Highly sensitive and reproducible SERS substrates with binary colloidal crystals (bCCs) based on MIM structures

Abstract

Surface-enhanced Raman scattering (SERS) is a powerful molecular vibrational spectrum characterization method, and has shown promising applications in surface science, life science, environmental monitoring, etc. Developing new simple processes to fabricate low-cost substrates is an essential prerequisite to promote and strengthen the practical application of the SERS technique. For this purpose, the present work reports on the development of a metal/insulator/metal (MIM) structure combined with polystyrene (PS) binary colloidal crystals (bCCs) based on nanosphere self-assembly and electron-beam evaporation technologies. The PS bCCs are used to form a dielectric layer sandwiched between a bottom Ag reflection layer and an upper Ag shell layer. Compared with single-sized colloidal spheres, the PS bCCs exhibit considerably richer morphologies and structures. In addition, the closely packed Ag shell arrays enhance the density of electromagnetic field “hot spots” thus increasing the SERS activity. The PS bCCs-based MIM substrate could achieve an enhancement factor (EF) of 1.10 × 108 and an ultralow detection limit for the Rhodamine 6G (R6G) molecule of about 10−14 M. The results demonstrate that the proposed substrates with a facile fabrication strategy, low cost, large area and high sensitivity have high potential applications of SERS sensors for bio- and chemical molecular analysis.