Combinatorial Approach to Find Nanoparticle Assemblies with Maximum Surface-Enhanced Raman Scattering

Plasmonic nanoparticles exhibit unique properties that distinguish them from other nanomaterials, including vibrant visible colors, the generation of local electric fields, the production of hot charge carriers, and localized heat emission. These properties are particularly enhanced in the narrow nanogaps formed between nanostructures. Therefore, creating nanogaps in a controlled fashion is the key to achieving a fundamental understanding of plasmonic phenomena originating from the nanogaps and developing advanced nanomaterials with enhanced performance for diverse applications. One of the most effective approaches to creating nanogaps is to assemble individual nanoparticles into a clustered structure. In this study, we present a fast, facile, and highly efficient method for preparing core@satellite (CS) nanoassembly structures using gold nanoparticles of various shapes and sizes, including nanospheres, nanocubes (AuNCs), nanorods, and nanotriangular prisms. The sequential assembly of these building blocks on glass substrates allows us to obtain CS nanostructures with a 100% yield within 4 h. Using 9 different building blocks, we successfully produce 16 distinct CS nanoassemblies and systematically investigate the combinations to search for the highest Raman enhancement. We find that the surface-enhanced Raman scattering (SERS) intensity of AuNC@AuNC CS nanoassemblies is 2 orders of magnitude larger than that of other CS nanoassemblies. Theoretical analyses reveal that the intensity and distribution of the electric field induced in the nanogaps by plasmon excitation, as well as the number of molecules in the interfacial region, collectively contribute to the unprecedentedly large SERS enhancement observed for AuNC@AuNC. This study not only presents a novel assembly method that can be extended to produce many other nanoassemblies but also identifies a highly promising SERS material for sensing and diagnostics through a systematic search process.