Gram scale continuous flow synthesis of silver-on-silica patchy particles with widely tunable plasmon resonances

Extensive research has been conducted on colloids that incorporate nanostructured noble metals, motivated in particular by their highly tunable optical properties. However, the lack of approaches that offer reproducibility, tunability and scalable production is limiting their exploitation in many application areas. Here we present a novel approach for the controlled formation of silver patches on silica spheres using gold nanocrystal seeds. The synthesis of the seeds and their attachment in very small numbers to the silica spheres is achieved without employing any surfactants, stabilizers or linker molecules. Using advanced transmission electron microscopy techniques, we show that electroless deposition of silver occurs at the introduced seeds and leads to a central protrusion from the metal patches not observed in earlier, seed-free work. We demonstrate both seeding and growth processes can be achieved in millimixer flow reactors. With this simple and scalable approach we provide compelling evidence for the use of seeds in producing targeted morphology and function. Specifically, patch size and optical properties can be tailored in a predictive manner by adjusting the density of seeds on the silica core particles as well as reagent concentrations during growth. As a result, our process can be used to obtain colloidal dispersions with localized surface plasmon resonance peaks anywhere in the range 400 nm to nearly 1300 nm. We confirm the scalability of our method by operating the growth process for around 70 minutes. Apart from changes in the first few minutes, the product properties remained rather stable and over a gram of high quality silver patch coated silica could be recovered. Our approach opens up exciting new avenues for applications which require larger amounts of plasmonic or anisotropic nanoparticles with tailored morphology and optical properties.

Additional Files:

Movies S1, S2 and S3 give more details of the tomography analysis shown in Figure 4 of the main article.