Ag-coated polymeric nanopillar array for quantitative chemical sensing by surface-enhanced Raman spectroscopy

Abstract

Surface-enhanced Raman spectroscopy (SERS) is undoubtedly one of the most useful physical chemistry techniques for highly sensitive molecular detection. It is now well understood that the plasmonic coupling effect at the nanometer gap junction between particles induces enormous electromagnetic enhancement that allows SERS signal to be detected with single-molecule sensitivity. In this study, we provide a simple, low-cost method, based on the production process of nanoporous anodic aluminum oxide (AAO), to fabricate polymeric nanopillar structure which can be used as high sensitivity SERS substrate. In details, the nanoporous anodic aluminum oxide was used as the template for the fabrication of uniform nanopillar array. The shape of nanopillar was carefully controlled by periodical modulation of anodizing and pore widening. And, to produce electric field for SERS, Ag nanoparticles were coated on the nanopillar array. The Ag-coated polymeric nanopillar substrate provided higher sensitivity of SERS spectra for Rhodamine 6G than Ag-coated flat polymeric substrate (without nanopillar). As the diameter of nanopillar was controlled by anodizing time accordingly, changes of nanogap size caused different SERS signal sensitivity. Furthermore, the shape of nanopillar and aging temperature were interestingly crucial factors for the improvement of sensitivity and reproducibility of SERS signal.