Fabrication of core shell Au@Ag supraparticles with 3D hotspots via evaporation self-assembly for sensitive surface enhanced Raman scattering detection

Three-dimensional (3D) plasmonic nanostructures exhibit excellent surface-enhanced Raman scattering (SERS) performance for detecting trace analytes. Nevertheless, fabrication of 3D plasmonic SERS substrates with non-close packed structures via simple evaporation assembly still remains a challenge. Here, we successfully prepared 3D supraparticles in millimeter scale via a simple evaporation assembly of highly concentrated core-shell Au@Ag nanoparticles (NPs) on hydrophobic surface. The formation of supraparticles could account for hydrophobic condensation effect, the huge numbers of spherical NPs, and unique core shell structure of Au@Ag NPs. Such supraparticle was consisting of more than 10(4) of Au@Ag NPs where nanogaps among NPs created plenty of 3D "hotspots". The supraparticles with non-close packed structure is benefit for the diffusion of more targets into the hotspots, leading to enhanced interactions that contribute to a higher sensitivity. It was demonstrated that supraparticles could provide great enhancement for SERS behavior, which was eight folds higher than that of Au@Ag NPs assembled 3D multilayered structures. In addition, supraparticles with excellent sensitivity and high reproducibility were successfully applied in the detection of pesticide and antibiotics both in organic and aqueous solvents. This work provides a new way for the fabrication of 3D plasmonic nanostructures with highly sensitive and reproducible SERS performance.