3D Self-Assembly of a Bilayer Nanoparticle Metasurface for Surface-Enhanced Raman Scattering (SERS) Sensing

Controllable periodic nanoparticle (NP) metasurfaces exhibit unique optical responses, which are crucial for applications in plasmonic sensing, photocatalysis, and nanoscale optical manipulation. Compared with monolayer NPs, bilayer NPs generate additional electromagnetic field localization effects between the layers, exhibiting enhanced light absorption and scattering. Here, we propose a novel method that assembles the monolayer NPs at a three-dimensional liquid-liquid interface (3D-LLI) into large-area two-dimensional bilayer NPs. This method not only allows for the construction of independent bilayer structures for fundamental research on metasurfaces but also enables the formation of "sandwich"-type interlayer structures for in situ SERS detection of both microparticle analytes such as polystyrene (PS), polyethylene terephthalate (PET), and poly(methyl methacrylate) (PMMA) and small molecules such as melamine, cysteine (Cys), and iminothiourazole (AMT).