Large Diameter Nanoparticle Building Blocks for the Bottom-Up Synthesis of Plasmonically Active Artificial Molecules

Abstract

DNA-mediated self-assembly of nanoparticles labelled with a specified number of DNA oligonucleotides has proven powerful for organizing nanocrystals into complex, multimeric nanostructures akin to "artificial molecules." This capability is particularly interesting for metallic nanoparticles because they electronically couple, which gives rise to emergent properties such as distance-dependent changes in their optical response or massive near-field enhancement. As the magnitude of plasmonic coupling scales with the size of the nanoparticle, large diameter nanoparticles (>30 nm) are required substrates for these applications. Due to their large size and greater colloidal instability, it has proven extremely challenging to isolate large nanoparticles labelled with a specified number of DNA molecules. In this dissertation, I describe the development of a purification technology, DNA-based affinity chromatography, which permits the isolation of nanoparticles up to 80 nm in diameter labelled with a single molecule of DNA for the first time. These monovalent nanoparticles can be used effectively as building blocks to self-assemble plasmonically active artificial molecules. A number of examples are demonstrated, including the synthesis of optical antennas which can enhance the fluorescence emission of nearby molecules. With access to larger diameter nanoparticle building blocks, it should be possible to prepare a variety of plasmonically active nanocomposites which heretofore have been synthetically inaccessible.