The use of anodic aluminum oxide membranes as a sensing platform for surface-enhanced Raman spectroscopy

Despite the potential sensitivity and the wide range of applications for Surface Enhanced Raman Spectroscopy (SERS), it can not be used as a routine diagnostic tool due mainly to the poor reproducibility of the high intensty SERS signals. In order to obtain reproducibly strong SERS signals, both lithographic and non-lithographic approaches are intensively investigated to produce large-area nanopatterned SERS substrates displaying periodically decorated arrays of nanostructures. Herein, two non-lithographic methods for fabricating periodically decorated plasmonic nanoparticle arrays by using anodic aluminum oxide membranes are presented. These membranes are a class of special biomaterials that are produced from high purity aluminum via two step anodization protocol. The production of these substrates are easy and highly controllable and compared to lithography it is cost-effective. The first part of the study proposes the use of nanobump-decorated barrier sides of the anodic aluminum oxide membranes (AAMs) as SERS substrates. In order to investigate the effect of surface topography on SERS signal intensities, the nanobump-decorated surface (NBDS) is further treated with wet etching to create periodic arrays of nanocraters. SEM and AFM characterizations are performed for the produced platforms. After coating with an optimized thickness of Au through PVD, SERS signal intensities of the nanocrater decorated surfaces (NCDS) and NBDS counterparts are compared by using two different model dyes, Methylene Blue and Congo Red. The experimental data is then confirmed with computer simulations using Comsol 5.0 Optics Module and Lumerical FDTD Solutions. Reproducibility of the signals and the lowest detectable concentration are also investigated. In the second part of the study, the effect of the AAMs pore-size is examined, as they are used as molds to obtain periodically nanopillar-decorated polycarbonate surfaces. Two different pore-sized AAMs are used and silver reduction is performed by coating the surfaces with polydopamine, for the facile creation of plasmonic effect. The obtained surfaces are characterized by SEM and AFM. The intensities of the SERS signals from the obtained surfaces are compared by using Methylene Blue and also is verified with computer simulations using Lumerical FDTD Solutions.