Track-etched Membrane Filters Research Articles

Ion transport across bilayer lipid membranes using a track-etched membrane filter

Bilayer lipid membranes (BLM) are widely employed to study the electrochemical behavior across cell membranes, particularly the ion transport in the presence of hydrophobic ions or ionophores. However, owing to the physical fragility of BLMs, they are readily broken down by external shocks, such as the applications of a potential difference, current, and vibration. Thus, in this study, a facile method for enhancing the physical stability of BLMs was developed using a track-etched membrane (TM). Physically stable BLMs were rapidly fabricated within the apertures of TM by dropping an n-decane solution containing lecithin and cholesterol on TM. Therefore, BLM formation was confirmed by capacitance measurement, and the estimated membrane thickness and mean capacitance were 3.5 ± 0.4 nm and 0.51 ± 0.05 μF cm−2, respectively. The applied membrane potential could be extended to ≥1.5 V, which is approximately 10 times higher than those of conventional BLMs, and the lifetime exceeded 40 min. The applicability of the fabricated BLM was verified by electrochemical measurements during ion transport.

Investigation of the Tendency of Carbon Fibers to Disintegrate into Respirable Fiber-Shaped Fragments

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative.

A flow-based enzyme-free biosensor fabricated using track-etched membrane electrodes: Selective and sensitive detection of uric acid

A flow-based, enzyme-free biosensor for the selective and sensitive determination of uric acid was developed using track-etched membrane electrodes (TEMEs). The proposed sensor system comprises a pre-reactor electrode to decompose interfering species, such as L-ascorbic acid, and a detector electrode to detect uric acid. TEMEs were prepared by sputter deposition of gold on a track-etched membrane filter. Acetylene black (AB) was introduced as an electrode catalyst by simple filtration with the TEME, and the sensitivity for uric acid using the AB-decorated Au-TEME was much greater than that with bare Au-TEME. The insertion of the 2-aminoethanethiol-modified Au-TEMEs as pre-reactor electrodes upstream of the AB-decorated detector electrode eliminated the interference caused by the co-existence of L-ascorbic acid because the interfering species were electrolyzed at the pre-reactor electrode prior to detection of uric acid. The proposed sensor system was incorporated into a flow-injection analysis system to evaluate the sensor performance. The detection limit of uric acid was 0.6 μM. A recovery test by standard addition to human urine samples also showed satisfactory results.

Sizing of giant unilamellar vesicles using a metal mesh with a high opening ratio

Size control of giant unilamellar vesicles (GUVs) has been challenged extensively for realizing quantitative assays within these biomimetic reactors. Although microfluidics-based monodisperse GUV generation methods have shown tremendous progress, they are often difficult and still not available for general users. Meanwhile, the conventional bulk methods, which are more flexible in compositions, only generate polydisperse GUVs with a linear dimension ranging more than two orders of magnitude. Here, we characterized the sizing protocol of GUVs using the metal mesh with a large opening area ratio (>35%). Unlike the conventional track-etched membrane filters with a small opening area ratio (<10%), the present method enabled fast filtration (<10 min) to remove GUVs smaller than the mesh size without delicate flow control. We demonstrated that the combination of extrusion and filtration with selected filters produced GUV populations with fairly narrow size distributions (<30% C.V. in diameter).

Liquid filtration of nanoparticles through track-etched membrane filters under unfavorable and different ionic strength conditions: Experiments and modeling

Nanoparticle deposition experiments under unfavorable conditions were conducted experimentally and theoretically. The 0.2 and 0.4µm rated track-etched membrane filters were challenged with 60, 100, 147, 220, 350 and 494nm polystyrene latex (PSL) particles with different ionic strengths ranging from 0.005 to 0.05M. The capillary tube model, with replacing the viscosity of air to water, was used to estimate the initial efficiency, or the transport efficiency of the particles to the filter surface, which was corrected in a second step by allowing the detachment of the nanoparticles according to the sum of adhesive and hydrodynamic torques. The adhesive torques were derived from surface interactions accessed by the extended DLVO theory. Calculation results showed that the adhesive torque of a particle located in the calculated primary minimum was slightly larger than the hydrodynamic torque, resulting in particle deposition. However, experimental data clearly indicated that detachment occurred. This could only be explained by the presence of additional hydration forces, leading to a larger separation which became relevant at high ionic strengths. By including hydration into our theoretical framework, experiment and theory were in very good agreement under all different ionic strength conditions. The findings allow a basic understanding of surface interactions between nanoparticles and membranes in micro- and ultra-filtration applications for drinking water production, wastewater treatment and particle free water production in industries.

Aggregation of microparticles of a water-soluble polycrystalline substance in pores

We have proposed synthesis of polydisperse particles of poorly soluble substances through precipitation in pores of a water-soluble matrix. As a matrix, we used sucrose pressed under mass production conditions. In its pores, we obtained highly dispersed BaSO4 particles precipitated by reacting Ba(NO3)2 and Na2SO4. The BaSO4 particles were separated from the aqueous phase using a track-etched membrane filter and characterized by electron microscopy.

Development of Filterability Test Method for Gel Retention Performance for UV Curable Ink Jet Inks

The purpose of this study was to provide a test method for gel retention performance of nonwoven filters for UV curable ink jet inks. Gel marked with elemental silver was formed from simulated UV curable ink. The silver marked gel was dispersed in the simulated UV curable ink by ultrasonic vibration. Large size gels were removed by pre-filtration with a track-etched membrane filter which had uniform 10 &#x3BC;m round shaped pores. Then the ink was subjected to filterability test to determine gel retention. Mass of silver element accumulated on filter medium was measured by ICP-MS after filter medium was dissolved in hot acid.Gel retention performance of nonwoven filters was compared as demonstration of effectiveness of this method. Characteristics of the gel in dynamic viscoelasticity, size and silver element release were investigated as well.

Alum Settling and Filtration Treatment of Liquid Swine Manure

A physical/chemical treatment train, which involved preliminary settling for 24 h followed by coagulation/flocculation of supernatant, and filtration, was applied to raw flushed swine manure in bench- and pilot-scale experiments to investigate the effectiveness of the treatment train against the removal of total suspended solids (TSS) and total phosphorus (TP). Alum was used as a coagulant at an average dose of 1600 mg L-1. In the bench-scale experiments, alum treatment was performed using a jar test apparatus, and filtration was achieved by using polycarbonate track-etched membrane filters of pore sizes of 10 and 20 m. At the pilot plant, coagulation, flocculation, and clarification were achieved in a custom-designed sludge blanket clarifier equipped with inclined plate settlers, followed by media filtration in a set of three patented Martin filter columns containing glass beads of different void sizes ranging from 5 to 25 m. Overall percent reductions in TSS and TP were 85% (from 9944 to 1470 mg L-1) and 64% (from 449 to 163 mg L-1) in the bench-scale experiments and were 76% (from 3945 to 936 mg L-1) and 75% (from 164 to 40 mg L-1) in the pilot plant treatment, respectively. Preliminary settling was found to be a very effective step, which removed 53% to 56% and 22% to 28% of TSS and TP, respectively, from the raw liquid swine manure. Moderate reduction in chemical oxygen demand was also observed, while the treatment train had little effect on total Kjeldahl nitrogen and dissolved solids. Particle size distribution analysis showed that most of the phosphorus in the liquid manure was associated with particles <10 m in size and that coagulation and flocculation could enhance the phosphorus removal considerably. At the end of the pilot-scale experiment, approximately 70% and 50% of the initial mass of TSS and TP was removed from the liquid swine manure, respectively, as preliminary settling sludge, whose volume was accounted for approximately 36% of the volume of initial raw manure.

Optical Microwell Assay of Membrane Transport Kinetics

In optical single transporter recording, membranes are firmly attached to flat solid substrates containing small wells or test compartments (TC). Transport of fluorescent molecules through TC-spanning membrane patches is induced by solution change and recorded by confocal microscopy. Previously, track-etched membrane filters were used to create solid substrates containing populations of randomly distributed TCs. In this study the possibilities offered by orderly TC arrays as created by laser microdrilling were explored. A theoretical framework was developed taking the convolution of membrane transport, solution change, and diffusion into account. The optical properties of orderly TC arrays were studied and the kinetics of solution change measured. Export and import through the nuclear pore complex (NPC) was analyzed in isolated envelopes of Xenopus oocyte nuclei. In accordance with previous reports nuclear transport receptor NTF2, which binds directly to NPC proteins, was found to be translocated much faster than “inert” molecules of similar size. Unexpectedly, NXT1, a homolog of NTF2 reportedly unable to bind to NPC proteins directly, was translocated as fast as NTF2. Thus, microstructured TC arrays were shown to provide optical single transporter recording with a new basis.

Membrane-controlled reagent-delivery systems--a new approach for the continuous production of reagent and standard solutions.

A new simple and robust system for the production of standard solutions, based on the mass-transfer of analytes through membranes, is described. The device consists of a cone-shaped reservoir vessel, filled with a concentrated solution of the analyte and separated from a liquid acceptor stream by a membrane. Mass-flow from donor to acceptor solution is controlled by the mass-transfer-affecting properties of the active membrane area, which is determined by the hole in a template (diameter 0.8 mm) placed between the membrane and the acceptor-channel. Using nitrate as model analyte and a track-etched membrane filter (pore size 0.1 microm) dilution factors up to 2,400,000 with long-term reproducible accuracy of < 2% have been achieved. Adjustment of a requested concentration is possible by varying either the flow rate of the acceptor stream or the concentration of the reservoir solution.

Filtration capture immunoassay for bacteria: optimization and potential for urinalysis

A novel assay utilizing immuno-labeling, filtration, and electrochemistry for the rapid detection of bacteria has been optimized for the detection of Escherichia coli O157:H7. Bacteria were specifically labeled with alkaline phosphatase conjugated polyclonal antibodies and captured on a polycarbonate track-etched membrane filter (0.2 μm pore size). The filter was then placed directly against a glassy carbon electrode, incubated with enzyme substrate, and the product detected by square wave voltammetry. The high speed and capture efficiency of membrane filtration and inherent sensitivity of electrochemical detection produced a 25-min assay with a detection limit of 5×10 3 E. coli O157:H7 per ml using a filtration volume of 100 μl (i.e. 500 cells filtered). The labeling, filtration, and electrochemical steps were optimized, and the assay performance using electrochemical and colorimetric detection methods was compared. The assay was used to detect E. coli O157:H7 that was spiked into filter-sterilized urine at clinically relevant concentrations.