Silver-particle-based surface-enhanced Raman scattering spectroscopy for biomolecular sensing and recognition

In this study, we demonstrate that 2-mu m-sized Ag (mu Ag) 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 mu Ag powders are very efficient substrates for both the infrared and Raman-spectroscopic characterization of molecular adsorbates prepared in a similar manner on silver surfaces; we can obtain an infrared spectrum of organic molecules adsorbed on mu Ag particles with a very high signal-to-noise ratio by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and the Raman spectrum of organic monolayers on powdered silver is an SERS spectrum. The agglomeration of mu Ag particles in a highly concentrated buffer solution could be prevented by the layer-by-layer deposition of cationic and anionic polyelectrolytes such as poly(allylainine hydrochloride) (PAH) and poly(acrylic acid) (PAA). In fact, prior to depositing PAA and PAH, 4-aminobenzenethiol (4-ABT) was assembled on the surfaces of the mu Ag particles as SERS markers. Because of the presence of amine groups of 4-ABT. PAA could be readily deposited on the mu Ag particles. On the other hand, the outermost PAA layer could also be derivatized with biotinderivatized poly(L-lysine). The nonspecific interaction of poly(L-lysine) with proteins could be suppressed by grafting poly(ethylene glycol) into the biotin-derivatized poly(L-lysine) molecules. On the basis of the nature of the SERS peaks of 4-ABT, it was confirmed that these biotinylated mu Ag powders were effective in selectively recognizing the streptavidin arrays. Because a number of different molecules can be used as SERS-marker molecules. such as probable 4-ABT, commercially available mu Ag powders Must be a prospective material in molecular sensing/recognition, particularly via SERS.