The incorporation of metal nanoparticles with various size and shapes provides silica gels with optical functionalities arising from the characteristic optical properties of the starting nanoparticle dispersions. The uniform distribution of the preformed nanoparticles and their mutual separation within the gels are key factors to maintain single-particle properties. These requirements are achieved by coating the nanoparticles with thin silica shells, which greatly enhance their stability and ensure separation between metal nanoparticle cores. The great advantage of this procedure is its ability to use nanoparticles with tailored shapes and thus to expand the possible functionalities to be implemented. We show the incorporation of gold nanorods with varying aspect ratio, which allows to have well-defined absorption bands even in the near infrared. (C) 2003 Elsevier B.V. All rights reserved.