Surface enhanced Raman with anodized aluminum oxide films

Aluminum is not a platform of choice for surface enhanced Raman scattering (SERS) experiments despite its large negative permittivity value (larger than gold or silver at optical wavelengths). It is also widely believed that an oxide layer on top of any platform substantially impedes SERS signals. Yet, anodized aluminum oxide may be perforated in an organized fashion and we have used it to examine SERS of single walled carbon nanotubes (SWCNTs) at micron length and fullerene (C60) at the nanoscale. The signal-to-noise ratio of the corresponding Raman signals exhibited a large signal enhancement for SWCNTs but not for C60. We attributed the SERS to the formation of standing surface charge waves in this subwavelength environment.     

Surface enhanced Raman scattering of biospecies on anodized aluminum oxide films

Traditionally, aluminum and anodized aluminum oxide films (AAO) are not the platforms of choice for surface-enhanced raman scattering (SERS) experiments despite of the aluminum’s large negative permittivity value. Here we examine the usefulness of aluminum and nanoporous alumina platforms for detecting soft biospecies ranging from bacterial spores to protein markers. We used these flat platforms to examine SERS of a model protein (cytochrome c from bovine heart tissue) and bacterial cells (spores of Bacillus subtilis ATCC13933 used as Anthrax simulant) and demonstrated clear Raman amplification.     

Synthesis of nanoporous activated iridium oxide films by anodized aluminum oxide templated atomic layer deposition

Iridium oxide (IrOx) has been widely studied due to its applications in electrochromic devices, pH sensing, and neural stimulation. Previous work has demonstrated that both Ir and IrOx films with porous morphologies prepared by sputtering exhibit significantly enhanced charge storage capacities. However, sputtering provides only limited control over film porosity. In this work, we demonstrate an alternative scheme for synthesizing nanoporous Ir and activated IrOx films (AIROFs). This scheme utilizes atomic layer deposition to deposit a thin conformal Ir film within a nanoporous anodized aluminum oxide template. The Ir film is then activated by potential cycling in 0.1 M H₂SO₄ to form a nanoporous AIROF. The morphologies and electrochemical properties of the films are characterized by scanning electron microscopy and cyclic voltammetry, respectively. The resulting nanoporous AIROFs exhibit a nanoporous morphology and enhanced cathodal charge storage capacities as large as 311 mC/cm².     

Interactions of bovine serum albumin with aluminum polyoxocations and aluminum hydroxide

Interactions of aqueous solutions of aluminum polyoxocations (Al13-mers and Al30-mers) and aluminum hydroxide suspensions of varying particle sizes (26, 55, and 82 nm) with a model protein, bovine serum albumin (BSA), have been investigated using potentiometry, conductometry, viscometry, 27Al solution NMR, UV-vis spectroscopy, dynamic light scattering, zeta-potential measurements, thermogravimetry, X-ray diffraction, and scanning electron microscopy. Increasing amounts of BSA partially convert Al13-mers and, to a larger extent, Al30-mers into amorphous Al hydroxide without gel formation. At the same time, BSA molecules can form unstable aggregates in the Al polyoxocation solutions which redisperse easily upon standing. In the case of Al hydroxide sols, BSA addition causes substantial gelation, the extent of which is proportional to the amount of BSA added and inversely related to the Al hydroxide particle size. Upon freeze-drying or centrifugation of Al species-BSA solutions, an interesting sheetlike morphology with 150-200 nm wide nanoribbons is observed for pure Al hydroxide nanoparticles and for solutions of Al polyoxocations with the highest amount of BSA studied. On the basis of the combined solution, colloidal and solid-state characterization of model Al species-BSA systems, a qualitative model of possible interactions in the Al polyoxocation-BSA and Al hydroxide-BSA systems is proposed wherein core-shell hybrid nanoparticles are formed from protein "core" and Al polyoxocation "shell" or Al hydroxide "core" and protein "shell".     

Technology of fabrication and study of porous oxide films on aluminum alloys

Technology for fabrication of porous anodic oxide films on aluminum alloys is suggested. All the films have good electrical parameters in a wide temperature range. The results obtained were used to fabricate metal-insulator substrates for manufacture of electronic devices.     

多孔阳极氧化铝膜的制备研究

在直流恒压下,在不同的酸性溶液中对铝片实施两步阳极氧化制备多孔氧化铝膜,在磷酸溶液中制得的模板孔径大,并且电解时间缩短,加快了制备模板的过程。同时利用阳极氧化初期电流密度的变化,分析了多孔氧化铝膜的形成机理。     

Concentration effects on partitioning of dextrans and serum albumin in porous glass

Partitioning of three dextrans and bovine serum albumin (BSA) in controlled-pore glass beads was measured by a batch mass balance technique. For all solutes the measured partition coefficient increased with bulk phase concentration, and the relationship appeared to be linear up to 0.05 g/mL for the dextrans. The measured slopes of partition coefficient versus concentration were compared with predictions using a hard-sphere theory, and while the agreement was tolerable for BSA, the dextran results were much lower than the theory dictated except for very small pores, in which case it was speculated that molecular weight polydispersity resulted in anomalous partitioning of the smaller components.     

Mechanical properties of anodized coatings over molten aluminum alloy

A method to measure interfacial mechanical properties at high temperatures and in a controlled atmosphere has been developed to study anodized aluminum surface coatings at temperatures where the interior aluminum alloy is molten. This is the first time that the coating strength has been studied under these conditions. We have investigated the effects of ambient atmosphere, temperature, and surface finish on coating strength for samples of aluminum alloy 7075. Surprisingly, the effective Young's modulus or strength of the coating when tested in air was twice as high as when samples were tested in an inert nitrogen or argon atmosphere. Additionally, the effective Young's modulus of the anodized coating increased with temperature in an air atmosphere but was independent of temperature in an inert atmosphere. The effect of surface finish was also examined. Sandblasting the surface prior to anodization was found to increase the strength of the anodized coating with the greatest enhancement noted for a nitrogen atmosphere. Machining marks were not found to significantly affect the strength.     

Pushing the size limits in the replication of nanopores in anodized aluminum oxide via the layer-by-layer deposition of polyelectrolytes

We report on the successful replication of the smallest pores in anodized aluminum oxide (AAO) via the layer-by-layer (LBL) deposition of polyelectrolytes to date to yield free-standing, open nanotubes with inner and outer diameters (±2σ) down to 37 ± 4 and 52 ± 19 nm, respectively. This work is based on the fabrication of defined arrays of highly regular nanopores by anodic oxidation of aluminum. Pores with pore diameters between 53 ± 9 and 356 ± 14 nm and interpore distances between 110 ± 3 and 500 ± 17 nm were obtained using an optimized two-step anodization procedure. 3-(Ethoxydimethylsilyl)propylamine-coated pores were replicated by alternating LBL deposition of poly(styrenesulfonate) and poly(allylamine). The detrimental adsorption of polyelectrolyte on the top surface of the template that typically results in partial pore blocking was eliminated by controlling the surface energy of the top surface via deposition of an ultrathin gold layer. The thickness of the deposited LBL multilayer assembly at the pore orifice agreed to within the experimental error with the thicknesses measured by variable angle spectroscopic ellipsometry and atomic force microscopy (AFM) for layers assembled on flat substrates. The selective dissolution of the alumina template afforded free-standing, open polymer nanotubes that were stable without any cross-linking procedure. The nanotubes thus obtained possessed mean outer diameters as small as 52 nm, limited by the size of the AAO template.     

Application of anodized aluminum in fluorescence detection of biological species

Thin nanoporous alumina obtained by anodization of aluminum films offers promising advantages for application in fluorescence-based biological sensors including convenient preparation, increased density of binding sites, and improved collection efficiency of fluorescence. These advantages are illustrated in the detection of streptavidin using biotin covalently bound to the surface of alumina nanopores. Fluorescence intensity enhancement as high as 7 times is observed in nanopores in comparison to flat glass surface.      

Investigation of mechanical properties of anodized aluminum using dilatometric measurements

Mechanical properties of anodized aluminum were studied using the results of dilatometric measurements of thermal expansion of anodized Al (the symmetric structure Al(2)O(3)-Al-Al(2)O(3)). The 100-microm-thick Al(2)O(3 )oxide layer was formed in 4% aqueous solution of oxalic acid in the galvanostatic regime at a current density of 20 mA cm(-2). Measurements of thermal expansion of anodized Al (Al and Mg alloy of 2.7-3.2%, and 0.3-0.6% Mn, and 0.5-0.8% Si) with the thickness of initial Al from 0.6 to 3.7 mm and ceramic from Al(2)O(3) in the temperature range of 20-500 degrees C were conducted using an automatic quartz dilatometer. Intrinsic stress in the Al layer, the values of the modulus of elasticity, and the porosity of Al oxide formed on Al of different thickness are calculated.     

Fabrication of three dimensional interconnected porous carbons from branched anodic aluminum oxide template

In this communication, the morphology of double branched anodic aluminum oxide (AAO) templates from linear down or step down function of anodizing voltage is discussed. The interconnected AAO film is obtained when the thin pore wall at the final branched channels is dissolved by chemical etching. The three-dimensional interconnected porous carbons are fabricated by carbonization of polyimide film which is negative replicated from the layered interconnected AAO template.     

Syntheses of rare-earth metal oxide nanotubes by the sol-gel method assisted with porous anodic aluminum oxide templates

In this paper, we report a versatile synthetic method of ordered rare-earth metal (RE) oxide nanotubes. RE (RE=Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) oxide nanotubes were successfully prepared from corresponding RE nitrate solution via the sol-gel method assisted with porous anodic aluminum oxide (AAO) templates. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction (XRD) have been employed to characterize the morphology and composition of the as-prepared nanotubes. It is found that as-prepared RE oxides evolve into bamboo-like nanotubes and entirely hollow nanotubes. A new possible formation mechanism of RE oxide nanotubes in the AAO channels is proposed. These high-quantity RE oxide nanotubes are expected to have promising applications in many areas such as luminescent materials, catalysts, magnets, etc.     

The effect of nanometer size of porous anodic aluminum oxide on adsorption and fluorescence of tetrahydroxyflavanol

Nanoporous anodic aluminum oxide, which was obtained by two-step electrochemical anodization aluminum process, showed strong physical adsorption capability of tetrahydroxyflavanol (THOF). The fluorescence peak of THOF was also dependent on its environment because the surrounding electron field affected the molecule luminescence in nanoporous alumina. The effect of nanometer size on adsorption and fluorescence of THOF is observed. The mechanism is primarily discussed.     

Enhanced solubilization of bovine serum albumin in reverse micelles by compressed CO2

The effect of compressed CO2 on the solubilization of bovine serum albumin (BSA) in water/sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)/isooctane reverse micelles was studied by observing phase behavior and recording UV-visible spectra under different conditions. The pH values within the water cores of reverse micelles at different CO2 pressures were also determined. The solubilization capacity of the reverse micelles for the protein increased considerably as CO2 pressure increased within the low-pressure range, but decreased at higher CO2 pressures, so that the micelles eventually lost their ability to solubilize the protein. The effect of CO2 on the stability of the reverse micelles played an important role in the relationship between pressure and protein solubility. A "multicomplex" model was proposed to explain these effects. The different solublization capacities within different pressure ranges demonstrates the unique advantage of using compressed CO2 in the extraction of proteins with reverse micelles.     

Standardization of aluminum oxide and detection of polycyclic aromatic hydrocarbons on aluminum oxide

Luminescence methods are described for detecting polycyclic aromatic hydrocarbons (6-, 5-, 4-, and 3-ring) on aluminum oxide after separation by dry-column chromatography. A method is reported for standardizing the water content in the aluminum oxide used for dry-column chromatography. A water content of 4.74% was chosen to define the activity of aluminum oxide because there was minimum overlap among the PAH bands.     

Electrochemical analysis of the structure and formation kinetics of a porous anodic aluminum oxide

A technique is proposed for an electrochemical study of the morphology of porous anodic aluminum oxide films. The technique involves an analysis of anodic polarization curves recorded while linearly increasing potential. A phenomenological model describing the experimental curves is developed. The method may be used for studying the film formation kinetics     

Chemisorption of hydrogen on aluminum oxide

Russian Chemical Bulletin -