SPR and SERS characteristics of gold nanoaggregates with different morphologies

In this study, surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS) characteristics of gold nanoaggregates with different morphologies are examined to elucidate the correlation between SPR and SERS of the object. Nanoaggregates, defined as random aggregates (hereafter RA), elongated aggregates (hereafter EA) and two-dimensional layered aggregates (hereafter 2DLA) are fabricated by immobilizing colloidal gold nanoparticles on glass substrates. The color variation observed in the RA and EA samples indicates the variation in localized SPR excitations excited on the samples. The RA sample mostly shows a broadened and shifted SPR peak centered at 570 nm in addition to another peak in the longer wavelength region (similar to 700 nm), whereas in the EA sample a weak blue-shifted peak is observed near 450 nm in addition to a broadened peak centered at 570 nm covering a trail for another one near 700 nm. In the case of the 2DLA sample, more than one SPR peaks are observed in the longer wavelength region. The SERS observation confirms million times higher enhancement at least in Raman intensity using the gold nanoaggregates adsorbed by dye molecules. The EA sample of gold nanoparticles shows similar to 5 times higher enhancement in Raman signal compared to that of the RA and 2DLA sample.