Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone

The ion concentration polarization (ICP) phenomenon is one of the most prevailing methods to preconcentrate low-abundance biological samples. The ICP ...

Korea Institute of Science and Technology

Generation and self-replication of monolithic, dual-scale polymer structures by two-step capillary-force lithography.

Fabrication of monolithic bridge structures by vacuum-assisted capillary-force lithography.

Solvent-assisted decal transfer lithography by oxygen-plasma bonding and anisotropic swelling.

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This feature article provides an overview of the recently developed two-step UV-assisted capillary force lithography and its application to fabricating well-defined micro/nanoscale hierarchical structures. This method utilizes an oxygen inhibition effect in the course of UV irradiation curing and a two-step moulding process, to form multiscale hierarchical or suspended nanobridge structures in a rapid and reproducible manner. After a brief description of the fabrication principles, several examples of the two-step UV-assisted moulding technique are presented. In addition, emerging applications of the multiscale hierarchical structures are briefly described.

UV-assisted capillary force lithography for engineering biomimetic multiscale hierarchical structures: From lotus leaf to gecko foot hairs.

Cet article fonctionnalit&#xE9; fournit un aper&#xE7;u de la r&#xE9;cemment mis au point en deux &#xE9;tapes UV assist&#xE9;e par lithographie force capillaire et son application &#xE0; la fabrication bien d&#xE9;finies micro / nanom&#xE9;trique des structures hi&#xE9;rarchiques. Ce proc&#xE9;d&#xE9; utilise un effet d&#x26;#39;inhibition d&#x26;#39;oxyg&#xE8;ne dans le courant de durcissement d&#x26;#39;irradiation UV et un processus en deux &#xE9;tapes de moulage, pour former multi&#xE9;chelles hi&#xE9;rarchiques ou en suspension des structures nanobridge de mani&#xE8;re rapide et reproductible. Apr&#xE8;s une br&#xE8;ve description des principes de fabrication, plusieurs exemples de ces deux &#xE9;tapes UV assist&#xE9;e par technique de moulage sont pr&#xE9;sent&#xE9;s. En outre, les applications &#xE9;mergentes des structures multi-&#xE9;chelles hi&#xE9;rarchiques sont bri&#xE8;vement d&#xE9;crits.

UV assist&#xE9;e par lithographie force capillaire pour d&#x26;#39;ing&#xE9;nierie multi-&#xE9;chelle biomim&#xE9;tiques structures hi&#xE9;rarchiques: De feuille de lotus &#xE0; poils des pieds de Gecko

Dieser Sonderbeitrag &Uuml;bersicht der neu entwickelten zweistufigen UV-gest&uuml;tzte Kapillare Kraft Lithografie und seine Anwendung zur Herstellung von klar definierten Mikro/Nano hierarchischer Strukturen. Diese Methode verwendet einen Sauerstoff-Hemmung-Effekt im Laufe der Heilung von UV-Bestrahlung und Gu&szlig; Schritten, um Strukturen zu bilden Multiskalen hierarchische oder ausgesetzten Nanobridge eine schnelle und reproduzierbare Weise. Nach eine kurze Beschreibung der Herstellung Grunds&auml;tze sind einige Beispiele der zweistufig UV-gest&uuml;tzte Gu&szlig;-Technik pr&auml;sentiert. Dar&uuml;ber hinaus entstehen Anwendungen von der Multiscale, das hierarchische Strukturen kurz beschrieben werden.

UV-gest&uuml;tzte Kapillare Kraft Lithografie f&uuml;r Ihre biomimetische Multiskalen hierarchische Strukturen: vom Lotusblatt zu Gecko Fu&szlig; Haare.

Questo articolo fornisce una panoramica della litografia UV-assistita forza capillare recentemente sviluppato in due fasi e la sua applicazione a fabbricare ben definite strutture gerarchiche di micro/su scala nanometrica. Questo metodo utilizza un effetto di inibizione dell&#39;ossigeno nel corso della polimerizzazione di irradiazione UV e un processo di stampaggio in due fasi, a formare strutture multiscala nanobridge gerarchica o sospesi in maniera rapida e riproducibile. Dopo una breve descrizione dei principi di fabbricazione, vengono presentati alcuni esempi della tecnica di stampaggio assistito da UV due fasi. Inoltre, emergenti applicazioni di multiscale strutture gerarchiche sono brevemente descritti.

Litografia UV-assistita forza capillare per ingegneria biomimetici multiscala strutture gerarchiche: dalla foglia di loto al geco piede peli.

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Este reportaje ofrece una visi&#xF3;n general de la recientemente desarrollada en dos fases con ayuda de la litograf&#xED;a ultravioleta fuerza capilar y su aplicaci&#xF3;n a la fabricaci&#xF3;n de bien definidas micro / nano estructuras jer&#xE1;rquicas. Este m&#xE9;todo utiliza un efecto de inhibici&#xF3;n de ox&#xED;geno en el curso de la irradiaci&#xF3;n UV de curado y un proceso de dos pasos de moldeo, para formar estructuras multiescala nanobridge jer&#xE1;rquicos o suspendido en una manera r&#xE1;pida y reproducible. Despu&#xE9;s de una breve descripci&#xF3;n de los principios de fabricaci&#xF3;n, varios ejemplos de los dos pasos de UV-asistida t&#xE9;cnica de moldeo se presentan. Adem&#xE1;s, las aplicaciones emergentes de las estructuras jer&#xE1;rquicas de m&#xFA;ltiples escalas, se describen brevemente.

UV asistida por Litograf&#xED;a fuerza capilar para la ingenier&#xED;a biomim&#xE9;tica estructuras jer&#xE1;rquicas multiescala: De hoja de loto a los pelos de los pies del Gecko

We present a novel continuous-flow nanofluidic biomolecule/cell concentrator, utilizing the ion concentration polarization (ICP) phenomenon. The device has one main microchannel which bifurcates into two channels, one for a narrow, concentrated stream and the other for a wider but target-free stream. A nanojunction [cation-selective material (Nafion)] is patterned along the tilted concentrated channel. Application of an electric field generates the ICP zone near the nanojunction so that biomolecules and cells are guided into the narrow, concentrated channel by hydrodynamic force. Once biomolecules from the main channel are continuously streamed out to the concentrated channel, one can achieve a continuous flow of the same sample solution but with higher concentrations up to 100-fold. By controlling hydrodynamic resistance of the main and concentrated channel, the concentration factors can be adjusted. We demonstrated the continuous-flow concentration with various targets, such as bacteria [fluorescein sodium salt, recombinant green fluorescence protein (rGFP), red blood cells (RBCs), and Escherichia coli ( E. coli )]. Specially, fluorescein isothiocyanate (FITC)-conjugated lectin from Lens culinaris (lentil) (FITC-lectin) was tested on the different buffer conditions to clarify the effect of polarities of the target sample. This system is ideally suited for a generic concentration front-end for a wide variety of biosensors, with minimal integration-related complications.

Continuous-flow biomolecule and cell concentrator by ion concentration polarization.

In this work, we investigated multiple vortical flows inside the ion concentration polarization (ICP) layer that forms due to a coupling of applied electric fields and the semipermeable nanoporous junction between microchannels. While only a primary vortex near perm-selective membrane is traditionally known to lead to electrokinetic instability, multiple vortexes induced by the primary vortex were found to play a major role in the electrokinetic instability. The existence of multiple vortexes was directly confirmed by experiments using particle tracers and interdigitated electrodes were used to measure the local concentration profile inside the ICP layer. At larger applied electric fields, we observed aperiodic fluid motion due to electrokinetic instabilities which develop from a coupling of applied electric fields and electrical conductivity gradients induced by the ICP. The electrokinetic instability at micro-nanofluidic interfaces is important in the development of various electro-chemical-mechanical applications such as fuel cells, bio-analytical preconcentration methods, water purification/desalination and the fundamental study of ion electromigration through nanochannels and nonporous perm-selective membranes.

Multi-vortical flow inducing electrokinetic instability in ion concentration polarization layer.

We consider electroconvective fluid flows initiated by ion concentration polarization (ICP) under pressure-driven shear flow, a scenario often found in many electrochemical devices and systems. Combining scaling analysis, experiment, and numerical modeling, we reveal unique behaviors of ICP under shear flow: a unidirectional vortex structure, its height selection, and vortex advection. Determined by both the external pressure gradient and the electric body force, the dimensionless height of the sheared electroconvective vortex is shown to scale as (ϕ(2)/U(HP))(1/3), which is a clear departure from the previous diffusion-drift model prediction. To the best of our knowledge, this is the first microscopic characterization of ion concentration polarization under shear flow, and it firmly establishes electroconvection as the mechanism for an overlimiting current in realistic, large-area ion exchange membrane systems such as electrodialysis. The new scaling law has significant implications on the optimization of electrodialysis and other electrochemical systems.

Shear flow of an electrically charged fluid by ion concentration polarization: scaling laws for electroconvective vortices.

The ion concentration polarization (ICP) phenomenon at micronanofluidic interfaces has been extensively utilized to preconcentrate low-abundance biological samples. Although preconcentration by ICP is robust, its multiphysics phenomenon does not permit a clear prediction of the preconcentration conditions and sites. Here, we present a new method for spatiotemporally defining preconcentration, which can generate target-condensed plugs in a very specific region (<100 μm) regardless of the operating conditions (time, applied voltage, ionic strength, and pH). In contrast to previous devices that use only ion depletion, this device uses merged ICP zones with opposite polarity, i.e., ion depletion and ion enrichment. In this regard, ICP is initiated between two line-patterned cation exchange membranes. When voltage is applied across two membranes, an ion depletion (enrichment) zone occurs on the anodic (cathodic) side of the membranes. Two ICP zones are then merged and confined between the membranes. Consequently, the preconcentration action is also confined between the membranes. We demonstrate that fluorescent dyes are always preconcentrated at the designated location at all lengths of operating time and at broad voltage (0.5-100 V), ionic strength (1-100 mM KCl), and pH (3.7-10.3) ranges. This device successfully condenses proteins up to 10000-fold in a specific region of the channel (100 × 50 × 10 μm(3)) in 10 min. This work not only characterizes the unique scientific phenomenon of ICP overlapping but also opens the possibility of integrating ICP preconcentrators into commercial analysis equipment, which requires a known, stationary preconcentration site.

Spatiotemporally Defining Biomolecule Preconcentration by Merging Ion Concentration Polarization.

We present a novel paper-based flow fractionation system for preconcentration and field-flow separation. In this passive fluidic device, a straight channel is divided into multiple daughter channels, each of which is connected with an expanded region. The hydrodynamic resistance of the straight channel is predominant compared with those of expanded regions, so we can create steady flows through the straight and daughter channels. While the expanded regions absorb a great amount of water via capillarity, the steady flow continues for 10 min without external pumping devices. By controlling the relative hydrodynamic resistances of the daughter channels, we successfully divide the flow with flow rate ratios of up to 30. Combining this bifurcation system with ion concentration polarization (ICP), we develop a continuous-flow preconcentrator on a paper platform, which can preconcentrate a fluorescent dye up to 33-fold. In addition, we construct a field-flow separation system to divide two different dyes depending on their electric polarities. Our flow fractionation systems on a paper-based platform would make a breakthrough for point-of-care diagnostics with specific functions including preconcentration and separation.

Paper-Based Flow Fractionation System Applicable to Preconcentration and Field-Flow Separation.

Chloride ion, the majority salt in nature, is ∼52% faster than sodium ion (DNa+ = 1.33, DCl- = 2.03[10(-9)m(2)s(-1)]). Yet, current electrochemical desalination technologies (e.g. electrodialysis) rely on bipolar ion conduction, removing one pair of the cation and the anion simultaneously. Here, we demonstrate that novel ion concentration polarization desalination can enhance salt removal under a given current by implementing unipolar ion conduction: conducting only cations (or anions) with the unipolar ion exchange membrane stack. Combining theoretical analysis, experiment, and numerical modeling, we elucidate that this enhanced salt removal can shift current utilization (ratio between desalted ions and ions conducted through electrodes) and corresponding energy efficiency by the factor ∼(D- - D+)/(D- + D+). Specifically for desalting NaCl, this enhancement of unipolar cation conduction saves power consumption by ∼50% in overlimiting regime, compared with conventional electrodialysis. Recognizing and utilizing differences between unipolar and bipolar ion conductions have significant implications not only on electromembrane desalination, but also energy harvesting applications (e.g. reverse electrodialysis).

Enhanced Salt Removal by Unipolar Ion Conduction in Ion Concentration Polarization Desalination.

Microfluidic paper-based analytical devices (μPADs) for molecular detection have great potential in the field of point-of-care diagnostics. Currently, a critical problem being faced by μPADs is improving their detection sensitivity. Various preconcentration processes have been developed, but they still have complicated structures and fabrication processes to integrate into μPADs. To address this issue, we have developed a novel paper-based preconcentrator utilizing ion concentration polarization (ICP) with minimal addition on lateral-flow paper. The cation selective membrane (i.e., Nafion) is patterned on adhesive tape, and this tape is then attached to paper-based channels. When an electric field is applied across the Nafion, ICP is initiated to preconcentrate the biomolecules in the paper channel. Departing from previous paper-based preconcentrators, we maintain steady lateral fluid flow with the separated Nafion layer; as a result, fluorescent dyes and proteins (FITC-albumin and bovine serum albumin) are continuously delivered to the preconcentration zone, achieving high preconcentration performance up to 1000-fold. In addition, we demonstrate that the Nafion-patterned tape can be integrated with various geometries (multiplexed preconcentrator) and platforms (string and polymer microfluidic channel). This work would facilitate integration of various ICP devices, including preconcentrators, pH/concentration modulators, and micro mixers, with steady lateral flows in paper-based platforms.

Microfluidic paper-based biomolecule preconcentrator based on ion concentration polarization.

There is an increasing need for the desalination of high concentration brine (>TDS 35,000 ppm) efficiently and economically, either for the treatment of produced water from shale gas/oil development, or minimizing the environmental impact of brine from existing desalination plants. Yet, reverse osmosis (RO), which is the most widely used for desalination currently, is not practical for brine desalination. This paper demonstrates technical and economic feasibility of ICP (Ion Concentration Polarization) electrical desalination for the high saline water treatment, by adopting multi-stage operation with better energy efficiency. Optimized multi-staging configurations, dependent on the brine salinity values, can be designed based on experimental and numerical analysis. Such an optimization aims at achieving not just the energy efficiency but also (membrane) area efficiency, lowering the true cost of brine treatment. ICP electrical desalination is shown here to treat brine salinity up to 100,000 ppm of Total Dissolved Solids (TDS) with flexible salt rejection rate up to 70% which is promising in a various application treating brine waste. We also demonstrate that ICP desalination has advantage of removing both salts and diverse suspended solids simultaneously, and less susceptibility to membrane fouling/scaling, which is a significant challenge in the membrane processes.

Purification of High Salinity Brine by Multi-Stage Ion Concentration Polarization Desalination.

Corrigendum: Purification of High Salinity Brine by Multi-Stage Ion Concentration Polarization Desalination.

Nanofluidic resistive pulse sensing (RPS) has been extensively used to measure the size, concentration, and surface charge of nanoparticles in electrically conducting solutions. Although various methods have been explored for improving detection performances, intrinsic problems including the extremely low particle-to-pore volume ratio (<0.01%) and fast nanoparticle translocation (10-1000 µs) still induce difficulties in detection, such as low signal magnitudes and short translocation times. Herein, we present an aqueous two-phase system (ATPS) in a nanofluidic RPS for amplifying translocation signals and decreasing translocation speeds simultaneously. Two immiscible aqueous liquids build a liquid-liquid interface inside nanopores. As particles translocate from a high-affinity liquid phase into a lower-affinity one, the high-affinity liquid forms a conformal coating on the particles, which increases the effective particle size and amplifies the current-blockage signal. The translocation time is also increased, as the ATPS interface impedes the particle translocation. For 20 nm particles, 7.92-fold and 5.82-fold enhancements of signal magnitude and translocation time can be achieved. To our knowledge, this is the first attempt to improve nanofluidic RPS by treating an interface of solution reservoirs for manipulating target particles rather than nanopores. This direct particle manipulation allows us to solve the two intrinsic problems all at once.

Rhokyun Kwak

Center for BioMicrosystems

Korea Institute of Science and Technology

Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone

Rhokyun Kwak

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Center for BioMicrosystems

Korea Institute of Science and Technology

Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone

Center for BioMicrosystems