Abstract
Sub-wavelength diameter holes in thin metal layers can exhibit remarkable optical features that make them highly suitable for (bio)sensing applications. Either as efficient light scattering centers for surface plasmon excitation or metal-clad optical waveguides, they are able to form strongly localized optical fields that can effectively interact with biomolecules and/or nanoparticles on the nanoscale. As the metal of choice, aluminum exhibits good optical and electrical properties, is easy to manufacture and process and, unlike gold and silver, its low cost makes it very promising for commercial applications. However, aluminum has been scarcely used for biosensing purposes due to corrosion and pitting issues. In this short review, we show our recent achievements on aluminum nanohole platforms for (bio)sensing. These include a method to circumvent aluminum degradation—which has been successfully applied to the demonstration of aluminum nanohole array (NHA) immunosensors based on both, glass and polycarbonate compact discs supports—the use of aluminum nanoholes operating as optical waveguides for synthesizing submicron-sized molecularly imprinted polymers by local photopolymerization, and a technique for fabricating transferable aluminum NHAs onto flexible pressure-sensitive adhesive tapes, which could facilitate the development of a wearable technology based on aluminum NHAs.
Highlights
Nanophotonic devices are nanostructures that facilitate the generation, propagation, manipulation, and detection of light [1]
We employed the following process flow to fabricate Al NHAs on glass substrates: (1) deposition of a 100-nm-thick Al layer on glass supports by electron-beam thermal evaporation; (2) ZEP520 resist coating of the Al surface, followed by electron-beam lithography (EBL) exposure to define the nanoholes and subsequent resist development; (3) inductively coupled plasma (ICP) etching of the Al film using the patterned EBL resist as a mask; and (4) rinsing of the etched Al surface to remove residual chloride ions
We have recently found that Al NHAs fabricated on PC compact discs (CDs) surfaces according to the procedure described in Section 3 can be detached by using a general purpose Pressure-sensitive adhesive (PSA) (Scotch) tape [38]
Summary
Nanophotonic devices are nanostructures that facilitate the generation, propagation, manipulation, and detection of light [1]. Remarkable examples of the former are Mach-Zehnder [4] and Young interferometers [5], microring [6], Fabry-Perot [7], and photonic crystal [8] resonators, whereas metal nanoparticles [9] and nanoholes in metal films [10] are the most representative plasmonic nanostructures applied to the field of biosensors Concerning nanoplasmonic devices, those based on metallic subwavelength holes are appealing because of their geometrical simplicity and the possibility of being reliably and uniformly mass-produced through lithographic means [11,12], facilitating massive parallelism. NHAs are ideal structures for the implementation of multiplexed-detection platforms with integrated microfluidics because of their high spatial density and smaller sensing areas than those used in conventional surface plasmon resonance (SPR) coupling techniques like those based on prisms Regarding isolated nanoholes, these can excite surface plasmons [13] and act as metal-clad optical waveguides [12,15].
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