We develop novel nanomaterials and investigate the properties of the materials for a wide range of applications. The fundamental understanding gained from our research impacts many areas of science and engineering, include micro- and nano-scale device fabrication, nano-scale imaging, nanolithography, catalysis, solar energy conversion, and sensor development.
The broad nature of the multi-disciplinary research requires methods and tools from analytical chemistry, surface chemistry, biochemistry, materials science, nano\microfabrication, optics, spectroscopy, and microscopy. We regular interface with scientists and engineers outside of the Chemistry Department through collaborations and the use of scientific instruments.
Designer plasmonic systems with tunable optical properties
We study the use of structural design and assembly to control the optical properties of plasmonic nanomaterials. The designer plasmon-active systems have unique optical properties that may be tailored through individual structure fabrication and spatially-controlled surface chemistry. The research approaches focus on the fabrication and optical characterization of well-defined, irregularly-shaped metal nanostructures and the development of surface functionalization methods to build multi-particle assemblies. The long term goal is to use the fundamental understanding of the correlation of optical properties with metal structure shape and assembly as a basis for tailoring the plasmonic properties. One of our interests is how light can be manipulated at the nanoscale using these plasmonic architectures. For example, controlling the magnitude and extent of localization of electromagnetic fields is critical for optimizing signals in surface-enhanced spectroscopy and tuning the sensitivity and probe depth for a wide range of applications from sensing to energy transfer.
Plasmonic antennas for probing chemical dynamics at the nanoscale
We work with other investigators in the NSF Center for Chemical Innovation: Chemistry at the Space Time Limit (CaSTL) to probe chemical processes at the space-time limit by combining plasmonic antennas with ultrafast spectroscopy. In our research, we manipulate plasmons through creating plasmonic architectures with optical antenna-like behavior. The goal is to combine structural control of the plasmonic materials in order to manipulate fields to define probe volumes and enhance signals to enable nanoscale and single molecule spectroscopy and microscopy measurements. We have projects with George Schatz (Northwestern University), Ara Apkarian, Eric Potma, Nien-Hui Ge, and Kumar Wickramasinghe (University of California-Irvine). We interface regularly through regular center meetings, seminars, workshops, and retreats, providing students and post docs with unique opportunities for expanding scientific experiences, networking, and training in communications and career development. We are collaborating with Steve Blair (University of Utah) on simulations of the optical properties of plasmonic antennas.
Novel approaches for synthesis of metal nanoparticles
In order to simplify functionalization of nanoparticles and aid application in aqueous-based solutions, we are developing new synthetic approaches.For example, we have developed a simple synthesis of gold and silver nanoparticles using a polymer for reduction of the metal salt and stabilization of the particles once formed. The method, based on a single step process that takes place in water, produces metal nanoparticles that are dispersed within the aqueous solution. Other synthetic approaches are based on novel reducing agents that serve dual roles and provide control of the properties of the materials.
Synthesis, interfacial chemistry, and catalytic activity of metal nanoclusters
We introduced the use of 9-borabicyclo [3.3.1] nonane (9-BBN) as a reducing agent for the facile, single-step synthesis of AuNPs with sizes < 5nm. In the case of thiol-stabilized AuNPs produced using 9-BBN, the particles are nearly monodisperse having an average size of 3.3 nm. The reduction methodology is applicable in the synthesis of AuNPs in the presence of a wide range of w-functionalized thiol ligands. The process also is applicable in production of ligand protected silver, palladium, and platinum nanoparticles with an average diameter of < 5.0 nm. We extended the use of 9BBN as a mild reducing agent to produce phosphine-stabilized gold nanoparticles with sizes of less < 3 nm. This synthesis is a simple, single-step process that does not require a phase transfer agent eliminating rigorous cleaning steps. In addition, slow reducing character of 9-BBN provides control of particle size and size dispersion. We have demonstrated that the synthesis produces particles as small as 1.2 nm in average diameter by changing the reaction temperature. We are studying the synthesis in detail with a focus on the role of the ligands (alkylthiols and phosphines) and the ability to use temperature to control the size and size dispersion of the nanoparticles. We are using the ability to incorporate a wide range of stabilizing ligands after synthesis to study the effects of these molecules on the properties of the nanoparticles, such as application in catalysis.
In collaboration with Ilya Zharov, we are combining catalytically active nanoparticles or complexes with supports in order to work with robust, recyclable catalytic materials. We are pursuing the use of silica nanoparticles as a support material that can be further functionalized with polymer brushes to control the local environment of the catalysts. As a second approach, we are using nanodiamond as an especially chemically and mechanically robust support for catalysts.
SPR microscopy for array-based analysis of biomolecule interactions
Molecular recognition plays a central role in biology by controlling cellular processes such as enzymatic catalysis, transport, regulation and communication. We are developing and applying high-throughput sensing methods based on surface plasmon resonance (SPR) to study molecular recognition between biomolecules. SPR-based sensing provides real-time, quantitative analysis of biomolecule interactions (e.g., protein-DNA, protein-protein, protein-vesicle) without the need for labels. Detailed information about the strength and specificity of biomolecule interactions impacts medical research, diagnostics, drug discovery and fundamental molecular biology studies. We are working with Bruce Gale (Mechanical Engineering, University of Utah) to integrate a new microfluidics system with our SPR microscope. In the current configuration, the system provides 48 separate flow channels for in situ biomolecule immobilization and subsequent high-throughput biomolecule interaction analysis. In situ biomolecule immobilization and label-free, real-time kinetic analysis of biomolecule interactions potentially will impact the field of proteomics and extend high-throughput analysis to more biomimetic systems involving membrane-like systems. One area of interest in immunogenicity analysis for informed decision about biological drug therapies. We are working with John Rose (Neurology, University of Utah and VA Hospital) to develop and implement an approach for immunogenicity assessment of antibody-based drug therapies which is a growing area for treating many diseases ranging from immune-system disorders such as Multiple Sclerosis to cancer.