COLLOIDAL METAL-FILMS AS A SUBSTRATE FOR SURFACE-ENHANCED SPECTROSCOPY

Colloidal films of gold and silver were prepared on glass or quartz sl ides. The slides were derivatized with (3-mercaptopropyl)trimethoxysil ane and subsequently reacted with aqueous metal colloids for variable time periods. The formation of the sulfur-metal bond provides a stable colloidal film on the surface. Because of the electrostatic interacti on between individual particles, a semiregular structure is produced, as can be seen from electron micrographs. The unique property of the c olloidal film is that they possess the optical properties of colloidal metals and the convenience of solid substrates. The effect of the die lectric constant of solvents on the optical frequencies, as well as th e specific interaction of the solvent molecules with the metal on the plasmon resonances, was examined in detail. The colloidal films exhibi t strong enhancement of Raman scattering and fluorescence emission fro m molecules adsorbed on the surface. Enhancement of fluorescence was o bserved for fluorescein-labeled molecules spaced 0-200 Angstrom away f rom the surface. These substrates can be used in a number of analytica l applications, such as surface-enhanced spectroscopies as well as for fundamental studies of plasmon resonances in small metal particles.