Reversible Aggregation of Covalently Cross-Linked Gold Nanocrystals by Linker Oxidation

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.

Nanocatalysts for High Selectivity Enyne Cyclization: Oxidative Surface Reorganization of Gold Sub-2-nm Nanoparticle Networks

“…To the best of our knowledge, little is known on the effects of such type of oxidative treatment on thiolated Au NPs. 100 − 108 We analyzed by XPS the resulting materials, as exemplified for the oxidized Ox-DAd-S@AuNPs 50% ( Figure 8 ). Treatment with m- CPBA was preferred to PIDA because of milder reaction conditions.…”

“…The gold NPs were treated with the organic oxidation agents phenyliodine­(III) diacetate (PIDA, 70 °C, 18 h) or meta -chloroperoxybenzoic acid ( m- CPBA) at 20 °C for 2 h, avoiding the addition of silver salts. To the best of our knowledge, little is known on the effects of such type of oxidative treatment on thiolated Au NPs. − We analyzed by XPS the resulting materials, as exemplified for the oxidized Ox-DAd-S@AuNPs 50% (Figure ). Treatment with m- CPBA was preferred to PIDA because of milder reaction conditions.…”

Uniform Supported Metal Nanocrystal Catalysts Prepared by Slurry Freeze-Drying

“…Spheroidal, citrate-capped Au NCs with a diameter of 12–14 nm were synthesized in water using a published method and purified by centrifuge dialysis filtration, which removes molecular solutes without causing aggregation or loss of NCs (see the Experimental Methods section and Figure S1). ,, A known amount of a powdered support material (microcrystalline cellulose (MCC), TiO 2 nanocrystals, γ-Al 2 O 3 nanocrystals, SiO 2 nanoparticles, or carbon nanopowder) was then added to the purified NC dispersion and the mixture shaken (for TiO 2 , Al 2 O 3 , SiO 2 , and carbon) or sonicated and then shaken (for MCC) to make a homogeneous slurry, frozen in dry ice at −78 °C, and freeze-dried in a homebuilt lyophilizer (Figure S2). MCC was selected for study because it is an insoluble, chemically robust, and low-cost organic support, while TiO 2 , γ-Al 2 O 3 , SiO 2 , and activated carbon are common inorganic supports.…”

Reversible assembly of nanoparticles: theory, strategies and computational simulations

“…Similarly to the previous example, the reversibility of this process was achieve by consecutively adding dithiol and ozone. 148…”

“…Similarly to the previous example, the reversibility of this process was achieve by consecutively adding dithiol and ozone. 148 By contrast to the above examples, the use of crosslinking agents that indirectly interact with the surface of NPs to control their assembly process is based on the modulation of noncovalent interactions. This strategy has been widely exploited using supramolecular systems.…”