Nanogap engineering of 3D nanoraspberries into 2D plasmonic nanoclusters toward improved SERS performance.

3D raspberry-like core/satellite nanostructures were prepared by controlled surface functionalization of silica spheres using crosslinked poly(4-vinylpyridine) (P4VP) chains with known binding affinity for gold nanoparticles (AuNPs). The 3D SiO 2 - g -P(4VP- co -DVB)/AuNP nanoraspberries can be further transformed into 2D plasmonic nanoclusters by etching the silica core with hydrofluoric acid (HF). After the transformation, the interparticle distance between the AuNPs dramatically reduced from a 10 nm scale to sub 2 nm. Owing to the strong electromagnetic field generated by the plasmonic coupling between AuNPs in very close proximity, the established P(4VP- co -DVB)/AuNP nanoclusters provided strong and undisturbed Raman signals as a SERS substrate. In addition, benefiting from the stabilizing effect of the crosslinked P(4VP- co -DVB) network, the prepared SERS substrate has the advantages of good uniformity, stability and reproducibility, as well as strong SERS enhancement, endowing it with great potential for rapid and efficient SERS detection.