The hemispherical barrier oxide layer (BOL) closing the bottom tips of hexagonally distributed arrays of cylindrical nanochannels in nanoporous anodic alumina (NAA) membranes is structurally engineered by anodizing aluminum substrates in three distinct acid electrolytes at their corresponding self-ordering anodizing potentials. These nanochannels display a characteristic ionic current rectification (ICR) signal between high and low ionic conduction states, which is determined by the thickness and chemical composition of the BOL and the pH of the ionic electrolyte solution. The rectification efficiency of the ionic current associated with the flow of ions across the anodic BOL increases with its thickness, under optimal pH conditions. The inner surface of the nanopores in NAA membranes was chemically modified with thiol-terminated functional molecules. The resultant NAA-based iontronic system provides a model platform to selectively detect gold metal ions (Au3+) by harnessing dynamic ICR signal shifts as the core sensing principle. The sensitivity of the system is proportional to the thickness of the barrier oxide layer, where NAA membranes produced in phosphoric acid at 195 V with a BOL thickness of 232 ± 6 nm achieve the highest sensitivity and low limit of detection in the sub-picomolar range. This study provides exciting opportunities to engineer NAA structures with tailorable ICR signals for specific applications across iontronic sensing and other nanofluidic disciplines.

Model light-confining Tamm plasmon cavities based on gold-coated nanoporous anodic alumina photonic crystals (TMM–NAA–PCs) with spectrally tunable resonance bands were engineered. Laplacian and Lorentzian NAA–PCs produced by a modified Gaussian-like pulse anodization approach showed well-resolved, high-quality photonic stopbands, the position of which was precisely controlled across the visible spectrum by the periodicity in the input anodization profile. These PC structures were used as a platform material to develop highly reflective distributed Bragg mirrors, the top sides of which were coated with a thin gold film. The resulting nanoporous hybrid plasmonic–photonic crystals showed strong light-confining properties attributed to Tamm plasmon resonances at three specific positions of the visible spectrum. These structures achieved high sensitivity to changes in refractive index, with a sensitivity of ∼106 nm RIU–1. The optical sensitivity of TMM–NAA–PCs was assessed in real time, using a model chemically selective binding interaction between thiol-containing molecules and gold. The optical sensitivity was found to rely linearly on the spectral position of the Tamm resonance band, for both Laplacian and Lorentzian TMM–NAA–PCs. The density of self-assembled monolayers of thiol-containing analyte molecules formed on the surface of the metallic film directly contributes to the dependence of sensitivity on TMM resonance position in these optical transducers. Our findings provide opportunities to integrate TMM modes in NAA-based photonic crystal structures, with promising potential for optical technologies and applications requiring high-quality surface plasmon resonance bands.

Random lasing provides new opportunities to engineer cost-competitive, highly controllable, and integrable light sources for a broad range of photonic technologies such as sensing, hyperspectral imaging, high-resolution spectroscopic analysis, and photonic circuits. In this study, we engineer the self-organized structure of nanoporous anodic alumina (NAA) through the electrochemical oxidation of aluminum to generate a palette of model nanoporous platforms with tailored, hexagonally distributed, straight cylindrical nanopores. The inner surface of these platforms is functionalized with a model organic fluorophore via micellar solubilization of a surfactant. The resultant organic–inorganic composite structures provide model platforms to develop optically pumped solid-state random lasers with well-resolved, intense lasing bands. The effect of NAA’s geometric features on the random lasing characteristics of these model platforms is elucidated by precisely engineering its nanopore diameter, nanopore length, interpore distance, and ordering. Structural engineering of NAA makes it possible to tune and maximize random-lasing emissions, resulting in strong, polarized lasing at ∼628 nm characterized by a remarkably high-quality-gain product of ∼1433, a polarization quality of ∼0.9, and a lasing threshold of ∼0.87 mJ pulse–1.