In addition to their size-dependent properties, anisotropic nanoparticles often exhibit shape-dependent properties such as the dependence of the localized surface plasmon resonance of gold nanorods on the aspect ratio of the nanorod. Nanoparticle surface chemistry can also be affected by shape, which has important implications for nanoparticle synthesis and assembly. Much of the research into the shape-dependent surface chemistry of nanoparticles has focused on the anisotropic functionalization of gold nanorods. Over the past decade there have been many publications demonstrating the selective functionalization of the ends of gold nanorods leading to end-to-end assembly. Recently, it has been shown that the anisotropic surface chemistry of gold nanorods can be applied to selectively coat the ends with silica, or by first functionalizing the ends with poly(ethylene glycol) methyl ether thiol (PEG-SH) to coat the sides. It has been suggested that by selectively reacting with the surfaces at the ends of the nanorods the PEG-SH blocks the ends while cetyltrimethylammonium bromide at the sides templates silica shell growth; however, side-silica shells are difficult to reproduce. After studying the reaction conditions leading to side-silica shell formation it was found, surprisingly, that the oxidation state of PEG-SH is an important factor for the synthesis of side silica shells. We have demonstrated that when the added PEG-SH is in the form of a thiol no silica shells form but when the disulfide is used side silica shells form.

Oxidation state dependence of capping agent for site-selective silica coating of gold nanorods

253rd National Meeting (2017)

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