Alumina Nanochannels Research Articles

Synthesis and Magnetoelectric Properties of NiFe$lt;inf$gt;2$lt;/inf$gt;O$lt;inf$gt;4$lt;/inf$gt;-BiFeO$lt;inf$gt;3$lt;/inf$gt; Nanotubes

xNFO-(1-x)BFO (NFO-BFO) nanotube arrays were fabricated by means of Sol-Gel method utilizing nanochannel alumina as templates. Scanning electron microscopy study revealed that the outer diameter of nanotube was about 70 nm, and the internal diameter was about 50 nm, the length was about 80 m. Meanwhile, ferroelectric phase BFO of perovskite structure and ferromagnetic phase NFO of spinel structure were formed through self-assembly growth in X-ray diffraction patterns. Significant ferromagnetic and polarized characteristics of nano- tube arrays were demonstrated by means of magnetic and ferroelectric measurement at room temperature, and the direction of easy magnetization was along the long axis. With increasing ratio of NFO, the magnetic and polarized properties of nanotube arrays increased gradually. The calculation results of NFO's ferromagnetic contribution in- dicated that magnetoelectric coupling effect existed in the NFO-BFO composite nanotube arrays.

Unveiling the Hard Anodization Regime of Aluminum: Insight into Nanopores Self-Organization and Growth Mechanism

Pores growth mechanism and their self-ordering conditions are investigated for nanoporous alumina membranes synthesized by hard anodization (HA) of Al in a broad range of anodic conditions, covering oxalic acid electrolytes with concentrations from 0.300 M down to 0.075 M and potentiostatic anodization voltages between 120 and 225 V. The use of linear sweep voltammetry (LSV) and scanning and transmission electron microscopy, together with image analysis techniques allow one to characterize the intrinsic nature of the HA regime. HA of aluminum is explained on the basis of a phenomenological model taking into account the role of oxalate ions and their limited diffusion through alumina nanochannels from a bulk electrolyte. The depletion of oxalate ions at the bottom of the pores causes an increased growth of the alumina barrier layer at the oxide/electrolyte interface. Furthermore, an innovative method has been developed for the determination of the HA conditions leading to self-ordered pore growth in any given electrolyte, thus allowing one to extend the available range of interpore distances of the highly ordered hexagonal pore arrangement in a wide range of 240-507 nm, while keeping small pore diameters of 50-60 nm.

A novel biomimetic logic gate for sensitive and selective detection of Pb(II) base on porous alumina nanochannels

A novel biomimetic logic gate sensor for Pb2 + is established using porous alumina membrane nanochannels modified with morpholino and DNA. It is based on electrochemical detection, and the current response from the diffusion flux of Fe(CN)63 − is influenced by the steric blockage and charge repulsion in nanochannels. A limit of detection (0.1 nM) and good linear range (0.1 nM–5 μM) for Pb2 + analysis are achieved in the tenth cycle. The sensing strategy shows prospective application in drug release, artificial ion channels, DNA logic gates for controlling biomolecule, and ion translocation.

Effects of Processing Temperatures of Nickel Plating on Capacitance Density of Alumina Film Capacitor.

We observed the effects of nickel plating temperatures for controlling the surface morphologies of the deposited nickel layers on the alumina nano-pores. The alumina nano-channels were filled with nickel at various processing temperatures of 60-90 degrees C. The electrical properties of the alumina film capacitors were changed with processing temperatures. The electroless nickel plating (ENP) at 60 degrees C improved the nickel penetration into the alumina nano-channels due to the reduced reaction rate. Nickel layers are uniformly formed on the high aspect ratio alumina pores. Due to the uniform nickel electrode, the capacitance density of the alumina film capacitors is improved by the low leakage current, dissipation factor and equivalent series resistance. Alumina film capacitors made by ENP at 60 degrees C had a high capacitance density of 160 nF/cm2.

Morpholino-functionalized nanochannel array for label-free single nucleotide polymorphisms detection.

The sensitive identification of single nucleotide polymorphisms becomes increasingly important for disease diagnosis, prevention, and practical applicability of pharmacogenomics. Herein, we propose a simple, highly selective, label-free single nucleotide polymorphisms (SNPs) sensing device by electrochemically monitoring the diffusion flux of ferricyanide probe across probe DNA/morpholino duplex functionalized nanochannels of porous anodic alumina. When perfectly matched or mismatched target DNA flows through the nanochannels modified with probe DNA/morpholino duplex, it competes for the probe DNA from morpholino, resulting in a change of the surface charges. Thus, the diffusion flux of negatively charged electroactive probe ferricyanide is modulated since it is sensitive to the surface charge due to the electrostatic interactions in electric double layer-merged nanochannels. Monitoring of the change in diffusion flux of probe enables us to detect not only a single base or two base mismatched sequence but also the specific location of the mismatched base. As is demonstrated, SNPs in the PML/RARα fusion gene, known as a biomarker of acute promyelocytic leukemia (APL), have been successfully detected.

Dual-response for Hg2+ and Ag+ ions based on biomimetic funnel-shaped alumina nanochannels.

Biomimetic dual-ion-responsive nanochannels were developed by the principles of metal-ion-mediated base pairs of the responsive T-/C-rich single strand DNA (ssDNA). The responsive ssDNA was immobilized into the funnel-shaped alumina nanochannels, which were fabricated using the anodization technology and pore-widening process. In neutral solution, the conformation of the ssDNA changed from a loosely packed structure into a duplex structure by interacting with Hg2+ or Ag+ ions (T-Hg2+-T or C-Ag+-C complexes). The decreasing ionic currents through the nanochannels were utilized to detect concentrations of Hg2+ or Ag+ ions. The conversion of duplex-quadruplex of Ag+ ions and DNA could be triggered by changing the pH value of aqueous solutions to 4.5, whereas it did not happen in Hg2+ ions solution. Thus, the ssDNA-modified alumina nanochannels selectively responded to Hg2+ and Ag+ ions at pH 4.5 with different ionic transportation properties. The biomimetic dual-ion-responsive nanochannels promised great potential in multiplexed ion sensing.

Quantitative detection of potassium ions and adenosine triphosphate via a nanochannel-based electrochemical platform coupled with G-quadruplex aptamers.

The development of synthetic nanopores and nanochannels that mimick ion channels in living organisms for biosensing applications has been, and still remains, a great challenge. Although the biological applications of nanopores and nanochannels have achieved considerable development as a result of nanotechnology advancements, there are few reports of a facile way to realize those applications. Herein, a nanochannel-based electrochemical platform was developed for the quantitative detection of biorelated small molecules such as potassium ions (K(+)) and adenosine triphosphate (ATP) in a facile way. For this purpose, K(+) or ATP G-quadruplex aptamers were covalently assembled onto the inner wall of porous anodic alumina (PAA) nanochannels through a Schiff reaction between -CHO groups in the aptamer and amino groups on the inner wall of the PAA nanochannels under mild reaction conditions. Conformational switching of the aptamers confined in the nanochannels occurs in the presence of the target molecules, resulting in increased steric hindrance in the nanochannels. Changes in steric hindrance in the nanochannels were monitored by the anodic current of indicator molecules transported through the nanochannels. As a result, quantitative detection of K(+) and ATP was realized with a concentration ranging from 0.005 to 1.0 mM for K(+) and 0.05 to 10.0 mM for ATP. The proposed platform displayed significant selectivity, good reproducibility, and universality. Moreover, this platform showed its potential for use in the detection of other aptamer-based analytes, which could promote its development for use in biological detection and clinical diagnosis.

Custom-designed arrays of anodic alumina nanochannels with individually tunable pore sizes

We demonstrate a process to selectively tune the pore size of an individual nanochannel in an array of high-aspect-ratio anodic aluminum oxide (AAO) nanochannels in which the pore sizes were originally uniform. This novel process enables us to fabricate arrays of AAO nanochannels of variable sizes arranged in any custom-designed geometry. The process is based on our ability to selectively close an individual nanochannel in an array by using focused ion beam (FIB) sputtering, which leads to redeposition of the sputtered material and closure of the nanochannel with a capping layer of a thickness depending on the energy of the FIB. When such a partially capped array is etched in acid, the capping layers are dissolved after different time delays due to their different thicknesses, which results in differences in the time required for the following pore-widening etching processes and therefore creates an array of nanochannels with variable pore sizes. The ability to fabricate such AAO templates with high-aspect-ratio nanochannels of tunable sizes arranged in a custom-designed geometry paves the way for the creation of nanophotonic and nanoelectronic devices.

A light-powered bio-capacitor with nanochannel modulation.

An artificial bio-capacitor system is established, consisting of the proton-pump protein proteorhodopsin and a modified alumina nanochannel, inspired by the capacitor-like behavior of plasma membranes realized through the cooperation of ion-pump and ion-channel proteins. Capacitor-like features of this simplified system are realized and identified, and the photocurrent duration time can be modulated by nanochannel modification to obtain favorable square-wave currents.

Coupling of a single-photon emitter in nanodiamond to surface plasmons of a nanochannel-enclosed silver nanowire.

A finite element method is applied to study the coupling between a nitrogen vacancy (NV) single photon emitter in nanodiamond and surface plasmons in a silver nanowire embedded in an alumina nanochannel template. We investigate the effective parameters in the coupled system and present detailed optimization for the maximum transmitted power at a selected optical frequency (650 nm). The studied parameters include nanowire length, nanowire diameter, distance between the dipole and the nanowire, orientation of the emitter and refractive index of the surrounding. It is found that the diameter of the nanowire has a strong influence on the propagation of the surface plasmon polaritons and emission power from the bottom and top endings of the nanowire.

Paranematic-to-nematic ordering of a binary mixture of rodlike liquid crystals confined in cylindrical nanochannels.

We explore the optical birefringence of the nematic binary mixtures 6CB_{1-x}7CB_{x} (0 ≤ x ≤ 1) embedded into parallel-aligned nanochannels of mesoporous alumina and silica membranes for channel radii of 3.4 ≤ R ≤ 21.0 nm. The results are compared with the bulk behavior and analyzed with a Landau-de Gennes model. Depending on the channel radius the nematic ordering in the cylindrical nanochannels evolves either discontinuously (subcritical regime, nematic ordering field σ<1/2) or continuously (overcritical regime, σ>1/2), but in both cases with a characteristic paranematic precursor behavior. The strength of the ordering field, imposed by the channel walls, and the magnitude of quenched disorder varies linearly with the mole fraction x and scales inversely proportionally with R for channel radii larger than 4 nm. The critical pore radius, R_{c}, separating a continuous from a discontinuous paranematic-to-nematic evolution varies linearly with x and differs negligibly between the silica and alumina membranes. We find no hints of preferred adsorption of one species at the channels walls. By contrast, a linear variation of the nematic-to-paranematic transition point T_{PN} and of the nematic ordering field σ versus x suggests that the binary mixtures of cyanobiphenyls 6CB and 7CB keep their homogeneous bulk stoichiometry also in nanoconfinement, at least for channel diameters larger than ∼7 nm.

Molecular ordering of the discotic liquid crystal HAT6 confined in mesoporous solids

An optical polarimetry study of the orientational order of a discotic liquid crystal (DLC), 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6), confined into parallel-aligned cylindrical nanochannels of mesoporous alumina, silica, and silicon membranes as a function of temperature and channel radius (3.4–21.0nm) is presented. In contrast to the bulk state, the birefringence resulting from the confined discotic liquid crystal, exhibits a continuous temperature evolution and is positive indicating a dominating face-on (homeotropic) type molecular ordering with respect to the channel walls. Pronounced hysteresis effects observed in the experiment are traced to different nucleation sites of the low-temperature phase upon cooling and the high-temperature phase upon heating. Deviations from the Gibbs–Thomson scaling of the phase transition temperature for channel diameters below 10nm are traced to splay distortions of the confined liquid crystal.

Solid phases of spatially nanoconfined oxygen: A neutron scattering study

We present a comprehensive neutron scattering study on solid oxygen spatially confined in 12 nm wide alumina nanochannels. Elastic scattering experiments reveal a structural phase sequence known from bulk oxygen. With decreasing temperature cubic γ-, orthorhombic β- and monoclinic α-phases are unambiguously identified in confinement. Weak antiferromagnetic ordering is observed in the confined monoclinic α-phase. Rocking scans reveal that oxygen nanocrystals inside the tubular channels do not form an isotropic powder. Rather, they exhibit preferred orientations depending on thermal history and the very mechanisms, which guide the structural transitions.

Thermotropic orientational order of discotic liquid crystals in nanochannels: an optical polarimetry study and a Landau-de Gennes analysis.

Optical polarimetry measurements of the orientational order of a discotic liquid crystal based on a pyrene derivative confined in parallelly aligned nanochannels of monolithic, mesoporous alumina, silica, and silicon as a function of temperature, channel radius (3-22 nm) and surface chemistry reveal a competition of radial and axial columnar orders. The evolution of the orientational order parameter of the confined systems is continuous, in contrast to the discontinuous transition in the bulk. For channel radii larger than 10 nm we suggest several, alternative defect structures, which are compatible both with the optical experiments on the collective molecular orientation presented here and with a translational, radial columnar order reported in previous diffraction studies. For smaller channel radii our observations can semi-quantitatively be described by a Landau-de Gennes model with a nematic shell of radially ordered columns (affected by elastic splay deformations) that coexists with an orientationally disordered, isotropic core. For these structures, the cylindrical phase boundaries are predicted to move from the channel walls to the channel centres upon cooling, and vice-versa upon heating, in accord with the pronounced cooling/heating hystereses observed and the scaling behavior of the transition temperatures with the channel diameter. The absence of experimental hints of a paranematic state is consistent with a biquadratic coupling of the splay deformations to the order parameter.

Alumina Membrane with Hour‐Glass Shaped Nanochannels: Tunable Ionic Current Rectification Device Modulated by Ions Gradient

A new alumina membrane with hour‐glass shaped nanochannels is reported using the double‐side anodization method and the subsequently in situ pore opening procedure, which is applied to develop the tunable ionic current rectification devices that were modulated by ions gradient. By regulating the pH gradient, tunable ionic current rectification properties which are mainly dependent on the asymmetric surface charge density or polarity distribution on the inner walls of the nanochannels can be obtained. The enhanced ionic current rectification properties were presented due to the synergistic effect of the voltage driven ion flow and diffusion driven ion flow with the application of pH and electrolyte concentration gradients. Therefore, such specific alumina nanochannels would be considered as a promising candidate for building bioinspired artificial ion channel systems.

Enzymatic reactivity of glucose oxidase confined in nanochannels

The construction of nanodevices coupled with an integrated real-time detection system for evaluation of the function of biomolecules in biological processes, and enzymatic reaction kinetics occurring at the confined space or interface is a significant challenge. In this work, a nanochannel–enzyme system in which the enzymatic reaction could be investigated with an electrochemical method was constructed. The model system was established by covalently linking glucose oxidase (GOD) onto the inner wall of the nanochannels of the porous anodic alumina (PAA) membrane. An Au disc was attached at the end of the nanochannels of the PAA membrane as the working electrode for detection of H2O2 product of enzymatic reaction. The effects of ionic strength, amount of immobilized enzyme and pore diameter of the nanochannels on the enzymatic reaction kinetics were illustrated. The GOD confined in nanochannels showed high stability and reactivity. Upon addition of glucose to the nanochannel–enzyme system, the current response had a calibration range span from 0.005 to 2mM of glucose concentration. The apparent Michaelis–Menten constant (Kmapp) of GOD confined in nanochannel was 0.4mM. The presented work provided a platform for real-time monitoring of the enzyme reaction kinetics confined in nanospaces. Such a nanochannel–enzyme system could also help design future biosensors and enzyme reactors with high sensitivity and efficiency.

Instabilities of Teflon AF thin films in alumina nanochannels and adhesion of bi-level Teflon AF nanopillars

In this paper, a novel replica-molding technique for fabrication of bi-level Teflon AF nanopillars, as an electrostatic-based dry adhesive, is reported. The technique reported herein relies on the concurrent heating and cooling of the Teflon AF melt which filled vertically aligned alumina nanochannels as the mold. Unlike conventional polymer infiltration methods which consist of filling the mold by only heating the polymer above its glass transition temperature, in the current method, the polymer melt was also simultaneously cooled down during the infiltration process. Concurrent cooling of the Teflon AF melt allowed control over the interfacial instabilities of the polymer thin film, which formed ahead of the polymer melt upon its infiltration into the alumina nanochannels. By doing so, the geometrical properties of the peculiar fluffy nanostructure which was subsequently developed—after removal of the mold—on top of the extremely high aspect-ratio Teflon AF nanopillars (200 nm in diameter, ∼25 μm tall) were modified. The height of the base nanopillars was measured and the structural properties (i.e., surface area fraction and roughness) of the fluffy nanostructure terminating the base nanopillars at the tip were quantified. Next, the effects of the topographical properties of the bi-level Teflon AF nanopillars on their adhesion, in both the normal and shear directions, were investigated. Tribological results were discussed in detail to clarify the contribution of the structural properties of the fabricated dry adhesive toward its remarkable adhesion and friction forces generated via contact electrification. It is worthwhile to mention that bi-level Teflon AF nanopillars with these specific structural properties have generated enhanced adhesion and friction strengths, up to ∼2.1 and 13 N cm−2, respectively.

Cellular level classification of breast cancer through proteomic markers using nanochannel array sensors.

A nanochannel-based sensor for cellular level classification of breast cancer metastasis has been designed. Our approach to the classification of cell's likelihood to metastasize is based on screening for levels of expression of specific proteomic biomarkers associated with breast cancer stem cells. Proteomic activity for four breast cancer cell lines for three specific markers (PDGFR, ALDH1A1 and ALDH1A3) was quantified. The nanochannel sensor is an electrochemical immunoassay and comprises of alumina nanochannel arrays integrated on to a gold microelectronic platform. The sensor operates on the principle of electrochemical impedance spectroscopy. Test cell lysate samples from SUM159 invasive, SUM159 noninvasive, HC1143 and DCIS cell lines were classified as those having a high likelihood of metastases based on the levels of proteomic activity evaluated against the three key markers. The lowest proteomic activity measured was 0.1 ng/ml with PDGFR, 100 ng/ml with ALDH1A1 and 100 ng/ml with ALDH1A3, correlating to the detection of unit stem cell count. Original submitted 9 November 2012; Revised submitted 29 July 2013.

Ion Transport Traversing Bioinspired Ion Channels at Bionic Interface

Ion transport is especially crucial in normal body function, which is regulated by specialized ion channels. In this report, the simple hydrophilic alumina nanochannel is constructed at liquid/liquid (L/L) interface to simulate veritably and compactly complex cross-channel ion transfer processes of living systems in a similar physiological saline environment. The selectivity and regulation that are known for being two important characteristics of ion channels were achieved due to controllable electrosurface properties of alumina nanochannel. This channel shows good selectivity for ion with low electronegativity. The regulatory role of ion channel in confined space was achieved by varying diameters of nanochannel and lengths of ions travel path. In addition, a new theory based on the Randles-Sevcik equation is proposed for evaluation of cross-channel ion transfer in this article for the first time. The ingenious design strategy is demonstrated to be a useful means for investigating the complex cross-channe...

Nanofluidic Diode Based on Branched Alumina Nanochannels with Tunable Ionic Rectification

In this work, the synthetic alumina nanochannels with bi-, tri-, and tetra-branched geometry structures exhibited ionic current rectifications with nonlinear I-V curves. Such diode performance of the branched alumina nanochannel is mainly dependent on the cooperative asymmetry of the branched structure and the surface-charge distribution on inner walls. By regulating the geometry, electrolyte pH, and solution concentration, the tunable ionic rectification properties are effectively obtained including both the rectification ratios and the rectifying direction that were deduced from the converted ion selectivity. This nanofluidic diode may open up a new opportunity for the application of the complex nanofluidic devices in contrast to previously reported channels to provide molecular analysis, controlled mass transport, drug release, and various logic gate operations.