Nanostructured thin-film materials with surface-enhanced optical properties

We report the rational design and development of nanostructured thin-film m aterials that are highly efficient for surface-enhanced optical processes s uch as surface-enhanced Raman scattering (SERS). These materials consist of fractionated colloidal Ag particles in the size ranges of 30-50, 50-80, 80 -100, and > 100 nm. The basic rationale comes from correlated optical and t opographic studies of single nanoparticles, which reveal a strong relations hip between particle size and the excitation wavelength for efficient optic al enhancement. The enhancement efficiencies are dependent on the particle size, the excitation wavelength, and the presence of activating ions such a s Cl- and Br-. These nanostructured. films provide a reproducible SERS subs trate for ultrasensitive detection and spectroscopy of native biological mo lecules.