Proposed Substrates For Reproducible Surface-Enhanced Raman Scattering Detection

The electromagnetic contribution to the surface-enhanced Raman scattering (SERS) derives from the distribution of electromagnetic hot spots around nanostructured metal surfaces. For an optimized SERS signal, analyte molecules need to be placed within the intense electric fields localized at these hot spots. Using numerical simulations, we demonstrate the possibility of creating controllable hot spots through proper engineering of the plasmonic modes supported by periodic arrays of nanoscale cavities in thin silver films. We investigate the tunability of surface plasmon resonance wavelength and local field enhancement by systematically varying the sample thickness, periodicity, and the nanocavity morphology. The gradual evolution of the absorption spectrum with these parameters helps reveal the relative contributions from surface plasmon polaritons propagating or localized at the metal surfaces. The calculations suggest that when the nanocavities are deep relative to the film thickness, there is strong confinement of surface plasmons which produces several orders of magnitude enhanced electric fields across the cavity bottom surfaces. Enhanced local electric field at the bottom of the cavity provides an efficient optical trap and the system can be used for reproducible SERS detection, especially for big nanometer sized biomolecules. © 2011 American Chemical Society