High-yield assembly of soluble and stable gold nanorod pairs for high-temperature plasmonics

Colloidal synthetic approaches to discrete, soluble plasmonic architectures, such as nanorod pairs, offer numerous advantages relative to lithographic techniques, including compositionally asymmetric structures, atomically smooth surfaces, and continuous fabrication. Density-driven colloidal assembly, such as by solvent evaporation, produces some intriguing structures, e.g., particle chains; however, controllability and post-processibility of the final architecture is inadequate. Also the limited quantity of product nominally comprises a broad distribution of assembly size and type. Herein, the high-yield formation of soluble, stable, and compositionally discrete gold nanorod (Au NR) architectures by inducing-then arresting-flocculation is demonstrated using bifunctional nanorods and reversible modulation of solvent quality to deplete and reassemble an electrostatic stabilization layer, thereby eliminating the need for an additional encapsulant. Analogous to dimer formation during step-growth polymerization, the initial yield of Au nanorod side-by-side pairs can be greater than 50%. The high solubility and stability of the assembly enable purification, scale-up of nanomolarity solutions, and subsequent chemical modification of the assembled product. As an example, in situ silica deposition via Stöber synthesis onto the assembled pair produces highly processable nanostructures with a single pair of embedded Au NRs at their center, which exhibit thermal stability at temperatures in excess of 700 °C.