Track-etched Polycarbonate Membranes Research Articles

Transport properties of electrodeposited copper telluride (Cu2Te) nanowires embedded in polycarbonate track-etch membrane

In this paper, electronic transport properties of electrodeposited copper telluride (Cu2Te) nanowires at room temperature (303 K) embedded in polycarbonate track-etch membranes (Whatman, 6 μm thick, pores density of order 108 pores/cm2) as template with pores of diameter 200, 100 and 50 nm have been reported. Scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffractometry (XRD) were used to characterize the morphology and structure of the nanowires. I–V measurements of copper telluride nanowires of different diameter have shown symmetric and ohmic behavior in the voltage range used in this experiment. The temperature (T) dependent electrical conductivity measurements over a temperature (T) range of 308–423 K reveal that the electrical conductivity increases with increasing temperature and decreases as the size of the nanowires reduces. The electrical conductivity (at T ≥ room temperature) was observed significantly higher in copper telluride nanowires of higher diameter compared to lower diameter which attributes to the size effect. The activation energies (E a ) are found to be 2.34, 3.11 and 5.01 meV in low-temperature range of 308–340 K and 0.15, 0.28 and 0.57 meV in high-temperature range of 340–423 K for 200, 100 and 50 nm nanowires respectively. The temperature dependence of electrical resistance measurements has shown the nanowires have negative temperature coefficient of resistance (TCR).

Synthesis of CdS nanostructures using template-assisted ammonia-free chemical bath deposition

CdS micro- and nano-structures (micro/nanotubes and nanostructured films) were obtained by ammonia-free chemical bath deposition using polymer templates (ion track-etched polycarbonate membranes and poly(styrene-hydroxyethyl methacrylate) nanosphere arrays). The semiconductor structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoluminescence and electrical measurements. The diameters of CdS tubes are between 300nm and few microns and the lengths are up to tens of micrometers. The SEM images prove that the CdS films are nanostructured due to the deposition on the polymer nanosphere arrays. For both CdS structures (tubes and films) the XRD patterns show a hexagonal phase. The optical studies reveal a band gap value of about 2.5−2.6eV and a red luminescence at ∼1.77eV. A higher increase of conductivity is observed for illuminating the CdS nanostructured film when compared to the simple semiconductor film. This is a consequence of the periodic patterning induced by the polymer nanosphere array.

Structure, growth and magnetic property of hard magnetic CoPtP nanowires synthesized by electrochemical deposition

This paper reports the electrochemical synthesis and characterization of one dimensional hard magnetic CoPtP nanowires. Three electrode potentiostatic electrochemical technique was used to deposit nanowires into a nanoporous track-etched polycarbonate membrane with a nominal pore diameter 50nm and thickness around 6–9μm. The room temperature electrolyte used for the deposition of nanowires consists of 60g/lt CoSO47H2O, 4.1g/lt H2PtCl6, 4.5g/lt NaHPO2 and 25g/lt B(OH)3. The structural morphology was observed by scanning electron microscope and transmission electron microscope. The magnetic property of the nanowires was measured by vibrating sample magnetometer before removing the template. The coercive fields were measured to be 143kAm−1 and 103kAm−1 for parallel (H║) and perpendicular to the nanowire axis, respectively. The higher coercivity value for H║ indicating nanowires' easy magnetization direction lies along the nanowires' axis. The average composition of the CoPtP nanowires was determined by electron dispersive spectroscopy and the crystallinity was measured by X-ray diffractometer.

Fabrication of functional silicon-based nanoporous membranes

Macroscopic porous membranes with pore diameter uniformity approaching the nanometer scale have great potential to significantly increase the speed, selectivity, and efficiency of molecular separations. We present fabrication, characterization, and molecular transport evaluation of nanoporous thin silicon-based sieves created by laser interferometric lithography (LIL). This fabrication approach is ideally suited for the integration of nanostructured pore arrays into larger microfluidic processing systems, using a simple all-silicon lithographic process. Submilli-meter-scale planar arrays of uniform cylindrical and pyramidal nanopores are created in silicon nitride and silicon, respectively, with average pore diameters below 250 nm and significantly smaller standard error than commercial polycarbonate track etched (PCTE) membranes. Molecular transport properties of short cylindrical pores fabricated by LIL are compared to those of thicker commercial PCTE membranes for the first time. A 10-fold increase in pyridine pore flux is achieved with thin membranes relative to commercial sieves, without any modification of the membrane surface.

Ultrasensitive detection of ovarian cancer marker using immunoliposomes and gold nanoelectrodes

Mucin-16 (MUC16) is the established ovarian cancer marker used to follow the disease during or after treatment for epithelial ovarian cancer. The emerging science of cancer markers also demands for the new sensitive detection methods. In this work, we have developed an electrochemical immunosensor for antigen MUC16 using gold nanoelectrode ensemble (GNEE) and ferrocene carboxylic acid encapsulated liposomes tethered with monoclonal anti-Mucin-16 antibodies (αMUC16). GNEEs were fabricated by electroless deposition of the gold within the pores of polycarbonate track-etched membranes. Afterwards, αMUC16 were immobilized on preformed self-assembled monolayer of cysteamine on the GNEE via cross-linking with EDC-Sulfo-NHS. A sandwich immunoassay was performed on αMUC16 functionalized GNEE with MUC16 and immunoliposomes. The differential pulse voltammetry was employed to quantify the faradic redox response of ferrocene carboxylic acid released from immunoliposomes. The dose–response curve for MUC16 concentration was found between the range of 0.001–300UmL−1. The lowest detection limit was found to be 5×10−4UmL−1 (S/N=3). We evaluated the performance of this developed immunosensor with commercial ELISA assay by comparing results obtained from spiked serum samples and real blood serum samples from volunteers.

Biomimetic hydrogels gate transport of calcium ions across cell culture inserts

Control of the in vitro spatiotemporal availability of calcium ions is one means by which the microenvironments of hematopoietic stem cells grown in culture may be reproduced. The effects of cross-linking density on the diffusivity of calcium ions through cell culture compatible poly(2-hydroxyethyl methacrylate) [poly(HEMA)]-based bioactive hydrogels possessing 1.0 mol% 2-methacryloyloxyethyl phosphorylcholine (MPC), 5 mol% N,N-(dimethylamino)ethylmethacrylate (DMAEMA) and ca. 17 mol% n-butyl acrylate (n-BA) have been investigated to determine if varying cross-link density is a viable approach to controlling transport of calcium across hydrogel membranes. Cross-linking density was varied by changing the composition of cross-linker, tetraethyleneglycol diacrylate (TEGDA). The hydrogel membranes were formed by sandwich casting onto the external surface of track-etched polycarbonate membranes (T = 10 μm, φ = 0.4 μm pores) of cell culture inserts, polymerized in place by UV light irradiation and immersed in buffered (0.025 HEPES, pH 7.4) 0.10 M calcium chloride solution. The transport of calcium ions across the hydrogel membrane was monitored using a calcium ion selective electrode set within the insert. Degree of hydration (21.6 ± 1.0%) and void fraction were found to be constant across all cross-linking densities. Diffusion coefficients, determined using time-lag analysis, were shown to be strongly dependent on and to exponentially decrease with increasing cross-linking density. Compared to that found in buffer (2.0-2.5 × 10⁻⁶ cm²/s), diffusion coefficients ranged from 1.40 × 10⁻⁶ cm²/s to 1.80 × 10⁻⁷ cm²/s and tortuosity values ranged from 1.7 to 10.0 for the 1 and 12 mol% TEGDA cross-linked hydrogels respectively. Changes in tortuosity arising from variations in cross-link density were found to be the primary modality for controlling diffusivity through novel n-BA containing poly(HEMA)-based bioactive hydrogels.

Nernst–Planck/Poisson model for the potential response of permselective gold nanopores

The recent introduction of ionophore-modified nanopores opened a new route for the fabrication of ion-selective electrodes with unique advantages. With this prospect we studied the potential response of modified and unmodified permselective gold nanopores obtained by electroless gold plating in the pores of track etched polycarbonate membranes. Anion and cation permselective membranes were synthesized by chemical modification of gold nanopores with thiol derivatives bearing either quaternary ammonium or sulfonate functionality, respectively. In all cases a good correlation was found between the experimental potential responses and numerical solutions of the Nernst–Planck/Poisson equation obtained by finite-element simulation. Similar to conventional polymeric ion-exchanger electrodes a co-ion interference region, i.e., Donnan failure, was found at high concentration regime that was exploited theoretically to estimate the surface charge density on the gold nanopores. Depending on the modification of the pore interior surface charge densities in the range of ca. +5 to −40mC/m2 were found. Together with confirming the potential generating mechanism the effect of the pore diameter and surface charge density of the nanoporous membranes on the potential response is discussed in detail.

Electroanalysis of urinary l-dopa using tyrosinase immobilized on gold nanoelectrode ensembles

The performance of an amperometric biosensor constructed by associating tyrosinase (Tyr) enzyme with the advantages of a 3D gold nanoelectrode ensemble (GNEE) is evaluated in a flow-injection analysis (FIA) system for the analysis of l-dopa. GNEEs were fabricated by electroless deposition of the metal within the pores of polycarbonate track-etched membranes. A simple solvent etching procedure based on the solubility of polycarbonate membranes is adopted for the fabrication of the 3D GNEE. Afterward, enzyme was immobilized onto preformed self-assembled monolayers of cysteamine on the 3D GNEEs (GNEE-Tyr) via cross-linking with glutaraldehyde. The experimental conditions of the FIA system, such as the detection potential (−0.200 V vs. Ag/AgCl) and flow rates (1.0 mL min−1) were optimized. Analytical responses for l-dopa were obtained in a wide concentration range between 1 × 10−8 mol L−1 and 1 × 10−2 mol L−1. The limit of quantification was found to be 1 × 10−8 mol L−1 with a resultant % RSD of 7.23% (n = 5). The limit of detection was found to be 1 × 10−9 mol L−1 (S/N = 3). The common interfering compounds, namely glucose (10 mmol L−1), ascorbic acid (10 mmol L−1), and urea (10 mmol L−1), were studied. The recovery of l-dopa (1 × 10−7 mol L−1) from spiked urine samples was found to be 96%. Therefore, the developed method is adequate to be applied in the clinical analysis.

High-flowrate, compact electroosmotic pumps with porous polymer track-etch membranes

This paper reports the experimental investigations of electroosmotic (EO) pumps with four types of porous polymer membranes: porous polycarbonate track-etch membranes, porous polyester track-etch membranes, mixed cellulose ester membranes, and nylon membranes. We characterized EO pumping performance using deionized (DI) water and 1mM sodium tetraborate buffer in terms of flowrate and current. The measured flowrate and current show a linear dependency on an applied voltage, as expected by theory. The increasing order of both the parameters is polycarbonate, polyester, mixed cellulose ester, and nylon for both DI water and buffer. We compared EO pumping with porous polymer membranes to that with porous glass as a benchmark in terms of the flowrate normalized by the pumping area and applied voltage and flowrate per current. The experiments show that porous polymer membranes excel over porous glass in most cases. From the results about flowrate per current, we can estimate that the zeta potential of most porous polymer membranes used in this paper is greater than that of porous glass. The best performance was found with polycarbonate track-etch membranes as 0.051mlV−1cm−2 with buffer and 2.4mlmin−1mA−1 with DI water. The normalized flowrate with DI water is 0.016mlV−1cm−2, which is lower than the previously reported value with porous anodic alumina membranes. Porous polymer membranes however have the advantages of membrane flexibility and excellent bonding with other polymeric structures, compared with porous anodic alumina membranes. We demonstrated a miniature 2cm3 EO pump by taking the advantage of the flexible characteristics. This EO pump has a cylindrical shape with a large pumping area per pump volume, which is beneficial for miniaturization. The miniature EO pump shows good pumping performance in our short-term experiments (less than 10min).

Synthesis and morphological studies of ZnCuTe ternary nanowires via template-assisted electrodeposition technique

ZnCuTe nanowires have been successfully synthesized via template-assisted one step electrodeposition technique from an aqueous solution of zinc sulphate (ZnSO4·7H2O), copper sulphate (CuSO4·5H2O) and tellurium oxide (TeO2) at room temperature (303 K). Nanowires of diameter 200, 100 and 50 nm have been synthesized on copper and indium tin oxide coated glass substrates using track-etch polycarbonate membranes (Whatman). The morphologies and structures of electrodeposited ZnCuTe nanowires were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM confirmed the formation of nanowires and reveal that the morphologies of nanowires have diameter equal to the diameter of the templates used. The XRD pattern have shown a preferential growth of ZnCuTe nanowires along the (119) direction and the structure corresponding to hexagonal structure. Energy dispersive X-ray analysis confirmed that the zinc copper telluride nanowires are constituted of elements Zn, Cu and Te.

Stimuli-Responsive Polymeric Membranes through Graft Copolymerization of N-Isopropylacrylamide onto Polycarbonate Track Etched Membranes for Biomedical Applications

Stimuli-responsive polymeric membranes have attracted the attention of researchers all around the world owing to their potential applications in the fields of controlled drug delivery, bioseperation, water treatment, and chemical sensors. N-isopropylacrylamide (NIPAAM) is well known for its novel thermo-sensitive behavior in aqueous media, was successfully grafted on the surface and in the pores of polycarbonate track etched membrane (PCTE).The influence of reaction parameters such as monomer concentration, reaction time, reaction temperature and concentration of the initiator on the grafting yield was investigated in detail. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of these parameters. Maximum percentage of grafting (92%) was obtained at benzoyl peroxide concentration = 0.08M, NIPAAM concentration = 6 v/v, and reaction temperature at 600°C in a reaction time of 5h. The microstructure and morphology of the PCTE-g-NIPAAM membranes were characterized through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) studies. Water Contact Angle Measurement was used to study the hydrophilic behavior of the grafted membranes. These grafted membranes were investigated for their swelling behavior. The thermo-sensitive behavior of the PCTE-g-NIPAAM membranes was studied. The diffusion coefficient of the model drug salicylic acid through pristine PCTE and the PCTE-g-NIPAAM membranes was determined

Size selective DNA transport through a nanoporous membrane in a PDMS microfluidic device

A microfluidic counter current dialysis device for size based purification of DNA is described. The device consists of two polydimethylsiloxane (PDMS) channels separated by a track etched polycarbonate membrane with a 50 nm pore size. Recovery of fluorescein across the membrane was compared with 10 and 80 nucleotide (nt) ssDNA to characterize the device. Recovery of all three analytes improved with decreasing flow rate. Size selectivity was observed. Greater than 2-fold selectivity between 10 nt and 80 nt ssDNA was observed at linear velocities less than 3mm s(-1). Increasing the ionic strength of the buffer increased transport across the membrane. Recovery of 80 nt ssDNA increased over 4-fold by adding 30 mM NaCl to the buffer. The effect was size dependent as 10 nt showed a smaller increase while the recovery of fluorescein was largely unaffected by increasing the ionic strength of the buffer.

Electrical Properties of Electrodeposited ZnCuTe Ternary Nanowires Embedded in Polycarbonate Membrane

The electrical properties of electrodeposited zinc-copper-telluride (ZnCuTe) nanowires embedded in polycarbonate track-etch membrane (Whatman) having pore-diameters of 200, 100 and 50nm have been studied and reported in this paper. Scanning electron microscopy (SEM) confirmed the formation of the nanowires of uniform diameter equal to the diameter of the templates used. I-V measurements at room temperature (303K) reveal that the nanowires of diameter 200, 100 and 50nm have linear and ohmic characteristics. Higher electron transport was observed in larger diameter nanowires compared to smaller ones which may be attributing to size effect. The temperature-dependent electrical transport measurements over a temperature range 308–423K reveal that the temperature dependence of electrical conductivity increases with increasing temperature and decreases as the nanowires size decreases. The study reveals that ZnCuTe nanowires have negative temperature coefficient of resistance (TCR).

Influence of Deposition Potential on Structure of ZnO Nanowires Synthesized in Track-Etched Membranes

Single-crystal ZnO nanowires long up to several microns were fabricated by one-step electrochemical deposition. A template-based process employing track-etched polycarbonate (TE-PC) membranes was used for this purpose. The morphology and the structure characteristics of the ZnO nanowires were analyzed by means of Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM), and Selected Area Electron Diffraction (SAED). The growth process conditions turned out to have a marked influence on the crystal nature and morphology of the nanowires. Deposition rates ranging from 0.4 nm s−1 and up to 0.6 nm s−1 were recorded for the growth of ZnO nanowires. The obtained results showed that by using carefully controlled deposition conditions single crystalline nanowires and fine-grained structures can be routinely obtained.

Extrusion of electroformed giant unilamellar vesicles through track-etched membranes

Unilamellar vesicle populations having a narrow size distribution and mean radius below 100nm are preferred for drug delivery applications. In the present work, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was used to prepare giant unilamellar vesicles (GUVs) by electroformation and multilamellar vesicles (MLVs) by thin film hydration. Our experiments show that in contrast to MLVs, a single-pass extrusion of GUVs through track-etched polycarbonate membranes at moderate pressure differences is sufficient to produce small liposomes having low polydispersity index. Moreover, we observe that the drug encapsulating potential of extruded liposomes obtained from GUVs is significantly higher compared to liposomes prepared by extrusion of MLVs. Furthermore, our experiments carried out for varying membrane pore diameters and extrusion pressures suggest that the size of extruded liposomes is a function of the velocity of GUV suspensions in the membrane pore.

Free‐Standing Aluminium Nanowire Architectures Made in an Ionic Liquid

We report on the electrochemical synthesis of free-standing aluminium nanowire architectures through a template-assisted electrodeposition technique. For this purpose, nuclear track-etched polycarbonate membranes were employed as templates. One side of the template was sputtered with a thin gold film to serve as a working electrode. Subsequently the nanowires were made in the ionic liquid 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl)/AlCl(3) (40/60 mol %) under potentiostatic conditions. Two different electrodeposition procedures were employed to fabricate strongly adherent Al nanowire structures on an electrodeposited Al layer. In the first procedure, electrodeposition simultaneously occurs along the pores of the template and on the Au-sputtered side of the template. In the second procedure, electrodeposition takes place in two different steps: first a thick supporting film of Al is deposited on the sputtered side of the membrane and second Al nanowires are grown within the pores. After chemical dissolution of the membrane in dichloromethane, an aluminium foil of a controlled thickness with a three-dimensional nanowire structure on one side was obtained. Different nanowire architectures, such as free-standing nanowires, vertically aligned tree-shaped arrays, and bunched nanowire films, were obtained. Such nanowire architectures are of particular interest for applications in Li-ion micro-batteries.

Ion exchange properties of sulfonated polycarbonate and polyimide track etch membranes

Heterogeneous sulfonation was successfully utilized to convert the surfaces of PC and PI track etched membranes with 20 nm pores into ion exchange membranes. Short sulfonation times of 1–5 min using gaseous sulfuric trioxide were sufficient to achieve good coverage of ion exchange sites on the membrane surface yet minimal structural damage to the bulk material. Consequently, the ion exchange capacities were relatively low, up to 0.015 meq/g, compared to literature. Electroselectivity typical of ion exchange materials was observed for these membranes and metal uptake of higher valences was preferred Eu 3+ > Co 2+ > Cs +. Clear differences in metal uptake properties were measured between the sulfonated PC and PI membranes with different ions. As a consequence of relatively high metal uptake and certain experiment set up also Donnan exclusion was determined to play a role in the overall ion exchange process.

Preparation of nickel nanowire within polycarbonate membrane and removing polycarbonate by KrF excimer laser

Nikel nanowire arrays were fabricated by potentiostatic electrodeposition into track-etched polycarbonate (PC) membranes. By electrochemical deposition of nickel, nanowires were grown in the single pores. The nanowires were contacted by sputtering a gold layer on top of the membrane. The distinct difference in laser ablation thresholds offers the selective material removal. After preparation of nanowires, polycarbonate membranes were irradiated by KrF excimer laser, 248 nm, at fluence of 0.13 J/cm2, at 1 Hz pulse repetition rate in order to remove polycarbonate. Scanning electron microscopy and X-ray diffraction were employed to characterize the structural and morphological properties of the nanowires. Magnetic properties of nanowires were measured through a magnetization hysteresis curves, using vibrating sample magnetometer (VSM). Key words: Electrodeposition, nanowires, nickel, nuclear track membrane, excimer laser.

Magnetically Induced Decrease in Droplet Contact Angle on Nanostructured Surfaces

We report a magnetic technique for altering the apparent contact angle of aqueous droplets deposited on a nanostructured surface. Polymeric tubes with embedded superparamagnetic magnetite (Fe(3)O(4)) nanoparticles were prepared via layer-by-layer deposition in the 800 nm diameter pores of polycarbonate track-etched (PCTE) membranes. Etching away the original membrane yields a superparamagnetic film composed of mostly vertical tubes attached to a rigid substrate. We demonstrate that the apparent contact angle of pure water droplets deposited on the nanostructured film is highly sensitive to the ante situm strength of an applied magnetic field, decreasing linearly from 117 ± 1.3° at no applied field to 105 ± 0.4° at an applied field of approximately 500 G. Importantly, this decrease in contact angle did not require an inordinately strong magnetic field: a 15° decrease in contact angle was observed even with a standard alnico bar magnet. We interpret the observed contact angle behavior in terms of magnetically induced conformation changes in the film nanostructure, and we discuss the implications for reversibly switching substrates from hydrophilic to hydrophobic via externally tunable magnetic fields.

Advance in preparation of magnetic nanowires and its application in biosensors

Magnetic nanowires not only have nanometer properties, but also have magnetic property of giant magnetoresistance. Recently, nanowires were applied widely in high density hard disk slider, super magnetic storage element, micro-sensors, micro-engine, biomedical engineering, etc. This artical reviews the current preparation method of nanowires, the template synthesis, including several general templates such as track-etched porous polycarbonate membrane, porous anodic aluminum oxide membrane and carbon nanotubes, as well asgrowth patterns of nanowires in the templates. The applications of nanowires in several biosensors are introduced.The applications will greatly improve current ways of sensor detection, which will open up new areas of the field of biosensor study. Key words: Magnetic nanowires; Biosensors; Giant magnetoresistance; Anodic aluminum oxide; Electrochemical deposition