POROUS SOL-GEL SILICATES CONTAINING GOLD PARTICLES AS MATRICES FOR SURFACE-ENHANCED RAMAN-SPECTROSCOPY

Silicate glass made by the sol-gel technique containing physically enc apsulated gold particles is a unique matrix for surface-enhanced Raman spectroscopy (SERS). The matrix is optically transparent and contains pores that are large enough to allow small molecules such as pyridine and pyrazine in solution to diffuse through the solid glass to the go ld particles (diameters of the order of 100 Angstrom). Two methods of preparing the glass are discussed. A photochemical method uses organom etallic gold precursor compounds that are dissolved in the sol and enc apsulated in the growing silicate network. UV irradiation of the doped monoliths causes the photodeposition of gold particles within the sil ica gel or xerogel. The particle size is controlled by the irradiation time and by the form of the matrix at the time of deposition. Second, colloidal gold in aqueous solution is mixed with the sol and the inor ganic glass forms around the particles. The particles are characterize d by their electronic absorption spectra, x-ray diffraction and transm ission electron microscopy. The transparent, porous monoliths are exce llent substrates for SERS. The sol-gel matrix stabilizes the gold part icles (in comparison with colloids in liquid media) and SERS can be us ed to detect molecules that penetrate the matrix. The SERS effect is v erified by the enhancement of the Raman bands and by the changes in th eir polarization ratio.