Sequentially Self-Assembled Rings-in-Mesh Nanoplasmonic Arrays for Surface-Enhanced Raman Spectroscopy

The discovery of the surface-enhanced Raman scattering (SERS) effect provided a revolutionary solution to the issue of low sensitivity in Raman spectroscopy. For more widespread application of SERS analysis, however, practical fabrication of well-defined ultrasmall nanostructures having large SERS signal enhancement capability and large-area signal uniformity is still a major challenge. Here, we report that rings-in-mesh Au nanostructures, which can be obtained by the consecutive self-assembly of polystyrene nanospheres and block copolymers (BCPs) with far different length scales, provide multiple advantages for SERS analysis in terms of signal amplification and measurement reproducibility. Significant signal enhancement is achieved by the hierarchical geometry composed of a submicrometer nanomesh and sub-10-nm nanogaps, which can be obtained from the self-assembly phenomena of polystyrene nanospheres and siloxane-based BCPs, respectively. Moreover, the two-dimensionally isotropic characteristics of the concentric nanoring structures eliminate the angular dependence of the SERS signal intensity and provide excellent reproducibility of measurement over a large area.