SERS response from gold nanorods and dumbbells

Abstract

It is now believed that the on-resonance excitation of the plasmonic nanoparticle is necessary to increase the Raman signal intensity of nearby molecules. On this basis, researchers try to fabricate rationally designed nanoparticles for surface-enhanced Raman scattering (SERS) applications with plasmon resonance close to wavelength of excitation. However, existing experiments show inconsistent results of measuring the dependence of the enhancement factor as a function of nanopaticle plasmon resonance. To fill the gap, we use the method of controllable etching to prepare set of Au nanorod colloids with the equal concentration, nanorod width, shape and tunable plasmon resonance that incrementally spanned 650-920 nm. Nanorods were functionalized with 4-nitrobenzenethiol and surface-enhanced Raman spectra were measured in colloid under 785 nm laser excitation. As a result we observe weak correlation between nanorod plasmon peak and SERS response. The ratio of SERS signals for on-resonance and of-resonance excitation was below 2. Nanorods were further overgrowth to have dumbbell morphology. This transformation leads to strong increase in SERS enhancement factor. Thus tuning of nanoparticles shape is more important factor towards highest SERS response compared to nanoparticle plasmonic peak.