The use of anodized alumina molds for the fabrication of polymer nanopillar arrays as SERS substrates with tunable properties

Abstract

Due to the increasing interest for the sensitive detection of molecules in various scientific fields, surface-enhanced Raman spectroscopy (SERS) arises as a powerful technique that can provide single molecule sensing capability as well as fingerprint specificity. In order to obtain highly enhanced and reproducible Raman signals for such purposes, fabrication of periodically engineered nanostructures with projected hotspot formation is intensively studied. Herein, we report a non-lithographic method for fabricating periodic arrays of plasmonic nanopillars displaying tunable spectral features by employing nanoporous anodic alumina molds (AAMs). AAMs with ˜80 nm and ˜100 nm pore sizes were used to fabricate drop-casted polycarbonate films possessing small nanopillar arrays (SNPC) and large nanopillar arrays (LNPC), respectively. These films were then modified with a facile polydopamine (PDA)-assisted Ag coating step. The SERS spectra of the resultant Ag@SNPC and Ag@LNPC platforms indicate that both the mold topography as well as the coating period has a direct influence on the enhancement of the Raman signals of a model reporter dye. The Ag@LNPC platforms always displayed intensified SERS signals compared to Ag@SNPC counterparts, and this trend was confirmed with simulation studies. The intensity difference was attributed to improved probability of hotspot formation for the more closely arranged nanoantennas on the Ag@LNPC platform. Both substrates showed enhanced SERS signals compared to Ag deposited flat PC substrates and reproducible signals with relative standard deviation values ˜10% were obtained from independently prepared samples.