Nanoporous Alumina Membranes Research Articles

Synaptic Response of Fluidic Nanopores: The Connection of Potentiation with Hysteresis.

Iontronic fluidic ionic/electronic components are emerging as promising elements for artificial brain-like computation systems. Nanopore ionic rectifiers can be operated as a synapse element, exhibiting conductance modulation in response to a train of voltage impulses, thus producing programmable resistive states. We propose a model that replicates hysteresis, rectification, and time domain response properties, based on conductance modulation between two conducting modes and a relaxation time of the state variable. We show that the kinetic effects observed in hysteresis loops govern the potentiation phenomena related to conductivity modulation. To illustrate the efficacy of the model, we apply it to replicate rectification, hysteresis and conductance modulation of two different experimental systems: a polymer membrane with conical pores, and a blind-hole nanoporous anodic alumina membrane with a barrier oxide layer. We show that the time transient analysis of the model develops the observed potentiation and depression phenomena of the synaptic properties.

Spin echo small-angle neutron scattering using superconducting magnetic Wollaston prisms.

We show the implementation of superconducting magnetic Wollaston prisms for spin echo small-angle neutron scattering. Two calibration methods for the spin echo length are presented: one utilizing spin echo modulated small-angle neutron scattering and the other based on the neutron refraction by quartz wedge crystals. Our experimental results with polystyrene nano-particle colloids showcase the system's efficacy in measuring both dilute and concentrated colloidal systems. Additionally, investigations into the pore diameter and pitch of a nano-porous alumina membrane demonstrate its capability in analyzing nano-porous materials. Furthermore, we discuss potential optimizations to further extend the accessible spin echo length.

Fabrication and Optimisation of Alumina Nanoporous Membranes for Drug Delivery Applications: A Comparative Study.

Neurodegenerative disorders cause most physical and mental disabilities, and therefore require effective treatment. The blood-brain barrier (BBB) prevents drug molecules from crossing from the blood to the brain, making brain drug delivery difficult. Implantable devices could provide sustained and regulated medication to solve this problem. Two electrolytes (0.3 M oxalic acid and 0.3 M sulphuric acid) were used to anodise Al2O3 nanoporous membranes, followed by a third anodisation in concentrated H2SO4 to separate the through-hole membranes from the aluminium substrate. FTIR, AFM, and SEM/EDX were used to characterise the membranes' structure and morphology. The effects of the anodisation time and electrolyte type on the AAO layer pore density, diameter, interpore distance, and thickness were examined. As a model drug for neurodegenerative disorders, donepezil hydrochloride (DHC) was loaded onto thin alumina nanoporous membranes. The DHC release profiles were characterised at two concentrations using a UV-Vis spectrophotometer. Oxalic acid membranes demonstrated an average pore diameter of 39.6-32.5 nm, which was two times larger than sulphuric acid membranes (22.6-19.7 nm). After increasing the anodisation time from 3 to 5 h, all of the membranes showed a reduction in pore diameter that was stable regardless of the electrolyte type or period. Drug release from oxalic acid-fabricated membranes was controlled and sustained for over 2 weeks. Thus, nanoporous membranes as implantable drug delivery systems could improve neurodegenerative disease treatment.

The Influence of the Structural Parameters of Nanoporous Alumina Matrices on Optical Properties

In this work, two types of nanoporous alumina membranes were prepared and tested. Structural features of the samples obtained by using different acids were investigated by scanning electron microscopy (SEM). And further SEM-images were analyzed by different types of fractal dimension estimation methods. The transmission and scattering of accelerated He+ ions were studied in experiments on the ion irradiation of dielectric channels based on porous alumina. An ion accelerator was used as a source of the He+ beam with an energy of 1.7 MeV. Ion scattering was studied by Rutherford backscattering spectrometry. Helium transition through nanoporous alumina at various angles between the normal to the sample and the beam direction were observed. It is shown that the porous structure of anodic aluminum oxide is excellent as a dielectric matrix of nanocapillaries. Owing to the small angle scattering, it allows for the transportation of the accelerated charged particles through the dielectric capillaries, and, as a result, the localization of high energy ion irradiation effects. Additionally, according to the transmission of UV–V is spectra, the energy gaps of samples obtained were calculated.

Effect of nanoporous membranes thickness in electrochemical biosensing performance: application for the detection of a wound infection biomarker.

Introduction: Nanoporous alumina membranes present a honeycomb-like structure characterized by two main parameters involved in their performance in electrochemical immunosening: pore diameter and pore thickness. Although this first one has been deeply studied, the effect of pore thickness in electrochemical-based nanopore immunosensors has been less taken into consideration. Methods: In this work, the influence of the thickness of nanoporous membranes in the steric blockage is studied for the first time, through the formation of an immunocomplex in their inner walls. Finally, the optimal nanoporous membranes were applied to the detection of catalase, an enzyme related with chronic wound infection and healing. Results: Nanoporous alumina membranes with a fixed pore diameter (60 nm) and variable pore thicknesses (40, 60, 100 μm) have been constructed and evaluated as immunosensing platform for protein detection. Our results show that membranes with a thickness of 40 μm provide a higher sensitivity and lower limit-of-detection (LOD) compared to thicker membranes. This performance is even improved when compared to commercial membranes (with 20 nm pore diameter and 60 μm pore thickness), when applied for human IgG as model analyte. A label-free immunosensor using a monoclonal antibody against anti-catalase was also constructed, allowing the detection of catalase in the range of 50-500 ng/mL and with a LOD of 1.5 ng/mL. The viability of the constructed sensor in real samples was also tested by spiking artificial wound infection solutions, providing recovery values of 110% and 118%. Discussion: The results obtained in this work evidence the key relevance of the nanochannel thickness in the biosensing performance. Such findings will illuminate nanoporous membrane biosensing research, considering thickness as a relevant parameter in electrochemical-based nanoporous membrane sensors.

Enhancing the Antifouling Properties of Alumina Nanoporous Membranes by GO/MOF Impregnated Polymer Coatings: In Vitro Studies.

Nanoporous membranes (NPMBs) have been the focus of interest of many scientists in the last decade. However, the fouling phenomenon that takes place during the implantation period blocks pores and causes failure in the local implant. In this study, alumina NPMBs were developed using electrochemical anodization through two steps. Furthermore, graphene oxide (GO), free and impregnated with ZIF-8 MOF, was synthesized and loaded in a mixture of PVDF/PVP polymer matrix at different ratios, and was applied to the produced NPMBs using spin-coater. The NPMBs were characterized before and after coating by SEM/EDX, TEM, FTIR, XRD, contact angle and AFM. The antifouling features of the NPMBs were analyzed against two different bacterial species. The prepared alumina NPMBs demonstrated homogeneous porous structures with pore sizes ranging from 36 to 39 nm. The coated layers were proven to possess microporous coatings on the surfaces of the NPMBs. The numbers of released ions (Al and Zn) from the coated NPMBs were below the allowed limits. Bovine serum albumin (BSA) uptake in artificial cerebrospinal fluid (ACSF) was impressively reduced with the presence of coating materials. In addition, the antifouling behavior of the coated NPMBs against the selected strains of bacteria was greatly enhanced compared with the pure alumina NPMBs. Finally, NPMBs' uncoated and polymer-coated membranes were tested for their ability to deliver donepezil HCl. The results reveal the downregulation of donepezil release, especially from NPMBs coated with PVDF/PVP 0.5GO. It is advised to use the current antifouling materials and techniques to overcome the limitations of the inorganic NPMBs implants.

GdFe-based nanostructured thin films with large perpendicular magnetic anisotropy for spintronic applications

In this study, we investigated the impact of geometric factors on the magnetic anisotropy of Gd-Fe alloy thin films deposited on nanoporous alumina membranes. By synthesizing Gd-Fe alloy nanostructure thin films with different hole diameters (ranging from 45 to 90 nm) and keeping the layer thickness and lattice parameters fixed at 45 nm and 105 nm, respectively, we observed a significant perpendicular magnetic anisotropy (PMA) in samples with hole diameter above 65 nm. The transition from in-plane to out-of-plane magnetization in Gd-Fe alloy nanostructure thin films occurred at a critical antidot hole diameter of 75 nm. The observed variations in coercivity and remanence with the nanohole diameter are attributed to substantial changes in the magnetization mechanisms induced by the nanoholes. This novel induction of PMA in Gd-Fe alloy nanostructure thin films through the manipulation of geometric parameters in the antidot arrays opens new possibilities for tailoring the magnetic behavior of ferromagnetic metals with pronounced PMA.

Simulation and Analysis of Anodized Aluminum Oxide Membrane Degradation.

Microelectromechanical systems (MEMS)-based filter with microchannels enables the removal of various microorganisms, including viruses and bacteria, from fluids. Membranes with porous channels can be used as filtration interfaces in MEMS hemofilters or mini-dialyzers. The main problems associated with the filtration process are optimization of membrane geometry and fouling. A nanoporous aluminum oxide membrane was fabricated using an optimized two-step anodization process. Computational strength modeling and analysis of the membrane with specified parameters were performed using the ANSYS structural module. A fuzzy simulation was performed for the numerical analysis of flux through the membrane. The membrane was then incorporated with the prototype for successive filtration. The fluid flux and permeation analysis of the filtration process have been studied. Scanning electron microscope (SEM) micrographs of membranes have been obtained before and after the filtration cycles. The SEM results indicate membrane fouling after multiple cycles, and thus the flux is affected. This type of fabricated membrane and setup are suitable for the separation and purification of various fluids. However, after several filtration cycles, the membrane was degraded. It requires a prolonged chemical cleaning. High-density water has been used for filtration purposes, so this MEMS-based filter can also be used as a mini-dialyzer and hemofilter in various applications for filtration. Such a demonstration also opens up a new strategy for maximizing filtration efficiency and reducing energy costs for the filtration process by using a layered membrane setup.

Feasibility and safety of a nanoporous system for intrathecal pseudodelivery of anti‐amyloid therapies: proof‐of‐concept in mice

AbstractBackgroundThe cerebrospinal (CSF) sink therapeutic strategy hypothesizes that clearing soluble beta‐amyloid from the CSF results in removing brain beta‐amyloid (Aβ) (1). We proposed a new way of achieving the CSF sink effect by means of an innovative route of drug delivery, named intrathecal pseudodelivery (ITPD) of drugs. ITPD is based on an implantable device endowed with semipermeable nanoporous membranes that are permeable to soluble Aβ but not to monoclonal antibodies (mAb) (2). In this study, we aimed to show proof‐of‐concept of a fully implantable device for ITPD in combination with mAbs for selectively clearing Aβ from CSF in a mouse model of Alzheimer’s Disease (AD)MethodWe encapsulated flat alumina nanoporous membranes of a pore size of 10.0 nm, and we coupled the capsule with a reservoir and a catheter. The system was implanted in symptomatic 34‐week‐old male (n = 6) and female (n = 4) APPswe/PS1dE9 mice and their wild‐type littermates (n = 10), with the capsule/reservoir placed subcutaneously and the catheter connected to the right lateral ventricle. Devices were infused with either artificial CSF (aCSF) (n = 10), or an anti‐Aβ mAb solution (n = 10). After surgery, animal welfare and body weight were monitored for up to 30 days. Behavioral tests were carried out before and 30 days after implantation.ResultImplantation procedure was successful, with a rapid animal recovery period of 15 minutes after the surgery. In 5 of the implanted mice complications related to anesthesia were reported, but none was severe. For the preliminary behavioral analyses, a partial improvement in cognitive functions was evidenced, with no significant adverse effects at any of the time points.ConclusionThese findings provide proof‐of‐concept on nanoporous systems for ITPD of anti‐Aβ therapies that replicate previous feasibility and safety studies and, together with ongoing studies assessing efficacy, provide further validation of this therapeutic route in AD.

(Invited) harnessing the Barrier Oxide Layer of Nanoporous Anodic Alumina for Iontronic Sensing

The hemispherical barrier oxide layer (BOL) closing the 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. Rectification efficiency of ionic current associated with the flow of ions across the anodic BOL increases with its thickness, under optimal pH conditions. The inner surface of 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. Figure 1

Gold nanoparticles engineered nanoporous membrane with sandwich structure for sensitive electrochemical quantification of exosome

Exosome has been identified as an excellent potential biomarker for tumor diagnosis. Herein, electrochemical aptasensor for exosome detection was developed via a sandwich-structured nanoporous membrane which was fabricated by assembling multilayer gold nanoparticles (mulAu) and monolayer gold nanoparticles (monAu) on the opposite side of a nanoporous alumina membrane (NAM). The tumor-derived exosomes can be efficiently captured by the specific probes confined on the monAu side of the membrane. And the mulAu side that was tightly attached with a Si wafer allowed the electrochemical exosome detection by monitoring the amperometric signal of ferricyanide that transported across the nanochannel array of the membrane. After optimization of pore diameter of the NAM, base sequence of the capture probe and incubation temperature as well as incubation time for exosomes, this NAM-based electrochemical aptasensor was applied to the quantification of the MCF-7 cells-derived exosomes. The steady state current displayed linearity relationship with the concentration of the exosomes in a broad range of 103 to 107 particles μL−1, along with a detection limit of 2.8 × 102 particles μL−1. By changing capture probe, this sandwich-structured membrane could be further extended to label-free, sensitive and rapid quantification of other tumor-associated vesicles.

Electrochemical monitoring of enzymatic cleavage in nanochannels with nanoparticle-based enhancement: determination of MMP-9 biomarker

For the first time the use of nanoparticles as carriers of an enzymatic substrate immobilized inside nanoporous alumina membranes is proposed with the aim of amplifying the nanochannel blocking produced and, consequently, improving the efficiency of an enzyme determination through enzymatic cleavage. Streptavidin-modified polystyrene nanoparticles (PSNPs) are proposed as carrier agents, contributing to the steric and the electrostatic blockage due to the charge they present at different pH values. Electrostatic blockage is the predominant effect that governs the blockage in the interior of the nanochannel and is dependent not just in the charge inside the channel, but also in the polarity of the redox indicator used. Hence, the effect of using negatively charged ([Fe(CN)6]4−) and positively charged ([Ru(NH3)6]3+) redox indicator ions is studied for the first time. Under the optimum conditions, matrix-metalloproteinase 9 (MMP-9) is detected at clinically relevant levels (100–1200 ng/mL) showing a detection limit of 75 ng/mL and a quantification limit of 251 ng/mL with good reproducibility (RSD: 8%) and selectivity, also showing an excellent performance in real samples with acceptable recovery percentages (in the range around 80–110%). Overall, our approach represents a cheap and fast sensing methodology of great potential in point-of-care diagnostics.Graphical

Enhanced nonlinearities in hybrid structure based on nanoporous membrane and a metallohelicate with promising application in nanophotonics and NLO.

The main purposes of this work are designing new hybrid structures based on alumina nanoporous membranes with specific metallosupramolecular structure as well as studies of their usefulness in nonlinear optics (NLO). The NLO studies of the hybrid material is performed on the basis of two methods: the first by the Maker fringe technique, where the second harmonic generation (SHG) signal is recorded by rotating the sample; and the second by SHG imaging microscopy, where the SHG signal is collected point by point on the sample surface. The enhanced SHG signals were obtained without the use of the corona poling method needed during the experiment on thin films in our previous works and clearly shows the efficiency of hybrid materials based on nanoporous membranes as promising materials in devices developed based on NLO.

Exchange Bias Effect of Ni@(NiO,Ni(OH)2) Core/Shell Nanowires Synthesized by Electrochemical Deposition in Nanoporous Alumina Membranes.

Tuning and controlling the magnetic properties of nanomaterials is crucial to implement new and reliable technologies based on magnetic hyperthermia, spintronics, or sensors, among others. Despite variations in the alloy composition as well as the realization of several post material fabrication treatments, magnetic heterostructures as ferromagnetic/antiferromagnetic coupled layers have been widely used to modify or generate unidirectional magnetic anisotropies. In this work, a pure electrochemical approach has been used to fabricate core (FM)/shell (AFM) Ni@(NiO,Ni(OH)2) nanowire arrays, avoiding thermal oxidation procedures incompatible with integrative semiconductor technologies. Besides the morphology and compositional characterization of these core/shell nanowires, their peculiar magnetic properties have been studied by temperature dependent (isothermal) hysteresis loops, thermomagnetic curves and FORC analysis, revealing the existence of two different effects derived from Ni nanowires' surface oxidation over the magnetic performance of the array. First of all, a magnetic hardening of the nanowires along the parallel direction of the applied magnetic field with respect their long axis (easy magnetization axis) has been found. The increase in coercivity, as an effect of surface oxidation, has been observed to be around 17% (43%) at 300 K (50 K). On the other hand, an increasing exchange bias effect on decreasing temperature has been encountered when field cooling (3T) the oxidized Ni@(NiO,Ni(OH)2) nanowires below 100 K along their parallel lengths.

Towards the maximization of nanochannels blockage through antibody-antigen charge control: Application for the detection of an Alzheimer’s disease biomarker

Although size and charge effects in nanochannels have been previously approached for electrochemical immunosensing, as far as we know, thorough studies on the effect of both the antibody and the antibody/antigen immunocomplex charges at different pHs have not been deeply reported. In this context, we present here an unprecedented study of such parameters, applied also for the first time for the detection of an Alzheimer’s disease (AD) biomarker. AD detection is currently based in time consuming and expensive techniques, so that the development of alternative analytical strategies for facilitating its diagnosis is still a need. To reach that purpose, we propose here the development of a nanochannel-based system for the electrochemical monitoring of Tau protein, an important AD biomarker. Tau protein is selectively captured by specific antibodies immobilized in the inner walls of the nanochannels of nanoporous alumina membranes. The captured Tau protein blocks the nanochannel and difficulties the passage of red-ox indicator ions, which is voltammetrically monitored using an indium tin oxide/poly(ethylene terephthalate) (ITO/PET) electrode as transducer. The charges of both the antibody and the Tau antigen at different pHs and their effect on the diffusion of the red-ox indicator ions to the electrode are carefully evaluated to maximize the electrostatic blocking of the nanochannels upon the immunocomplex formation. The developed biosensing system allows the determination of Tau protein with a detection limit of 4.3 ng/mL, which is within the range of clinical interest, showing also excellent recovery percentages in human plasma samples.

In Situ Synthesis of CuO/Cu2O Nanoparticle-Coating Nanoporous Alumina Membranes with Photocatalytic Activity under Visible Light Radiation

We report the synthesis and characterization of CuO/Cu2O film supported on nanoporous alumina membranes (NAMs) and the photocatalytic properties in the removal of the organic pollutant methyl orange (MO). For this purpose, transparent nanostructured membranes were fabricated and sequentially modified with APTS ((3-aminopropyl)-trimethoxysilane) and EDTAD (ethylenediaminetetraacetic dianhydride) to form a highly functionalized surface with high density of carboxyl groups, which easily complex with copper cations. The Cu2+-modified membranes were annealed in a chemical vapor deposition (CVD) furnace to form a well-ordered nanostructured coating of CuO/Cu2O with photocatalytic properties. These modifications were followed by characterization with FT-IR and UV–visible spectra, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS). Finally, the photocatalytic performance of the NAM-CuO/Cu2O nanostructured membranes was tested in the aqueous removal of MO dye as a model reaction system. Our results revealed 50% photocatalytic removal of MO under continuous light irradiation for 2 h. The procedure presented in this work provides an adequate approach for the fabrication of nanostructured devices with photocatalytic properties for the degradation of organic compounds.

Influence of heat transfer and wetting angle on condensable fluid flow through nanoporous anodic alumina membranes.

The flow of isobutane and of freon 142b (1-chloro-1,1-difluoro-ethane) through anodic alumina membranes with pore diameters between 18 and 60 nm in a capillary condensation regime is experimentally and theoretically explored. The capillary condensation effect increases the membrane permeance for condensable gases from 25 to 150 m3(STP) m-2 bar-1 h-1 at certain conditions. To describe the experimental results, a model is suggested accounting for heat transfer from the condensing to the evaporating meniscus, different boundary conditions for the heat transfer between the environment and the membrane, and wettability of the pore wall. The proposed model indicates a large influence of heat supply from the environment to the membrane on the permeance in the capillary condensation regime and a moderate influence of condensate contact angle in the range of 0-60°. Measuring the temperature of the permeate side of the membrane allows to find a suitable boundary condition to describe heat transfer. The obtained boundary condition yields an excellent fit of experimental results of condensate flow through membranes with different pore diameters for the two utilized fluids. Also, confocal Raman spectroscopy gave evidence on the fraction of pores filled with condensate.

Electrical surface properties of nanoporous alumina membranes: influence of nanochannels' curvature, roughness and composition studied via electrokinetic experiments.

Among classical nanoporous oxide membranes, anodic aluminum oxide (AAO) membranes, made of non-connected, parallel and ordered nanochannels, are very interesting nanoporous model systems widely used for multiple applications. Since most of these applications involve local phenomena at the nanochannel surface, the fine description of the electrical surface behavior in aqueous solution is thus of primordial interest. Here, we use an original experimental approach combining several electrokinetic techniques (tangential and transverse streaming potential as well as electrophoretic mobility experiments) to measure the ζ-potential and determine the surface isoelectric points (IEPs) of several AAOs having different characteristic sizes and compositions. Using such an approach, all the different surfaces available in AAOs can be probed: outer surfaces (top and bottom planes), pore wall surfaces (i.e., inner surfaces) and surfaces created by the grinding of the AAOs. We find clear IEP differences between the outer, pore wall and ground surfaces and discuss these in terms of nanochannel and surface morphology (curvature and roughness) and of modifications of the chemical environment of the surface hydroxyl groups. These results highlight the heterogeneities between the different surfaces of these AAO membranes and emphasize the necessity to combine complementary electrokinetic techniques to properly understand the material, an approach which can be extended to many nanoporous systems.

Алюмооксидные нанопористые мембраны как основа функциональных нанокомпозитных материалов

In the present study, we report about results of obtaining nanocomposite materials based on various types of nanoporous alumina membranes (NAM). The NAM were fabricated by two ways: (I) — using the technique of thinning the barrier layer of porous anodic alumina; (2) — by two-layer galvanostatic electrochemical anodization of aluminium samples. Using atomic force microscopy, it was found that a method of thermal decomposition of K2MnO4 leads to the formation of nanoparticles γ-MnO2 with size ~ 20 nm on the surface and in the pores of NAM, and the use of the method of photochemical synthesis of Ag nanoparticles with a size of ~ 30 nm.

Creation of unique shapes by coordination of alumina nanopores and carbon nanowalls

This work presents experimental results on the synthesis of сarbon nanowalls (CNWs) with predefined morphology on the surface of the nanoporous alumina membrane using two different methods, namely radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) and radical-injection (RI)-PECVD. Obtained samples were characterized by the methods of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. From the microstructure analyses of CNWs, it has been observed that there is a time dependence on the reproducibility of membrane morphology by CNWs. At the early stage of nanowalls growth, nanowalls prefer to grow around the edges of nanopores and continue to grow vertically with time. In RF-PECVD, the nanopores’ size begins to shrink drastically and pores are completely covered by secondary flake-like nanowalls after 25 minutes of growth. In the case of CNWs grown using RI-PECVD, nanowalls are more vertical and self-supported. This is because of the rapid and sustained production of hydrogen radicals that prevent the secondary growth of carbon nanowalls. In addition, the influence of pores diameter and membrane thickness on the growth of RI-PECVD CNWs was revealed.