Current Research Projects

Core-Shell and Composite Nanostructures for Photovoltaic Applications. This project investigates the fundamental design and operating parameters of novel nanostructured materials with applications for energy conversion in order to help meet world energy demand. We have developed a series of core-shell nanomaterials that have exhibited a doubling in efficiency compared to shell-only versions. These new structures have the potential to dramatically enhance solar energy conversion. Initial studies focused on dye sensitized solar cells, and we are now working to expand our successes into solid-state devices which have greater long term stability. In these studies, nanomaterials are designed, prepared, and tested for their photovoltaic efficiency. TarrFigure1Novel core-shell nanoarchitectures are fabricated and the relationships between nanostructure andbehavior are determined. Synthetic procedures include several approaches: 1) formation of oxide nanotube arrays in alumina or polycarbonate templates followed by growth of metal cores through electrochemical deposition, 2) electrochemical growth of metal nanowire arrays in templates followed by semiconductor deposition as a shell on the arrays, and 3) physical deposition of semiconductor nanoparticle films or polymer films in and around preformed metal nanowire arrays using spin coating of nanocrystal inks or polymer solutions. Once fabricated, new nanoarchitectures will be characterized for morphology (FESEM and TEM), crystal structure (electron and X-ray diffraction), optical properties (absorbance, scattering, surface plasmon resonance), photovoltaic performance (current-voltage curves and wavelength dependent incident photon to electron conversion efficiency), and electron transport properties (electrochemical impedance spectroscopy). With slight modifications, these nanostructures can also be studied for photochemical water splitting and related processes.

 

 

Photochemistry of Petroleum from the Deepwater Horizon: Products, Mechanisms, and Toxicity (NSF $468,156, Oct. 2011 – Sept. 2014). Petroleum is a vital energy and chemical feedstock resource for the US and world economies. However, crude oil can cause serious environmental harm if released into natural systems. The Deepwater Horizon spill highlighted the severe risks that are posed by oil recovery activities. In order to mitigate these risks, it is essential to obtain a thorough understanding of oil behavior upon its release into the environment. Unfortunately, such an understanding TarrFigure2has not yet been obtained. Photochemistry is a major transformative process acting on oil present in aquatic systems. In order to gain a better understanding of how oil interacts with sunlight, we systematically assess its photochemistry under conditions relevant to those occurring during and after the Deepwater Horizon spill. We utilize optical spectroscopy and mass spectrometry (collaboration with NHMFL) to determine photochemical changes in oil composition. We also utilize chemical probe methods to measure reactive transient species formed during solar irradiation of oil under varying conditions. Nanomaterials are prepared and tested for their catalytic activity, including observation of changes in photoproducts and mechanisms. Toxicity of photoproducts is also assessed.

Effect of Photochemistry on Biotransformation of Crude Oil (BP/Gulf of Mexico Research Initiative $1,469,126, Jan. 2013 – Dec. 2015). The goals of this collaborative project are to: 1) gain a fundamental understanding of the behavior of Deepwater Horizon crude oil components when exposed to sunlight at the marine surface under a range of relevant conditions, and 2) understand how the photochemical transformations impact toxicity and biodegradation.

TarrFigure3These goals, as well as educational impacts, are achieved through the following objectives:

1) Determine photoproducts and reaction mechanisms for simulated sunlight exposed oil compounds exposed on the surface of sea water;
2) Determine the impact of dispersants on the photochemical rates, products, and mechanisms for simulated sunlight exposed oil compounds in or on sea water;
3) Determine the effects of photocatalyst nanoparticles on the rate, products, and mechanisms of oil compounds exposed to                                                                                     simulated sunlight in or on sea water;
4) Determine how prior phototreatments (items 1-3 above) impact toxicity and biodegradation (aerobic and anaerobic) of the oil and its components;
5) Provide research experiences for undergraduates and high school students and teachers.

Nanoparticles for Detection of Biological Analytes or Targeted Drug Delivery.We have several projects in this area:
A) We utilize quantum dots as platforms for detection of important biomarkers in blood or other biological fluids. We have previously demonstrated the ability of quantum dots to be attached to microparticles as well as the ability to conjugate the quantum dots or the microparticles to antibodies. We have further shown that antibody labeled quantum dots (or quantum dot loaded microparticles) can be used to selectively detect important biomarkers at physiological relevant concentrations. We have succeeded in multiplex detection of three breast cancer biomarkers using a fluorescent immunoassay. In order to expand the capabilities of these methods, we will develop a bar code type system in which quantum dots of different colors are loaded in controlled ratios into microparticles. These results allow simultaneous detection of numerous biomarkers in a single screening assay that can be applied to blood samples to allow the diagnosis of several diseases or used for detection of foodborne pathogens.
B) We utilize quantum dots to probe membranes behavior, including investigation of interfacial enzyme processes. We have incorporated quantum dots into artificial membranes and utilized fluorescence resonance energy transfer to probe membrane behavior. By use of an organic fluorophore and quantum dots, we observed the enzymatic cleavage of membrane head groups in real time. We also were able to observe inhibition of the enzyme by relevant drug molecules. Future work is aimed at studying additional membrane processes and at developing these techniques for use in living cells.
C) We developed protein nanoparticles as platforms for imaging, targeted drug delivery, and site-specific drug release. We have prepared nanoparticles by polymerization of human serum albumin (HSA) and loaded these ~100-200 nm particles with smaller particles (e.g. magnetic nanoparticles, gold nanoshells, and gold nanorods) or organic molecules (e.g. fluorophores or drugs). The HSA particles can be readily surface functionalized with antibodies or other surface groups to allow selective delivery of the HSA particles to targeted cells with subsequent release of the contents.
D) We have encapsulated magnetite in silica shells and have surface functionalized these composite nanomaterials with amine reactive species. We have shown that these composites an be used to selectively bind to proteins, allowing easy separation and subsequent identification of accessible amino acids by HPLC-MS-MS of separated and digested peptides. We are currently working to apply this technology to the isolation of membrane or lipid bound proteins.

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REU Site: Summer Research Program in Materials Science and Nanotechnology
(NSF $315,000, May 2013 – April 2016, project funded four times consecutively since 2003)
This project provides summer research experiences for undergraduate students. From 2003-2013, 92 students have participated, with 64% being minority students and 57% being female.

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