A multiple coupling approach to produce high-performance SERS substrates

Creating hotspots with significantly enhanced electromagnetic (EF) field, efficiently placing target molecules in hotspot region, and achieving uniform and reproducible Raman signals are three critical issues for developing high-performance SERS substrates. In this work, large area gold nanoparticle cluster pillar array with a gold mirror at bottom was facilely fabricated by combined use of nanosphere lithography and self-assembly approach. It is both theoretically and experimentally found that through multiple coupling interactions, the electromagnetic fields at interparticle gaps within the gold clusters were significantly enhanced in our three-dimentional (3D) pillar array substrates, which can result in one order of magnitude stronger as compared with random gold clusters on a two-dimentional planar case. Due to the periodic stucture, our substrates also possess the capbility of producing highly uniform and reproducible SERS signals. Attractively, in our case, a photoresponsive polymer was used for the formation of pillar array structure. Its unique photoinduced deformation makes it possible to reversibly open and close the gaps of the closely packed Au NP array, thus enabling efficient placement or entrapment of probe molecules into hotspot sites between adjacent nanoparticles.