Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T51: Invited Session: Soft Matter Nanophotonics: DNA-Directed Assemblies of Metal Clusters and Metal Nanoparticles |
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Sponsoring Units: GSOFT DCMP Chair: Elisabeth Gwinn, University of California, Santa Barbara Room: Grand Ballroom C1 |
Thursday, March 5, 2015 11:15AM - 11:51AM |
T51.00001: DNA base pairing by noble metal cations: Structure and electronic properties from Density Functional Theory Invited Speaker: Olga Lopez-Acevedo Metallo-base pair interactions are two to three times larger than the conventional hydrogen-bond pair interaction. Such high stability can drive the formation of helices and higher-order structures with the possibility to design novel DNA-based nanomaterials \footnote{T. Biver \textbf{Coordination Chemistry Reviews} 257 (2013) 27-65}. Nucleobases and noble metal atoms (Au,Ag) have wide range of possible interacting sites depending on both the metal charge (ion, cation or neutral) and chemical nature \footnote{L. Espinosa Leal and O. Lopez-Acevedo, \textbf{Nanotechnology Reviews} to appear 2015, arXiv.1403.3494}. I will overview the electronic properties, both ground state and optical, of metallo-DNA structures obtained by global optimization and Density Functional Theory, discussing the effect of pairing and inclusion of backbone on the metal-base elementary unit. [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:27PM |
T51.00002: DNA templates silver clusters with magic sizes and colors for multi-cluster fluorescent assemblies Invited Speaker: Stacy Copp The natural inclusion of information in DNA, a vital part of life's rich complexity, can also be exploited to create diverse structures with multiple scales of complexity. Now emerging in novel photonic applications, DNA-stabilized silver clusters (Ag$_N$-DNA) are compelling examples of multi-scale DNA-directed assembly: individual fluorescent clusters, each templated by specific DNA base motifs, can then be arranged together in DNA-mediated multi-cluster assemblies with nanoscale precision. We discuss how DNA imbues Ag$_N$-DNA with unique features. Our optical data on pure Ag$_N$-DNA show that DNA base-cationic silver ligands impose rod-like shapes for neutral silver clusters, whose length primarily determines fluorescence color [1]. This shape anisotropy leads to the aspherical Ag$_N$-DNA magic number cluster sizes and ``magic color'' groupings [2]. We exploit DNA's sequence properties to extract multi-base motifs that select certain magic cluster sizes, using machine learning algorithms applied to large data sets [3]. With these base motifs, we design DNA scaffolds to arrange multiple atomically precise Ag$_N$ together in nanoscale proximity. We demonstrate that clusters are stable when held at separations below 10 nm, both in bicolor, dual cluster DNA clamp assemblies [4] and in one-dimensional assemblies of atomically precise clusters arrayed on DNA nanotubes.\\[4pt] [1] D. Schultz \textit{et al.}, Adv. Mater. \textbf{25}, 2797 (2013).\\[0pt] [2] S. M. Copp \textit{et al.}, J. Phys. Chem. Letters. \textbf{5}, 959 (2014).\\[0pt] [3] S. M. Copp \textit{et al.}, Adv. Mater. \textbf{26}, 5839 (2014).\\[0pt] [4] D. Schultz, S. M. Copp \textit{et al.}, ACS Nano \textbf{7}, 9798 (2013). [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 1:03PM |
T51.00003: Plasmonic Enhancement of Raman Signal using Complex Metallic Nanostructures based on DNA Origami Invited Speaker: Gleb Finkelstein DNA-based nanostructures, such as ``DNA origami,'' have recently emerged as one of the leading techniques for precise positioning of nanoscale materials in fields ranging from computer science to biomedical engineering. The origami is composed of a single scaffold DNA strand to which smaller ``staple`` strands are attached through DNA complementarity. The staples help to fold the scaffold strand into the designed structure of a predetermined shape. The resulting templates are highly addressable and have proven to be versatile tools for site-specific placement of various nanocomponents, such as metallic nanoparticles, quantum dots, fluorophores, etc. Building upon massively paralleled assembly mechanism of the origami and its ability to position nanocomponents, one may hope to utilize it for biosensing purposes. One attractive goal is the Raman spectroscopy, which provides a highly specific chemical fingerprint. Unfortunately, the Raman scattering cross section is small; Surface Enhanced Raman Spectroscopy (SERS) enhances the otherwise weak Raman signal by trapping the analyte molecules in the regions of intense electric field produced near rough metallic surfaces. These ``hot spots`` can be understood as resulting from localized surface plasmon modes resonantly exited by the incident laser excitation. We have earlier shown that metallic nanoparticles controllably attached to DNA origami can be further enlarged via an in-solution metallization; this technique allowed us to build metallic structures of complex topology. Recently, we have performed Raman spectroscopy of molecules attached to these metallic assemblies. Specifically, DNA origami is first used to organize the metallic structures, followed by a covalent attachment of Raman-active molecules to the metal. We found that the substrates with four nanoparticles per origami produce a strongly enhanced Raman signal compared to the control samples with only one nanoparticle per origami for the same particle density. Furthermore, in the samples with four particles per origami the Raman signal systematically decayed as a function of the laser exposure time. Similar behavior has been previously reported and attributed to photo-damaging effects of the high intensity fields at the ``hot spots.'' In the samples with four nanoparticles per origami, the hot spots are located between the pairs of NPs; the one-particle control samples lacking the inter-particle hot spots showed no decay of the Raman signal, confirming our conclusion. [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:39PM |
T51.00004: DNA-bridged Chiroplasmonic Assemblies of Nanoparticles Invited Speaker: Nicholas Kotov Chirality at nanoscale attracts a lot of attention during the last decade. A number of chiral nanoscale systems had been discovered ranging from individual nanoparticles to helical nanowires and from lithographically defined substrates. DNA bridges make possible \textit{in-silico} engineering and practical construction of complex assemblies of nanoparticles with of both plasmonic and excitonic nature. In this presentation, expected and unexpected optical effects that we observed in chiral plasmonic and excitonic systems will be demonstrated. Special effort will be placed on the transitioning of theoretical and experimental knowledge about chiral nanoscale systems to applications. The most obvious direction for practical targets was so far, the design of metamaterials for negative refractive index optics. The results describing the 3D materials with the highest experimentally observed chiral anisotropy factor will be presented. It will be followed by the discussion of the recent developments in analytical application of chiral assemblies for detection of cancer and bacterial contamination. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 2:15PM |
T51.00005: DNA-mediated self-assembly of polyhedral plasmonic clusters Invited Speaker: Vinothan N. Manoharan A metafluid is a collection of electromagnetic resonators that have an isotropic response to incoming light. Because the resonators need not be oriented in any particular direction, metafluids are perhaps the simplest metamaterial to fabricate -- if one can first design resonators with an isotropic response. Such structures can in principle be self-assembled from metallic colloidal particles. The challenge is to organize these 100-nm-scale metallic particles into high-symmetry clusters, such as tetrahedra, that have very little variability between structures, so that the electric and magnetic resonances of all the clusters are at the same frequency. I will discuss how DNA can be used to assemble bulk suspensions of polyhedral colloidal clusters, using both equilibrium and non-equilibrium methods\footnote{Schade, Holmes-Cerfon, Chen, Aronzon, Collins, Fan, Capasso, Manoharan, \textsl{PRL} 148303 (2013)}. I will also discuss how the yield of the structures is related to statistical mechanical and geometrical considerations. [Preview Abstract] |
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