Plasmon-sampled surface-enhanced raman excitation spectroscopy on silver immobilized nanorod assemblies and optimization for near infrared (λ_ex = 1064 nm) studies

For many Surface-Enhanced Raman Spectroscopy (SERS) applications, the enhancing substrate must exhibit a number of critical properties that include low cost, robustness, and reproducibly high enhancement over large areas of the substrate. In this study we investigate the SERS fundamental enhancement factor of silver Immobilized Nanorod Assembly (AgINRA) substrates as a function of both the dielectric sphere diameter (310-780 nm) and the input laser wavelength (633-1064 nm) with a technique called plasmon-sampled surface-enhanced Raman excitation spectroscopy (PS-SERES). The nonresonant molecule benzenethiol was chosen as the probe molecule. Higher enhancement factors (EFs) were measured as the plasmon resonance and excitation wavelength's relative separation were optimized and both moved toward the infrared region, ultimately eclipsing the 10⁸ mark. This is the highest EF to date measured on this type of large-area substrate. The enhancement factors reported here are the result of efficient coupling between free space photons and the surface plasmon states in the metal INRA substrate. Coupled with their robustness and ease of fabrication, these results further underscore the value and versatility of metal INRA substrates in the field of surface-enhanced Raman spectroscopy.