Gold Nanooctahedra with Tunable Size and Microfluidic-Induced 3D Assembly for Highly Uniform SERS-Active Supercrystals

Shape-controlled synthesis of uniform noble metal nanoparticles (NPs) is crucial for the development of future plasmonic devices. The use of nanocrystals with well-defined morphologies and crystallinity as seed particles is expected to provide excellent shape control and monodispersity. We report the aqueous-based seed-mediated growth of monodisperse gold octahedra with wide range of sizes (50–150 nm in side length) by reducing different amounts of HAuCl4 on preformed single crystalline gold nanorods using butenoic acid as reducing agent. Butenoic acid plays a key role as a mild reducing agent as well as favoring the thermodynamic control of the reaction. The uniformity of the as-prepared Au octahedra combined with the use of a microfluidic technique based on microevaporation will allow the self-assembly of octahedra into uniform 3D supercrystals. Additionally, these plasmonic substrates exhibit high and uniform SERS signals over extended areas with intensities increasing with the Au nanoparticle size.