Green synthesis of multi-dimensional plasmonic coupling structures: Graphene oxide gapped gold nanostars for highly intensified surface enhanced Raman scattering

Abstract

Graphene-mediated surface-enhanced Raman scattering (SERS) substrates are currently explored for ultrasensitive detection and expected to provide uniform SERS response by the virtue of graphene and plasmonic metal nanostructures. Here, we integrated graphene oxide (GO) and anisotropic metal nanostructures to create a novel multiple coupling system, in which ultrathin GO as nanospacer was sandwiched between two layers of closely packed gold nanostars (AuNSts). The sandwiched hybrid was prepared through alternative loading of AuNSts and graphene oxide (GO) film via filtration and spin-coating methods in the absence of any polymer stabilizer or organic linkage agent. The morphologies and plasmon resonance of AuNSts could be tuned by simply adjusting the synthesis parameters. Due to the multi-dimensional plasmonic coupling in horizontally and vertically patterned AuNSts, extra chemical enhancement and outstanding molecule harvesting capability from GO interlayer, the as-prepared AuNSt-GO-AuNSt sandwich structures manifested ultrahigh sensitivity and excellent reproducibility (the signal variations <6%). A detection limit of rhodamine-6G (R6G) as low as 10−13 M and a high enhancement factor of 6.64 × 107 were achieved. Particularly, the AuNSt-GO-AuNSt system was applied to detect erythrosine B and chrysoidin down to 10−9 M as well as offer spectroscopic identification in complicated solutions, indicating great potential practical applications for the rapid and sensitive on-site monitoring, especially for food and environmental safety.