A preparative scheme is presented for controlled modification of gold nanoparticles (NPs) by using reversible binding to a polymeric solid support through boronic acid chemistry. Octanethiol-capped Au NPs were bound to a boronic acid functionalized resin by custom-synthesized bifunctional linker molecules. The NPs were chemically released from the resin to the solution, with one (or a few) linker molecules embedded in their capping layer. This was confirmed by rebinding the linker-derivatized NPs to a boronic resin, exploiting the reversibility of the boronic acid/diol chemistry. The same scheme was employed to demonstrate a new method for affinity separation of NPs by means of a solid-phase reaction. The use of boronic acid provides versatility and chemical reversibility, while the polymeric solid support affords the separation and preparative aspects. The method presented here may be useful in various facets of NP handling, manipulation, and separation.

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Gold nanoparticles (NPs) are essential components in the design of various functional systems of nanometer dimensions. Their properties are determined by their size and the chemical composition of their capping layer. We have recently presented a scheme for controlled modification of Au NP capping layers by reversible binding to a polymeric solid support via boronic acid chemistry. Octanethiol-stabilized Au NPs were bound reversibly to a polymeric resin derivatized with boronic acid groups. Specially synthesized bifunctional linker molecules carrying a diol on one end and a thiol on the other were bound to the boronic moieties on the resin via the diol group, enabling attachment of Au NPs to the linkerloaded resin through the thiol moiety of the linkers. The resin-bound NPs could be released back to solution by cleaving the boronate ester between the resin and the linker, leaving one (or a few) linker molecule(s) on the NPs. The released NPs retained their properties (optical, solubility) and could be rebound to boronic resins through the linker molecules on their surface. This process of reversible NP binding to a polymeric solid support is studied here in detail. Several boronic-modified resins and linker molecules were prepared and investigated. The chemical conditions for cleavage of the boronate ester were found to be different for NP-free and NP-loaded resins, varying with the type of diol on the linker molecules. Reversible NP binding to high-surface-area solid supports may be useful for preparative reactions on NPs, including controlled NP modification, design of synthetic schemes for modification of NPs under protected conditions, and prevention of NP-NP interactions during chemical manipulation.

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