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REU Past Students

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  • Nastasia Allred - Chemical Engineering, Tennessee Technological University

    Nastasia AllredEducational Institution: Tennessee Technological University
    List of Mentors: Dr. Rizia Bardhan & Will Erwin
    Program: NSF TN-SCORE
    Research Project: Plasmon Enhanced Tandem Dye-Sensitized Solar Cells
    Poster: NSF REU Nastasia Allred Poster.pdf
    Research Abstract:  
    Our current energy economy faces environmental concerns, as well as concerns of lacking availability of fossil fuels. In 2013, roughly 80% of energy consumption in the U.S. was achieved through fossil fuels, while only 0.3% of the energy consumed was produced by solar resources.1 Dye sensitized solar cells (DSSCs) show promise because they are less expensive and made of more easily recyclable, less hazardous materials than silicon photovoltaics (Si-PVs); however, one of the major problems with DSSCs is that they do not reach high enough efficiencies to compare to Si-PVs. In this work, two approaches to enhancing DSSC efficiency are complementary to each other; i) making a tandem DSSC with two types of sensitizing dye and ii) by incorporating tunable plasmonic particles into the devices. Each DSSC has a mesoporous TiO2 layer onto which an organic dye is adsorbed. In this study, the tandem DSSCs consist of cells using N719 (red) and N749 (black) dyes. The cells are arranged such that the light source strikes the cell containing the N719 dye first. This is such that the light not absorbed by the red dye now has the chance to be absorbed by the black dye, thus increasing the cell’s light harvesting capabilities. Plasmon enhancement is accomplished by incorporating broad resonance Au@Ag bimetallic nanoparticles into the mesoporous semiconductor layer, thereby increasing the scattered light and overall photocurrent of the device.

  • Efrem Beraki - Eletrical Engineering, Georgia Institute of Technology

    Efrem BerakiEducational Institution: Georgia Institute of Technology
    List of Mentors: Dr. Sharon Weiss & Yiliang Zhao
    Program: NSF REU
    Research Project: Kinetic Analysis of Porous Silicon Biosensors
    Poster: NSF REU Efrem Beraki.pdf
    Research Abstract:   
    This research investigates the molecular binding kinetics and detection sensitivity differences between mesoporous optical biosensors of closed-end porous films and open-ended, flow-through membranes. A porous silicon material system is employed due to its many advantages for biosensing applications, including a large active sensor surface area and tunable porosity and pore size, as well as it amenability to standard silicon lithographic processing techniques. Size-selective sensing and relatively high detection sensitivities have already been demonstrated in closed-end porous silicon biosensors. Here, we describe the fabrication process to realize porous silicon membrane sensors, which is based on photolithographic patterning and reactive ion etching of a silicon wafer followed by selective electrochemical etching to form the porous silicon regions. We then seek to characterize and compare the performance of closed-end and membrane style porous silicon sensors. The binding kinetics of the porous silicon sensors were evaluated by flowing different molecules through a flow-cell attached to each sensor and monitoring the change in the Fabry-Perot interference pattern as a function of time and flow rate.  A comparison of the detection sensitivity of closed-end and membrane sensors can be made by evaluating the rate of change of the interference pattern, as well as the saturation time for which all available binding sites are occupied. This work is expected to lead to the realization of lab-on-chip compatible porous silicon membrane sensor arrays capable of fast response, high sensitivity, and simultaneous detection of multiple analytes.

  • Matthew Billingsley - Chemical Engineering, Rose-Hulman Institute of Technology

    Matthew BillingslyEducational Institution: Rose-Hulman Institute of Technology
    List of Mentors: Dr. Peter Cummings & Andrew Summers
    Program: NSF REU
    Research Project: Investigating Wear Mechanisms of Alkylsilane Monolayers through Molecular Dynamics Simulation
    Poster: NSF REU Matthew Billingsly Poster.pdf
    Research Abstract:  
    Alkylsilane monolayers have been proposed as lubricants for microelectromechanical and nanoelectromechanical systems (MEMS and NEMS), having been shown to reduce friction and wear and protect surfaces from oxidation. However, these monolayers are known to degrade over time, whereby chains break off of the surface. In this study, we utilize molecular dynamics (MD) simulations to study the frictional properties of hexylsilane monolayers attached to silica substrates, focusing on the effects of monolayer wear. Wear is introduced in a controlled manner by randomly detaching a specified fraction of chains from each substrate. Frictional properties and free-chain mobility (i.e., broken chains) are investigated as function of induced monolayer wear. For crystalline silica substrates, we find that normal load has a negligible effect on the mobility of free chains; mobility is instead correlated with the fraction of broken chains. Amorphous systems reveal a higher degree of free-chain mobility compared to crystalline systems with identical levels of induced wear, which we correlate to the increased surface roughness of the amorphous substrates. Furthermore, systems with amorphous substrates have higher coefficients of friction (COF), suggesting an inclination toward increased wear at all conditions.

    • Co-author journal publication
      A.Z. Summers, C.R. Iacovella, M.R. Billingsley, S.T. Arnold, P.T. Cummings, C. McCabe, “Influence of Surface Morphology on the Shear-Induced Wear of Alkylsilane Monolayers: Molecular Dynamics Study,” Langmuir, 32, 10 2348-2359 (2015).
    • Conference Presentations
      -A.Z. Summers, M.R. Billingsley, C.R. Iacovella, P.T. Cummings, C. McCabe, “Investigating the Shear-Induced Wear of Alkylsilane Monolayers through Molecular Dynamics Simulation,” SERMACS 2014, Sheraton Music City Hotel, Nashville, TN, October, 2014.
      -A.Z. Summers, C.R. Iacovella, M.R. Billingsley, S.T. Arnold, P.T. Cummings, C. McCabe, “Investigating the Shear-Induced Wear of Alkylsilane Monolayers through Molecular Dynamics Simulation,” Poster presented at the 15th Annual Nanoscience and Nanotechnology Forum, Vanderbilt University, Nashville, TN, November, 2014.
  • Elijah Brown - Electrical Engineering, Austin Peay State University

    Educational Institution: Austin Peay State University
    List of Mentors: Dr. Kirill Bolotin & Alex Wynn
    Program: NSF TN-SCORE
    Research Project: Nano-capacitors: Investigating Electrical Fields between Different 2-Dimensional Materials

    Research Abstract:
    Graphene is one of the most diverse and exciting materials currently being investigated by researchers. Graphene is known as a 2-Dimensional material, it is called this because electrons are only moving through the material in two dimensions. 2-Dimensional materials are observed as a one to three atom thick substance typically called a mono-layer. There are many other materials available to researchers that can produce mono-layers besides Graphene, such as molybdenum disulfide, tungsten disulfide, and niobium diselenide among others. Artificially creating new materials by stacking mono-layered substances such as these is becoming commonplace. When Graphene is stacked with some materials, such as the forementioned ones, researchers have witnessed the effects of sending an electric current through them, an electrical field begins to form in the gap between them. Generally researchers have taken for granted that the electrical field building up between these layers is due to the mechanics of charge transfer. However, there have been several other plausible speculations that could possibly explain this event; such as the suggestion of a characteristic called FRET (florescence resonance energy transfer). To allow for the testing of this hypothesis measurable devices will have to be fabricated. Capacitors are a commonly used component of analog electronic circuits. Capacitors are made using two electrically conductive plates separated by a small gap, as voltage is pushed through the plates over time an electrical field will build up between them. Since the stacked mono-layers behave like capacitors, it is possible to put them through the same physics tests as capacitors, and should prove or disprove that charge transfer is responsible for the phenomenon.

  • Kathryn Bumila - Chemical Engineering, Worcester Polytechnic Institute

    Katie BumilaEducational Institution: Worcester Polytechnic Institute
    List of Mentors: Dr. John Wilson & Max Jacobson
    Program: NSF REU
    Research Project: Developing New Amphiphilic Diblock Co-Polymers for Delivery of Cytosolicly Active Immunostimulants
    Poster: NSF REU Katie Bumila Poster.pdf
    Research Abstract:   
    A major barrier to synthetic vaccine development is inefficient delivery of immunostimulatory adjuvant molecules to the cytosol of antigen presenting cells. In order to overcome this challenge, we are developing pH-responsive diblock copolymers that can be utilized as nano-carriers for these adjuvants. A successful nano-carrier must form stable micelles under physiological conditions as well as have endosomal escape capabilities to promote delivery to cytosolic pathogen recognition receptors. A library of amphiphilic diblock copolymers was synthesized in order to compare the effect of the hydrophobic group on nanoparticle properties and drug delivery qualities. The hydrophobic groups compared were butyl methacrylate (BMA) and hexyl methacrylate (HMA), as components of [poly(ethylene glycol)]-block-[2-dimethylaminoethyl methacrylate-co-BMA] and [poly(ethylene glycol)]-block-2-[dimethylaminoethyl methacrylate-co-HMA] polymers, respectively. The second blocks were designed to have compositions of 20%, 30%, and 40% BMA or HMA. To determine the polymer’s ability to form micelles, dynamic light scattering was performed over a range of pH 5.8-7.4. This experiment showed that the polymer containing 30% HMA, 40% HMA, and 40% BMA successfully formed 13-18 nm diameter micelles at pH 7.4 and transitioned to unimeric polymer chains with decreasing pH. Next, a hemolysis assay was performed across the same pH range. The results showed that 40% BMA displayed the greatest membrane disruptive characteristics at pH 5.8 and pH 6.2, however, at most pH values 20% HMA and 30% HMA were significantly more hemolytic than their BMA counterpart. Lastly, a cell viability assay was carried out to determine if any of the polymers were harmful to cells. The results showed an average of 80% or higher cell viability at concentrations ranging from 0.01-10 μg/ml, with the 40% HMA polymer appearing the least cytotoxic. In conclusion, initial results suggest that PEG-bl-DMAEMA-co-BMA and PEG-bl-DMAEMA-co-HMA are promising cytosolically active nano-carriers. However, the novel HMA containing polymers could prove to be even more efficacious for this application because of the increased membrane destabilizing activity and particle stability associated with longer hydrophobic chains. 

    • Conference Presentation
      K. Bumila, M. Jacobson, S. Sevimli, and J. T. Wilson, “Developing New Amphiphilic Diblock Copolymers for Delivery of Cytosolically Active Imunostimulants” 2014 AIChE Annual Meeting, Atlanta, GA, November, 2014.
  • Ashton Davis - Mathematics, LyMoyne-Owen College

    Ashton DavisEducational Institution: LeMoyne-Owen College
    List of Mentors: Dr. Cary Pint & Andrew Westover
    Program: NSF TN-SCORE
    Research Project: Remote Charging for Light Integrated Energy Storage Systems via Lasers
    Poster: NSF REU Ashton Davis Poster.pdf
    Research Abstract:
    As we move into the future, finding new methods of obtaining energy has become a priority of research. Solar Panels have proven to be an efficient means of converting energy from sunlight to electricity and super capacitors have proven to be one of the most efficient energy storage systems for our future. This project is focused on combining both of these technologies in order to have an energy storage device that can obtain a charge remotely with a supercapacitor integrated on the back of the solar cell. One potential method of remotely charging these integrated energy storage devices is through the use of LASERS. LASERS give a form of transmissible energy that can be used at any time. One of the great advantages of lasers is their high wall plug efficiency allowing for efficient energy in addition to its remote capabilities Not only do lasers have great energy efficiencies, but they can be used distances farther than kilometers away and being paired with a supercapacitor, the device can be charged rapidly. This technology will allow for high efficiency remote charging of a variety of energy storage devices ranging from UAVs, household electronics, robotics etc. The research and findings of this project are promising to greatly improving everyday energy usage.

  • Elizabeth Delesky - Materials Science & Engineering, University of Florida

    Elizabeth DeleskyEducational Institution: University of Florida
    List of Mentors: Dr. Eva Harth & Kelly Gilmore
    Program: NSF REU
    Research Project: Biodegradable Polyester Hydrogels for Sustained Drug Delivery
    Poster: NSF REU Elizabeth Delesky Poster.pdf
    Research Abstract:   
    Hydrogels have recently emerged as promising materials for drug delivery applications for both synthetic and biological cargo. However, many of the current systems are limited due to the non-degradable nature of the gels. Polyester hydrogels synthesized using oxime click chemistry are an attractive option as drug delivery vehicles due to their biocompatibility and degradability. In this study, we have utilized a copolymer comprised of δ-valerolactone and 2-oxepane-1,5-dione as well as an amino-oxy functionalized polyglycidol to synthesize these gels. Hydrogels were synthesized using three different ratios of the two reactants in order to tune the swelling and degradation profiles. The swelling profiles revealed that maximum swelling occurs within the first few hours.  Swelling was observed after degradation began as the ester linkages were hydrolyzed, which allowed water to infiltrate the gels and increase the mass as the gels degraded.  Both the swelling and degradation profiles revealed that increasing the amount of cross-linker prevents rapid degradation of the hydrogel. The free drug release rate of these hydrogels was also studied, using brimonidine as a model drug, as well as release rates incorporating the drug into an additional complex, such as β-cyclodextrin. β-cyclodextrin can be homogeneously dispersed through the hydrogel to provide an ancillary boundary for the drug and prolong the release.

    • Elizabeth was awarded a NSF Graduate Research Fellowship
  • Amadou Fall - Chemistry, Tennessee State University

    Amadou FallEducational Institution: Tennessee State University
    List of Mentors: Dr. Janet Macdonald  & Andrew LaCroix
    Program: NSF TN-SCORE
    Research Project: Investigating the electronic coupling of quantum dot-ligand interaction
    Poster: NSF REU Amadou Fall Poster.pdf
    Research Abstract:  
    Photocatalysis and the use of solar cells are having an ever increasing importance in our search for renewable energies. Quantum dots, which are nanoscale particles of semiconductors (in our case Cadmium selenide), are a driving force in this endeavor. Reasons for this include that they are inexpensive to make, have a strong molar absorptivity, and are easily tunable to the desired size.  The synthetic methods used to obtain monodisperse samples of different sizes require charge transfer inhibiting organic ligands. The Macdonald group has discovered a crystal-bound ligand system that can increase nanoparticle stability and charge transfer efficiency. We optimized the synthesis of CdSe@ZnS core-shell nanoparticles to increase the quantum yield. Hydrolysis of the ester group in dodecyl-3-mercaptopropionate-capped CdSe@ZnS core-shell nanoparticles results in a red shift in absorbance and fluorescence, which could be due to energetic overlap of the carboxylate ligand and the CdSe@ZnS core-shell nanoparticle. In this project we plan to compare the results of our seed, shelling, and hydrolysis with the Brus quantum confinement equation to determine if the observed electronic interaction is with the valence or conduction band. We can use the results of the data to design better and more efficient photocatalytic and photovoltaic devices.  

    • Co-author journal publication
      M.J. Turo, X. Shen, N.K. Brandon, S. Castillo, A.M. Fall, S.T. Pantelides, and J.E. Macdonald “Dual-Mode Crystal-Bound and X-type Passivation of Quantum Dots” Chemistry Communications, 52 (82) 12214-12217, (2016).
    • Conference Presentations
      -A. Fall, S. Castillo, N. Brandon, A. La Croix, and J. Macdonald, “Investigating the electronic coupling of quantum dot-ligand interaction” 2014 ACS Southeast Regional Meeting, Nashville, TN, October, 2014.
      -A. Fall, S. Castillo, N. Brandon, A. La Croix, and J. Macdonald, “Investigating the electronic coupling of quantum dot-ligand interaction” 2014 Annual Biomedical Research Conference for Minority Students, San Antonio, TX, November, 2014.
      -A. Fall, S. Castillo, N. Brandon, A. La Croix, and J. Macdonald, “Investigating the electronic coupling of quantum dot-ligand interaction” 249th Annual American Chemical Society National Meeting and Exposition, Denver, CO, March, 2015.
  • Nicholas Morgan - Chemical Engineering, University of Oklahoma

    Nicholas MorganEducational Institution: University of Oklahoma
    List of Mentors: Dr. Peter Pintauro & Devon Powers
    Program: NSF REU
    Research Project: Optimizing the Fabrication of Solution-Cast Membranes
    Poster: NSF REU Nicholas Morgan Poster.pdf
    Research Abstract:   
    As the current fossil fuel-based economy continues to present environmental challenges and issues of sustainability, the fuel cell shows promise to be a highly efficient source of clean energy in the near future. Integral to the operation of a fuel cell is the membrane, which separates the cathode and the anode and provides pathways for proton transport. For efficient operation, the membrane must exhibit high proton conductivity, robust mechanical strength, and low fuel crossover. The most common proton transport material used is perfluorosulfonic acid (PFSA) polymer, sold by DuPont under the name Nafion. This material exhibits high conductivities but also relatively high crossover rates for many fuel and oxidants used in fuel cells such as methanol or bromine species, leading to the degradation of catalysts at the electrodes. Additionally, Nafion’s poor mechanical strength poses a problem due to excessive swelling during each on/off cycle. To make up for these deficiencies, Nafion can be mixed with an inert reinforcing polymer such as polyvinylidene fluoride (PVdF), resulting in a favorable reduction in swelling and fuel crossover but also a loss of conductivity. In the present study, Nafion-PVdF membranes were fabricated by solvent casting, where a solution containing the two polymers is spread on a glass plate to form a film that is dried in an oven, producing a 50-100 μm-thick membrane. We investigate the effect of using N,N-dimethylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone as casting solvents and the effect of varying annealing times and temperatures on the conductivity, water uptake, and swelling properties of these blended membranes. We also vary the Nafion-to-PVdF ratio for each solvent to map the ranges over which the most successful solvent-annealing combination can be applied. Results indicate that the annealing condition that yields the highest conductivity is not solely a function of solvent but of both solvent and proportion of Nafion, with membranes containing the highest and lowest proportions of Nafion showing sensitivity to higher annealing temperatures and subsequent losses in conductivity. Phase separation is observed to consistently lead to a loss in conductivity as well. Water uptake and swelling properties appear to be constant and largely independent of solvent and annealing conditions. Future work will include testing additional combinations of solvents, annealing conditions, and Nafion proportions in order to draw further conclusions about the interactions of these parameters, as well as examining fuel crossover and tensile strength.

  • David Needell - Math & Physics, Bowdoin College

    David NeedellEducational Institution: Bowdoin College
    List of Mentors: Dr. David Cliffel & Gabriel LeBlanc
    Program: NSF REU
    Research Project: Biohybrid Solid State Solar Cells
    Poster: NSF REU David Needell Poster.pdf
    Research Abstract: 
    While traditional p-n junction photovoltaic panels continue to be the most popular solar cell currently available, the cost of processing and constructing these cells have limited their dissemination into the energy market.  For this, alternative solar cells constructed from organic and easier to obtain materials aim to be one solution to this problem.  Photosystem I (PSI) is an essential part of the photosynthetic process present in green plant cells and cyanobacteria – a protein responsible for exciting a free electron given an incident photon. PSI’s abundance in nature and nearly perfect quantum efficiency make PSI a prime candidate for use in solar cells. 

    The ultimate aim of this research is to determine if a biohybrid, solid-state solar cell – constructed from inexpensive conductive substrates – can generate electrical power.  Conductive and transparent Reduced Graphene Oxide (rGO) and Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) served as the counter and working electrode in the solid-state cell, respectively. Current-voltage analyses and photochronoamperometry tests show that both rGO and PEDOT:PSS can be successfully incorporated into a fully functional, solid-state biohybrid cell with a doped semiconducting substrate.  This information gives strong support to the construction of a working, metal free, and biohybrid solid-state solar cell with rGO, PSI, and PEDOT:PSS.  Future work includes refining the technique of constructing this metal free, flexible solar cell and improving the orientation alignment of the multilayered PSI film.  

    • Co-author journal publication
      J.C. Beam, G. LeBlanc, E.A. Gizzie, B.L. Ivanov, D.R. Needell, M.J. Shearer, G.K. Jennings, C.M. Lukehart, and D.E. Cliffel, “Construction of a Semiconductor Biological Interface for Solar Energy Conversion: p-Doped Silicon/Photosystem I/Zinc Oxide,” Langmuir, 31, 10002-10007 (2015).
  • Jason Ray Alfaro - Physics, Juanita College

    Jason Ray AlfaroEducational Institution: Juanita College
    List of Mentors: Dr. Qi Zhang & Kristina Kitko
    Program: NSF REU
    Research Project: Effects of Cholesterol Enhancement on Cell Properties in the Presence of Graphene
    Poster: NSF REU Jason Ray Alfaro Poster.pdf
    Research Abstract:   
    Graphene is a two-dimensional carbon crystal with remarkable mechanical strength and a singular electrical conductivity, a combination that has led to surging interest in its biomedical applications. However, this demands a clear understanding of graphene’s interaction with cell surface molecules and its impact on cell function. Here,  based upon the observed increase of synaptic surface cholesterol in cells directly growing on bare graphene, we propose that graphene interacts with cholesterol. This increase changes the amount, the release probability, the turnover mode and the reuse rate of synaptic vesicles, which results in a presynaptic potentiation of neurotransmission. Further spectral analysis of fluorophore interaction with graphene reveals a time-dependent fluorescence decay that is unique from that of the fluorophore, consistent with the interaction involving energy transfer. Assaying for the cholesterol concentration of culture media in the presence of graphene may provide direct insight into this interaction. These data may be further supported by an increase in the membrane resistance in the presence of graphene, although additional verification is necessary. Our findings highlight a molecular mechanism underlying graphene's effect on the lipid membrane and cell signaling, which infers caution as well as opportunity in basic research and translational implementation of graphene. 

  • Jesús Sosa-Rivera - Biotechnology, Universidad del Este

    Jesus Sosa-RiveraEducational Institution: Universidad del Este
    List of Mentors: Dr. Craig Duvall
    Program: NSF REU
    Research Project: Localized Delivery of a Chemotherapeutic from Cell-Degradable Polymeric Films
    Poster: NSF REU Jesus Sosa-Rivera Poster.pdf
    Research Abstract:  
    Cancer is the second leading cause of death worldwide. In gastric cancer, most patients are treated by tumor resection in the early progression stages. However, recurrence of cancer at the margin of resection can occur in 50% of cases.  Secondary, more systemic treatments like chemotherapy and external radiation are the current gold-standard treatments for inhibiting cancer recurrence but produce systematic totoxicities that can severely limit the long term survival of the patient. To limit these systemic toxicities, we hypothesize that prolonged, localized drug delivery at the tumor resection margins will prevent cancer cells proliferation and tumor recurrence. Here, we propose to incorporate a hydrophobic, anti-neoplasmic drug into a hydrophobic, acidically-inert, polymeric film to achieve prolonged drug release and sustained inhibition of cancer cell proliferation in the harsh environment of the stomach. These films were made with poly(thioketal) (PTK) polymers, which are both stable across a wide range of pH values and are specifically degraded by cell-produced reactive oxygen species (ROS). The PTK polymers, synthesized from biocompatible mercaptoethyl ether (MEE) monomers, were rigorously characterized and then incorporated into films by solvent casting with a non-degradable hexamethylene diisocyante trimer (HDIt). The PTK-UR films were loaded with either Nile Red (fluorescent hydrophobic model drug) or the strong anti-tumor hydrophobic drug 10-hydroxycamptothecin (HCPT), which has seen limited clinical use due to its poor aqueous solubility but has great potential as a locally delivered chemotherapeutic (Wolinsky, JB. et al 2010). In preliminary studies, Nile Red-loaded PTK-UR films demonstrate gradual, sustained levels of drug release when incubated in an ROS-producing medium, while demonstrating minimal drug release when incubated in saline. Ongoing studies are evaluating the cytotoxic activity of released HCPT and drug release under stomach-mimicking acidic conditions, while futures studies will evaluate the sustained cytotoxic effect of released HCPT both in vitro and in vivo.

    • Conference Presentation
      J.Rivera-Sosa, J.R. Martin, C. L. Duvall, “Long term delivery of a chemotherapeutic from cell degradable polymeric films” Annual Biomedical Research Conference for Minority Students (ABRCMS) San Antonio, TX, November, 2014.
      *Poster award in engineering, physics and mathematics category
  • Lucas Thal - Biochemistry, University of Tennessee, Knoxville

    Louis ThalEducational Institution: University of Tennessee, Knoxville
    List of Mentors: Dr. David Cliffel & Gabriel LeBlanc
    Program: NSF TN-SCORE
    Research Project: A New Method for Improving Solar Energy Conversion: Side Selective Modification of Photosystem I
    Poster: NSF REU Poster Louie Thal.pdf
    Research Abstract:  
    Adverse environmental impacts caused by traditional methods for harnessing energy have prompted the search for clean renewable energy. Recently, solar power has been at the forefront of researchers’ investigations for viable new, sustainable sources of energy. Solar cell devices on the market convert solar radiation to electricity at around 10-20% efficiency. They are constructed with inorganic materials (e.g. silicon, indium, and tellurium) that are resource- and cost-limiting. Alternatively, biohybrid cells produce photocurrent when integrated with the plant protein Photosystem I (PSI)—a sterically stable transmembrane redox protein found in light-dependent photosynthesis. This approach offers extremely efficient solar conversion (approaching 100% at specific wavelengths) without resource depletion. Given that the charge separation that occurs in is unidirectional with regard to PSI’s molecular orientation, the protein must be oriented on electrodes such that the P700 chlorophylls are aligned away from the electrode. Visual inspection of the crystal structure of the protein extracted from spinach (PDB ID: 2WSF), reveals that the hydrophilic areas are similar in both basic and acidic acid compositions.  This similarity allows for the protein to bind to electrodes in both upright (P700 distal from the electrode) and inverted orientations. Previous research has shown that increasing the fraction of upright oriented proteins on electrode in turn increases photocurrent produced [1]. We can accomplish this by modifying the chemical properties of the hydrophilic regions to promote surface asymmetry so that the stromal/luminal sides of the protein have different affinities for the underlying electrode. Side-selective functionalization of extracted PSI was performed by pre-extraction EDC/Sulfo-NHS coupling to glutamic and aspartic acids with thiol terminated adducts on the stromal side of the thylakoid. We have shown that the functionalization was successful by performing - UV-vis and fluorescence spectroscopic analysis. We have also developed a chromatographic purification procedure that would potentially remove the unmodified proteins from the bulk sample. Currently, we are performing electrochemical analysis on the effectiveness of the functionalized samples.  Further optimization of this method will create a new library of ligands to adjoin allowing for many new biomolecular applications.

    • Conference Presentations
      -L. Thal, E. Gizzie, G. LeBlanc, G.K. Jennings, and D. E. Cliffel, “A New Method for Improving Solar Cell Conversion: Side Selective Modification of Photosystem I” 2014 ACS Southeast Regional Meeting, Nashville, TN, October, 2014.
      -L. Thal, E. Gizzie, G. LeBlanc, G.K. Jennings, and D. E. Cliffel, “A New Method for Improving Solar Cell Conversion: Side Selective Modification of Photosystem I” 249th Annual American Chemical Society National Meeting and Exposition, Denver, CO, March, 2015.
    • Louie was awarded a Vanderbilt Chemistry-Biology Interface Training Grant
  • Holly Thomas - Mechanical Engineering, St. Ambrose University

    Holly ThomasEducational Institution: St. Ambrose University
    List of Mentors: Dr. Melissa Skala & Jason Swartz-Tucker
    Program: NSF REU
    Research Project: Metabolic Imaging of Human Breast Carcinoma Treatments
    Poster: NSF REU Holly Thomas Poster.pdf
    Research Abstract:  
    Human breast carcinoma is known to dramatically alter cellular metabolism. Rather than generating ATP through oxidative phosphorylation, cancerous cells utilize aerobic glycolysis, which requires an increase in glucose consumption. Current autofluorescence imaging techniques, particularly two-photon microscopy, are capable of detecting changes in cellular metabolism by quantifying biological markers of cellular metabolic rate. These markers include the autofluorescent metabolic co-enzymes NADH and FAD, and two-photon microscopy is used to measure their fluorescence lifetimes and relative intensities (redox ratio). These measurements reflect enzyme activity and relative rates of cellular glycolysis, respectively. However, redox ratio and lifetime analysis neglects the possible effects of glucose uptake and mild hyperthermia in breast cancer cells. To measure glucose uptake in breast cancer cells, cells were incubated with the fluorescent glucose molecule 2-NBDG and imaged at the NADH and 2-NBDG emission wavelengths using two-photon microscopy. Additionally, cells were treated with the anticancer drugs trastuzumab, paclitaxel, and XL147 to investigate their effects on 2-NBDG uptake. The findings demonstrated a significant (p<0.05) decrease in 2-NBDG fluorescence in cells treated with anticancer drugs from those that were left untreated. Furthermore, treated and untreated breast cancer cells were incubated with iron oxide-coated gold nanorods and imaged at the NADH, FAD, and nanoparticle emission wavelengths to determine whether the presence of gold nanorods altered cellular metabolism. Controlled photothermal heating of nanorods in distilled water verified that the nanorods are capable of being heated, yet two-photon imaging indicated that the nanorods were not functionalized properly for in vitro applications. Further work must be done to properly functionalize the nanorods and image them in vitro to measure variations in cellular metabolism. 2-NBDG fluorescence imaging will likely be expanded to measure glucose uptake in three-dimensional organoids with the goal of implementing these measurements to determine the most beneficial treatment for breast cancer patients on an individual basis.

  • Vincent Viola - Physics, Rhodes College

    Vincent ViolaEducational Institution: Rhodes College
    List of Mentors: Dr. Peter Pintauro & Jun Woo Park
    Program: NSF TN-SCORE
    Research Project: Solvent Effects on Single-Fiber Electrospinning and Membrane Properties
    Poster: NSF REU Vincent Viola Poster.pdf
    Research Abstract:   
    Fuel cells utilize redox chemistry to convert chemical energy of various fuels, for example hydrogen, into electrical energy.  They provide environmentally friendly alternative to conventional energy conversion devices, like internal combustion engines, that use fossil fuels. However, currently available fuel cells still require optimization to improve their performance and lifetime. The key areas of interest are more durable and cheaper catalysts and better membranes.  This study focuses on novel proton conducting membranes fabricated using single-fiber electrospinning of Nafion-PVDF (polyvinylidene fluoride) blends. Here, a solution of Nafion and PVDF mixture is electrospun onto a rotating and oscillating aluminum target forming a porous mat of thickness 120-200 μm. The mat is then annealed at elevated temperture (150-210oC) and hotpressed at 182oC and 24000lb, to close the pores and create dense, defect free proton conducting membrane. Finally, the membrane is preconditioned in boiling 1M H2SO4 and then boiling water.  The goal of this study is to understand the effect of electrospinning solvent, composition and post-processing conditions on the membrane proton conductivity, water uptake and swelling. The conductivity was measured using four-electrode Bekktech cell. Water uptake was measured gravimetrically and areal swelling was determined by comparing membrane’s dry and wet dimensions.   The most desired characteristics were obtained for membranes electrospun from 80% Nafion and 20% PVDF, pre-compacted and annealed at 150oC for 1.5 hours under vacuum. The obtained conductivity was in the range 0.066-0.070 S/cm, the gravimetric swelling was in the range 12.91-13.74% mg/mg, and the areal swelling was in the range 15.59159681-17.98638329% mm2/mm2.   Selected membranes will later be tested in hydrogen, direct methanol and hydrogen-bromine fuel cells.

  • Patrick Wellborn - Chemistry & Engineering, Washington & Lee University

    Patrick WellbornEducational Institution: Washington and Lee University
    List of Mentors: Dr. Kane Jennings & Max Robinson
    Program: NSF REU
    Research Project: Bridging the Gap: Photosystem I Initiated Polymer Growth for Solid-State Solar Cell Applications
    Poster: NSF REU Patrick Wellborn Poster.pdf
    Research Abstract:  
    Photosystem I (PSI) is a photocatalytic membrane protein contained within the thylakoid membranes of plants.  Boasting ~1 V light-induced charge-separation and near-unity quantum yield, PSI has garnered interest as a photoactive species in next generation biohybrid solar cell devices.  Order-of-magnitude improvements in generated photocurrents have been observed for PSI-integrated systems utilizing a liquid electrolyte mediator to transport photoexcited electrons from PSI to the anode.  However, practical devices of this sort introduce problems of degradation and expense. Solid-state devices eliminate the need for liquid mediation, shuttling photoexcited electrons directly using solid conductive materials, creating a more durable device.

    This study explores a PSI-initiated polymerization technique, providing a route to more efficient PSI-PSI electron transport within the active layer of solid-state devices.  Incident amino acid residues from PSI are used as initiators for Surface-Initiated Ring-Opening Metathesis Polymerization (SI-ROMP). A fluoro-alkyl substituted norbornene monomer—characterized by fast growth kinetics and a unique spectroscopic signature—was chosen for preliminary studies. Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PMIRAS) and three-electrode photochronoamperometry were used to establish retained secondary structure and photoactivity during each step of the polymerization process.

    Two methods of polymer attachment were utilized on PSI monolayers and multilayers: lysine-based attachment using amine termini and glutamic and aspartic acid-based attachment using carboxylic acid termini. Both methods proved successful for polymer growth, achieving ~10nm of growth on monolayers and hundreds of nanometers of growth on PSI multilayers. Results of polymer growth were characterized using goniometry, ellipsometry, profilometry, and IR. With no previous literature indicating polymer growth on proteins via SI-ROMP, this study acts as a proof-of-concept with promising results. Future work entails the synthesis of an anchored polythiophene (PT) monomer to a norbornene backbone, providing for a covalently-wired and highly conjugated polymer matrix for efficient PSI-PSI charge mediation. 

    • Patrick was awarded a NSF Graduate Research Fellowship
  • Anna Yanchenko - Physics & Math, University of Virginia

    Anna YanchenkoEducational Institution: University of Virginia
    List of Mentors: Dr. Richard Haglund & Rod Davidson
    Program: NSF REU
    Research Project: Electric-Field-Induced Second-Harmonic Generation in Asymmetric Nanogaps
    Poster: NSF REU Anna Yanchenko Poster .pdf
    Research Abstract:  
    Asymmetric plasmonic nanoparticles can be used to generate and control the spatial distribution of electric fields at the nanoscale in order to efficiently generate second-harmonic light and control its polarization response. Electric-field-induced second-harmonic generation (EFISH) allows for the optical modulation of second-harmonic light using an external, applied electric field.  Previous work has shown modulation of EFISH signals using DC electric fields in plasmonic grating geometries. (Brongersma, Science 2011) The governing mechanism in second-harmonic generation is a second order, nonlinear process controlled by a tensor, χ(2), which vanishes under central symmetry.  In our experiments, we fabricated novel asymmetric gold nanogaps and demonstrated that they produced second-harmonic light with a conversion efficiency on the order of 10-11.  Three plasmonic geometries were fabricated to create unique electric field gradients on a length scale of the order of 100nm.  Finite-difference time-domain (FDTD) simulations and experimental extinction spectra of the nanogaps were performed, and the nanogaps were found to have broad plasmonic resonances at 800 nm.  The plasmons were excited with a horizontally polarized ultrafast Ti:Sapphire laser at 800nm and a spatial light modulator was used to compress these pulses to ~20fs. The SHG efficiency resulting from this plasmon excitation was measured as a function of power.  PMMA was then deposited into the nanogaps, and we found that the PMMA red-shifted the plasmon resonance and reduced the SHG conversion efficiency due to absorption by the PMMA.  Future experiments are planned with additional centrosymmetric materials, such as Si, Si3N4, and SiO2, non-centrosymmetric materials, like GaAs, and ferroelectric materials, such as BaTiO3.  Additionally, the relation between the polarization of the incoming pulse and the produced SHG will be explored and further experiments are planned to pump the gold nanogaps with a different frequency of light (1053 nm), with potential applications for optical switching.

    • Co-author journal publication
      R.B. Davidson, II, A. Yanchenko, J. Ziegler, S. Avanesyan, B. Lawrie, and R.F. Haglund, Jr., “Ultrafast Plasmonic Control of Second Harmonic Generation,” ACS Photonics, 3 (8), 1477-1481, (2016). 
    • Conference Presentation
      A. Yanchenko, R. Davidson, J. Ziegler, R. Marvel, S. Avanesyan, R. Haglund, “Electric-Field-Induced Second-Harmonic Generation in Serrated Nanogap Arrays” Southeastern Section of the American Physical Society” Columbia, SC, November 2014.