Ion Concentration Polarization Research Articles

Engineering Multi-field-coupled Synergistic Ion Transport System Based on the Heterogeneous Nanofluidic Membrane for High-Efficient Lithium Extraction

HighlightsThe first construct of a multi-field-coupled synergistic ion transport system (MSITS) in Li+ extraction is proposed.Effectively suppress the ion concentration polarization effect of the ion-enrichment zone at the membrane interface.The MSITS equipped with heterogeneous membrane exhibited outstanding separation performance with Li+ flux of 367.4 mmol m−2 h−1 and Li+/Co2+ selectivity of 216,412, outperforming previous reports.

In Situ Growth of Imine‐Bridged Anion‐Selective COF/AAO Membrane for Ion Current Rectification and Nanofluidic Osmotic Energy Conversion

AbstractFacing the energy crisis, using the salinity gradient between seawater and freshwater for osmotic energy conversion is a direct way to obtain energy. So far, most nanofluidic membranes utilized for osmotic energy generation are cation‐selective. Given that both anion‐ and cation‐selective membranes have the identical importance for energy conversion devices, it is of great significance to develop anion‐selective membranes. Herein, an anion‐selective membrane is synthesized by in situ growth of imine‐bridged covalent organic framework (COF) on ordered anodic aluminum oxide (AAO) at room temperature. The imine groups and residual amino groups of COF can combine with protons in neutral solution, enabling the COF positively charged and efficiently transport of anions. Particularly, due to the asymmetry in the charge and structure of COF/AAO, the as‐prepared membrane exhibits excellent ionic current rectification property, which can inhibit ion concentration polarization effectively and possess high ion selectivity and permeability. Using the present COF/AAO membrane, salinity gradient energy can be successfully harvested from solutions with high salt content, and the output power density reached 17.95W m−2 under a 500‐fold salinity gradient. The study provides a new avenue for construction and application of anion‐selective membranes in the smart ion transport and efficient energy conversion.

Janus Metal–Organic Framework Membranes Boosting the Osmotic Energy Harvesting

The unique ion-transport properties in nanoconfined pores enable nanofluidic devices with great potential in harvesting osmotic energy. The energy conversion performance could be significantly improved by the precise regulation of the "permeability-selectivity" trade-off and the ion concentration polarization effect. Here, we take the advantage of electrodeposition technique to fabricate a Janus metal-organic framework (J-MOF) membrane that possesses rapid ion-transport capability and impeccable ion selectivity. The asymmetric structure and asymmetric surface charge distribution of the J-MOF device can suppress the ion concentration polarization effect and enhance the ion charge separation, exhibiting an improved energy harvesting performance. An output power density of 3.44 W/m2 has been achieved with the J-MOF membrane at a 1000-fold concentration gradient. This work provides a new strategy for fabricating high-performance energy-harvesting devices.

Microvalve-Based Tunability of Electrically Driven Ion Transport through a Microfluidic System with an Ion-Exchange Membrane.

Microfluidic channels with an embedded ion permselective medium under the application of electric current are commonly used for electrokinetic processes as on-chip ion concentration polarization (ICP) and bioparticle preconcentration to enhance biosensing. Herein, we demonstrate the ability to dynamically control the electrically driven ion transport by integrating individually addressable microvalves. The microvalves are located along a main microchannel that is uniformly coated with a thin layer of an ion-exchange membrane (IEM). The interplay of ionic transport between the solution within the microchannel and the thin IEM, under an applied electric current, can be locally tuned by the deformation of the microvalve. This tunability provides a robust and simple means of implementing new functionalities into lab-on-a-chip devices, e.g., dynamic control over multiple ICP layers and their associated preconcentrated molecule plugs, multiplex sensing, suppression of biofouling, and plug dispersion, while maintaining the well-known application of microvalves as steric filtration.

DCas9-Mediated PCR-Free Detection of Oncogenic Mutation by Nonequilibrium Nanoelectrokinetic Selective Preconcentration.

Cutting-edge nanoelectrokinetic technology in this work provides a breakthrough for the present clinical demands of molecular diagnosis to detect a trace amount of oncogenic mutation of DNA in a short time without an erroneous PCR procedure. In this work, we combined the sequence-specific labeling scheme of CRISPR/dCas9 and ion concentration polarization (ICP) mechanism to separately preconcentrate target DNA molecules for rapid detection. Using the mobility shift caused by dCas9's specific binding to the mutant, the mutated DNA and normal DNA were distinguished in the microchip. Based on this technique, we successfully demonstrated the dCas9-mediated 1-min detection of single base substitution (SBS) in EGFR DNA, a carcinogenesis indicator. Moreover, the presence/absence of target DNA was identified at a glance like a commercial pregnancy test kit (two lines for positive and one line for negative) by the distinct preconcentration mechanisms of ICP, even at the 0.1% concentration of the target mutant.

Electrokinetic Enrichment and Label-Free Electrochemical Detection of Nucleic Acids by Conduction of Ions along the Surface of Bioconjugated Beads.

In this paper, we report a method to integrate the electrokinetic pre-enrichment of nucleic acids within a bed of probe-modified microbeads with their label-free electrochemical detection. In this detection scheme, hybridization of locally enriched target nucleic acids to the beads modulates the conduction of ions along the bead surfaces. This is a fundamental advancement in that this mechanism is similar to that observed in nanopore sensors, yet occurs in a bed of microbeads with microscale interstices. In application, this approach has several distinct advantages. First, electrokinetic enrichment requires only a simple DC power supply, and in combination with nonoptical detection, it makes this method amenable to point-of-care applications. Second, the sensor is easy to fabricate and comprises a packed bed of commercially available microbeads, which can be readily modified with a wide range of probe types, thereby making this a versatile platform. Finally, the sensor is highly sensitive (picomolar) despite the modest 100-fold pre-enrichment we employ here by faradaic ion concentration polarization (fICP). Further gains are anticipated under conditions for fICP focusing that are known to yield higher enrichment factors (up to 100,000-fold enrichment). Here, we demonstrate the detection of 3.7 pM single-stranded DNA complementary to the bead-bound oligoprobe, following a 30 min single step of enrichment and hybridization. Our results indicate that a shift in the slope of a current-voltage curve occurs upon hybridization and that this shift is proportional to the logarithm of the concentration of target DNA. Finally, we investigate the proposed mechanism of sensing by developing a numerical simulation that shows an increase in ion flux through the bed of insulating beads, given the changes in surface charge and zeta potential, consistent with our experimental conditions.

Synaptic Plasticity of a Microfluidic Memristor with a Temporary Memory Function Based on an Ionic Liquid in a Capillary Tube

Fluidic memristor devices have received tremendous attention for smooth resistance switching in artificial synapses due to the ion migration, concentration polarization, and redox reactions mechanism. Here we provide a novel method of preparing microfluidic memristor with superior stability, robustness, and ultralow cost. The structure of the two-terminal memristor device is Cu/[MMIm][Cl]: H2O/Cu, C5H9N2Cl. The ionic liquid of 1,3-dimethylimidazole chloride salt was used as representative IL to display resistive memory properties in a cylindrical microchannel of a capillary. The fabricated device shows hysteretic and bipolar I–V characteristics of memristor, which can respond to external stimuli, e.g., space length between two electrodes and applied voltage. Meanwhile, this artificial synapse can mimic synaptic plasticity under various pulse stimuli stably and repeatedly, which results in temporary memory behavior. Such device exhibits great potential value in the area of neuromorphic artificial synapses and memory states.

Effect of air bubbling on electroless Pd plating for the practical application of hydrogen selective membranes.

In this study, an air bubbling electroless plating (ELP) method was newly developed for the production of Pd composite membranes. The air bubble ELP alleviated the concentration polarization of Pd ions, making it possible to achieve a plating yield of 99.9% in 1 h and form very fine Pd grains with a uniform layer of ∼4.7 μm. A membrane with a diameter of 25.4 mm and a length of 450 mm was produced by the air bubbling ELP, achieving a hydrogen permeation flux of 4.0 × 10-1 mol m-2 s-1 and selectivity of ∼10 000 at 723 K with a pressure difference of 100 kPa. To confirm the reproducibility, six membranes were produced by the same method and assembled in a membrane reactor module to produce high-purity hydrogen by ammonia decomposition. Hydrogen permeation flux and selectivity of the six membranes at 723 K with a pressure difference of 100 kPa were 3.6 × 10-1 mol m-2 s-1 and ∼8900, respectively. An ammonia decomposition test with an ammonia feed rate of 12 000 mL min-1 showed that the membrane reactor produced hydrogen with >99.999% purity and a production rate of 1.01 Nm3 h-1 at 748 K with a retentate stream gauge pressure of 150 kPa and a permeation stream vacuum of -10 kPa. The ammonia decomposition tests confirmed that the newly developed air bubbling ELP method affords several advantages, such as rapid production, high ELP efficiency, reproducibility, and practical applicability.

Laser-Assisted Scalable Pore Fabrication in Graphene Membranes for Blue-Energy Generation.

The osmotic energy from a salinity gradient (i. e. blue energy) is identified as a promising non-intermittent renewable energy source for a sustainable technology. However, this membrane-based technology is facing major limitations for large-scale viability, primarily due to the poor membrane performance. An atomically thin 2D nanoporous material with high surface charge density resolves the bottleneck and leads to a new class of membrane material the salinity gradient energy. Although 2D nanoporous membranes show extremely high performance in terms of energy generation through the single pore, the fabrication and technical challenges such as ion concentration polarization make the nanoporous membrane a non-viable solution. On the other hand, the mesoporous and micro porous structures in the 2D membrane result in improved energy generation with very low fabrication complexity. In the present work, we report femtosecond (fs) laser-assisted scalable fabrication of μm to mm size pores on Graphene membrane for blue energy generation for the first time. A remarkable osmotic power in the order of μW has been achieved using mm size pores, which is about six orders of magnitudes higher compared to nanoporous membranes, which is mainly due to the diffusion-osmosis driven large ionic flux. Our work paves the way towards fs laser-assisted scalable pore creation in the 2D membrane for large-scale osmotic power generation.

Continuous Submicron Particle Separation Via Vortex-Enhanced Ionic Concentration Polarization: A Numerical Investigation.

Separation and isolation of suspended submicron particles is fundamental to a wide range of applications, including desalination, chemical processing, and medical diagnostics. Ion concentration polarization (ICP), an electrokinetic phenomenon in micro-nano interfaces, has gained attention due to its unique ability to manipulate molecules or particles in suspension and solution. Less well understood, though, is the ability of this phenomenon to generate circulatory fluid flow, and how this enables and enhances continuous particle capture. Here, we perform a comprehensive study of a low-voltage ICP, demonstrating a new electrokinetic method for extracting submicron particles via flow-enhanced particle redirection. To do so, a 2D-FEM model solves the Poisson-Nernst-Planck equation coupled with the Navier-Stokes and continuity equations. Four distinct operational modes (Allowed, Blocked, Captured, and Dodged) were recognized as a function of the particle's charges and sizes, resulting in the capture or release from ICP-induced vortices, with the critical particle dimensions determined by appropriately tuning inlet flow rates (200-800 [µm/s]) and applied voltages (0-2.5 [V]). It is found that vortices are generated above a non-dimensional ICP-induced velocity of U*=1, which represents an equilibrium between ICP velocity and lateral flow velocity. It was also found that in the case of multi-target separation, the surface charge of the particle, rather than a particle's size, is the primary determinant of particle trajectory. These findings contribute to a better understanding of ICP-based particle separation and isolation, as well as laying the foundations for the rational design and optimization of ICP-based sorting systems.

Advancement in Soft Iontronic Resistive Memory Devices and Their Application for Neuromorphic Computing

The aqueous electrolyte can be a deformable and stretchable liquid material for iontronic resistive memory devices. An aqueous medium makes a device closer to the brain‐like system with the movement of ions. This review paper proposes advances in liquid resistive memories and neuromorphic computing behavior to emulate electronic synapses. Primarily, the aqueous iontronic resistive memories can be used to study electrode and active layer materials and different device structures. Hence, herein, a timely and comprehensive study of these devices using ionic liquids, hydrogels, salt solutions, and soft electrodes to classify the device mechanism is presented. The filament formation is discussed in detail based on ion concentration polarization, electrode metallization, and movements of ions and charged molecules, which result in the formation of the metal dendrite. To manufacture a higher‐performance memory, device parameters should be optimized based on aqueous electrolytes, electrode materials, and other device design parameters. Aqueous electrolytes have smooth neurotransmission ability to fabricate brain‐inspired resistive memories with stable performance and device repeatability with smooth ion transmission. Aqueous electrode materials can be reliable for neural interface activities to compute electronic synapsis with electrical and chemical properties to ensure device reliability for a longer time period.

Three-dimensional ready-to-pick reservoir-based preconcentrator with a pillar-structured channel for miRNA applications

A sample preconcentration technique that exceeds a microfluidic device’s limited processing volume (up to microliters) is critical for real sample pretreatment applications. Here, we have developed a 3D-printed preconcentrator with a pillar structure (3DP2) to enrich the biological samples up to hundreds of microliter scales (700 μL) within 20 min by utilizing ion concentration polarization (ICP). We designed three-dimensional ready-to-pick reservoirs serially connected with a pillar-structured channel to enable large-volume preconcentration by balancing the preconcentrating forces (depletion, electrophoretic, and electroosmotic force) generated by ICP. Using the I-t and I-V curves, we confirmed that ICP performance was enhanced due to a pillar structure’s suppression of the vortex. Finally, we preconcentrated bovine serum albumin (BSA) and micro ribonucleic acid-21 (miRNA-21) two-fold. Moreover, depending on their size and charge, these were concentrated at different locations and could be extracted easily using pipettes. We believe that this study provides a novel strategy for downstream applications.

Analyte Enrichment via Ion Concentration Polarization with Hydrogel Plugs Polymerized in PDMS Microchannels by a Facile and Comprehensive Method for Improved Polymerization.

Hydrogels are incorporated into microfluidic devices to provide enhanced functionality by enabling processes such as enzyme immobilization, sample enrichment, and ionic current rectification. However, in the microfluidic devices with the commonly used material poly(dimethylsiloxane) (PDMS), hydrogels are very difficult to polymerize in situ in an ambient atmosphere because of the high oxygen concentration in PDMS. Even with very high (1.8%) photoinitiator concentrations, the polymerized hydrogel does not completely fill the microchannel. Here, we report a facile and broadly applicable protocol that utilizes microchannel pretreatment with 20% benzophenone in acetone to provide a hydrogel plug that completely fills the microchannel cross section by consuming the oxygen in the PDMS substrate near the microchannel wall. Both negatively charged and neutral hydrogels are polymerized from monomer solutions that utilize the photoinitiator/solvent combinations of VA-086 in water and benzophenone or IRG in DMSO. The photoinitiators were tested at different concentrations and in devices with different levels of oxidation. The hydrogel morphology is characterized using phase contrast microscopy and is related to the hydrogel's performance for concentration enrichment and ionic current rectification. A novel method is employed to confine the precursor solution in desired locations so that a photomask is not required for the spatial control of the plug location. Among six hydrogel formulations, at 100 V, the best current rectification factor obtained is ∼600 and the best analyte enrichment achieved is ∼120-fold in 5 min. This method provides a rapid and simple approach to increase the capabilities of PDMS microfluidic devices through improved polymerization of nanoporous hydrogels.

Influences of electroosmotic flow on ionic current through nanopores: A comprehensive understanding

Continuum simulations become an important tool to uncover the mysteries in nanofluidic experiments. However, fluid flow in simulation models is usually unconsidered. Here, systematical simulations are conducted to provide a quantitative understanding of influences from electroosmotic flow (EOF) on ionic transport through nanopores by both types of models with and without consideration of EOF. In nanopores of less than ∼10 nm in diameter, counterions dominate ionic current, which is always promoted obviously by the convective effect of EOF. In the diameter range from ∼10 to ∼30 nm, strong EOF induces ion concentration polarization or ion depletion inside nanopores, which causes significant decreases in ionic current. For nanopores larger than ∼30 nm, due to convective promotion and inhibition of EOF on the transport of counterions and anions, considerable nanopore selectivity to counterions maintains in cases with EOF. Though the difference in total current between both cases decreases with further pore size increasing, the difference in cation/anion current is still considerable. From our results under various pore parameters and applied conditions, the fluid flow should be considered in the simulation cases when EOF is strong. Our work may provide useful guidance for simulation conductance.

Insight the role of electrolyte in electrokinetic stacking of targets by ion concentration polarization on a paper fluidic device

Insight the role of electrolyte in electrokinetic stacking of targets by ion concentration polarization on a paper fluidic device

(Invited) Applications of Novel Electrochemical Technologies for Sustainable Fuel/Chemical Production and Resources Recovery

Electrochemical processes offer R&D opportunities toward decarbonization and resource recovery for circular economics. Innovate material produced by advancing manufacture techniques further widens its applications. In this presentation, we will discuss electrochemical process designs and material innovation to address technical and economic challenges of separations in biochemical/ biofuel production, resources recovery, CO2 utilization and impaired water treatment. In separations, the electrically driven force enabling selective capture of charged species and/or in-situ aqueous pH manipulation provides high energy efficiency, low capital footprint and cost for industrial applications compared to other separation technologies, e.g., separations by pressure-driven, thermally driven and biological-related. The common practices known are electrodialysis (ED), electrodeionization (EDI), capacitive deionization (CDI), cation intercalation desalination (CID), and ion concentration polarization (ICP). In these techniques, concentrated ions are separated from the liquid energy use is correlated with the quantity of ions removed. Therefore, the selective target capture provides “fit-for-purpose” separations. Pressure-driven processes cannot tune salinity for fit-for-purpose quality desalination but are effective at organic and biological species removal that electrochemical processes are not able to do. Thermal-driven processes cannot tune salinity for fit-for-purpose quality but are effective at organic and biological species removal. Biological-related processes typically apply bioelectrochemical reactions via microbes and bacteria to drive the removal of ions from the solution. In biological processes, ions are removed from the water solution. The ability to produce fit-for-purpose water has not been explored with biological processes, but they can treat targeted organics and biologicals. Compared to the pressure-driven membrane separation technologies used most in industrial separations, applications of selective separations have increased in recent years and becomes important to address the challenges of technology adaptation to climate change. For examples, the production of biofuel and bio-products to reduce green-house gas emission from fossil fuel and the non-conventional water supply for water-energy nexus have required high energy efficient and cost effective separation technologies. Innovative electrochemical separations can provide transformational impacts in advancing selective separations for highly energy efficient, small capital footprints and low processing cost. It, thus, enables the paradigm-shift of using alternative fuels and water supplies for industrial applications. We will discuss the key process performance metrics, energy consumption and processing rate, of various electrochemical technologies applied in biorefinery, waste to energy and water energy nexus to separate charges species from “dilute” aqueous phase. The ions separation performance demonstrated from various aqueous streams include 1) Inorganic and organic salts removal/capture in lignin valorization. and from bioprocessing streams in biofuel production; 2) volatile fatty acid removal/capture as well as biogas purification from solid waste anaerobic digester for waste to energy; 3) selective desalination of hardness, alkalinity, silica, and ammonia from impaired water for cooling water supply; 4)Capture and delivery for CO2 utilization. Critical issues in process design and material property to achieve electrochemical separation rate and energy efficiency for economic viability will be discussed.

Heterogeneous Two-dimensional lamellar Ti3C2Tx membrane for osmotic power harvesting

Osmotic energy generated from salinity gradients has been recognized as a novel blue energy source. Membrane-based reverse electrodialysis (RED) is a promising strategy for harvesting electric power from salinity difference. However, practical RED process often suffers from the low energetic efficiency due to the inherent ion concentration polarization phenomenon. Here, a heterogeneous two-dimensional lamellar Ti3C2Tx membrane with asymmetric geometry and charge properties was designed. The diode-like transport behavior with unidirectional ion conduction was observed, suggesting a preferential transport direction in the Ti3C2Tx hetero-nanochannel. When applied as the osmotic energy generators, the heterogeneous Ti3C2Tx membranes produced a maximum output power density of 16 W/m2 on mixing the natural brine and river water, higher than the commercialization benchmark (5 W/m2). Theoretical calculations confirmed that the asymmetric membrane architecture achieved a balance between effectively weakening the concentration polarization and maintaining the high ion selectivity. This study is a significant step forward in the field of designing artificial nanofluidic membranes and highly efficient osmotic energy conversion systems.

Mitigating the Kinetic Hindrance of the Poly/Single-Crystalline Ni-Rich Cathode-Based Electrode via Formation of the Superior Electronic/Ionic Pathway

In previous work, it was confirmed that even if the same cathode active material is used, the performance of the electrode could be improved by solving issues such as the electrochemically inactive areas caused by nonuniform dispersion of the conductive agents, electrolyte penetration blocking caused by agglomerated carbon black, and low electrode porosity. Herein, the use of CNTs, a material with excellent dimensional stability and high electron conductivity (103 S cm–1) as conductive agent, is expected to be a solution that can reduce ion concentration polarization at high C rates by increasing the electrode porosity, as well as maintaining a good electron pathway. Therefore, in this study, we investigate how the addition of CNTs affects the performance of poly/single-crystalline Ni-rich NCM-based cathode electrodes. The results confirm that by adding CNTs to the poly/single-crystalline Ni-rich NCM-based electrode under high-rate (540 mA g–1) cycle conditions, the cycle retentions were improved by 3% in 50 cycles.

Ion concentration polarization-based multifunctional microfluidic device for analysis of intracellular components

We report a multifunctional microfluidic device that lyses cells and separates intracellular components (including proteins) as a novel cell analysis platform. The device exploits an amplified electric field in an ion-depletion region formed by a nanofluidic phenomenon termed ion concentration polarization (ICP). To enable the multifunctionality of the device, multiple electric streams were employed to generate multiple ICP zones where cell lysis and separation of nano-sized intracellular components were processed sequentially in a semi-continuous manner in a single device. The amplified electric field in the ion-depletion region provides a short processing time (within only a few seconds for each step), and the absence of the internal electrodes offers the advantages of simple, low-cost device fabrication and bubble-free operation compared with conventional electric-force-based microfluidic devices. Due to these unique features, we expect that the developed multifunctional microfluidic device can be a very useful tool as an integrated system for analyzing intracellular components such as DNAs and proteins which is still a challenging and important issue to the biochemist.

Nucleic Acid Detection with Ion Concentration Polarization Microfluidic Chip for Reduced Cycle Numbers of Polymerase Chain Reaction.

Nucleic acid detection is widely used in disease diagnosis, food safety, environmental monitoring and many other research fields. The continuous development of rapid and sensitive new methods to detective nucleic acid is very important for practical application. In this study, we developed a rapid nucleic-acid detection method using polymerase chain reaction (PCR) combined with electrokinetic preconcentration based on ion concentration polarization (ICP). Using a Nafion film, the proposed ICP microfluidic chip is utilized to enrich the nucleic acid molecules amplified by PCR thermal cycles. To demonstrate the capability of the microfluidic device and the hybrid nucleic-acid detection method, we present an animal-derived component detection experiment for meat product identification applications. With the reduced cycle numbers of 24 cycles, the detection can be completed in about 35 min. The experimental results show that this work can provide a microfluidic device and straightforward method for rapid detection of nucleic acids with reduced cycle numbers.