in a sustainable and responsible manner.

Participating student interns will receive 10 weeks of hands-on, interdisciplinary research experience in sustainable chemistry and chemical processes. Student interns will be engaged in research involving green synthesis, water purification and quality monitoring, renewable energy-related materials, and advanced imaging and spectroscopy. Students will also benefit from weekly journal clubs, mentoring faculty research presentations and networking dinners, and from participation in teaching modules on research ethics, statistics, laboratory and chemical safety, strategies for applying to graduate school, and professional development. All of the program activities are designed to sharpen the student?s critical and scientific thinking skills, provide them with experience in all aspects of research from experimental design through performance and analysis, and help to make them knowledgeable about sustainable chemistry and chemical processes.

Diamond's electronic properties are superior compared to currently used wide bandgap semiconductor materials. For electronic applications, diamond's high electron and hole mobility values enable high speed and high current operation, its low dielectric constant contributes to high frequency operation, its wide bandgap supports a high breakdown electric field and its high thermal conductivity supports high current operation. Diamond-based power and high frequency electronics will operate at power regimes not allowed by current semiconductor electronic devices. The impact is that the exceptional semiconductor properties of diamond will enable a new and more energy efficient class of higher-power, higher-voltage, and higher temperature electronic devices and will transform applications in transportation, manufacturing and energy sectors. To realize the potential of diamond for electronic diodes and transistors it is crucial that the electric field breakdown strength be large and that desired p-type and n-type doping profiles be achieved. The formation of doping profiles with desired variation in both the lateral and vertical directions are key to forming semiconductor junctions and controlling the electric field and breakdown voltages in diode and transistor devices. The goal of this project is to advance the scientific and engineering knowledge needed to form desired doping profiles for diamond electronic devices and to reduce the defects in diamond such that the full high voltage potential of diamond devices is achieved. An additional goal is to train graduate students and summer undergraduate student interns in diamond technology.

The formation of doping profiles in diamond material with desired variation in both the lateral and vertical directions are key to forming semiconductor junctions and controlling the electric field and breakdown voltages in diamond diode and transistor devices. The first objective of this project is develop the processes, know-how and understanding of forming controlled doping profiles in diamond for electronics by using ion implantation coupled with annealing. Diamond annealing will be studied at (1) high pressure and high temperature conditions and (2) metastable conditions of low pressure and high temperature with the surface of the diamond covered with hydrogen to prevent/slow the conversion of diamond to graphite. The second objective of this project is to develop processes, know-how and understanding to reduce point and dislocation defects in the diamond yielding electronic devices with higher breakdown voltages and lower leakage currents. The third objective is to develop the computation tools and diamond material properties understanding to predict doping profiles, to predict annealing process results for dopant activation, and to predict diamond electronic device characteristics.