Hexagonal Close-Packed Au@Ag Superlattices for Versatile and Cost-Effective SERS Platforms.

The rapid fabrication of low-cost surface-enhanced Raman scattering (SERS) substrates is highly desirable for chemical and biological sensing. Existing customized SERS substrates, such as Au or Ag nanostructures produced by physical deposition, frequently involve complex fabrication routes, which limits the scalability of SERS devices. Here, we present the hexagonal close-packed plasmonic superlattices as an efficient, low-cost and applicable SERS platform, fabricated by scalable seed-mediated growth and interfacial self-assembly methods. We systematically compared Ag, Au, and Au@Ag nanospheres (NSs) of different sizes and demonstrated that the plasmonic superlattices made by 55 nm Au@Ag NSs exhibit the strongest Raman response, highest sensitivity, lowest detection limit, good spatial uniformity, and broad applicability. Simulations and Raman mapping experiments further confirm that Au@Ag NSs achieve an optimal balance between hotspot density and plasmonic field intensity, allowing for direct identification and quantification of diverse biochemical targets.