Highly Tunable Growth and Etching of Silica Shells on Surfactant-Free Gold Nanostars

Herein, we report an efficient method to coat gold nanostars with a silica shell of variable thickness and then tunably etch it by using a mild silica etching reagent, NaBH4. This method generates a novel type of nanostar coating in which silica only covers the core, leaving the tips variably exposed.