Highly Concentrated Seed-Mediated Synthesis of Monodispersed Gold Nanorods

The extremely large optical extinction coefficient of gold nanorods (Au-NRs) enables their use in a diverse array of technologies, rnging from plasmonic imaging, therapeutics and sensors, to large area coatings, filters, and optical attenuators. Development of the latter technologies has been hindered by the lack of cost-effective, large volume production. This is due in part to the low reactant concentration required for symmetry breaking in conventional seed-mediated synthesis. Direct scale up of laboratory procedures has limited viability because of excessive solvent volume, exhaustive postsynthesis purification processes, and the generation of large amounts of waste (e.g., hexadecyltrimethylammonium bromide(CTAB)). Following recent insights into the growth mechanism of Au-NRs and the role of seed development, we modify the classic seed-mediated synthesis via temporal control of seed and reactant concentration to demonstrate production of Au-NRs at more than 100-times the conventional concentration, while maintaining independent control and narrow distribution of nanoparticle dimensions, aspect ratio, and volume. Thus, gram scale synthesis of Au-NRs with prescribed aspect ratio and volume is feasible in a 100 mL reactor with 1/100th of organic waste relative to conventional approaches. Such scale-up techniques are crucial to cost-effectively meet the increased demand for large quantites of Au-NRs in emerging applications.