Characteristics of surface-enhanced Raman scattering and surface-enhanced fluorescence using a single and a double layer gold nanostructure

This paper reports the characteristics of surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) using a unique SERS-active substrate comprised of a single layer and a double layer of two-dimensional (2D) gold nanostructure. Colloidal gold nanoparticles were immobilized on a glass substrate and a multi-purpose experimental setup was adopted to obtain surface plasmon resonance (SPR), SERS and SEF on a single platform. Inhomogeneous intensity distribution was observed in correlated images of SPR and SERS. Several laser lines were used as excitation sources for further SERS measurements. Higher SERS intensities were observed with longer wavelength excitations at the same spatial position. Fluorescence measurements were carried out using 514 nm line and SEF images were obtained using the same sample. Fluorescence emissions were found to be enhanced in the presence of 2D gold nanostructure. A series of SERS spectra were recorded by conducting ensemble SERS measurements at a periodic interval of 2 μm, crossing bare substrates, the single layer and the double layer of gold nanostructure. The double layer provides higher enhancement in SERS than that of the single layer. Polarization-selective SERS measurements obtained at the single layer and double layer showed a clear difference in their dispersions. SERS intensities of the analytes adsorbed at the single layer were fitted well with cos4θ dependence; however, for the double layer, the relationship was quite uncertain.