1 LARGE-SCALE LITHOGRAPHY-FREE FABRICATION OF SERS SUBSTRATES BY GOLD COATING OF ANODIC POROUS ALUMINA Marco Salerno, Gobind Das, Niranjan Patra, Andrea Toma, Enzo Di Fabrizio, Alberto Diaspro Italian Institute of Technology, via Morego 30, I-16163 Genova, Italy Self-assembled nanoporous anodic alumina coated with thermally evaporated gold is demonstrated as a large area substrate for surface-enhanced Raman scattering. Using crystal violet dye a competitive enhancement of 10 5 -10 7 is obtained, with remarkable fluorescence suppression. 1. Introduction Surface-enhanced Raman scattering (SERS) is an analytical technique extensively used in chemistry, biology and forensic science applications, due to its excellent sensitivity for molecular vibrations [1-3]. The overall enhancement of the Raman signal comes in SERS after a combination of an electromagnetic effect, due to resonant excitation of localized surface plasmons in noble metal surface structures, and on a chemical effect due to the efficient charge transfer between the substrate and the dye molecules. So far, the noble metal nanoparticulate pattern on the substrate has been obtained either by random deposition of colloidal particles [4,5], which can provide large areas, or by lithographical writing of features, which allows to fabricate highly regular patterns [6,7]. The drawbacks of these techniques are the lack of order in the obtained hot-spots, due to the stochastic character of the process, and the relatively small patterned surfaces (of typically mm 2 area), due to the serial character of the adopted high-resolution electron beam lithography technique, respectively. Trade-off between the two above limitations has been addressed so far mainly by means of natural lithography techniques, such as shadow evaporation through self-assembled arrays of polystyrene nanospheres [8]. Recently, use of anodic porous alumina (APA) has been proposed as a substrate with enhanced effective surface area for MEMS sensors [9]. In the field of SERS, APA has also been tested as a template for patterning of noble metal structures, mainly based on silver due to its high potential plasmon enhancement [10]. However, silver based SERS devices show poor durability, due to the fact that metal surface oxidizes rapidly in air. In this work, a commercial APA template was used as a starting substrate for the SERS device. The APA template was coated with a gold layer of ∼25 nm thickness, such that the large scale uniform surface features present on the APA were replicated into the overcoating gold features. Crystal violet was then deposited onto the gold coated APA substrate by means of chemisorption, such as to attain substance monolayer. Finally, SERS measurements were performed on the prepared APA based device, for the first time, to our knowledge, with the present combination of substrate and sensitive molecule. 2. Experimental 2.1. Preparation of the APA-based substrate The commercial APA selected for use was Whatman Anopore (purchased from SPI Supplies, West Chester, USA), in the variety of 200 nm pore diameter. This APA comes as self-standing discs, of which the oxide layer has been set free of the aluminium substrate.