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Abstract

Reliability and predictability in methods that produce pure, consistent, and monodisperse products is a hallmark in all aspects of chemistry. Within the subfields of nanomaterials and nanotechnology, due to the relatively short amount of time these areas of chemistry have had research dedicated to their study, there is room for improvement in the methods and techniques that are often used to synthesize these materials. I have been working on two aspects in this area of chemistry: to improve upon the synthetic techniques and mechanistic understandings of nanoparticle growth and to greatly expand the capabilities of discrete programmable self-assembly with highly uniform and robust universal building blocks. First, a purification technique known as depletion flocculation is demonstrated to purify gold bipyramids from the crude synthetic mixture containing roughly 70% shape impurities. The flocculation was shown possible owing to the use of benzyldimethylammonium chloride (BDAC) surfactant. The purified bipyramids were then used for further nanocrystal growth to create a new class of nanoparticles based on the original bipyramid seed. The bipyramids were also oxidized in the presence of surfactant at high temperatures to form highly monodisperse low aspect-ratio nanorods. The final structures of both the growth and oxidation procedures were shown to be highly dependent on the surfactant present in solution. Second, universal building blocks for the purpose of discrete programmable self-assembly were synthesized by a two-step procedure. A partial polymer encapsulation is performed in a binary solvent system in combination with a dual ligand functionalization. The surface energy of the nanoparticle is tuned by coating with a specific ratio of hydrophobic ligand to hydrophilic ligand that dictates the eventual surface coverage of the diblock copolymer. The coverage of the nanoparticle surface by the polymer renders that area inert to further functionalization. The second step involves the functionalization of the exposed surface by thiolated single-stranded DNA. The polymer confers site-specific and directional binding of the DNA, and the DNA allows for specific binding only to the complementary strand. This enables self-assembly between two nanoparticles functionalized with complementary DNA strands in a highly specific and preconceived fashion into discrete assemblies with exceptional control. I demonstrate 24 self-assemblies with the universal building blocks, many of which are not possible through any other self-assembly method. Finally, I show that the self-assembled structures can be functionalized with a stimuli-responsive DNA sequence. Specifically, in response to the pH of the solution, the triplex-capable DNA strand changes the interparticle distance, invoking an optical plasmonic response.

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