Stabilization of hydroxyl-group-terminated SERS-marker molecules on μAg particles by silanization

Micrometer-sized Ag (μAg) 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 μAg powders is a surface-enhanced Raman scattering (SERS) spectrum. To use μAg 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 μAg 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 μAg 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.

μAg powders covered with 4-mercaptophenol as SERS-marker molecules are readily coated with silica shells so that the powders can be used as a core material of molecular sensing/recognition units operating via SERS after target molecules are attached onto the silica layer.Figure optionsDownload as PowerPoint slide