Ag-nanocubes/graphene-oxide/Au-nanoparticles composite film with highly dense plasmonic hotspots for surface-enhanced Raman scattering detection of pesticide

Concentration of analyte molecules on or nearby plasmonic nanostructures is crucial for sensitive SERS detection. In this paper, a functional SERS system made of Ag-nanocubes/graphene-oxide/Au-nanoparticles (Ag-NCs/GO/Au-NPs) composite film on a hydrophobic surface is constructed for effective accumulation and thus sensitive detection of target analyte in water. High density of plasmonic hotspots are generated between Au nanoparticles-assembled film and the Ag-NCs/GO hybrid, remarkably improving SERS activity. The hydrophobic surface is used to concentrate the analyte molecules in an aqueous droplet onto the Ag-NCs/GO/Au-NPs film during the droplet drying process. The hydrophilic graphene oxide sheets can adsorb analyte molecules nearby the plasmonic nanoparticles. The corners of Ag nanocubes, and the narrow nanogaps between neighboring palsmonic nanoparticles, could provide high density of hotspots for high SERS activity. Due to the effective accumulation of analyte molecules on/nearby hotspots, sensitive SERS detection of pesticides has been realized. The fabricated SERS platform was employed to successfully detect an aqueous solution of rhodamine 6G with an ultralow concentration (0.5 pM), conforming the high SERS sensitivity. To show the potential for practical application, SERS detection of pesticides such as thiram and thiabendazole in drinking-water was realized with limits of detection (LODs) ~ 0.37 ppb and ~ 8.3 ppb respectively. The functional SERS system may have promising applications in inspection of food safety, monitoring environmental pollutants and so on.