Abstract
Anodic porous alumina (APA) is a nanostructured material used as a template in several nanotechnological applications. We propose the use of APA in ultra-thin form (<100 nm) for augmented surface-enhanced Raman scattering (SERS). Here, the effect of in-depth thinning of the APA nanostructures for possible maximization of SERS was addressed. Anodization was carried out on ultra-thin films of aluminum on glass and/or silicon, followed by pore-opening. Gold (Au) was overcoated and micro-Raman/SERS measurements were carried out on test target analytes. Finite integration technique simulations of the APA-Au substrate were used both for the experimental design and simulations. It was observed that, under optimized conditions of APA and Au thickness, the SERS enhancement is higher than on standard APA-Au substrates based on thin (~100 nm) APA by up to a factor of ~20 for test molecules of mercaptobenzoic acid. The agreement between model and experimental results confirms the current understanding of SERS as being mainly due to the physical origin of plasmon resonances. The reported results represent one step towards micro-technological, integrated, disposable, high-sensitivity SERS chemical sensors and biosensors based on similar substrates.
Highlights
Anodic porous alumina (APA) is a nanostructured material obtained through controlled anodization of aluminum (Al) substrates [1]
We will assign the thickness of the starting Al to the APA resulting from its full anodization
We have presented one step towards even more efficient APA-based surface-enhanced Raman scattering (SERS) substrates based on the fabrication of APA layers, called utAPA, thinner than 100 nm
Summary
Anodic porous alumina (APA) is a nanostructured material obtained through controlled anodization of aluminum (Al) substrates [1]. APA may find important primary applications in both photonics, for example, to make photonic crystals [4] and distributed feedback lasers [5], and in biological and biomedical studies as a substrate with controlled nanoscale roughness for optimized adhesion and the growth of living cells in cultures [6,7]. In the latter field, APA has been proposed as a substrate for drug delivery, taking advantage of the volume of the nanopores for loading and the subsequent localized elution of bioactive agents (molecules or nanoparticles) [8,9,10]. In an effort to combine both above-mentioned properties, namely the possible optoelectronic functionality of the nanostructure with the ability to sustain living cells on its surface, in our group, we have recently started to assemble dedicated APA-based devices aimed to perform surface-enhanced Raman scattering
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