Plasmonic Nanowires for Wide Wavelength Range Molecular Sensing.

Giovanni Marinaro,Andrea Giugni,Jurgen Kosel,Marco Allione,Enzo Di Fabrizio,Gobind Das,Patrizio Candeloro,Bruno Torre

doi:10.3390/ma11050827

Giovanni Marinaro, Andrea Giugni + Show 6 more

Open Access

https://doi.org/10.3390/ma11050827

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Abstract

In this paper, we propose the use of a standing nanowires array, constituted by plasmonic active gold wires grown on iron disks, and partially immersed in a supporting alumina matrix, for surface-enhanced Raman spectroscopy applications. The galvanic process was used to fabricate nanowires in pores of anodized alumina template, making this device cost-effective. This fabrication method allows for the selection of size, diameter, and spatial arrangement of nanowires. The proposed device, thanks to a detailed design analysis, demonstrates a broadband plasmonic enhancement effect useful for many standard excitation wavelengths in the visible and NIR. The trigonal pores arrangement gives an efficiency weakly dependent on polarization. The devices, tested with 633 and 830 nm laser lines, show a significant Raman enhancement factor, up to around 6 × 104, with respect to the flat gold surface, used as a reference for the measurements of the investigated molecules.

Highlights

Surface enhanced Raman scattering (SERS), one of the elected techniques in material science, as well as in biological investigation, for low molecular concentration detection and chemical bond analysis, has been greatly developed, demonstrating a sensitivity down to single molecule detection [1,2].By using SERS, it is possible to detect molecules adsorbed or lying in the proximity of the surface of metallic nanostructures, where a giant and strongly confined electric field is superimposed to a chemical SERS [3].A large amount of quite different SERS substrates has been already proposed, ranging from chemically roughened metallic surfaces to patterned nanostructures
We investigate the fabrication of forest-type gold nanowire SERS substrates by means of an optimized electrochemical technique, realizing them in a fast and cost-effective process with a large active area of cm2 range [25,26]
We studied partially immersed in plane, the anodic porous alumina (APA)

Summary

Introduction

Surface enhanced Raman scattering (SERS), one of the elected techniques in material science, as well as in biological investigation, for low molecular concentration detection and chemical bond analysis, has been greatly developed, demonstrating a sensitivity down to single molecule detection [1,2].By using SERS, it is possible to detect molecules adsorbed or lying in the proximity of the surface of metallic nanostructures, where a giant and strongly confined electric field (hot spots) is superimposed to a chemical SERS [3].A large amount of quite different SERS substrates has been already proposed, ranging from chemically roughened metallic surfaces to patterned nanostructures. As diverse as nano-spheres, -antennas, -cuboids, -holes, -triangles, honeycombs, etc., have been demonstrated to be a viable and effective solution. In all those systems, the aim is to obtain electrical near field localization at subwavelength scales. The enhancement is due to localized surface plasmon resonance (LSPR) of a single or of an interacting array of nanostructures [4,5]. Background Raman measurement, in the same figure, clearly indicates clearly that the substrate was free from any impurities.

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