Continuous flow synthesis of plasmonic gold patches and nearly-complete nanoshells on polystyrene core particles

Abstract

We describe the development of a T-mixer based continuous flow process for the coating of 86–500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth. After establishing a suitable flow rate for good mixing and sufficiently uniform product morphology we systematically investigate the main reaction parameters. This reveals a considerable tunability of the patch morphology and, by virtue of the localized surface plasmon resonance of gold, the optical properties of the product dispersions. In order to further widen the range of nanostructures accessible by our process, a second T-mixer was added. This introduced new gold precursor, leading to further growth of the patches that were formed after the first mixer. By this approach, nearly-complete gold nanoshells could be produced in high yield on both small and large core particles, without the unwanted production of free-standing gold nanoparticles. Due to the pronounced optical properties of nearly-complete gold nanoshells on small core particles, we could estimate from electrodynamic simulations the equivalent shell thickness to be as low as 8.6 nm. This is significantly thinner than can be routinely achieved using the standard seeded growth approach to synthesise gold nanoshells. Our results are therefore highly promising for the gram-scale synthesis of plasmon resonant nanostructures with designed optical properties.