Date of Award

December 2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Mathew M. Maye

Keywords

Anisotropy, DNA Origami, Quantum Rods, Self-assembly, Surface Chemistry

Subject Categories

Physical Sciences and Mathematics

Abstract

Semiconductor nanocrystals, like quantum dots (QDs) and quantum rods (QRs), have tunable optoelectronic properties that depend on their composition, size and asymmetry. A small change in size or aspect ratio can lead to measurable changes in optical absorption and photoluminescence emission energies, as well as varied degrees of polarized optical behaviors at those energies. My dissertation research focuses on investigating the role of anisotropy on the optoelectronic and colloidal properties of quantum rods, as well as using DNA-mediated self-assembly to align these quantum rods on DNA origami for energy transfer applications in biocompatible systems. First, CdSe of systematically varied aspect ratios and emission colors, as well as core/shell CdSe/CdS of different microstructures were synthesized and characterized. Next, the surface ligand chemistry of these nanocrystals with increasing aspect ratios was investigated. Specifically, the binding strength and surface coverage of phosphonic acid capping ligand was studied using a series of solution nuclear magnetic resonance spectroscopy (NMR) techniques, including the traditional one-dimensional 1H, as well as the more advanced two-dimensional diffusion ordered spectroscopy (DOSY) and relaxation ordered spectroscopy (ROSY). My work revealed that as the aspect ratio increases, there’s a transition of ligand binding from a tightly bound and close-packed monolayer model to a sparse, weakly bound, flat and wrapping system. To harness the unique anisotropic optical properties of these QRs in DNA-mediated assemblies, I modified their surface with both lipoic acid-appended zwitterion (LA-ZW) ligands using a photo-ligation route, and single-stranded DNA (ssDNA) using a protection-deprotection strategy. The resulted rods had good colloidal stabilities with the optical properties well-preserved in aqueous environments. Lastly, the functionalized QRs were assembled on DNA origami substrate in pre-designated patterns based on the design of capture strand arrays on DNA origami. As the QRs had different emission colors and were assembled into different QR-binding zones on origami with controlled orientations and distances. The morphologies and the optical characteristics of the assemblies were explored in light of potential Förster resonance energy transfer (FRET) gains.

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