Natural Graphene Plasmonic Nano-Resonators for Highly Active Surface-Enhanced Raman Scattering Platforms

Highly sensitive and uniform three-dimensional (3D) hybrid heterogeneous structures for use in surface-enhanced Raman scattering (SERS) experiments were fabricated by sequentially decorating high-quality, ultra-clean, graphene quantum dots (GQDs) and Ag nanoparticles (Ag-NPs) onto 3D-graphene. Finite-difference time-domain calculations and scanning Kelvin probe microscopy were used to verify that the Ag-NPs/GQDs/3D-graphene system facilitates substantial electromagnetic enhancement (due to the occurrence of two kinds of “gaps” between the Ag-NPs that form 3D “hot spots”) and additional chemical enhancement (in detecting some π-conjugated molecules). The SERS mechanism was explored in further detail via experimental analysis and confirmed by performing theoretical calculations. The large surface area of the 3D substrate (due to the large specific surface areas of the GQDs and 3D-graphene) results in a better enrichment effect which helps produce lower detection limits. In particular, the detection limits obtained using the Ag-NPs/GQDs/3D-graphene platform can reach 10⁻¹¹ M for rhodamine 6G, 10⁻¹⁰ M for methylene blue and dopamine, and 10⁻⁷ M for tetramethylthiuram disulfide and methyl parathion in apple juice (these are superior to most of the results reported using graphene-based SERS substrates). In summary, the 3D-platform Ag-NPs/GQDs/3D-graphene/Si shows outstanding SERS performance. It therefore has excellent application prospects in biochemical molecular detection and food safety monitoring.