Micrometer-sized Ag (mu Ag) powders are very efficient substrates for both the infrared and Raman spectroscopic characterization of molecular adsorbates assembled on silver. In particular, the Raman spectrum of organic monolayers on mu Ag powders is a surface-enhanced Raman scattering (SERS) spectrum. To use mu Ag powders as a core material for constructing molecular sensing/recognition units operating via SERS, it is first necessary to stabilize the SERS-marker molecules that are directly in contact with the mu Ag powders. One promising strategy is the fabrication of silica shells onto SERS-marker molecules, and herein we demonstrate its feasibility by choosing 4-mercaptophenol (4-MPH) as a model SERS-marker molecule. Due to the presence of the hydroxyl group of 4-MPH, silica was readily deposited onto mu Ag particles by the base-catalyzed hydrolysis of tetraethyl orthosilicate, and its subsequent condensation, to form a cagelike structure. The formation of silica shells was confirmed with infrared, Raman, and X-ray photoelectron spectroscopy, coupled with field emission scanning electron microscopy. We were able to tune the thickness of silica shells simply by varying the silanization reaction time. (c) 2006 Elsevier Inc. All rights reserved.