Combination of microfluidic high-throughput production and parameter screening for efficient shaping of gold nanocubes using Dean-flow mixing†
Metal nanoparticles and their special optical properties, the so-called localized surface plasmon resonance (LSPR), facilitate many applications in various fields. Due to the strong dependency of the LSPR on particle geometry, their synthesis is a challenging and time-consuming procedure especially for non-spherical shapes. In contrast, micromixers offer new experimental approaches and therefore enable the simplification of several processes. By using a zigzag micromixer (Dean-Flow-Mixer, DFM) that induces Dean-flow secondary flow patterns, we theoretically and experimentally show the mixing efficiency. Thus, we highlight the advantages of using it in the multistep synthesis of Au nanoparticles. Based on a narrow size distribution of Au nanocubes and an increased yield in combination with higher reproducibility, we depict the need for and advantage of the DFM to control the incubation times during the growth process. We further show that, by using the DFM, easy and very fast Au nanocube edge length tuning (53 nm, 58 nm, 70 nm and 75 nm) is possible by simultaneously reducing the consumption of the materials by up to 95%. We finally demonstrate the versatile abilities by using the DFM for parameter screening on examples of different halides and accessible bromide in the growth solutions. Therefore, we highlight the optimal concentration for the different growth regimes and the influences on the Au nanoparticle morphology (spheres, cubes and rods) and their defined shaping.