Synthesis of Magnetic Plasmonic Au/AgAu Heterostructures with Tunable Gap Width for Enhancing Raman Performance

For noble metal core–shell nanomaterials with gaps, inserting Raman reporter molecules into the gaps allows for great Raman enhancement and has found promising applications in molecular analysis, bioimaging, and other fields. Herein, we synthesized Au/AgAu core–shell nanostructures with rhodamine B molecules encapsulated in the nanogap. Au/AgAu heterostructures have magnetic plasmon resonance by selecting gold nanocups as the substrate and tunable gap width by adjusting the molar ratio between Au and Ag during growing the shell. The strong and adjustable plasmon coupling between the core and the shell results in prominent electromagnetic field enhancement. Under the synergistic effect of electromagnetic plasmon resonance and plasmon coupling, the Au/AgAu heterostructures show excellent surface Raman scattering signal. Au/AgAu core–shell nanostructures with ~ 3.2 nm nanogap width display the highest Raman intensity. As the gap width is further reduced, the Raman signal gradually decreases, which may be due to the fact that the thicker alloy shell weakens the light penetration and scattering. Our findings can provide the inspiration for synthesize gap-enhanced Raman tags based on magnetic plasmon coupling.