Hybridizing metal nanostructures with reduced graphene oxide (rGO) sheets often suffer from severe agglomeration, leading to poor aqueous dispersity of the resultant composite materials. Here, through the silicate sol-gel functionalization we had effectively overcome such issue and it offers the stable anchoring sites for the in situ growth of silver (Ag) nanostructures (NSs). This hybrid material demonstrated high aqueous dispersity and it exhibited excellent stability in water for a period of more than three months with almost no sedimentation. Ag NSs grown on rGO sheets provided the platform for the growth of AgHg-amalgam crystals upon the addition of Hg(II) ions in solution. The platform as a sensor-probe underwent a color change from yellow to colorless in the presence of Hg(II) ions. In the optical sensing based on the color changes, the detection limit was 3.6 nM and the linear range was 10-100 mM.