In our multidisciplinary group we focus on experimental methods drawn from a variety of disciplines, including chemistry, the clean-room nanofabrication techniques of electrical device engineers, and even biological assembly methods, to create new, controlled nanostructures with unique optical properties. Our major area of interest is in materials with collective electron oscillations, known as surface plasmons. More recently we have begun to integrate these materials with other media, such as semiconductor quantum dots, bulk semiconducting media, fluids, optically active (fluorescent) molecules, and biomolecules. We perform a variety of optical spectroscopies and imaging measurements on our structures, to characterize our structures as quantifiably as possible. We work closely with theorists in the Nordlander group, and others, to understand and refine our systems. We also collaborate with numerous other experimental groups on topics of mutual interdisciplinary interest, such as biomedical applications, single-molecule sensing, and energy applications.
Fundamental Science of Nanoscale Plasmonics
We have been interested for more than a decade in the localized plasmons of metallic and metal-based nanoparticles and nanostructures. The optical properties of these structures are quite fascinating, and include a strong effect of geometry on the optical resonant properties, size dependent effects controlling light absorption and scattering, and plasmon-plasmon interactions, as observed in reduced symmetry nanoparticles and finite nanoparticle aggregates. These latter systems are of particular interest, giving rise to a rich variety of coupled-oscillator behavior such as Fano resonances, electromagnetically induced transparency (EIT), sub- and superradiance, and other phenomena not yet observed in plasmonic systems. These phenomena are of both fundamental interest and because they enable new applications in a variety of technological needs that address problems of societal interest.
Ultrasensitive Chemical Sensing
We are interested in developing high-performance geometries that will allow us to couple to molecular systems for chemical analysis and identification. Plasmonic nanostructures allow us to develop substrates for numerous surface enhanced spectroscopies. These include: surface enhanced Raman spectroscopy (SERS), surface enhanced infrared absorption (SEIRA), and a combination of the two spectroscopies, which will ultimately allow us to identify individual molecules. Other surface-enhanced modalities such as surface plasmon resonance sensing and surface-enhanced fluorescence spectroscopy have been pursued in our group, and are of interest.
The sensitivity of plasmonic structures, in particular coherent plasmonic structures, to changes in their local dielectric environment is leading to the development of new approaches for active devices, where electrically responsive media can be used to change and manipulate plasmonic properties. This approach can be useful in the development of new, frequency-agile media and new types of detectors. The manipulation of scattered light into specific directions is also being pursued. A particularly exciting topic in the area of active plasmonics is catalysis: how can excitation of a surface plasmon modify or drive a chemical reaction near the metallic nanoparticle surface? This is a rapidly expanding and multidisciplinary field ripe for discoveries and new research directions.
We currently have several projects in collaboration with research groups at Baylor College of Medicine and U. T. M. D. Anderson Cancer Center. These projects involve (a) theranostic (diagnostic PLUS therapeutic) nanoparticles and their applications in cancer imaging and therapy, and (b) light-triggered gene therapy, where nanoparticle complexes are delivered inside of cells, then undergo light-induced release of DNA from their surface. These systems allow us to manipulate the internal state of living cells and to monitor their return to equilibrium in a manner that is unique to this approach.
We are currently pursuing several projects in the harvesting of solar radiation for energy applications. Plasmonic nanoparticles can be used to redirect incident light into the waveguide and evanescent surface modes of thin film photovoltaic devices. We are also currently collaborating with an Energy Frontier Research Center (EFRC) based at Los Alamos National Laboratory and the National Renewable Energy Laboratory (NREL), based on the carrier generation properties of semiconductor nanocrystals. Coupled quantum dot-plasmonic devices and materials are currently being investigated for their current-harvesting properties. We also have several projects in the area of solar thermal energy that are of interest for delivering new solutions for energy-demanding applications in developing countries, such as water purification, autoclaving, and electricity production, for Global Health needs.
For more information on our research, please visit our Publications Page