A new optically translucent material has been prepared that acts as a substrate for surface-enhanced Raman spectroscopy. This material is a silica matrix, synthesized by the sol-gel method and containing in situ precipitated AgCl particles which serve as precursors for nanoparticles of elemental silver. Reduction of AgCl to silver nanoparticles is achieved by UV irradiation. The SERS-active medium was distributed on glass supports (cover glass slips, 0.5 turn thick), hence producing thin, sturdy, and optically translucent substrates. SERS activity was evaluated by using brilliant cresyl blue and I-aminopyrene as model compounds. Parameters including the sol-gel composition, the aging period of the sol-gel, and the UV exposure time for photoreduction of the SERS medium were thoroughly investigated. These new substrates have exhibited long shelf lives; furthermore, they can be easily regenerated through a redox cycle involving chemical oxidation and photoreduction steps. In addition to use in direct chemical analysis, this novel type of SERS substrate can be used for indirect monitoring of HNO3 acid vapor via measurement of the SERS signal of 1-aminoyrene, which is attenuated as the substrate is oxidized by the acid vapor. (c) 2004 Elsevier B.V. All rights reserved.