SELF-ASSEMBLY AND CONTROLLED ASSEMBLY OF NANOPARTICLES

Open Access
Author:
Dillenback, Lisa
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 07, 2008
Committee Members:
  • Christine Dolan Keating, Committee Chair
  • Thomas E Mallouk, Committee Member
  • Philip C. Bevilacqua, Committee Member
  • Theresa Stellwag Mayer, Committee Member
Keywords:
  • metal nanowire
  • nanowire assembly
  • nanoparticle assembly
  • DNA-directed assembly
  • self-assembly
Abstract:
This thesis describes an exploration of interactions between metal nanoparticles and new techniques for their assembly. In Chapter 2, the self-assembly of 300-nm diameter Au, Ag and bimetallic Au-Ag nanowires was studied. Upon deposition onto a glass substrate from suspension in water, the wires self-assembled into densely packed well-ordered arrays. Electrostatic repulsion between the wires was necessary to prevent their aggregation. However, van der Waals forces were a major driving force behind the assembly. This was especially apparent in the assembly of the bimetallic Au-Ag nanowires, which showed a slight non-random preference for orientational ordering. The theoretical simulations of wire assembly at different temperatures strongly indicated that the orientational ordering was driven by the difference in van der Waals attraction between the metals. Chapter 3 describes the temperature-programmed assembly of DNA:Au nanoparticle bioconjugates. In this work, the temperature of the system was manipulated in order to take advantage of temperature-dependent melting properties of the DNA. Despite a 24% loss of DNA from the nanoparticle conjugates and a 14% exchange of DNA sequences between the conjugates when heated, significant control over the order in time of the assembly of multiple DNA:Au conjugate types is demonstrated. This assembly was performed using both sandwich style hybridization systems, in which a half of linking oligonucleotide is hybridized with a DNA sequence on one conjugate type and the other half is hybridized with a sequence on a second conjugate type, as well as with directly complementary hybridization systems. The conjugate types in the resulting assemblies were characterized both by gel electrophoresis and by monitoring the visible absorbance of the conjugate suspensions upon the addition of oligonucleotides complementary to those on the conjugates. In Chapter 4, initial experiments were performed to investigate the feasibility of an on-wire lithography method to fabricate Au nanowires with functionally distinct sides. Conditions for the selective etching of Ni and Ag were determined. The addition of two thiolated DNA sequences, as well as the use of two different DNA attachment chemistries, was explored. Silica-coated Au nanowires with one exposed Au end were synthesized, and Au nanoparticles were electrostatically assembled on the Au end of these wires. The Appendix describes the development of three desktop laboratory experiments for an undergraduate transition metal chemistry course. In a molecular symmetry lab, students used Dots and toothpicks to build molecular models and improve their visualization of symmetry elements. An electronic spectroscopy lab strengthened students' ability to relate ligand field strength and selection rules with the electronic absorption spectra of transition metal complexes. A ligand exchange lab demonstrated the concepts of relative formation constants and the chelate effect. Preliminary assessment to determine the effectiveness of the labs was also performed.