Self-assembled hierarchical nanostructures: towards advanced SERS optrodes

In this work, we report an easy-handling and low-cost method to controllably fabricate surface-enhanced Raman scattering (SERS) active substrates with high density of hot spots. The SERS substrate is composed of a regular pattern of hierarchical structures of plasmonic assisted nanospheres (HSNs). The HSNs exploit the architecture of self-assembled close-packed arrays (CPA) of nanospheres, with hexagonal symmetry. An additional layer of upper nanospheres is incorporated to generate another plot of intense hotspots situated within the nanogaps between adjacent nanospheres. Computational analyses were conducted to delineate the design principles and elucidate factors influencing SERS performance, as well as to pinpoint the most promising structural configurations. HSNs have been fabricated and morphologically characterized. Empirical assessment of the SERS response reveals that HSNs can serve as economically viable SERS substrates exhibiting enhanced performance compared to the more straightforward single-layer CPA arrangements. The proposed approach would represent a general strategy for the fabrication of periodic 3D hierarchical SERS nanostructures with superior performances for Lab on Fiber SERS optrodes.