Silver ions induced growth of plasmonic Au hexagonal star plates

Abstract

Au plates show substantial structural anisotropy, which leads to easily tuned plasmonic properties. Different shapes of Au plates have been reported: for example, the best-described triangles and hexagons. However, the limited number of sharp corners of Au plates hinders further studies on the properties and applications of Au plates. Here, Au hexagonal star plates were synthesized using AgNO₃ in a system consisting of polyvinyl pyrrolidone (PVP) and HAuCl₄. The selective site deposition of Ag⁺ on the edge of Au plates led to an uneven growth rate at various edge positions of the plates, which led to a shift in the growth trend of the plates from regular hexagons to polygons to hexagonal star plates. A series of Au structures were successfully obtained by adding other ions (I⁻, Br⁻, Cu²⁺, and Fe³⁺). Moreover, a surface-enhanced Raman spectroscopy (SERS) substrate was built using an Au hexagonal star plate and Au nanoisland, which showed excellent detection down to 10⁻¹¹ M concentration of Rhodamine 6G (R6G). This new synthetic route will not only help in the design of novel anisotropic plasmonic nanostructures but also facilitate a better understanding of the growth mechanisms of Au plates.