Synergistic plasmon resonance coupling and light capture in ordered nanoarrays as ultrasensitive and reproducible SERS substrates.

An effective SERS substrate for on-field detection needs to satisfy high sensitivity to analyte and signal reproducibility even in the special case of tilting or bending of substrates. Herein, we transferred monolayer AuNPs into a nanocavity to construct a Au particle-in-hemispherical honeycomb nanoarray (PIHHN) as an ultrasensitive and spatially reproducible SERS substrate. The capacity of detection for R6G in an optimal PIHHN substrate is as low as a concentration of 10 M, and the RSD of signal deviation is no more than 5.6%. FDTD simulations explain that placing AuNPs into a metallic nanocavity can capture and focus the light field to improve the interaction between the light and the substrate and provide the collective effect of multiple plasmon coupling, which can induce a stronger electromagnetic field. In addition, the system can generate more hot spots between AuNPs and between AuNPs and the metallic nanocavity. In particular, when the substrate is tilted or bent at an angle from 0° to 60°, the SERS performance remains stable due to the rotational symmetry of the PIHHN structure, which demonstrates the capability of on-field detection. Furthermore, the PIHHN substrate is employed as a highly sensitive multiplex sensor in on-field analysis for contaminated soil, achieving the detection of analytes down to 0.5 ppb.