Using Cation-Exchanged Nanorod Templates To Direct the Regioselective Growth and Plasmonic Coupling of Gold Nanoparticles

Plasmonic coupling of gold nanoparticles results in a red shift of the plasmon peak in the visible absorption spectrum, resulting in a color change that is sensitive to interparticle spacing. Here, we used multiple sequential partial cation exchange reactions to design heterostructured nanorod templates that define the regions onto which gold nanoparticles photodeposit. Starting with nanorods of copper sulfide (Cu_1.8S), we synthesized ZnS−CdS, CdS−ZnS−CdS, and ZnS−CdS−ZnS nanorods. Illumination with a blue LED light initiated the photodeposition of Au nanoparticles selectively onto the CdS regions. Subsequent cation exchange reactions transformed the CdS regions to Cu_1.8S and then to ZnS while also facilitating surface diffusion and migration of the photodeposited Au, which coalesced into single particles through a surface ripening process. This process produced nanorods that were fully ZnS but with Au nanoparticles anchored in distinct regions. The Au−ZnS−Au sample exhibited a red shift of the plasmon peak relative to Au−ZnS, due to plasmonic coupling of the Au particles on the ZnS nanorod support.