Resume

• 2010

  Member

  American Chemical Society

  Member

  Society for Neuroscience

  Member

  ACS Division of Analytical Chemistry

  English

  Research Fellowship

  Awarded for outstanding research and was used to subsidize cost of research

  BASF Corporation

  Innovative Graduate Research Award

  Awarded for the most innovative research at departmental poster session

  BASF Corporation

• 2009

  Member

  Society of Electroanalytical Chemistry

• 2008

  Doctor of Philosophy (Ph.D.)

  Dissertation: \"Advancing Microelectrode Technology for Neuroscience Applications\"\n\nAdvisor: Leslie A. Sombers

  Ph.D.

  Assistant Professor

  Analytical Chemistry

  North Carolina State University

• 2006

  Bachelor of Science (BS)

  Chemistry

  Lenoir-Rhyne College

  Cum Laude

  Advanced Inorganic Chemistry

  Neurobiology

  Mass Spectrometry

  Advanced Analytical Chemistry I & II

• 2004

  Tenth and Eleventh Annual Poster Session Winner

  March 2009 and 2010\n\n2 consecutive awards for outstanding research in the area of Analytical Chemistry

  NCSU Department of Chemistry

  10 Additional Undergraduate Awards

  May 2005 to May 2007\n\nScholarships and awards for academic achievements in mathematics and chemistry

  Transfer Credits

  Chemistry

  Catawba Valley Community College

• Designed and organized chemical demonstrations to inform eighth grade students at an underprivileged school about the field of chemistry and promote interest in the natural sciences. Additionally

  the students were enlightened on the benefits of higher education.

  East Lee Middle School

  Lee County Schools

  Sanford

  NC

  Research Poster Judge

  Critically reviewed research posters presented by undergraduates in the field of analytical and bioanalytical chemistry

  Southeast Regional Meeting of the ACS (SERMACS)

  Raleigh

  NC

  Science Exhibit Leader

  Designed and organized an exhibit entitled \"Investigating the Brain with Electrochemistry

  \" that informed and educated the general public on complex research topics by demonstrating the fundamentals of electrochemistry

  neuroscience

  and microfabrication. Exhibits were tailored to entertain all age ranges.

  ACS National Chemistry Week at the North Carolina Museum of Natural Sciences

  Analytical Chemistry

  Plasma Etching

  IR spectroscopy

  Electrochemistry

  Chemical Vapor Deposition

  AutoCAD

  HPLC

  Neuroscience

  TurboCAD

  Atomic Absorption Spectroscopy

  Raman Spectroscopy

  Electron Spin Resonance Spectroscopy

  CAD/CAM

  Microsoft Office

  Voltammetry

  Gas Chromatography

  Matlab

  Atomic Force Microscopy

  NI LabVIEW

  UV/Vis Spectroscopy

  Voltammetric Detection of Hydrogen Peroxide at Carbon Fiber Microelectrodes

  Leslie Sombers

  Hanna Oara

  Kelsey Whitehouse

  Audrey Sanford

  Hydrogen peroxide is a reactive oxygen species that is implicated in a number of neurological disease states and that serves a critical role in normal cell function. It is commonly exploited as a reporter molecule enabling the electrochemical detection of nonelectroactive molecules at electrodes modified with substrate-specific oxidative enzymes. We present the first voltammetric characterization of rapid hydrogen peroxide fluctuations at an uncoated carbon fiber microelectrode

  demonstrating unprecedented chemical and spatial resolution. The carbon surface was electrochemically conditioned on the anodic scan and the irreversible oxidation of peroxide was detected on the cathodic scan. The oxidation potential was dependent on scan rate

  occurring at +1.2 V versus Ag/AgCl at a scan rate of 400 V·s−1. The relationship between peak oxidation current and concentration was linear across the physiological range tested

  with deviation from linearity above 2 mM and a detection limit of 2 μM. Peroxide was distinguished from multiple interferents

  both in vitro and in brain slices. The enzymatic degradation of peroxide was monitored

  as was peroxide evolution in response to glucose at a glucose oxidase modified carbon fiber electrode. This novel approach provides the requisite sensitivity

  selectivity

  spatial and temporal resolution to study dynamic peroxide fluctuations in discrete biological locations.

  Voltammetric Detection of Hydrogen Peroxide at Carbon Fiber Microelectrodes

  Leslie Sombers

  J. Vincent Toups

  Technological advances have allowed background-subtracted fast-scan cyclic voltammetry to emerge as a powerful tool for monitoring molecular fluctuations in living brain tissue; however

  there has been little progress to date in advancing electrode calibration procedures. Variability in the performance of these handmade electrodes renders calibration necessary for accurate quantification; however

  experimental protocol makes standard post-calibration difficult

  or in some cases impossible. We have developed a model that utilizes information contained in the background charging current to predict electrode sensitivity to dopamine

  ascorbic acid

  hydrogen peroxide

  and pH shifts at any point in an electrochemical experiment. Analysis determined a high correlation between predicted sensitivity and values obtained using the traditional post-calibration method

  across all analytes. To validate this approach in vivo

  calibration factors obtained with this model at electrodes in brain tissue were compared to values obtained at these electrodes using a traditional ex vivo calibration. Both demonstrated equal powers of predictability for dopamine concentrations. This advance enables in situ electrode calibration

  allowing researchers to track changes in electrode sensitivity over time and eliminating the need to generalize calibration factors between electrodes or across multiple days in an experiment.

  An In Situ Electrode Calibration Strategy for Voltammetric Measurements In Vivo

  Leslie Sombers

  Methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK) are small endogenous opioid peptides that have been implicated in a wide variety of complex physiological functions including nociception

  reward processing

  and motivation. However

  our understanding of the role that these molecules play in modulating specific brain circuits remains limited

  largely due to challenges in determining where

  when

  and how specific neuropeptides are released in tissue. Background-subtracted fast-scan cyclic voltammetry coupled with carbon-fiber microelectrodes has proven to be sensitive and selective for detecting rapidly fluctuating neurochemicals in vivo. However

  many challenges exist for applying this approach to the detection of neuropeptides. We have developed and characterized a novel voltammetric waveform for the selective quantification of small tyrosine-containing peptides

  such as the ENKs

  with rapid temporal (sub-second) and precise spatial (10s of microns) resolution. We have established that the main contributor to the electrochemical signal inherent to M-ENK is tyrosine

  and that conventional waveforms provide poor peak resolution and lead to fouling of the electrode surface. By employing two distinct scan rates in each anodic sweep of this analyte-specific waveform

  we have selectively distinguished M-ENK from common endogenous interferents

  such as ascorbic acid

  pH shifts

  and even L-ENK. Finally

  we have used this approach to simultaneously quantify catecholamine and M-ENK fluctuations in live tissue. This work provides a foundation for real-time measurements of endogenous ENK fluctuations in biological locations

  and the underlying concept of using multiple scan rates is adaptable to the voltammetric detection of other tyrosine-containing neuropeptides.

  Multiple Scan Rate Voltammetry for Selective Quantification of Real-Time Enkephalin Dynamics

  Leslie Sombers

  Recent advances in science and technology have permitted the development of wireless systems that can make biochemical measurements within functioning tissue in behaving animals. However

  data transfer requirements and power limitations have significantly limited the applicability of these systems. In an effort to create protocols that will reduce the density of the data to be transferred and the power consumption of wireless systems

  this study evaluates reducing the sampling rate of a proven in vivo measurement technology

  fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes. Existing FSCV protocols to measure biochemical signaling in the brain were created without consideration for data density or power consumption. In this work

  the sampling rate of the FSCV protocol for detecting the neurotransmitter dopamine in functioning brain tissue was reduced from 10 Hz to 1 Hz. In vitro experiments showed that the 1 Hz protocol did not negatively affect sensor responsivity or selectivity. The reduced sampling rate was verified in vivo by directly monitoring dopamine fluctuations in intact brain tissue. The 1 Hz sampling rate reduces the quantity of data generated by an order of magnitude compared to the existing protocol

  and with duty cycling is expected to decrease power consumption by a similar value in wireless systems.

  Reducing Sample Rate of In Vivo Biochemical Measurements using Fast-Scan Cyclic Voltammetry

  Leslie Sombers

  Rapid changes in extracellular dopamine concentrations in freely moving or anesthetized rats can be detected using fast-scan cyclic voltammetry (FSCV). Background-subtracted FSCV is a real-time electrochemical technique that can monitor neurochemical transmission in the brain on a subsecond timescale

  while providing chemical information on the analyte. Also

  this voltammetric approach allows for the investigation of the kinetics of release and uptake of molecules in the brain. This chapter describes

  completely

  how to make these measurements and the properties of FSCV that make it uniquely suitable for performing chemical measurements of dopaminergic neurotransmission in vivo.

  Real-Time Chemical Measurements of Dopamine Release in the Brain

  Leslie Sombers

  Katherine McCaffrey

  J. Vincent Toups

  Amanda Corder

  Neurotransmission occurs on a millisecond timescale

  but conventional methods for monitoring non-electroactive neurochemicals are limited by slow sampling rates. Despite a significant global market

  a sensor capable of measuring the dynamics of rapidly fluctuating

  non-electroactive molecules at a single recording site with high sensitivity

  electrochemical selectivity

  and a subsecond response time is still lacking. To address this need

  we have enabled the real-time detection of dynamic glucose fluctuations in live brain tissue using background-subtracted

  fast-scan cyclic voltammetry. The novel microbiosensor consists of a simple carbon fiber surface modified with an electrodeposited chitosan hydrogel encapsulating glucose oxidase. The selectivity afforded by voltammetry enables quantitative and qualitative measurements of enzymatically-generated H2O2 without the need for additional strategies to eliminate interferents. The microbiosensors possess a sensitivity and limit of detection for glucose of 19.4 ± 0.2 nA mM-1 and 13.9 ± 0.7 μM

  respectively. They are stable

  even under deviations from physiological normoxic conditions

  and show minimal interference from endogenous electroactive substances. Using this approach

  we have quantitatively and selectively monitored pharmacologically-evoked glucose fluctuations with unprecedented chemical and spatial resolution. Furthermore

  this novel biosensing strategy is widely applicable to the immobilization of any H2O2 producing enzyme

  enabling rapid monitoring of many non-electroactive enzyme substrates.

  Enzyme-Modified Carbon-Fiber Microelectrode for the Quantification of Dynamic Fluctuations of Non-Electroactive Analytes Using Fast-Scan Cyclic Voltammetry

  Leslie Sombers

  The in vivo use of carbon-fiber microelectrodes for neurochemical investigation has proven to be selective and sensitive when coupled with background-subtracted fast-scan cyclic voltammetry (FSCV). Various electrochemical pretreatments have been established to enhance the sensitivity of these sensors; however

  the fundamental chemical mechanisms underlying these enhancement strategies remain poorly understood. We have investigated an electrochemical pretreatment in which an extended triangular waveform from −0.5 to 1.8 V is applied to the electrode prior to the voltammetric detection of dopamine using a more standard waveform ranging from −0.4 to 1.3 V. This pretreatment enhances the electron-transfer kinetics and significantly improves sensitivity. To gain insight into the chemical mechanism

  the electrodes were studied using common analytical techniques. Contact atomic force microscopy (AFM) was used to demonstrate that the surface roughness was not altered on the nanoscale by electrochemical pretreatment. Raman spectroscopy was utilized to investigate oxide functionalities on the carbon surface and confirmed that carbonyl and hydroxyl functional groups were increased by electrochemical conditioning. Spectra collected after the selective chemical modification of these groups implicate the hydroxyl functionality

  rather than the carbonyl

  as the major contributor to the enhanced electrochemical signal. Finally

  we have demonstrated that this electrochemical pretreatment can be used to create carbon microdisc electrodes with sensitivities comparable to those associated with larger

  conventionally treated cylindrical carbon fiber microelectrodes.

  Specific Oxygen-Containing Functional Groups on the Carbon Surface Underlie an Enhanced Sensitivity to Dopamine at Electrochemically Pretreated Carbon Fiber Microelectrodes

  Leslie Sombers

  Hydrogen peroxide (H2O2) is a critically important signaling molecule. Endogenous H2O2 mediates diverse physiological processes both intra- and intercellularly; and enzymatically generated H2O2 is a widely used reporter molecule at biosensors that rely on enzymes to detect non-electroactive species. However

  the development and application of electroanalytical methods for the direct detection of this molecule has been challenging because the electron transfer kinetics for the irreversible oxidation of H2O2 are slow. We comparatively characterize the electrochemical oxidation of H2O2 on bare and Nafion®-coated platinum and carbon-fiber microdisc electrodes using fast-scan cyclic voltammetry (FSCV). Using a waveform ranging from +0.2 to +1.3 V at 400 V s−1

  the electrocatalytic properties of the platinum surface were not readily apparent

  and the carbon-fiber microelectrode demonstrated greater sensitivity and selectivity toward H2O2. Nafion®-coating further enhanced detection on carbon electrodes. These results confirm that platinum electrodes

  with or without Nafion®

  will not work acceptably with this approach

  and confirm the value of carbon-fiber microelectrodes relative to more traditionally used platinum electrodes in the direct detection of rapid H2O2 fluctuations using FSCV.

  Comparison of Electrode Materials for the Detection of Rapid Hydrogen Peroxide Fluctuations Using Fast Scan Cyclic Voltammetry

  John Bargar

  Leslie Sombers

  Andrzej Jarzecki

  Although siderophores are generally viewed as biological iron uptake agents

  recent evidence has shown that they may play significant roles in the biogeochemical cycling and biological uptake of other metals. One such siderophore that is produced by A. vinelandii is the triscatecholate protochelin. In this study

  we probe the solution chemistry of protochelin and its complexes with environmentally relevant trace metals to better understand its effect on metal uptake and cycling. Protochelin exhibits low solubility below pH 7.5 and degrades gradually in solution. Electrochemical measurements of protochelin and metal–protochelin complexes reveal a ligand half-wave potential of 200 mV. The Fe(III)Proto3− complex exhibits a salicylate shift in coordination mode at circumneutral to acidic pH. Coordination of Mn(II) by protochelin above pH 8.0 promotes gradual air oxidation of the metal center to Mn(III)

  which accelerates at higher pH values. The Mn(III)Proto3− complex was found to have a stability constant of log β110 = 41.6. Structural parameters derived from spectroscopic measurements and quantum mechanical calculations provide insights into the stability of the Fe(III)Proto3−

  Fe(III)H3Proto

  and Mn(III)Proto3− complexes. Complexation of Co(II) by protochelin results in redox cycling of Co

  accompanied by accelerated degradation of the ligand at all solution pH values. These results are discussed in terms of the role of catecholate siderophores in environmental trace metal cycling and intracellular metal release.

  Trace Metal Complexation by the Triscatecholate Siderophore Protochelin: Structure and Stability

  James

  Roberts

  Lenoir-Rhyne University

  Catawba Valley Community College

  North Carolina State University

  Clark Tire

  CNC Technology

  Inc.

  • Advanced the current technology and knowledge of carbon-based electrochemical sensors for neuroscience applications\n• Investigated the role of surface chemistry on electron transfer to develop advanced microsensors\n• Novel real-time sensors were constructed and used to answer neuroscience questions related to drug addition

  behavior and neurodegenerative disease states\n• Utilized advanced statistical methods of data analysis to build predictive models\n• Developed software for obtaining amperometric measurements at microelectrodes with an additional program for advanced data analysis of recorded signal for peak fitting and concentration quantification\n• Developed software for HPLC system control and recording chromatograms

  with an additional program for analysis of chromatograms to determine separation parameters and analyte quantification \n• Assisted in the establishment of a new research group

  including instrument construction and software development\n• Trained and mentored new research group members on lab practices and experimental protocol\n• Developed laboratory safety protocols and established compliance with IACUC and DEA\n• Sucessfully mentored 7 undergraduate research students from the departments of Biomedical Enginnering

  Chemical Engineering

  Biochemistry

  Physics

  and Chemistry at NCSU and couple from the NSF funded REU Program\n• Published four peer reviewed articles and one chapter in a reference book\n• Performed 15 presentations at local and international scientific conferences

  including two invited talks at the BASF Corporation and the Gordon Research Seminar for Electrochemistry\n• Actively sought out collaborations with other departments

  including the departments of soil science and biomedical engineering

  Research Assistant

  Raleigh-Durham

  North Carolina Area

  North Carolina State University

  • Supervised and instructed general and quantitative chemistry laboratory sessions\n• Emphasized keeping complete and accurate scientific notes

  while performing precise experimentation\n• Mentored and tutored students who sought assistance for undergraduate chemistry concepts\n• Proctored and graded exams for general and quantitative chemistry courses\n• Assisted and instructed quantitative analysis course

  with focus on group discussion

  Teaching Assistant

  Raleigh-Durham

  North Carolina Area

  North Carolina State University

  • Improved design of CNC three-axis cutting machine

  assisted in development of operations manual

  and sold equipment\n• Designed parts with CAD software and utilized CAM to machine templates for woodworking industry \n• Administered off-site training for new clients and participated in company related trade shows and exhibits \n• Represented the organization in negotiations relating to vendors and successfully developed and maintained strong client relationships \n• Assisted design and construction of new commercial office building

  Vice President

  Hickory/Lenoir

  North Carolina Area

  CNC Technology

  Inc.

  Newton

  NC

  • Sustained vehicle function by providing preventative maintenance

  parts replacement and repair

  and suspension alignment\n• Executed proper recycling and disposal of vehicular waste\n• Maintained parts inventory

  Automotive Technician

  Clark Tire

  • Developed and instructed undergraduate chemistry laboratories

  while developing waste disposal protocols\n• Designed and performed chemical demonstrations for local area elementary schools to promote chemistry and the natural sciences\n• Organized and relocated entire chemistry department to new location

  Lab Technician

  Hickory/Lenoir

  North Carolina Area

  Catawba Valley Community College

  • Assisted in reestablishing an analytical instrumentation facility

  by repairing and calibrating instruments

  such as UV/VIS

  GC

  HPLC

  AA

  IR

  and FTIR\n• Newly rebuilt instruments were used to monitor leaching of mercury from dental filaments to establish toxicity\n• Waste water from local clothing dye plants were analyzed for potential fresh water contamination.

  Research Assistant

  Raleigh-Durham

  North Carolina Area

  Lenoir-Rhyne University