High purity separation of nanoparticle dimers and trimers for SERS hot spots

Here, we report the ensemble-averaged measurement of SERS hot spots EF from spatially isolated colloidal nanoclusters. This approach was achieved by well-defined Au@Ag core-shell NP dimers and trimers-the simplest structure to investigate SERS hot spots phenomenon. These hot spots units with similar nature were made up of uniform Au@Ag NPs attached by a close-paking Raman reporter monolayer, then stabilized by polymer encapsulation and enriched to high purity by differential centrifugation. To our knowledge this study is the most approximate description of SERS hot spots nanostructures for colloidal ensemble-averaged EF measurement. The calculated averaged EFs are 5.6×10³ for monomer and 0.7×10⁶ for hot spot in dimer. It indicated the SERS intensity of the molecule in gap region is higher than that in the outside region by factor of 125.