Method to incorporate anisotropic semiconductor nanocrystals of all shapes in an ultrathin and uniform silica shell

In this work, we present a method for the incorporation of anisotropic colloidal nanocrystals of many different shapes in silica in a highly controlled way. This method yields a uniform silica shell, with thickness tunable from 3 to 17 nm. The silica shell perfectly adapts to the shape of the nanocrystals, preserving their anisotropy, a crucial requisite for shape-dependent applications. Our method is based on an adaptation of the reverse microemulsion method. High control over the nucleation and growth of the shell is obtained by slowing down the hydrolysis and condensation rates of the silica precursor by lowering the ammonia concentration. This is shown to be essential for the formation of a uniform silica shell in the case of CdSe/CdS core/shell nanorods. Additionally, the general applicability of this method is demonstrated by coating different anisotropic semiconductor nanocrystals such as nanostars and 2D nanoplatelets. These results thus represent a crucial step toward the fabrication of highly processable and functionalized anisotropic nanoparticles.