No abstract

Covalent cross-linking of colloidal gold nanocrystals (Au NCs) with dithiol molecules is normally considered to be an irreversible self-assembly process. Left unchecked, dithiol-mediated aggregation results in the uncontrolled formation of polymeric NC-dithiolate precipitates. Here we demonstrate the reversible assembly and disassembly of dithiolate-linked precipitates and colloidal aggregates of Au NCs by oxidizing the dithiolate linkers with ozone. Destruction of the linkers results in the complete depolymerization of the NC aggregates/precipitates to re-form stable aqueous colloids of individual Au NCs with retention of the original NC size distribution. The process is repeatable by adding additional dithiol to reinitiate aggregation, although some irreversible fusion of the NCs occurs in subsequent cycles. This method for reversible self-assembly of covalently cross-linked Au NCs is simple, clean, reproducible, and effective for a variety of linkers. Extending reversibility to covalently bound NC assemblies creates new possibilities in plasmonic sensing and catalysis.