Our research is at the interface of materials chemistry, inorganic chemistry, biophysical chemistry and nanotechnology. Our primary goal is to develop inorganic nanomaterials for biological and energy-related applications, and understand the chemical interactions of these nanomaterials with their surroundings. A diverse range of projects are currently pursued in the group:
Inorganic Nanoparticle Fabrication and Functionalization.
"Finely-divided metals" such as gold, silver and copper have been known since Roman times for their brilliant colors. These brilliant colors arise fundamentally from the interaction of light with the conduction band electrons in these nanoscale metal particles, producing what is known as a plasmon resonance at particular optical frequencies. Nanorods, compared to nanospheres, have multiple plasmon bands whose position and intensity are intimately connected to the size, shape, degree of aggregation, and local dielectric environment of the nanorods. The absorption and scattering of light by gold and silver nanorods can be tuned throughout the visible and near-infrared portions of the electromagnetic spectrum. We have developed a set of synthetic approaches to fabricate gold and silver nanorods of controlled size and shape in high yields. Molecules can be placed on the nanorod surface using covalent attachment chemistries or polyelectrolyte layer-by-layer adsorption to position them at desired distances, and possibly orientations, from the nanoscale metal surface. On-particle reactions are being explored to improve the compatibility and ease of processing of these materials.
How Molecules Experience the Plasmonic Field; Toward Devices?
We are interested in how molecules are affected by the large electric fields and temperature excursions that occur upon plasmonic excitation. We therefore put interesting molecules at defined distances from the metal surface, using layer-by-layer polyelectrolyte wrapping, and measure photophysical properties. These molecule-nanoparticle assemblies can be incorporated into soft polymers for potential devices.
Cellular Imaging, Chemical Sensing, and Photothermal Therapy Using Gold Nanorods.
The strong plasmon bands of noble metal nanoparticles make them ideal for biological sensing and imaging applications. We have used the elastic light scattering properties of gold nanorods as "nano strain gauges" to measure the deformation of soft matrices by living cells. The inelastic light scattering (Raman) properties of gold nanorods can be used to interrogate the local chemical environment of the nanorods. Irradiation into nanorod plasmon bands causes large temperature jumps in the local environment, which we have exploited as a way to kill pathogenic bacteria (once the nanorods are surface-modified to recognize the bacteria).
Environmental Implications of Nanoparticles.
How are nanoparticles distributed and modified in complex biological systems? Can nanoparticles sequester or deliver small molecules across interfaces? How do these processes depend, if at all, on nanoparticle size, shape, aggregation state, and surface chemistry? These are questions that we seek to address using a battery of analytical, physical, and biochemical techniques.