Ion Concentration Polarization Research Articles

Segmental-porosity regulation of nanochannel membranes with anomalously improved ion selectivity for enhanced osmotic power generation

Nanochannel-based osmotic energy conversion can directly convert salinity gradient energy between solutions with different ion concentrations into electric energy. In the energy conversion process, the high-concentration side of the nanochannel membrane has high ion permeability but low ion selectivity, whereas the low-concentration side exhibits opposite properties, which is the inherent limitation of osmotic power. However, the relationship between ion selectivity and permeability is unclear, which hinders the improvement of the output power density. This paper reports a segmental-porosity regulation method to break through the inherent constraints of the ion selectivity–permeability trade-off. The nanochannel membrane was divided into three regions along the ion transport direction as upstream, midstream, and downstream. The porosities of these three regions were separately regulated to optimize the structures for ion selectivity–permeability matching. When a high porosity was adopted for the downstream region and a small and mediate porosity combination was used for the upstream and midstream regions, the highest output power density was achieved, which was 78.44% higher than that of a straight nanochannel with homogeneous porosity under a 100-fold concentration ratio. The outstanding osmotic power generation performance of the optimized segmental structure was attributed to the alleviated ion concentration polarization and unexpectedly improved ion selectivity. Finally, the process and underlying mechanisms of segmental-porosity regulation are also proposed. This paper reports a novel methodology for designing the structure and porosity of nanochannel membranes to enhance osmotic power generation.

Innovative Anode Design to Enhance Both Volumetric and Gravimetric Energy Densities of LiCoO2||Graphite Pouch Cells

AbstractThe ratio of the anode (negative electrode) and cathode (positive electrode) areal capacities (N/P ratio), is an important parameter for Lithium‐ion batteries. Considering the manufacturing tolerance and battery safety, almost all of the batteries keep the N/P ratio > 1. Deviating from this ratio can lead to lithium precipitation on the anode surface, which poses significant risks. Here, by using a gradient structured graphite (Gr) anode, a new design concept is proposed that the N/P ratio could be less than 1, which can effectively achieve higher energy density without sacrificing the battery safety. This is achieved by incorporating a small quantity of silver (Ag) nanoparticles into the bottom layer of the anode (Gr‐Agx), which effectively modulates the concentration polarization of lithium ions along the thickness of the electrode. Moreover, the volumetric energy density of 4 Ah LiCoO2||Gr‐Ag0.5 (N/P = 0.8) pouch cell increases by 14.5% compared with LiCoO2||Gr (N/P = 1.1). Furthermore, the universal applicability and efficacy of the N/P < 1 design paradigm in LiFePO4||Gr cells are validated.

Zwitterion Modified Polyacrylonitrile Fiber Separator for Long‐Life Zinc‐Ion Batteries

AbstractThe major challenges of aqueous zinc‐ion batteries (ZIBs) are the dendrite formation and the passivation of zinc metal anode, which restrict their practical applications. Herein, polyacrylonitrile (PAN) and zwitterionic surfactant (Sulfobetaine methacrylate, SBMA) are combined as a precursor to design a modified PAN nanofiber separator by electrospinning. SBMA with sulfonate group [SO3−] can alter the physical property of the precursor solution and electrostatic field during the electrospinning process. Besides, it can regulate the zinc ions crossing and homogenize the electric field by minimizing the zinc ion concentration polarization on the zinc foil surface due to the polar group. As a result, Zn symmetric cells with PAN@SBMA separators show long‐term stability (up to 1700 h), which outdistances the cell with GF‐D (only up to 50 h) under current density at 1 mA cm−2. Meanwhile, the Zn//PAN@SBMA//NH4V4O10 full cells have high specific capacity (236 mAh g−1) and excellent long‐term durability with 84.2% capacity retention after 2000 cycles at 5 A g−1. This work illustrates an easy and effective way to design a high ion transference number and functional PAN‐based separator for regulating Zn2+ deposition for the development of high‐performance ZIBs.

In Situ Synthesized HOF Ion Rectification Membrane with Ultrahigh Permselectivity for Nanofluidic Osmotic Energy Harvesting

AbstractThe utilization of salt concentration gradients as a renewable energy source represents a pivotal solution to the energy crisis. However, it is a persistent challenge to fabricate high‐performance ion permeable membranes with excellent ion permselectivity. In this work, hydrogen‐bonded organic framework (HOF) is in situ growth on anodic aluminum oxide (AAO) via chemical‐binding and solution‐processing strategy. The hydrogen bonding and π–π interactions forming the porous structure and the internal unprotonated carboxyl groups endow the HOF with superior cation selectivity and ion permeability. Furthermore, benefiting from the remarkable asymmetry of the prepared nanofluidic membrane arising from structure and charge of AAO and HOF, the HOF/AAO presents outstanding ion current rectification (ICR) characteristic, which can eliminate the ion concentration polarization (ICP) and power loss. Therefore, an impressive output power density with 500‐fold NaCl gradient is achieved as 75.2 W m−2 using the as‐prepared HOF/AAO, which is superior to most of reported membranes (7.0–40.0 W m−2). To show the critical role of HOF, 2D and 3D MOF with the same monomers are also synthesized, achieving decreased power densities of 36.2 and 58.3 W m−2 respectively. The present work provides a novel strategy to develop high‐performance nanofluidic ICR membranes for osmotic energy harvesting.

(Invited) Electric-Driven Preconcentrating Microfluidic Device for Enhancing Biomolecular Sensing

Preconcentration of biomolecules for detection on microfluidic platforms based on electrical kinetic trapping (EKT) through ion concentration polarization (ICP) has been well developed in the past decade. Biomolecules can be entrapped due to the equilibrium of forces between electro-osmosis and ICP when applying a voltage to the system. In tis study, I will introduce different type of ICPs including theory, mechanism and their limitation. I will also clarify the experimental ICP results based on different microfluidic channel design. A triboelectric nanogenerator (TENG)-driven nanofluidic preconcentrating device that is able to trigger ICP and subsequently cause the EKT of the biomolecules without using a conventional electrical power source was also introduced. The EKT and electrical characteristics of the TENG-based nanofluidic preconcentrator were studied. The preconcentration factors of the device can be found to be ~1000 folds. Several examples of preconcentration device integrating to biosensing techniques are presented in this talk. Some biomarkers are also demonstrated. Further, I will also demonstrate that these biosensors, combining with preconcentrators, can be integrated to a smartphone reader.

Classification of DNA Mixtures by Nanoelectrokinetic Driftless Preconcentration

Nanofluidic phenomena, particularly Ion Concentration Polarization (ICP), have been actively utilized for advancing various research fields, including chemical analysis and biomedical diagnostics, over the past century. While ICP can be used as effective preconcentration techniques in bio-/chemical analysis, there are few studies to investigate the shape of preconcentration plug, especially perpendicular distribution of analyte in the preconcentration plug. Previously we have reported the theoretical analysis of the distribution so that the types of plug were categorized as dumbbell or plug shape. In this study, we further investigated the classification of real DNAs within micro-/nanofluidic devices by examining the preconcentration dynamics of different DNA types under diverse electrical conditions. Our investigation successfully distinguished distinct preconcentration profiles for Short DNA, Multi-short DNAs, and Equitable DNA with introducing the concept of the Radius of Gyration for Fluorescence (RGF). We provided a quantitative framework to analyze and differentiate preconcentration shapes with reasonable precision. These findings not only deepen our understanding of DNA preconcentration dynamics but also provide implications for genetic diagnostics. As a simpler and more accessible pre-test tool, our research could be utilized as the efficient genetic testing, particularly in diagnosing disorders characterized by variations in DNA length.

Investigation of Operational Parameters for Nanoelectrokinetic Purification and Preconcentration.

This work reports on experimental investigations into the operational parameters of nanoelectrokinetic purification and preconcentration, especially utilizing on ion concentration polarization (ICP). ICP as a nanoscale electrokinetic phenomenon has demonstrated promising advances in various fields utilizing an ion depletion zone (IDZ) with a steep electric field gradient inside the ICP layer. However, the inevitable electrokinetic instability occurring within the IDZ has posed a challenge in operating the ICP system stably. To address the need for a stable and efficient ICP operation in various devices and applications, we propose an operational strategy along with conducted research to determine optimal operating ranges. In order to investigate the operational parameters, a unit voltage (VTH) is introduced as the threshold for initiating ICP. We examined the applicability of VTH across various operating ranges to ensure its effectiveness and versatility. In ICP purification, we categorize three modes (steady, burst, and unsteady) based on IDZ expansion and stability under varying VTH and flow rate conditions, presenting optimal operational conditions that minimize the voltage margin. In ICP preconcentration, a systematic investigation is conducted to observe the influence of background electrolyte concentration and voltage conditions on preconcentration efficiency, offering insights into the correlation between preconcentration factor, electrical conditions, and preconcentration time. Therefore, this research would contribute to the practical understanding of nanoelectrokinetics, providing insight into experimental designs. These findings are expected to offer valuable guidance to researchers aiming to utilize ICP's potential across a spectrum of applications, from purification to preconcentration, in the realm of micro/nanofluidic systems.

Active microparticle propulsion pervasively powered by asymmetric AC field electrophoresis

HypothesisSymmetry breaking in an electric field-driven active particle system can be induced by applying a spatially uniform, but temporally non-uniform, alternating current (AC) signal. Regardless of the type of particles exposed to sawtooth AC signals, the unevenly induced polarization of the ionic charge layer leads to a major electrohydrodynamic effect of active propulsion, termed Asymmetric Field Electrophoresis (AFEP). ExperimentsSuspensions containing latex microspheres of three sizes, as well as Janus and metal-coated particles were subjected to sawtooth AC signals of varying voltages, frequencies, and time asymmetries. Particle tracking via microscopy was used to analyze their motility as a function of the key parameters. FindingsThe particles exhibit field-colinear active propulsion, and the temporal reversal of the AC signal results in a reversal of their direction of motion. The experimental velocity data as a function of field strength, frequency, and signal asymmetry are supported by models of asymmetric ionic concentration-polarization. The direction of particle migration exhibits a size-dependent crossover in the low frequency domain. This enables new approaches for simple and efficient on-chip sorting. Combining AFEP with other AC motility mechanisms, such as induced-charge electrophoresis, allows multiaxial control of particle motion and could enable development of novel AC field-driven active microsystems.

Unipolar Ionic Diode Nanofluidic Membranes Enabled by Stepped Mesochannels for Enhanced Salinity Gradient Energy Harvesting.

Developing ionic diode membranes featuring asymmetric structures is in high demand for salinity gradient energy harvesting. These membranes offer benefits in mitigating ion concentration polarization, thereby promoting ion permeability. However, most reported works focus on the role of heterogeneous charge-based bipolar ionic diode membranes for ion concentration polarization suppression, with comparatively less attention given to maintaining ion selectivity. Herein, unipolar ionic diode nanofluidic mesoporous silica membranes featuring stepped mesochannels were developed via a micellar sequential oriented interfacial self-assembly strategy as a salinity gradient energy harvester. Due to the asymmetric mesochannels and unipolar structure (both sides carry negative charge), the ionic diode membranes exhibit a strong rectification ratio of ∼15.91 to facilitate unidirectional ion transport while maintaining excellent cation selectivity (cation transfer number of ∼0.85). Besides, the vertically aligned mesochannels significantly reduce ion transport resistance, generating a high ionic flux. Consequently, the unipolar ionic diode nanofluidic membranes demonstrate a power output of 5.88 W/m2 between artificial sea and river water. The unipolar feature gives notable enhancements of 296% and 144% in power output compared to the symmetric membrane and bipolar ionic diode membrane, respectively. This work opens up new routes for designing ionic diode membranes for salinity gradient energy harvesting.

Enhancement of Overlimiting Current in a Three-Dimensional Hierarchical Micro/Nanofluidic System by Non-uniform Compartmentalization

Overlimiting current (OLC) is a non-linear current response that occurs related to an ion concentration polarization (ICP) phenomenon in micro/nanofluidic systems and holds great importance since it represents the rate of selective ion transportation through perm-selective structure. For last two decades, numerous studies of OLC have been reported about understanding the fundamentals of nanoelectrokinetics and enhancing ion transportation through perm-selective membranes. Recent study reported that the alignment of non-uniform microspace near the perm-selective membranes in two-dimensional micro/nanofluidic systems can significantly enhance OLC, i.e., overlimiting conductance (σOLC). This is attributed to recirculation flow induced by combination of unbalanced electroosmosis and induced pressure driven flow among non-uniform microspaces. However, 2D micro/nanofluidic systems have limited practicality due to their small volume and low throughput. Herein, we tested the OLC enhancement using 3D-printed hierarchical micro/nanofluidic systems with respect to the non-uniformity of microspaces. The 3D microspaces were fabricated as a mesh structure using a conventional 3D printer. By comparing current–voltage measurement with each type of mesh, we experimentally confirmed the generation of recirculation flow among non-uniform meshes and ionic current enhancement in 3D hierarchical micro/nanofluidic system. Also, we further investigated the enhancement of overlimiting conductance depending on the mesh pattern. Furthermore, we validated that this effect of microscale non-uniform compartmentalization, both increasing surface area and aligning non-uniform spaces, appears not only at low molar concentration but at high molar concentrations. This demonstration can offer a strategy to design optimal electrochemical systems where a perm-selective ion transportation is crucial.

The role of ionic concentration polarization on the behavior of nanofluidic membranes

Water, the elixir of life, faces a pressing challenge—salinity. As humanity's demand for freshwater intensifies, the significance of efficient desalination processes becomes paramount. The promising prospects of nanofluidic membranes and unique electrokinetic phenomena like ion concentration polarization (ICP) signal optimistic strides in enhancing salt removal processes. This study is dedicated to elucidating the transport mechanism of buffer ions at interfaces between micro and nanochannels. To achieve this, we introduce a multiphysics coupling model that incorporates a boundary condition for the fixed surface voltage, offering a comprehensive description of the impact of nanochannel arrays. In this context, it is important to note that the nanochannel array is characterized by a positive charge density, akin to a cation exchange membrane (CEM), seamlessly integrated into the microchannel wall to serve as a cationic half-cell. The analysis involved solving governing equations, including the Poisson-Nernst-Planck, continuity, and Navier-Stokes equations, numerically using the finite element method in an unsteady state. Employing cylindrical nanochannel array configurations—single, dual, and triple—we scrutinized their impact on salt species concentration and removal efficiency under specified conditions (c0=1mM, ρv=2C/m3, LN=10μm, VT=26mV, Vsurr=4VT, VL/VR=8,t≥0.5 and ζ=−60mV). The single nanochannel array configuration demonstrated a relatively uniform salt distribution, achieving a removal efficiency of approximately 58%. The introduction of two nanochannel arrays at distinct locations resulted in a notable increase in removal efficiency, reaching 72%, particularly in the "down first" configuration, emphasizing a synergistic effect. The presence of three nanochannel arrays, each with varying lengths, produced intricate patterns, with the highest removal efficiency observed at 91% in the "different length" condition. This study emphasizes the superior desalination capabilities achievable through multiple nanochannel arrays, advancing our understanding of nanofluidic membrane applications for efficient water desalination. In conclusion, emulating electrodialysis membrane procedures, particularly by integrating an anionic half-cell, holds promise for further advancing desalination processes, offering a potential avenue to enhance efficiency.

Polyoxometalate-based plasmonic electron sponge membrane for nanofluidic osmotic energy conversion.

Nanofluidic membranes have demonstrated great potential in harvesting osmotic energy. However, the output power densities are usually hampered by insufficient membrane permselectivity. Herein, we design a polyoxometalates (POMs)-based nanofluidic plasmonic electron sponge membrane (PESM) for highly efficient osmotic energy conversion. Under light irradiation, hot electrons are generated on Au NPs surface and then transferred and stored in POMs electron sponges, while hot holes are consumed by water. The stored hot electrons in POMs increase the charge density and hydrophilicity of PESM, resulting in significantly improved permselectivity for high-performance osmotic energy conversion. In addition, the unique ionic current rectification (ICR) property of the prepared nanofluidic PESM inhibits ion concentration polarization effectively, which could further improve its permselectivity. Under light with 500-fold NaCl gradient, the maximum output power density of the prepared PESM reaches 70.4 W m-2, which is further enhanced even to 102.1 W m-2 by changing the ligand to P5W30. This work highlights the crucial roles of plasmonic electron sponge for tailoring the surface charge, modulating ion transport dynamics, and improving the performance of nanofluidic osmotic energy conversion.

Pore-Size-Dependent Role of Functional Elements at the Outer Surface and Inner Wall in Single-Nanochannel Biosensors.

Biological nanopores feature functional elements on the outer surfaces (FEOS) and inner walls (FEIW), enabling precise control over ions and molecules with exceptional sensitivity and specificity. This provides valuable inspiration to scientists for the development of intelligent artificial nanochannel-based platforms, with a wide range of potential applications, including biosensors. Much effort has been dedicated to investigating the distinct contribution of FEOS and FEIW of multichannel membrane biosensors. However, the intricate interactions among neighboring pores in multichannel biosensors have presented challenges. This underscores the untapped potential of single nanochannels as ideal candidates in this field. Here, we employed single nanochannel membranes with different pore sizes to investigate the distinct contributions of FEIW and FEOS to single-nanochannel biosensors, combined with numerical simulations. Our findings revealed that alterations in the negative charges of FEIW and FEOS, induced by target binding, have differential effects on ion transport, contingent upon the degree of nanoconfinement. In the case of smaller pores, such as 20 nm, the ion concentration polarization driven by FEIW can independently control ion transport through the surface's electric double layer. However, as the pore size increases to 40-60 nm, both FEIW and FEOS become essential for effective ion concentration polarization. When the pore size reaches 100 nm, both FEIW and FEOS are ineffective and thus unsuitable for biosensors. Simulations demonstrate that the observed phenomena can be attributed to the interactions between the charges of FEIW and FEOS within the overlapping electric double layer under confinement. These results underscore the critical role of pore size as a key parameter in governing the functionality of probes within or on nanopore-based biosensors as well as in the design of nanopore-based devices.

Enhanced desalination performance of an electrodialysis stack in over-limiting current by adding AC/Fe3O4 nanocomposite as a flow electrode

The primary aim of this study was to investigate the enhanced desalination performance of the electrodialysis (ED) stack under over-limiting current conditions. This was achieved by coupling the flow-electrode capacitive deionization (FCDI) process with the ED stack, incorporating an AC/Fe3O4 nanocomposite (NC) as a flow electrode in the electrode and concentrate compartments. The results obtained indicate that utilizing AC/Fe3O4 NC in the electrode compartment during the ED process, under a potential of 15 V, has led to a significant enhancement in desalination efficiency and current efficiency (CE). Specifically, the desalination efficiency and CE have increased from 60 % to 89.3 % and 35.9 % to 72 %, respectively, compared to the absence of AC/Fe3O4 NC. The desalination efficiency was increased to 93.24 % and the ASRR reached 1.46 μmol cm−2 min−1 by simultaneously adding AC/Fe3O4 NC to the electrode and concentrate compartments. This improvement can be attributed to a reduction in solution resistance, the electro-sorption of ions in the electrical double layer (EDL) of NC, as well as a decrease in ion concentration polarization. Moreover, it is likely that Fe3O4 nanoparticles of NC have resulted in electrical and membrane surface heterogeneity. These factors collectively contribute to the enhancement of the electroconvection phenomenon during the ED process.

On-Chip Electrochemical Sensing with an Enhanced Detecting Signal Due to Concentration Polarization-Based Analyte Preconcentration.

Here, we integrated two key technologies within a microfluidic system, an electrokinetic preconcentration of analytes by ion Concentration Polarization (CP) and local electrochemical sensors to detect the analytes, which can synergistically act to significantly enhance the detection signal. This synergistic combination, offering both decoupled and coupled operation modes for continuous monitoring, was validated by the intensified fluorescent intensities of CP-preconcentrated analytes and the associated enhanced electrochemical response using differential pulse voltammetry and chronoamperometry. The system performance was evaluated by varying the location of the active electrochemical sensor, target analyte concentrations, and electrolyte concentration using fluorescein molecules as the model analyte and Homovanillic acid (HVA) as the target bioanalyte within both phosphate-buffered saline (PBS) and artificial sweat solution. The combination of on-chip electrochemical sensing with CP-based preconcentration renders this generic approach adaptable to various analytes. This advanced system shows remarkable promise for enhancing biosensing detection in practical applications while bridging the gap between fundamental research and practical implementation.

Determination of Critical Dimensions of Microchannels to Ensure the Electrokinetic Biomolecule Preconcentration: Analytical and Numerical Studies.

Preconcentration of biomolecules based on ion concentration polarization (ICP) has been splendidly applied to various biomedical and chemical processes. However, in many circumstances, biomolecule preconcentration could not occur due to the lack of full studies on the preconcentration mechanism, especially on the effect of microchannel dimensions. In this work, we provide analytical studies on the critical dimensions (minimum and maximum) of microchannels for the preconcentration of biomolecules. These formulas are verified with the numerical results by fully solving the coupled governing equations: Poisson-Nernst-Planck and Navier-Stokes experiments with appropriate boundary conditions and assumptions. In addition, we examine the impact of operational parameters, such as electric potentials and critical external pressures, on the formation of the preconcentration. Moreover, two important results are provided for the first time, including the position of the preconcentrated biomolecule region and the concentration enhancement factor of the biomolecules. These analytical and numerical results are consistent with experimental observations and, therefore, could provide sharp insight into the mechanism of biomolecule preconcentration and give useful guidelines to better design and optimize ICP-based microfluidic preconcentration devices.

Dynamic and Asymmetrical Ion Concentration Polarization in Dual Nanopipettes.

Dual nanopipettes with two channels have been receiving great attention due to the convenient experimental setup and multiple measuring channels in sensing applications at nanoscale, while the involved dynamic and asymmetrical ion transport processes have not been fully elucidated. In this paper, both experimental and simulation methods are used to investigate the dynamic mass transport processes inside dual nanopipettes with two well-separated channels. The results present that the ion transport resistance through the two channels (R12) is always the add-up of the individual ones (R13 + R23) with respect to the bulk solutions, at various ionic strengths and scan rates. A constant zero-current potential is obtained when loading an asymmetrical electrolyte concentration in the two channels, and the zero-potential current displays a good linear relationship with the bulk concentration outside the pipet. Besides revealing the dynamic and asymmetrical concentration polarization in the dual nanopipettes, these results would also further promote the better usage of dual nanopipettes in electrochemical sensing and imaging applications.

Enhanced Salt Removal of Fresh Water by Recovery-Reduced Ion Concentration Polarization Desalination.

Here, we examine electromembrane systems for low-concentration desalination applicable to ultrapure water production. In addition to electrodialysis and ion concentration polarization (ICP) desalination, we propose a recovery-reduced ICP strategy for reducing the width of the desalted outlet for a higher salt removal ratio (SRR). The correlation between conductivity changes and thickness of the ion depletion zone is identified for electrodialysis, ICPH (1:1), and ICPQ (3:1) with a low-concentration feed solution (10 mM, 1 mM, 0.1 mM NaCl). Based on the experimental results, the scaling law and SRR for the electroconvection zone are summarized, and current efficiency (CE) and energy per ion removal (EPIR) depending on SRR are also discussed. As a result, the SRR of electrodialysis is mostly around 50%, but that of recovery-reduced ICP desalination is observed up to 99% under similar operating conditions. Moreover, at the same SRR, the CE of recovery-reduced ICP is similar to that of electrodialysis, but the EPIR is calculated to be lower than that of electrodialysis. Considering that forming an ion depletion zone up to half the channel width in the electromembrane system typically requires much power consumption, an ICP strategy that can adjust the width of the desalted outlet for high SRR can be preferable.

Charge-Gradient Sulfonated Poly(ether ether ketone) Membrane with Enhanced Ion Selectivity for Osmotic Energy Conversion.

Engineered asymmetric heterogeneous ion-selective membranes have become a focal point for their improved efficiency in harnessing osmotic energy from ionic solutions with varying salinity. However, achieving both energy conversion efficiency and excellent chemical stability necessitates effectively mitigating the formation of detrimental interface cracks between two different layers. We develop a charge-gradient sulfonated poly(ether ether ketone) (SPEEK) membrane (CG-SPEEK) on a large-scale using a straightforward coating method. As an osmotic energy generator, CG-SPEEK membrane achieves an impressive output power density of 9.2 W m-2 and exhibits ultrahigh cation selectivity (0.99), with an energy conversion efficiency of 48% at a 50-fold NaCl concentration gradient. The results highlight the ion diode effects of CG-SPEEK, driven by a charge density gradient that accelerates cation transport while suppressing ion concentration polarization. Density functional theory simulations provide further insights, revealing that the energy barrier for Na+ ion transport through CG-SPEEK membrane is lower than that through a homogeneous SPEEK membrane. This work not only enhances our understanding of ion transport dynamics but also establishes the CG-SPEEK membrane as a promising candidate for efficient osmotic energy conversion applications.

Locational enrichment of low-abundance analytes through force-environment-modulation microsystem with ion concentration polarization

Ion concentration polarization (ICP) effect in micro-nanofluidic devices can concentrate low-concentration molecules. In this paper, we proposed a novel ICP-based enrichment system with horizontal barriers that adjust the force environment of charged particles, to achieve specific locational analytes enrichment. Mechanism of analyte enrichment through force modulation is revealed through numerical simulation using microchannels with varied channels widths, which is further validated through physical experiment. Overall, a specific target-oriented structure and load regulation method was proposed, under which the low-abundance analytes could be locationally concentrated by ∼ 4000 times. This study is expected to develop an innovative method for specifically locational ion enrichment in terms of scientific principles, providing theoretical and technical support for concentration and detection of charged substances in both research and industry such as biology, environment, chemistry studies, etc.