Silver Particle and Silver Thiolate-Based Molecular Sensing/Recognition Units Operating via Surface-Enhanced Raman Scattering

We demonstrate that commercially available 2-μm-sized silver (μAg) powders can be used as a core material for constructing molecular sensing/recognition units operating via surface-enhanced Raman scattering (SERS). This is possible because μAg powders are very efficient substrates for both the infrared and Raman-spectroscopic characterization of molecular adsorbates prepared in a similar manner on silver surfaces. The agglomeration of μAg particles in a highly concentrated buffer solution can be prevented by the layer-by-layer deposition of cationic and anionic polyelectrolytes such as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) onto SERS-marker molecules assembled initially on μAg particles. The outermost PAA layer can be derivatized further, for instance, with biotin-derivatized poly(L-lysine). On the basis of the nature of the SERS peaks of marker molecules, the biotinylated μAg powders are readily confirmed to selectively bind to streptavidin arrays.