Dispersible gold nanorod dimers with sub-5 nm gaps as local amplifiers for surface-enhanced Raman scattering.

We report the synthesis of solution-dispersible, 35 nm diameter gold nanorod dimers with gaps as small as similar to 2 nm for surface-enhanced Raman scattering (SERS). Using on-wire lithography (OWL), we prepared tailorable dimers in high yield and high monodispersity (similar to 96% dimers) that produce both large and reproducible SERS signals with enhancement factors of (6.8 +/- 0.7) x 10(8) for single dimers in air and 1.2 x 10(6) for ensemble-averaged solution measurements. Furthermore, vie show that these structures, which are the smallest ever made by OWL, can be used to detect molecules on flat surfaces and in aqueous solutions. When combined, these attributes with respect to sensitivity, reproducibility, and tailorability lead to a novel and powerful local amplification system for SERS applications.