"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."
Intellectual Merit: Metamaterials are a new class of nano/bio related materials which possess unique optical properties derived from the structural design of the constituents rather than their individual chemistry. The PIs propose to use an integrated approach of theory, simulations and experiments to produce metamaterial structures in both 2D and 3D from metal nanoclusters through assembly of DNA functionalized nanoparticles. Nanoparticles grafted with single stranded (ss) DNA are great candidates for assembly because of the highly specific and tunable inter-particle interaction imparted by complementary sequences of DNA grafts. Metal nanoclusters are ideal for metamaterials because the coupled plasmon resonances in a nanocluster can possess both electric and magnetic features, thereby affecting the macroscopic optical properties. The novelty of the proposed work lies in: 1) the goal: Creation of metamaterials from clusters of DNA functionalized nanoparticles, which is the goal of this proposed work, to the best of the PIs' knowledge has not been attempted so far; 2) the proposed route: Most previous efforts for creation of metamaterials have been aimed at creating 2D ordered nanostructures by top down lithographic processes, while the PIs aim to develop bottom up approaches to form 2D and 3D clusters of DNA grafted metal nanoparticles with specific shape, size and inter-particle spacing, since optical properties depend primarily on the size, shape and metal filling fraction of cluster rather than the exact stacking of nanoparticles inside the cluster. Previous work on assembly of DNA grafted nanoparticles has focused on creating crystal structures, while our study will use DNA grafted nanoparticles to create nanoclusters with desired void fractions and cluster shape; 3) the building blocks: Others have only used nanoparticles isotropically grafted with ssDNA at high surface grafting, while the PIs will work with nanoparticles that have ssDNA grafted isotropically as well as anisotropically at low moderate grafting densities. Low moderate grafting densities and anisotropic placement of a finite number of ssDNA grafts will affect the directionality of the inter-particles interactions allowing for better control over the inter-particle distances and packing fraction which within the cluster. The specific aims of this project are: 1) to conduct molecular level theory and simulation studies to elucidate the effect of ssDNA graft length, sequence of bases, isotropic or anisotropic placement at varying grafting density on the structure of assembled cluster. 2) To use electromagnetic simulations to calculate the effective permittivity, permeability, impedance and refractive index for the structure of the various nanoclusters. 3) To utilize the predictions from theory and simulations to guide the experiments for creating nanoclusters of desired sizes, shapes and void fractions with reduced optical loss, enhanced the magnetic activity and ability for visible frequency operation. This work is a new direction for both PIs. For PI Jayaraman the proposed work would provide fundamental understanding of biomolecular recognition and guide future work on peptide guided assembly of nanoparticles. For PI Park, DNA functionalization will allow for greater and more precise control over the nanocluster structures, that has been elusive to him in his previous work.
Broader Impacts: The proposed work will transform materials engineering by creating a new class of materials with properties, although not forbidden by Maxwell's equations, are very difficult to find in nature. Traditionally much focus has been placed on designing the interface between two materials to affect their optical properties, but with metamaterials the desired optical properties can be built into the material by design. The unprecedented engineering freedom the metamaterial concept offers will fundamentally change the way materials research is conducted. Metamaterials will have a huge impact on stealth defense applications, novel imaging devices and enable new communications and computing technologies. Since the PIs come from different engineering backgrounds the proposed work will provide interdisciplinary research experiences for graduate students working on this project. The PIs also plan to attract undergraduates from under represented minorities to this project through the Research Experience for Undergraduates program in Functional Materials Science and Engineering, Women in Engineering Program, and through the Society for the Advancement of Chicanos and Native Americans (SACNAS). The results emanating from this work will be demonstrated in new elective courses on Multiscale modeling and simulations and Metamaterials to be offered by the PIs. To reach a much broader community and age groups the PIs will work with the Director of Broomfield library, to make this work available to the general public through nanotechnology related collections and exhibits.
