Synthesis of branched gold nanocrystals by a seeding growth approach

Synthesis of branched gold nanocrystals by a seeding growth approach is described. In this process, HAuCl₄ aqueous solution was supplied stepwise to grow the gold seeds (∼2.5 nm) into larger nanoparticles with a highly faceted particle structure (∼15-20 nm in diameter). Sodium dodecyl sulfate (SDS) served as a capping agent to facilitate the formation of highly faceted nanoparticles, and ascorbic acid was used as a weak reducing agent. The highly faceted nanoparticles then transformed into branched nanocrystals (∼40 nm in length) by further addition of the SDS-HAuCl₄ solution and ascorbic acid for particle growth. The branched nanocrystals show bipod, tripod, tetrapod, and pentapod structures and are composed of mainly (111) lattice planes. These multipods appear to grow along the twin boundaries of the initially formed highly faceted gold nanoparticles, as the twin boundaries on the pods originate from the centers of the branched nanocrystals. The concentration of ascorbate ions in the solution was found to have a profound influence on branch formation. These branched nanocrystals are stable to storage at low temperature (that is, 4°C), but they may slowly evolve into a multitwinned faceted crystal structure (that is, pentagonal-shaped decahedral structure) when stored at 30°C.