In this letter, we demonstrate for the first time the electrostatically driven assembly of (3-aminopropyl)triethoxysilane (APTES) and HAuCl4 in aqueous media into novel micrometer-scale supramolecular sheets and their subsequent transformation into small, stable APTES bilayer-capped gold nanoparticles through a the process. The nanoparticle formation mechanism is also discussed.