Gold Nanorods Assemblies with Nano Gaps

Gold nanorods continue to gather increasing interest due to their facile synthesis, unique optical properties, and potential for medical and electronic applications. To take advantage of these properties, several research groups are pursuing methods to self-assemble or to arrange these nanomaterials into useful formations.End-to-end assemblies are of particular appeal since gaps between the nanorods could serve as spacers for single-molecule electronic devices. Several successful approaches to accomplish end-to-end assembly have been reported in the literature; however, each of these approaches relies on modifying already synthesized gold nanorods by adding the desired linker agent.

Seeking a new bottom-up technique to generate gold nanorods assembled end-to-end, researchers have developed a novel method to grow the rods directly from chemically linked seed particles. The researchers started with citrate-stabilized gold nanoparticles, then allowed these seeds to self-assemble using a water-soluble dithiol-functionalized polyethylene glycol linker. The seed particle dimers were then exposed to growth conditions similar to those typically used to form unlinked gold nanorods, extending each rod to a length of 500 nm. About 55% of the rods grown using this method were linked end-to-end. Transmission electron microscopy revealed a gap of 1−2 nm between these linked rods, a size well-suited for placing a single molecule within the gap. The linked nanorods were flexible around the hinging molecule, demonstrated by flow linear dichroism. The researchers suggest that exposing the linked nanorods to a low-concentration solution of an electronically relevant molecule would result in one or a few molecules within each nanogap, enabling single-molecule electronic measurements.