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This study is the first realisation of true optical rugate filters (RFs) based on nanoporous anodic alumina (NAA) by sinusoidal waves. An innovative and rationally designed sinusoidal pulse anodisation (SPA) approach in galvanostatic mode is used with the aim of engineering the effective medium of NAA in a sinusoidal fashion. A precise control over the different anodisation parameters (i.e. anodisation period, anodisation amplitude, anodisation offset, number of pulses, anodisation temperature and pore widening time) makes it possible to engineer the characteristic reflection peaks and interferometric colours of NAA-RFs, which can be finely tuned across the UV-visible-NIR spectrum. The effect of the aforementioned anodisation parameters on the photonic properties of NAA-RFs (i.e. characteristic reflection peaks and interferometric colours) is systematically assessed in order to establish for the first time a comprehensive rationale towards NAA-RFs with fully controllable photonic properties. The experimental results are correlated with a theoretical model (Looyenga-Landau-Lifshitz - LLL), demonstrating that the effective medium of these photonic nanostructures can be precisely described by the effective medium approximation. NAA-RFs are also demonstrated as chemically selective photonic platforms combined with reflectometric interference spectroscopy (RIfS). The resulting optical sensing system is used to assess the reversible binding affinity between a model drug (i.e. indomethacin) and human serum albumin (HSA) in real-time. Our results demonstrate that this system can be used to determine the overall pharmacokinetic profile of drugs, which is a critical aspect to be considered for the implementation of efficient medical therapies.

Although nanoparticle-based targeted delivery systems have gained promising achievements for cancer therapy, the development of sophisticated strategies with effective combinatorial therapies remains an enduring challenge. Herein, we report the fabrication of a novel nanomaterial, so-called anodic alumina nanotubes (AANTs) for proof-of-concept cancer therapy by targeting cell signaling networks. This strategy is to target autophagic and endoplasmic reticulum (ER) stress signaling by using thapsigargin (TG)-loaded AANTs cotreated with an autophagy inhibitor 3-methyladenine (3-MA). We first show that AANTs are nontoxic and can activate autophagy in different cell types including human fibroblast cells (HFF), human monocyte cells (THP-1), and human breast cancer cells (MDA-MB 231-TXSA). Treatment with 3-MA at a nontoxic dose reduced the level of autophagy induced by AANTs, and consequently sensitized breast cancer cells to AANTs-induced cellular stresses. To target autophagic and ER stress signaling networking, breast cancer cells were treated with 3-MA together with AANTs loaded with the prototype ER stress inducer TG. We demonstrated that 3-MA enhanced the cancer cell killing effect of AANTs loaded with TG. This effect was associated with enhanced ER stress signaling due to the combination effect of TG and 3-MA. These findings not only demonstrate the excellent biocompatibility of AANTs as novel biomaterials but also provide new opportunities for developing ER- and autophagy-targeted delivery systems for future clinical cancer therapy.

In this study, we produce for the first time biomimetic films and microsized particles based on nanoporous anodic alumina distributed Bragg reflectors (NAA-DBRs) by a rational galvanostatic pulse-anodization approach. These biomimetic photonic structures can feature a broad range of vivid bright colors, which can be tuned across the UV-visible spectrum by engineering their nanoporous structure through different anodization parameters. The effective medium of NAA-DBRs films is systematically assessed as a function of the anodization period, the anodization temperature, and the current density ratio by reflectometric interference spectroscopy (RIfS). This analysis makes it possible to establish the most sensitive structure toward changes in its effective medium. Subsequently, specific detection of vitamin C molecules is demonstrated. The obtained results reveal that NAA-DBRs with optimized structure can achieve a low limit of detection for vitamin C molecules as low as 20 nM, a sensitivity of 227±4 nm μM(-1), and a linearity of 0.9985. Finally, as proof of concept, we developed a new photonic nanomaterial based on NAA-DBR microsized particles, which could provide new opportunities to produce microsized photonic analytical tools.

Herein, we present an interferometric sensor based on the combination of chemically functionalized nanoporous anodic alumina photonic films (NAA-PFs) and reflectometric interference spectroscopy (RIfS) aimed to detect trace levels of enzymes by selective digestion of gelatin. The fabrication and sensing performance of the proposed sensor were characterized in real-time by estimating the changes in effective optical thickness (i.e., sensing principle) of gelatin-modified NAA-PFs (i.e., sensing element) during enzymatic digestion. The working range (WR), sensitivity (S), low limit of detection (LLoD), and linearity (R(2)) of this enzymatic sensor were established by a series of experiments with different concentrations of gelatin (i.e., specific chemical sensing element) and trypsin (i.e., analyte), a model protease enzyme with relevant implications as a biomarker in the diagnosis of several diseases. The chemical selectivity of the sensor was demonstrated by comparison of gelatin digestion by other nonspecific enzyme models such as chymotrypsin and horseradish peroxidase. Furthermore, the role of the chemical sensing element (i.e., gelatin) was assessed by using hemoglobin instead of gelatin. Finally, we demonstrated that this sensor can be readily used to establish the kinetic parameters of enzymatic reactions. The obtained results revealed that the presented sensor has a promising potential to be used as a point-of-care system for fast detection of gastrointestinal diseases at early stages.

A smart and reversibly photoswitchable membrane based on an azobenzene photo-switch containing peptides attached inside the pores of nanoporous anodic alumina membranes (NAAMs) is presented. The transport of molecules of interest across the photoswitchable peptide (PSP) functionalized NAAMs can be effectively controlled and manipulated as a function of the photostationary state of the azobenzene group in a PSP., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Here, we report a detailed and systematic approach for studying the in vitro nanotoxicity study of high aspect ratio (HAR) nanomaterials using anodic alumina nanotubes (AANTs) as a nanomaterial model. AANTs with bio-inert properties and tailored aspect ratios ranging from 7.8 to 63.3 were synthesized by an electrochemical pulse anodization process. Cytotoxicity studies were conducted with RAW 264.7 mouse macrophage cells and MDA-MB 231-TXSA human breast cancer cells through several toxicity parameters, including cell viability and morphology, pro-inflammatory response, mitochondrial depolarization, lysosomal membrane permeabilization (LMP), induction of autophagy and endoplasmic reticulum (ER) stress. The resulting toxicity patterns were cell-type dependent and strongly related with AANTs dose, length of time, and importantly the AR of AANTs. Long AANTs triggered enhanced cell death, morphological changes, tumor necrosis factor α (TNF-α) release, LMP and ER stress than short AANTs. The toxic AR window of AANTs was determined to be 7.8, which is shorter than that of other previously reported HAR nanomaterials. This toxic AR window provides a promising opportunity to control the nanotoxicity of HAR nanomaterials for their advanced drug delivery application., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In this study, we present a nanoengineered therapeutic-releasing system based on aluminum wires featuring nanoporous anodic alumina layers and chitosan coatings. Nanoporous anodic alumina layers are produced on the surface of aluminum wires by electrochemical anodization. These nanoporous layers with precisely engineered nanopore geometry are used as nanocontainers for bovine serum albumin molecules labeled with fluorescein isothiocyanate (BSA-FITC), which is selected as a model drug. The surface of these therapeutic-releasing implants is coated with a biocompatible and biodegradable polymer, chitosan, in order to achieve a sustained release of protein over extended periods of time. The performance of this therapeutic-releasing device is systematically assessed through a series of experiments under static and dynamic flow conditions. In these experiments, the effect of such parameters as the number of layers of chitosan coating and the temperature and pH of the eluting medium is established. The obtained results reveal that the proposed therapeutic-releasing system based on nanoporous aluminum wires can be engineered with sustained release performance for up to 6.5 weeks, which is a critical factor for medical treatments using sensitive therapeutics such as proteins and genes when a localized delivery is desired.

The understanding of the electrochemical properties of nanopores is the key factor for better understanding their performance and applications for nanopore-based sensing devices. In this study, the influence of pore dimensions of nanoporous alumina (NPA) membranes prepared by an anodization process and their electrochemical properties as a sensing platform using impedance spectroscopy was explored. NPA with four different pore diameters (25 nm, 45 nm and 65 nm) and lengths (5 μm to 20 μm) was used and their electrochemical properties were explored using different concentration of electrolyte solution (NaCl) ranging from 1 to 100 μM. Our results show that the impedance and resistance of nanopores are influenced by the concentration and ion species of electrolytes, while the capacitance is independent of them. It was found that nanopore diameters also have a significant influence on impedance due to changes in the thickness of the double layer inside the pores.

Electrochemical anodization of pure aluminum enables the growth of highly ordered nanoporous anodic alumina (NAA) structures. This has made NAA one of the most popular nanomaterials with applications including molecular separation, catalysis, photonics, optoelectronics, sensing, drug delivery, and template synthesis. Over the past decades, the ability to engineer the structure and surface chemistry of NAA and its optical properties has led to the establishment of distinctive photonic structures that can be explored for developing low-cost, portable, rapid-response and highly sensitive sensing devices in combination with surface plasmon resonance (SPR) and reflective interference spectroscopy (RIfS) techniques. This review article highlights the recent advances on fabrication, surface modification and structural engineering of NAA and its application and performance as a platform for SPR- and RIfS-based sensing and biosensing devices.

Here, we report a study on the biocompatibility, cell uptake and in vitro delivery of tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) by new nano-carriers called anodic alumina nanotubes (AANTs) for potential cancer therapy. AANTs were electrochemically engineered by a unique pulse anodization process, which enables precise control of the nanotube geometry, and used here as nano-carriers for drug delivery. In vitro cytotoxicity and cell uptake of AANTs was assessed using MDA-MB231-TXSA human breast cancer cells and mouse RAW 264.7 macrophage cells. AANTs exhibited excellent biocompatibility in both cell lines over a time course of five days even at a maximum concentration of AANTs of 100 μgmL(-1). Transmission electron microscopy and fluorescence microscopy confirmed a significant uptake of AANTs by RAW 264.7 cells and breast cancer cells. AANTs loaded with the pro-apoptotic protein Apo2L/TRAIL showed exceptional loading capacity (104 ± 14.4 μgmg(-1) of AANTs) and demonstrated significant decrease in viability of MDA-MB231-TXSA cancer cells due to apoptosis induction. These results demonstrate that AANTs are promising nano-carriers for drug delivery applications., (Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.)

In this study, we report about the structural engineering and optical optimization of nanoporous anodic alumina rugate filters (NAA-RFs) for real-time and label-free biosensing applications. Structurally engineered NAA-RFs are combined with reflection spectroscopy (RfS) in order to develop a biosensing system based on the position shift of the characteristic peak in the reflection spectrum of NAA-RFs (Δλpeak). This system is optimized and assessed by measuring shifts in the characteristic peak position produced by small changes in the effective medium (i.e., refractive index). To this end, NAA-RFs are filled with different solutions of d-glucose, and the Δλpeak is measured in real time by RfS. These results are validated by a theoretical model (i.e., the Looyenga-Landau-Lifshitz model), demonstrating that the control over the nanoporous structure makes it possible to optimize optical signals in RfS for sensing purposes. The linear range of these optical sensors ranges from 0.01 to 1.00 M, with a low detection limit of 0.01 M of d-glucose (i.e., 1.80 ppm), a sensitivity of 4.93 nm M(-1) (i.e., 164 nm per refractive index units), and a linearity of 0.998. This proof-of-concept study demonstrates that the proposed system combining NAA-RFs with RfS has outstanding capabilities to develop ultrasensitive, portable, and cost-competitive optical sensors.

Herein, we present a comparative study about the sensing performance of optical biosensors based on photoluminescence spectroscopy (PLS) and reflectometric interference spectroscopy (RIfS) combined with nanoporous anodic alumina (NAA) platforms when detecting different analytes under distinct adsorption conditions. First, NAA platforms are structurally engineered in order for optimizing the optical signals obtained by PLS and RIfS. Then, the most optimal NAA platforms combined with PLS and RIfS are quantitatively compared by detecting two different analytes: d-glucose and l-cysteine under nonspecific and specific adsorption conditions, respectively. The obtained results demonstrate that such parameters as the analyte nature and adsorption conditions play a direct role in the sensing performance of these platforms. However, as this study demonstrates, PLS-NAA platforms are more sensitive than RIfS-NAA ones. The former shows better linearity (i.e., proportional change in the sensing parameter with analyte concentration), higher sensitivity toward analytes (i.e., sharper change in the sensing parameter with analyte concentration), and lower limit of detection (i.e., minimum detectable concentration of analyte).

A method for surface engineering of structural gradients with nanopore topography using the self-ordering process based on electrochemical anodization of aluminum is described. A distinct anodization condition with an asymmetrically distributed electric field at the electrolyte/aluminum interface is created by nonparallel arrangement between electrodes (tilted by 45°) in an electrochemical cell. The anodic aluminum oxide (AAO) porous surfaces with ordered nanopore structures with gradual and continuous change of pore diameters from 80 to 300 nm across an area of 0.5-1 cm were fabricated by this anodization using two common electrolytes, oxalic acid (0.3 M) and phosphoric acid (0.3 M). The formation of pore gradients of AAO is explained by asymmetric and gradual distribution of the current density and temperature variation generated on the surface of Al during the anodization process. Optical and wetting gradients of prepared pore structures were confirmed by reflective interferometric spectroscopy and contact angle measurements showing the ability of this method to generate porous surfaces with multifunctional gradients (structural, optical, wetting). The study of influence of pore structures on cell growth using the culture of neuroblastoma cells reveals biological relevance of nanopore gradients and the potential to be applied as the platform for spatially controllable cell growth and cell differentiation.

In this communication, we present a novel approach for control of drug release from porous materials. The method is based on deposition of a plasma polymer layer with controlled thickness which reduces a pore diameter and, hence, defines the rate of drug release.

Herein, we present an innovative strategy for optimizing hierarchical structures of nanoporous anodic alumina (NAA) to advance their optical sensing performance toward multi-analyte biosensing. This approach is based on the fabrication of multilayered NAA and the formation of differential effective medium of their structure by controlling three fabrication parameters (i.e., anodization steps, anodization time, and pore widening time). The rationale of the proposed concept is that interferometric bilayered NAA (BL-NAA), which features two layers of different pore diameters, can provide distinct reflectometric interference spectroscopy (RIfS) signatures for each layer within the NAA structure and can therefore potentially be used for multi-point biosensing. This paper presents the structural fabrication of layered NAA structures, and the optimization and evaluation of their RIfS optical sensing performance through changes in the effective optical thickness (EOT) using quercetin as a model molecule. The bilayered or funnel-like NAA structures were designed with the aim of characterizing the sensitivity of both layers of quercetin molecules using RIfS and exploring the potential of these photonic structures, featuring different pore diameters, for simultaneous size-exclusion and multi-analyte optical biosensing. The sensing performance of the prepared NAA platforms was examined by real-time screening of binding reactions between human serum albumin (HSA)-modified NAA (i.e., sensing element) and quercetin (i.e., analyte). BL-NAAs display a complex optical interference spectrum, which can be resolved by fast Fourier transform (FFT) to monitor the EOT changes, where three distinctive peaks were revealed corresponding to the top, bottom, and total layer within the BL-NAA structures. The spectral shifts of these three characteristic peaks were used as sensing signals to monitor the binding events in each NAA pore in real-time upon exposure to different concentrations of quercetin. The multi-point sensing performance of BL-NAAs was determined for each pore layer, with an average sensitivity and low limit of detection of 600 nm (mg mL−1)−1 and 0.14 mg mL−1, respectively. BL-NAAs photonic structures have the capability to be used as platforms for multi-point RIfS sensing of biomolecules that can be further extended for simultaneous size-exclusion separation and multi-analyte sensing using these bilayered nanostructures. [ABSTRACT FROM AUTHOR]

Nanoporous anodic alumina (NAA) has become one of the most promising nanomaterials in optical biosensing as a result of its unique physical and chemical properties. Many studies have demonstrated the outstanding capabilities of NAA for developing optical biosensors in combination with different optical techniques. These results reveal that NAA is a promising alternative to other widely explored nanoporous platforms, such as porous silicon. This review is aimed at reporting on the recent advances and current stage of development of NAA-based optical biosensing devices. The different optical detection techniques, principles and concepts are described in detail along with relevant examples of optical biosensing devices using NAA sensing platforms. Furthermore, we summarise the performance of these devices and provide a future perspective on this promising research field. [ABSTRACT FROM AUTHOR]

Abstract: Anodic aluminium oxide (AAO) has been investigated and utilized in numerous products for almost a century. But the rapidly increasing interest in nanoscale materials and their outstanding properties has propelled nanoporous AAO to the fore as one of the most popular nanomaterial with applications across a gamut of areas including molecular separation, catalysis, energy generation and storage, electronics and photonics, sensors and biosensors, drug delivery and template synthesis. Material fabrication of AAO is based on facile and inexpensive electrochemical anodization with the self-ordering process of nanopores not requiring any lithography or templating, and the outcome of the process are perfectly ordered and size controlled nanopores with distinctive pore geometries. Recent research on AAO is characterized by a remarkable trajectory of innovation, in particular with regards to control of surface functionality and, concomitantly, to the design of intricate structural features such as modulated, branched, and multilayered pore architectures. This review illuminates research on recent development of AAO focussing on surface and structural engineering, and on emerging applications. Key examples and critical preparative issues and resulting improvements sparking opportunities for further applications in AAO properties are discussed. We conclude this review with an outlook providing a critical perspective on future trends on surface and structural engineering of AAO. [Copyright &y& Elsevier]

This work presents template synthesis of ordered arrays of nickel, cobalt and nickel hexacyanoferrates (NiHCF) with several distinct morphologies such as dots, rods, and tubes. Anodic alumina oxide (AAO) with preferred pore diameters and thickness was fabricated by electrochemical anodization of aluminum used as template. Ni and Co nanostructures inside AAO template were prepared by electrodeposition using galvanostatic method. NiHCF nanostructures were prepared by electrochemical oxidation of Ni using cyclic voltametry (CV) in the presence of hexacyanoferrate ions. The morphology, chemical, and functional properties of prepared nanostructures were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray microscopy (EDAX), and electrochemical methods. The electrocatalytic properties of NiHCF nanorod arrays electrode and their potential for the detection of hydrogen peroxide and biosensing application were demonstrated. [ABSTRACT FROM AUTHOR]

Anodization of aluminum is an excellent nonlithographic alternative to conventional fabrication approaches for low-cost and large-scale synthesis of a variety of nanostructured materials. In this work, the preparation of anodic alumina oxide (AAO) with unique three-dimensional (3D) porous structures that consist of periodically perforated nanopores is reported. The fabrication method combines electrochemical anodization of aluminum and chemical etching. The key feature of this process is cyclic anodization where an oscillatory current signal was applied to create AAO with periodically shaped pore structures. Spatially specific dissolution of the pore walls was directed by modulated pore structures during chemical etching to generate hexagonally ordered arrays of holes with periodic distribution across the pore length. [ABSTRACT FROM AUTHOR]

Abstract: Anodized aluminium oxide (AAO) fabricated by electrochemical anodization of aluminium is used as the substrate for focused ion-beam (FIB) fabrication of single nanopore and nanopore arrays. The method is based on the controlled and selective removal of AAO barrier oxide film by FIB milling. FIB process with different milling conditions is applied to open single nanopores (diameter of 60 nm) or circular nanopore arrays with a different number of opened pores on AAO substrate. This process combines a low cost AAO substrate and FIB milling, and offers an economically viable alternative for the fabrication of nanopore devices with controlled dimensions for a range of applications in nanofluidics, molecular separations and biosensing. [Copyright &y& Elsevier]

Abstract: Pore opening and removal of the oxide barrier layer by wet chemical etching is the last and most critical step in the fabrication of anodic alumina oxide (AAO) with through-hole pore morphology. The time controlled etching method is dependent on many parameters that cannot provide reproducible pore diameters of fabricated AAO. To address the inconsistency of the chemical etching process and achieve fabrication of AAO with desired pore diameters we introduce an electrochemical method for detection of the pore opening point. The method is based on monitoring of current through AAO using a simple electrochemical permeation cell with two electrodes. The dissolution of the oxide barrier film in phosphoric acid and the pore opening point were detected by significant increases of the current between two electrodes during etching. Experimental demonstration and feasibility of this approach for routine fabrication of through-hole AAO membranes using different AAO samples and etching conditions (10–55°C) combined with scanning electron microscopy study are presented. It was demonstrated that with support of this method, nanometer scale control of the pore opening of AAO can be achieved by chemical etching. The method offers improved reproducibility in fabrication of AAO with desired pore diameters, particularly when AAO is fabricated using different anodization conditions (mild and hard anodization) and different acid solutions (sulfuric, oxalic, and phosphoric). [Copyright &y& Elsevier]

A new and facile method is described to prepare Janus-like nanoporous anodic aluminium oxide (AAO) membranes with distinctly different internal and external surface chemistry. [ABSTRACT FROM AUTHOR]

Herein, we present a systematic study on the development, optimisation and applicability of interferometrically coloured distributed Bragg reflectors based on nanoporous anodic alumina (NAA-DBRs) in the form of films and nanoporous microparticles as visual/colorimetric analytical tools. Firstly, we synthesise a complete palette of NAA-DBRs by galvanostatic pulse anodisation approach, in which the current density is altered in a periodic fashion in order to engineer the effective medium of the resulting photonic films in depth. NAA-DBR photonic films feature vivid colours that can be tuned across the UV-visible-NIR spectrum by structural engineering. Secondly, the effective medium of the resulting photonic films is assessed systematically by visual analysis and reflectometric interference spectroscopy (RIfS) in order to establish the most optimal nanoporous platforms to develop visual/colorimetric tools. Then, we demonstrate the applicability of NAA-DBR photonic films as a chemically selective sensing platform for visual detection of mercury(II) ions. Finally, we generate a new nanomaterial, so-called photonic dust, by breaking down NAA-DBRs films into nanoporous microparticles. The resulting microparticles (μP-NAA-DBRs) display vivid colours and are sensitive towards changes in their effective medium, opening new opportunities for developing advanced photonic nanotools for a broad range of applications. [ABSTRACT FROM AUTHOR]

In this paper, we present recent work from our group focussed on the fabrication of nanopore and nanotube arrays using self-ordered electrochemistry, and their application in several key areas including template synthesis, molecular separation, optical sensing, and drug delivery. We have fabricated nanoporous anodic aluminium oxide (AAO) with controlled pore dimensions (20-200nm) and shapes, and used them as templates for the preparation of gold nanorod/nanotube arrays and gold nanotube membranes with characteristic properties such as surface enhanced Raman scattering and selective molecular transport. The application of AAO nanopores as a sensing platform for reflective interferometric detection is demonstrated. Finally, a drug release study on fabricated titania nanotubes confirms their potential for implantable drug delivery applications. [ABSTRACT FROM AUTHOR]

Abstract: Nanoporous anodic aluminum oxide (AAO) has become one of the most popular materials with potential applications in numerous areas, including molecular separation, catalysis, energy generation and storage, electronics, photonics, sensing, drug delivery, and template synthesis. The fabrication of AAO is based on simple, cost-effective, self-ordering anodization of aluminum, which yields vertically-aligned, highly-ordered nanoporous structures. Due to its unique optical and electrochemical properties, nanoporous AAO has been extensively explored as a platform for developing inexpensive, portable sensing and biosensing devices. This article reviews AAO-based sensing and biosensing technologies, highlighting key examples of different detection concepts and device performance. We conclude with a perspective on the exciting opportunities for further developments in this research field. [Copyright &y& Elsevier]

Abstract: Transition metal hexacyanoferrate (MeHCF) have attracted extensive attention because of their outstanding properties including, electrocatalysis, molecular magnetism, biosensing and ion-exchange. This paper describes an approach for fabrication of ordered nanoarrays of Ni hexacyanoferrate (NiHCF) structures with different morphologies such as dots, rods and tubes in order to advance their properties and applications. The method is based on the conversion of Ni into NiHCF nanostructures by electrochemical oxidation in the presence of hexacyanoferrate ions, using nanoporous anodic alumina oxide (AAO) as a template. The structure and morphology of formed Ni and NiHCF nanoarrays were confirmed by scanning electron microscopy (SEM), showing agreement with the pore structures of the AAO template. The electrocatalytic activity of NiHCF nanorod array electrodes showed high catalytic properties for the detection of hydrogen peroxide and the potential to be used as a platform for direct biosensing applications. The ion-exchange ability of fabricated NiHCF nanostructures (nanorods and nanotubes) toward alkali cations such as Na+ has been successfully confirmed. [Copyright &y& Elsevier]

This work aims at introducing the synthesis process of carbon nanotubes (CNTs) inside nanoporous anodic alumina (NAA) templates adopting a catalyst-free chemical vapor deposition (CVD) approach under different conditions. The nanotubular structure of NAA is prepared according to tow-step anodization process. This provides a unique platform to grow CNTs with precisely controlled geometric features. The structural features, crystalline structures and chemical composition of the resulting CNTs-NAA composites were systematically characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Energy-dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR) as well as Raman spectroscopy. Preparing the CNTs according to this template technique allows us to obtain nanotubes which are open at one/both end(s) with a uniform diameter (10–200 nm) along the pore length (1–100 μm) without using any metal catalyst. [ABSTRACT FROM AUTHOR]

In this study, we report an innovative approach aiming to assess the binding affinity between drug molecules and human serum albumin by combining nanoporous anodic alumina rugate filters (NAA-RFs) modified with human serum albumin (HSA) and reflectometric interference spectroscopy (RIfS). NAA-RFs are photonic crystal structures produced by sinusoidal pulse anodization of aluminum that present two characteristic optical parameters, the characteristic reflection peak λpeak), and the effective optical thickness of the film (OTeff), which can be readily used as sensing parameters. A design of experiments strategy and an ANOVA analysis are used to establish the effect of the anodization parameters (Le., anodization period and anodization offset) on the sensitivity of HSA-modified NAA-RFs toward indomethacin, a model drug. To this end, two sensing parameters are used, that is, shifts in the characteristic reflection peak (ΔλPeak) and changes in the effective optical thickness of the film (ΔOTeff). Subsequendy, optimized NAA-RFs are used as sensing platforms to determine the binding affinity between a set of drugs (le., indomethacin, coumarin, sulfadymethoxine, warfarin, and salicylic add) and HSA molecules. Our results verify that the combination of HSA-modified NAA-RFs with RIfS can be used as a portable, low-cost, and simple system for establishing the binding affinity between drugs and plasma protdns, which is a critical factor to develop efficient medicines for treating a broad range of diseases and medical conditions. [ABSTRACT FROM AUTHOR]

This work presents the fabrication of carbon nanotube composite membranes with controllable nanotube dimensions (inner diameters and lengths) and surface chemistry and explores their influence on the transport properties and chemical based transport selectivity. These membranes were prepared by growing of vertically aligned multiwalled carbon nanotubes (MWCNTs) inside nanoporous anodic alumina membranes (NAAMs) through a catalyst-free chemical vapour deposition (CVD) approach. The deposition time during CVD process and the length of NAAMs were used to control nanotube dimensions. The thermal annealing and wet and dry oxidation processes were used to control the surface chemistry of inner walls of nanotubes from highly graphitic-hydrophobic to oxygen rich and hydrophilic. The structural features and chemical composition of the prepared membranes are characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The influence of the nanotube dimensions and surface chemistry on molecular transport properties of prepared membranes are assessed by analysing the transport of two models molecules with different hydrophilic–hydrophobic and charge properties. The obtained results reveal that the diffusional flux of model molecules through CNTs-NAAMs can be controlled by nanotube dimensions and surface chemistry of graphitic surface and these parameters can be used to tailor their chemical based molecular separation for specific applications. [ABSTRACT FROM AUTHOR]

Herein, we report on a rational electrochemical approach based on pulse anodization (PA) of aluminum for the fabrication of ultra-short anodic alumina nanotubes (AANTs) with exquisitely controlled dimensions. AANTs with average length 485 ± 180 nm and outer diameter 90 ± 10 nm were fabricated by PA with 0.3 M sulfuric acid and 10% ethanol. Our findings suggest that extensive Joule's heat generation at the nanopore's base is critical for optimized AANTs' liberation from pulse-anodized anodic aluminum oxide (AAO) nanostructure. The heat evolution results in an enhanced oxygen generation and a rapid voltage recovery during PA. While oxygen generation weakens the conjunction between cells, rapid voltage recovery generates asynchronous inner/outer wall structural modulation, which consequently facilitates structural cleavage of nanotubes along mild anodization/hard anodization (MA/HA) interfaces after acid etching. The understanding of AANTs fabrication mechanism enables us for the first time to fabricate ultra-short AANTs by reducing HA duration down to 1 second and using ethanol for enhancing heat generation. The resulting AANTs with controlled dimensions and high liberation yield offer new opportunities for advanced applications such as catalysis, template-assisted nanofabrication, optical sensing and drug delivery. [ABSTRACT FROM AUTHOR]

Nanoporous alumina (NPA) arrays prepared by electrochemical anodization have been attractive platform for application in molecular separations, biosensing, drug delivery and fuel cells due to their highly ordered pore structures, controllable pore dimensions and unique physical, optical, transport and electrochemical properties. However, there is still a lack of knowledge about the influence of the pore dimensions, shape and surface area on these properties. Hence the aim of this work is to use a focused ion beam (FIB) to mill a barrier layer of NPA to open a either single nanopore, several nanopores and 1 μm and 20 μm square areas of nanopore arrays to explore their electrochemical properties and biosensing performances. The internal surface of opened NPA nanopores was modified by covalent attachment of streptavidin and used for impedance label-free biosensing. The biosensor performance of this antibody modified nanopore biosensing platform was evaluated using various concentrations of biotin as a model analyte. Electrochemical impedance spectrometric (EIS) measurements of pore resistivity were carried out for different patterns of nanopore arrays. The results showed that small areas or number of pores provide better biosensing performance compared to large nanopore arrays. [ABSTRACT FROM AUTHOR]

Abstract: In this report, a label-free reflectometric interference spectroscopy (RIfS) based microchip biosensor for the detection of circulating tumour cells (CTCs) is demonstrated. Highly ordered nanoporous anodic aluminium oxide (AAO) fabricated by electrochemical anodization of aluminium foil was used as the RIfS sensing platform. Biotinylated anti-EpCAM antibody that specifically binds to human cancer cells of epithelial origin such as pancreatic cancer cells (PANC-1) was covalently attached to the AAO surface through multiple surface functionalization steps. Whole blood or phosphate buffer saline spiked with low numbers of pancreatic cancer cells were successfully detected by specially designed microfluidic device incorporating an AAO RIfS sensor, without labour intensive fluorescence labelling and/or pre-enhancement process. Our results show that the developed device is capable of selectively detecting of cancer cells, within a concentrations range of 1000–100,000cells/mL, with a detection limit of <1000cells/mL, a response time of <5min and sample volume of 50μL of. The presented RIfS method shows considerable promise for translation to a rapid and cost-effective point-of-care diagnostic device for the detection of CTCs in patients with metastatic cancer. [Copyright &y& Elsevier]

Abstract: This work presents the fabrication of gold nanotube membranes (GNT) using gold deposition on porous anodic aluminum oxide (AAO) template and demonstrates the catalytic properties generated by the nanostructured gold surface. AAO membranes were prepared by electrochemical anodization of Al in 0.3M oxalic acid electrolyte. Electroless gold deposition on AAO was performed via several steps using commercially available gold plating solutions. Scanning electron microscopy (SEM) images confirm that the gold nanotubes formed inside AAO pores have characteristic nanoclustered morphology as a result of the nucleation process during gold deposition. It was found that catalytic properties of GNT membranes depend on the size of gold nanoclusters which can be controlled by pH during nucleation process. The excellent catalytic properties (catalytic rate constant k =0.132min−1) of the GNT membranes were demonstrated by testing catalytic conversion of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) in the presence of NaBH4 as a reductant. The correlation between the size of gold nanoclusters and catalytic activity was verified showing the capability of controlling and further improving catalytic properties of GNT membranes. [Copyright &y& Elsevier]

Abstract: Structural and chemical modification of porous anodic alumina (AAO) membranes was investigated with the aim of fine-tuning pore diameters and chemical selectivity. AAO membranes from commercial sources with pore diameters (20, 100 and 200nm) were used as the substrate. Atomic layer deposition (ALD) of silica (SiO2) has been used for membrane structural modification using tris(tert-butoxy)silanol and trimethylaluminium as the precursor couple. By adjusting the number of ALD deposition cycles (3–20), the effective pore diameter of AAO membranes was significantly reduced to desired values (<10nm) improving the separation properties of commercial membranes. The chemical functionalization of silica coated AAO membranes with a perfluorodecyldimethylchlorosilane (PFDS) shows that the transport and selectivity properties of silica composite AAO membranes can be varied by functionalization using silane chemistry. The hydrophobic PFDS-modified membranes showed enhanced sensitivity (flux ratio 5.52) to the transport of hydrophobic molecules (tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy), over hydrophilic molecules (rose bengal (RB)). Structural and chemical properties of modified membranes were confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), dynamic secondary ion mass spectrometry (DSIMS), and contact angle measurements. The resultant silica coated commercial AAO membranes with specific surface chemistry and controlled pore size are applicable for advanced molecular separation, cell culture, tissue engineering, biosensing and drug delivery. [Copyright &y& Elsevier]