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. However, the applications of SERS in quantitative detection are still far from well established, due to the difficulty in obtaining reproducible SERS substrates, and hence the SERS signal intensities. Therefore, fabrication of highly reliable SERS substrates is a significant part of SERS development. 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 ordered nanopillar array was successfully realized by pouring acrylate monomer into the AAO template and subsequential curing. 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. Various chemicals, such as rhodamine 6G and some proteins, on the Ag-coated nanopillar array were detected by SERS. The Ag-coated polymeric nanopillar substrate provided higher sensitivity of SERS spectra for various chemicals than Ag-coated flat polymeric substrate (without nanopillar). As the diameter of nanopillar was controlled by anodizing voltage accordingly, changes of nanogap size caused different SERS signal sensitivity. Furthermore, the shape of nanopillar, thickness of Ag-coated layer, and aging temperature were interestingly crucial factors for the improvement of sensitivity and reproducibility of SERS signal.