👉 Gold colloids have been uniformly coated with silica using the silane coupling agent (3-aminopropyl)trimethoxysilane, which acts as a primer to make the gold surface vitreophilic. Following the initial formation of a thin silica layer in aqueous solution, the particles can be transferred to ethanol for further silica growth via the Stƶber method. The silica shell thickness can be precisely controlled, and after appropriate surface modification, the particles can be dispersed in nearly any solvent. By adjusting the silica layer thickness and the refractive index of the surrounding medium, the optical properties of the colloidal dispersions can be finely tuned. The measured optical spectra of these coated particles align well with theoretical predictions based on Mie theory for coreāshell structures.