Three-dimensional AgNPs-graphene-AgNPs sandwiched hybrid nanostructures with sub-nanometer gaps for ultrasensitive surface-enhanced Raman spectroscopy

Abstract We report a novel and efficient fabrication strategy for three-dimensional (3D) AgNPs-monolayer graphene-AgNPs (AGA) hybrid sandwiched nanoplasmonic structure. The structure is constructed by one layer of 2D AgNPs and one layer of 3D AgNPs using monolayer graphene as a spacer, which combines the advantages of graphene-veiled AgNP substrate, 3D crumpled graphene-AgNPs hybrid structure and traditional AGA sandwiched structure with sub-nanometer gaps to obtain the excellent performance in both light-graphene interaction and surface-enhanced Raman scattering (SERS) sensing capability. The fabricated 3D AGA structure exhibits a 424-fold enhancement of the Raman response of graphene. When being used as SERS substrate, 3D AGA has demonstrated remarkable SERS detection sensitivity among all existing AGA structures. 3D AGA exhibits the high Raman enhancement factors of up to 2.7 × 10 9 and a detection limit of as low as 1.0 × 10 −14  M for Rhodamine 6G (R6G) molecules. Finite element numerical simulations reveal that the 3D AGA structure supplies an electric field enhancement up to 191 times.