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Optimizing electrochemical and electroless methods toward the surface-specific modification of Au nanorods Fisher, Elizabeth A.

Abstract

The controlled modification of gold nanorods has important implications for their successful applications in a wide variety of fields. In this work, electrochemical and electroless methods for the surface-specific modification of gold were optimized with the aim of developing a site-specific strategy for the functionalization of gold nanorods. Electrochemistry and fluorescence microscopy techniques were used to investigate the surface-specific modification of alkanethiol-coated gold bead electrodes, which served as a macroscopic model system for the nanorods. 11-mercaptoundecanoic acid (MUA) was partially removed from the electrodes by reductive desorption and the uncovered regions were modified with a fluorophore-functionalized, thiolated DNA molecule. Single crystal gold bead electrodes were employed in order to study and optimize the modification methods on all crystallographic surfaces under identical conditions. Two methodologies for the surface-specific modification of gold bead electrodes were investigated. In the first, a potential was applied to the electrode using a potentiostat, and it was determined that the SAM could be reductively removed selectively from the Au{111} surfaces of the electrodes by a 5 minute electrochemical application of any potential from -0.75 V to -0.8 V vs. Ag|AgCl. In the second method, the electrode potential was set electrolessly by adding a strong reducing agent, sodium borohydride, to the electrolyte. In the absence of oxygen, it was found that the electroless MUA desorption closely resembled the results obtained electrochemically, and that Au{111}-selective modification of the gold bead electrode was achieved at potentials near -0.75 V vs. Ag|AgCl. The electroless modification strategy was then applied to MUA-stabilized gold nanorods. Preliminary results indicate that sodium borohydride successfully removes alkanethiol from gold nanorod surface, enabling them to be modified with thiolated, fluorophore-labelled DNA.

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