Nanostructured Thin-Film Materials with Surface-Enhanced Optical Properties

We report the rational design and development of nanostructured thin-film materials that are highly efficient for surface-enhanced optical processes such 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 topographic studies of single nanoparticles, which reveal a strong relationship between particle size and the excitation wavelength for efficient optical enhancement. The enhancement efficiencies are dependent on the particle size, the excitation wavelength, and the presence of activating ions such as Cl- and Br-. These nanostructured films provide a reproducible SERS substrate for ultrasensitive detection and spectroscopy of native biological molecules.