Advanced Nanoporous Anodic Alumina-Based Optical Sensors for Biomedical Applications

Abstract

Close-packed hexagonal array nanopores are widely used both in research and industry. A self-ordered nanoporous structure makes anodic aluminum oxide (AAO) one of the most popular nanomaterials. This paper describes the main formation mechanisms for AAO, the AAO fabrication process, and optical sensor applications. The paper is focused on four types of AAO-based optical biosensor technology: surface-Enhanced Raman Scattering (SERS), surface Plasmon Resonance (SPR), reflectometric Interference Spectroscopy (RIfS), and photoluminescence Spectroscopy (PL). AAO-based optical biosensors feature very good selectivity, specificity, and reusability.

Effect of Au Plasmonic Material on Poly M-Toluidine for Photoelectrochemical Hydrogen Generation from Sewage Water

“…These two phenomena can appear well through the optical analyses (Figure 5A,B) and the electrochemical curve and H2 moles produced (Figure 6a-f). Under the light incident, there is an electron transfer from the LUMO to HUMO for the PMT [60]; then, these electrons oscillate on the surface of the PMT and transfer the energy from the Au to PMT. The wide range of absorbance related to the PMT/Au composite increases the electron generation on the surface that is finally collected on the PMT surface under the LSPR process [61].…”

Anodic Alumina Membranes: From Electrochemical Growth to Use as Template for Fabrication of Nanostructured Electrodes

“…Intermediate pore diameters (~70 nm) can be achieved by anodizing in 0.45 M oxalic acid. Additionally, the pore aspect ratio (length/width) can be easily controlled by adjusting the passed electrical charge, while the inter-pore distance can be varied in dependence on anodizing voltage, typically, in the interval 2.5 ÷ 2.8 nm V −1 [44,45].…”

“…PAA has found increasing diffusion as a template for nanostructured materials [20,31,41,45,47,48], for applications in microelectronics [49,50], solar cells [30,[51][52][53], filtration [16,54,55], batteries [56][57][58][59], separation of biomolecules [60,61], catalysts [62,63], and other bio-medical sectors [64,65]. The success of PAA as the template is due to its easy dissolution after the filling up of the pores, leading to 1D parallel and perpendicular nanostructures.…”

On the Nature of Self-Organization of Porosity During Aluminum Anodization

“…2−4 New applications regarding PAOX are characterized by the publication of advanced synthesis methods for nanomaterials, for which PAOX serves both as a template 5 and as a basis for the production of photonic crystals, 6 hierarchical pore structures, 7 ordered three-dimensional, interconnected nanostructures, 2 and sensors. 5,8 This popularity of PAOX for various nanotechnological applications is mainly due to the simplicity of its synthesis, 2,6,9,10 which is realized by a straightforward electrochemical process governed by the type of electrolyte, its bulk concentration c 0 and temperature T. 5,7,11 As a consequence of the simplicity of the experimental fabrication, many studies have been published in the past decades which investigate the influence of the mentioned parameters on the structural properties of PAOX and the arrangement of its pores. 5,7,11 In the so-called "self-ordering regime" 12 at specific electrical potentials ΔU max , the pores self-organize to form a hexagonal closed packing or honeycomb structure.…”

“…Aluminum is probably the most important under all these metallic elements. Since the discovery of the structural features of porous aluminum oxide (PAOX) on anodized aluminum in 1953 by Keller et al, a widespread scientific interest has emerged in which new findings continue to be published. − New applications regarding PAOX are characterized by the publication of advanced synthesis methods for nanomaterials, for which PAOX serves both as a template and as a basis for the production of photonic crystals, hierarchical pore structures, ordered three-dimensional, interconnected nanostructures, and sensors. , This popularity of PAOX for various nanotechnological applications is mainly due to the simplicity of its synthesis, ,,, which is realized by a straightforward electrochemical process governed by the type of electrolyte, its bulk concentration c 0 and temperature T . ,, As a consequence of the simplicity of the experimental fabrication, many studies have been published in the past decades which investigate the influence of the mentioned parameters on the structural properties of PAOX and the arrangement of its pores. ,, In the so-called “self-ordering regime” at specific electrical potentials ΔU max , the pores self-organize to form a hexagonal closed packing or honeycomb structure . It can occur several times within the applicable ΔU -range. , Beside these experimental findings, a number of theoretical − and semiempirical − theories exist to explain or predict PAOX and the nature of its formation. − These existing theories can be categorized into different fields, which deal with either the pore initiation and formation, , the initiation of the porous structure and its growth, , the dependencies of the PAOX properties on the applied current or voltage, , or the self-organization of pores including their arrangement. ,,, Nevertheless, the self-organization process of pore arrangement and its relation to the ΔU max values is currently still far...…”