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We describe the fabrication of optimized plasmonic substrates in the form of immobilized nanorod assemblies (INRA) for surface-enhanced Raman spectroscopy (SERS). Induded are high-resolution scanning electron micrograph (SEM) images of the surface structures, along with a mechanistic description of their growth. It is shown that, by varying the size of support microspheres, the surface plasmon resonance is tuned between 330 and 1840 nm. Notably, there are predicted optimal microsphere sizes for each of the commonly used SERS laser wavelengths of 532, 633, 785, and 1064 nm. [ABSTRACT FROM AUTHOR]

Here we discuss some of the challenges of using dimers of spheres for SERS at long wavelengths. We show that the field enhancement in the gap between two spheres scales with a local surface plasmon metric, effectively limiting the range of wavelengths for which the largest SERS enhancements can be obtained for this class of structures to the near-IR. [ABSTRACT FROM AUTHOR]

Determining the existence of any direct spectral relationship between the far-field scattering properties and the near-field Raman-enhancing properties of surface-enhanced Raman spectroscopy (SERS) substrates has been a challenging task with only a few significant results to date. Here, we prove that hot spot dominated systems show little dependence on the far-field scattering properties because of differences between near- and far-field localized surface plasmon resonance (LSPR) effects as well as excitation of new plasmon modes via a localized emitter. We directly probe the relationship between the near- and far-field light interactions using a correlated LSPR-transmission electron microscopy (TEM) surface-enhanced Raman excitation spectroscopy (SERES) technique. Fourteen individual SERS nanoantennas, Au nanoparticle aggregates ranging from dimers to undecamers, coated in a reporter molecule and encased in a protective silica shell, were excited using eight laser wavelengths. We observed no correlation between the spectral position of the LSPR maxima and the maximum enhancement factor (EF). The single nanoantenna data reveal EFs ranging from (2.5 ± 0.6) × 104 to (4.5 ± 0.6) × 108 with maximum enhancement for excitation wavelengths of 785 nm and lower energy. The magnitude of maximum EF was not correlated to the number of cores in the nanoantenna or the spectral position of the LSPR, suggesting a separation between near-field SERS enhancement and far-field Rayleigh scattering. Computational electrodynamics confirms the decoupling of maximum SERS enhancement from the peak of the scattering spectrum. It also points to the importance of a localized emitter for radiating Raman photons to the far-field which, in nonsymmetric systems, allows for the excitation of radiative plasmon modes that are difficult to excite with plane waves. Once these effects are considered, we are able to fully explain the hot spot dominated SERS response of the nanoantennas. [ABSTRACT FROM AUTHOR]