Ion Transport In Nanochannels Research Articles

Gate-All-Around Nanopore Osmotic Power Generators.

Nanofluidic channels in a membrane represent a promising avenue for harnessing blue energy from salinity gradients, relying on permselectivity as a pivotal characteristic crucial for inducing electricity through diffusive ion transport. Surface charge emerges as a central player in the osmotic energy conversion process, emphasizing the critical significance of a judicious selection of membrane materials to achieve optimal ion permeability and selectivity within specific channel dimensions. Alternatively, here we report a field-effect approach for in situ manipulation of the ion selectivity in a nanopore. Application of voltage to a surround-gate electrode allows precise adjustment of the surface charge density at the pore wall. Leveraging the gating control, we demonstrate permselectivity turnover to enhanced cation selective transport in multipore membranes, resulting in a 6-fold increase in the energy conversion efficiency with a power density of 15 W/m2 under a salinity gradient. These findings not only advance our fundamental understanding of ion transport in nanochannels but also provide a scalable and efficient strategy for nanoporous membrane osmotic power generation.

Artificial nanochannels for highly selective detection of miRNA based on the HCR signal amplification

Artificial solid-state nanochannels have nanoscale spatial confinement and unique ion transport properties that have been widely used in biosensing, nanofluidic devices, and nucleic acid sequencing. However, most of the nanochannel sensors for miRNA detection are grounded on the complementary pairing of bases, lacking signal amplification, which limits its application in many fields. Herein, we proposed a signal amplification strategy for miRNA-182 detection based on introducing hybridization chain reaction (HCR) in artificial nanochannels to improve the detection sensitivity. In this method, the capture DNA (cDNA) was anchored in the nanochannel, and when the target miRNA appeared, the hairpin probes H1, H2, and initiator were introduced to trigger the HCR reaction to form long nucleic acid double strands, which significantly enhanced the negative charge and affected ion transport in nanochannel. The nanochannel sensor performed excellent selectivity to the target miRNA-182, and it can realize the detection of miRNA-182 with an ultra-low concentration of 1.65 aM, which can be further applied to the detection of miRNA-182 in actual biological samples. Moreover, the nanochannel system was proved by using the AND logic gate that cDNA, initiator, H1, H2, and miRNA-182 are indispensable for successfully triggering HCR. This work provides a simple and efficient signal amplification method for miRNA detection, which considerably expands the application of nanochannel sensors and holds great prospects in biomedical and clinical detection.

Electrokinetic ion transport of viscoelastic fluids in a pH-regulated nanochannel

The objects of nanofluidics-based biological detection are usually viscoelastic fluids, and the rheological properties of viscoelastic fluids can have complex effects on electroosmotic flow and electrokinetic ion transport in nanochannels. However, researchers have mainly focused on Newtonian fluids. In this study, numerical simulations were performed on the electrokinetic ion transport of viscoelastic fluids in a pH-regulated nanochannel. The Oldroyd-B model is used to describe the behavior of the polyacrylamide (PAM) solution, and the Poisson-Nernst-Planck model is used to describe the potential and ion concentration in the electrolyte solution. Compared with the Newtonian fluid, at pH = 8, the PAM solution of cp = 500 ppm has a larger region of low ion concentration in front of the nanochannel entrance and has a larger region of high ion concentration behind the nanochannel exit. When the pH is increased to 8, the surface charge density |σw| increases sharply, which is about 5 times of that at pH = 6. At pH = 8, cKCl = 20 mM, and cp = 500 ppm, two distinct vortices appear behind the nanochannel exit, and rotate in opposite directions.

Tracking Ion Transport in Nanochannels via Transient Single-Particle Imaging.

The transport behavior of ions in the nanopores has an important impact on the performance of the electrochemical devices. Although the classical Transmission-Line (TL) model has long been used to describe ion transport in pores, the boundary conditions for the applicability of the TL model remain controversial. Here, we investigated the transport kinetics of different ions, within nanochannels of different lengths, by using transient single-particle imaging with temporal resolution up to microseconds. We found that the ion transport kinetics within short nanochannels may deviate significantly from the TL model. The reason is that the ion transport under nanoconfinement is composed of multi basic stages, and the kinetics differ much under different stage domination. With the shortening of nanochannels, the electrical double layer (EDL) formation would become the "rate-determining step" and dominate the apparent ion kinetics. Our results imply that using the TL model directly and treating the in-pore mobility as an unchanged parameter to estimate the ion transport kinetics in short nanopores/nanochannels may lead to orders of magnitude bias. These findings may advance the understanding of the nanoconfined ion transport and promote the related applications.

Fast Ions Transportation in Nanochannel with ATPase‐Like Structure

Ion transport plays an important role in various biological processes because of the ability of ions to move rapidly in biological ion channel‐confined spaces. For example, rapid proton transport in ATPases is attributed to confined channel spaces and conjugated sites. According to molecular dynamics simulations, the confined spaces and conjugated sites in nanochannels can enhance ion transport. Herein, it is demonstrated that the ATPase‐like structures of sulfonic acid‐modified covalent organic framework nanochannels, which promote the formation of highly ordered and continuous water molecular chains and confined spaces, can support ion (H+, Li+, Na+, and K+) transport rates that are an order of magnitude higher than those of bulk water. The ion transport rates in the nanochannel are superior to those in other artificial channels. Moreover, the selectivity of cations in the nanochannel is evaluated using the diffusion potential with a concentration gradient. The simulations and experimental results demonstrate that confined spaces and conjugated sites are crucial for efficient ion transport in nanochannels modified by sulfonic acid groups as cation conductor materials.

2D CdPS3-based versatile superionic conductors

Ion transport in nanochannels is crucial for applications in life science, filtration, and energy storage. However, multivalent ion transport is more difficult than the monovalent analogues due to the steric effect and stronger interactions with channel walls, and the ion mobility decreases significantly as temperature decreases. Although many kinds of solid ionic conductors (SICs) have been developed, they can attain practically useful conductivities (0.01 S cm−1) only for monovalent ions above 0 °C. Here, we report a class of versatile superionic conductors, monolayer CdPS3 nanosheets-based membranes intercalated with diverse cations with a high density up to ∼2 nm−2. They exhibit unexpectedly similar superhigh ion conductivities for monovalent (K+, Na+, Li+) and multivalent ions (Ca2+, Mg2+, Al3+), ∼0.01 to 0.8 S cm−1 in the temperature range of −30 ‒ 90 °C, which are one to two orders of magnitude higher than those of the corresponding best SICs. We reveal that the high conductivity originates from the concerted movement of high-density cations in the well-ordered nanochannels with high mobility and low energy barrier. Our work opens an avenue for designing superionic conductors that can conduct various cations and provides possibilities for discovering unusual nanofluidic phenomena in nanocapillaries.

Electrokinetic ion rectification in the coupling asymmetric charged nanochannel

Ion transport in nanochannels attracts increasing attention with the advance of nanotechnology, where ion rectification has been intensively studied due to its diode-like electrokinetic behavior. However, the electrochemical interface in most ion rectification is not uniform but involves asymmetric-charged characteristics that offer new degrees of electrical double layer (EDL) confinement. Herein, we investigate the ion transport in coupling asymmetric charged nanochannel to evaluate how the asymmetric geometry and surface charge influences the ion rectification performance. The results show that at low surface charge gradient, the coupling effect enhances ion rectification performance. While at high surface charge gradient, an anomalous electrokinetic behavior is observed that coupling effect deteriorates ion rectification performance. Further analysis discloses that the enhancement-deterioration transition threshold depends on the coordination mechanism of asymmetric geometry and surface charge. It is found that the asymmetric geometry shaped nanochannel with low surface charge gradient and homogeneous geometry shaped nanochannel with high surface charge gradient have the better ion rectification performance. This work fills the gap in understanding the coupling asymmetry effect on ion rectification, providing the useful guidance to design nanofluidic energy devices.

Electrokinetic energy conversion in the nanochannel coupled with surface charge and slip effects

Inspired by the universal phenomena in nature and advances in nanotechnology, the ion transport in nanochannel receives increasing attention and shows great promising in energy conversion. The precedent studies generally predicted the ion transport by tuning the single physical parameter, the understanding of ion dynamics in the real multi-physical coupling systems is still scarce. Here, an ion transport model coupled with surface charge and slip effects is proposed to investigate the energy conversion behavior in nanochannel. The results show that the surface charge density increases with the increasing bulk concentration, nanochannel size and solution pH. The original boundary slip tends to decrease the surface charge density and the surface charge in turn reduces the boundary slip significantly, which manifests the strong coupling effect of diverse factors. The output power and energy conversion efficiency increases first and then decrease with the increasing bulk concentration and pH. The increase of channel size is beneficial for promoting output power, but unfavorable on energy conversion efficiency. More important, the boundary slip greatly enhances the output power and energy conversion efficiency, leading to a maximum output power and energy conversion efficiency is 2.7 pW and 30%, respectively. As a proof of concept, this work shows the distinct deviation in power generation in ion nanochannel with the constant and dependent physical property, providing the useful information to guide the design of real fluidic energy devices.

Synergistic Effect of Electrostatic Interaction and Ionic Dehydration on Asymmetric Ion Transport in Nanochannel/Ion Channel Composite Membrane.

Ion transport in nanochannels of a size comparable to that of hydrated ions exhibits unique properties due to the synergistic effect of various forces. Here, we design a nanochannel/ion channel composite (NIC) membrane that shows a high ion current rectification (ICR) ratio in different electrolytes. Experimental and theoretical results demonstrate that the synergistic effect of electrostatic interaction and ionic dehydration plays an important role in regulating the ICR behavior of the NIC membrane. We find that electrostatic attraction between ions and the channel surface in the ultraconfined space increases the probability of ionic dehydarion, resulting in different dehydration energy costs for different ions. This further alters the driving force for ion transport and thus regulates ICR of the NIC membrane. This work provides fundamental knowledge of ion transport in ion channels, which aids in the understanding of the function of biological systems and the design of high-performance nanochannel devices.

Chemically Converted Graphene Nanosheets for the Construction of Ion-Exclusion Nanochannel Membranes.

Water and ion transport in nanochannels is an intriguing topic that has been extensively investigated in several energy- and environment-related research fields. Recently developed two-dimensional (2D) materials are ideal building blocks for constructing confined nanochannels by self-stacking. Among these, graphene oxide (GO) is the most frequently employed as the starting material because of its excellent solution processability. Since solvation of the GO nanostructure usually impairs the function of nanochannels, in this study, chemically converted graphene was prepared using a one-step method, to simultaneously acquire the desired stability and functionality of the nanochannels. The confined channels with high charge densities are capable of excluding ∼90% NaCl solutes from water in a pressure-driven filtration process. This surpasses the performance of most GO desalination membranes reported in the literature. Thus, this study provides useful information for the feasible development of ion-exclusion nanochannel membranes based on the proposed nanochannel-confined charge repulsion mechanism.

Electrowetting-Mediated Transport to Produce Electrochemical Transistor Action in Nanopore Electrode Arrays.

Understanding water behavior in confined volumes is important in applications ranging from water purification to healthcare devices. Especially relevant are wetting and dewetting phenomena which can be switched by external stimuli, such as light and electric fields. Here, these behaviors are exploited for electrochemical processing by voltage-directed ion transport in nanochannels contained within nanopore arrays in which each nanopore presents three electrodes. The top and middle electrodes (TE and ME) are in direct contact with the nanopore volume, but the bottom electrode (BE) is buried beneath a 70 nm silicon nitride (SiNx ) insulating layer. Electrochemical transistor operation is realized when small, defect-mediated channels are opened in the SiNx . These defect channels exhibit voltage-driven wetting that mediates the mass transport of redox species to/from the BE. When BE is held at a potential maintaining the defect channels in the wetted state, setting the potential of ME at either positive or negative overpotential results in strong electrochemical rectification with rectification factors up to 440. By directing the voltage-induced electrowetting of defect channels, these three-electrode nanopore structures can achieve precise gating and ion/molecule separation, and, as such, may be useful for applications such as water purification and drug delivery.

Influence factors of thermal driven ion transport in nano-channel for thermoelectricity application

Many attentions have been paid on discussing isothermal transport in electrolyte-filled wall-charged nano-pores or nano-channels, while the non-isothermal transport has been scarcely considered before. In this work, a calculation model based on Poisson–Nernst–Planck equation is established to describe the thermal driven ion transport in nano-channels. The effects of different influence factors on the ion transport is carefully studied, including effects of the temperature difference across nano-channel, the ion concentration, the half-width of nano-channel, and the length of nano-channel. Results turn out that: performances of nano-channel batteries can be classified and simplified by using characteristic parameters and ion concentrations; the ion concentration of about 1 mol•m−3 and the nano-channel half width (h) of about 1 nm is optimal for thermoelectricity applications, and if the optimal nano-channel length of about 85 h and the optimal temperature difference of about 85 K are further applied, the thermally induced power of the system can be maximized. This study is expected to supply some information for designing a nano-channels system with high thermos-electric energy conversion efficiencies.

Regulating Ion Transport in a Nanochannel with Tandem and Parallel Structures via Concentration Polarization

The unique phenomena of ion selectivity and ion current rectification (ICR) in nanofluidics have been widely used to construct bioinspired channels and organs, sensors, and power generators. However, the excellent performance of a single nanochannel does not show a linear increase when it is scaled up into multiple nanochannels in tandem and parallel structure, and in some cases, it even shows a reverse trend. Understanding of this scaling-up inconsistency in nanofluidics is essential to the design of functional devices. Here, we provide a method for investigating the ion transport properties in multiple nanochannels in tandem and parallel connections. We find that interfacial resistance caused by ion concentration polarization (ICP) in tandem and parallel nanochannels has a significant impact on ICR, showing a nonlinear scaling-up feature with the tandem number and a decreased trend with the parallel number, which is not expected in electronic devices. We further verify that it is feasible to regulate ion transport in tandem and parallel nanochannels by adding gap distances between nanochannels in tandem and parallel structures to decouple the ICP region between nanochannels. This study provides fundamental insights into the ion transport properties in nanofluidic circuits, which hold promise for the design of high-performance nanofluidic devices in the fields of separation, energy, and sensors.

Electrical Field Regulation of Ion Transport in Polyethylene Terephthalate Nanochannels.

Rectified ion transport in nanochannels is the basis of ion channels in biological cells and has inspired emerging nanochannel applications in ion separation, Coulter counters, and biomolecule detection and nanochannel energy harvesters. In this work we fabricated a polyethylene terephthalate (PET) conical nanochannel using latent ion track etching technique and then systematically studied the ion transport and influence of cation species on the nanochannel surface with cyclic I-V measurement. We discovered the electrical regulation of the reversible and irreversible modification of the nanochannel transportation by bivalent and trivalent cations, revealing the existence of the switching threshold voltage which can control the current rectification in bivalent solution. The proposed mechanism of the transport state transition in the PET nanochannel mimics behaviors of voltage-gated biological ion channels. These findings provide new insight into the understanding of the ion channel signaling and translocation control of charged particles in nanochannel applications.

Dynamic Curvature Nanochannel-Based Membrane with Anomalous Ionic Transport Behaviors and Reversible Rectification Switch.

Biological nanochannels control the movements of different ions through cell membranes depending on not only those channels' static inherent configurations, structures, inner surface's physicochemical properties but also their dynamic shape changes, which are required in various essential functions of life processes. Inspired by ion channels, many artificial nanochannel-based membranes for nanofluidics and biosensing applications have been developed to regulate ionic transport behaviors by using the functional molecular modifications at the inner surface of nanochannel to achieve a stimuli-responsive layer. Here, the concept of a dynamic nanochannel system is further developed, which is a new way to regulate ion transport in nanochannels by using the dynamic change in the curvature of channels to adjust ionic rectification in real time. The dynamic curvature nanochannel-based membrane displays the advanced features of the anomalous effect of voltage, concentration, and ionic size for applying simultaneous control over the curvature-tunable asymmetric and reversible ionic rectification switching properties. This dynamic approach can be used to build smart nanochannel-based systems, which have strong implications for flexible nanofluidics, ionic rectifiers, and power generators.

Bio-inspired temporal regulation of ion-transport in nanochannels.

Temporal regulation of mass transport across the membrane is a vital feature of biological systems. Such regulatory mechanisms rely on complex biochemical reaction networks, often operating far from equilibrium. Herein, we demonstrate biochemical reaction mediated temporal regulation of mass transport in nanochannels of mesoporous silica sphere. The rationally designed nanochannels with pH responsive electrostatic gating are fabricated through a hetero-functionalization approach utilizing propylamine and carboxylic acid moieties. At basic pH, cationic small molecules can diffuse into the nanochannels which release back to the solution at acidic pH. The transient ion transport is temporally controlled using a base as fuel along with esterase enzyme as the mediator. The slow enzymatic hydrolysis of a dormant deactivator (ethyl acetate) determines the lifetime of transient encapsulated state, which can be programmed easily by modulating the enzymatic activity of esterase. This system represents a unique approach to create autonomous artificial cellular models.

Flexible, Bio-Compatible Nanofluidic Ion Conductor

Ion transport in nanochannels has unique behaviors such as charge selectivity and high ionic conductivity. Due to their simple structure, the photolithographic nanochannels have been widely used to understand the fundamentals of nanofluidic ion transport. However, for practical applications, especially biorelated applications, a scalable, flexible, mechanically stable, and biocompatible nanofluidic device engineered with charge selectivity and high ionic conductivity is more desirable. Herein, we report a scalable biomass material, namely, bacterial cellulose (BC), with excellent mechanical strength, flexibility, and biocompatibility for nanofluidic ion transport. The BC film is a 3-dimensional (3D) interconnected network of 10–30 nm thick cellulose nanofibers, containing 1–2 nm nanochannels with large negatively charged surface groups. After a facile TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation treatment, the zeta potential of the cellulose nanofibers significantly improves from −13 mV ...

Enzyme Catalysis Induced Polymer Growth in Nanochannels: A New Approach to Regulate Ion Transport and to Study Enzyme Kinetics in Nanospace

AbstractMethod that could regulate the ion transport in nanochannel in an efficient and rapid manner is still a challenge. Here, we introduced enzyme‐catalysis‐induced polymer growth in nanochannels to develop a new method to regulate the ion transport and evaluate the enzyme catalysis kinetics in nano‐space. As a model enzyme, Horseradish peroxidase (HRP) was immobilized in the nanochannels through a volume‐controlled‐drying method. In the presence of H2O2, HRP catalyzed o‐phenylenediamine (o‐PD) to trigger its polymer growth, in turn blocked the ion transport and led to the decrease of the ion current. Taking advantages of the high efficiency of enzyme catalysis and the nano‐confinement of nanochannels, the system readily achieved blocking ratios of ion current even reaching 99.6 % of the initial. Based on above concept, we developed a new method to evaluate the enzyme catalysis kinetics in nano‐confined space. By comparing with those in free state in solution and absorbed on planar surface, HRP confined in nanochannels presented similar apparent Michaelis constant (Km) values for the substrate H2O2 but much higher Km values for the substrate o‐PD, due to the steric hindrance and diffusion suppression. The enzyme‐catalysis‐induced polymerization in nanochannels might lead to new concept for the nano‐blocking/switching and provide a new platform for single molecule analysis and detection.

Gated Water Transport through Graphene Nanochannels: From Ionic Coulomb Blockade to Electroosmotic Pump

Understanding and controlling water or ion transport in nanochannels plays an important role in further unravelling the transport mechanism of biological membrane channels and designing functional nanofluidic devices. Molecular dynamics simulations were conducted to investigate water and ion transport in graphene nanochannels. Similar to electron coulomb blockade phenomenon observed in quantum dots, we discovered an ionic coulomb blockade phenomenon in our graphene nanochannels, and another two ion transport modes were also proposed to rationalize the observed phenomena under different electric-field intensities. Furthermore, on the basis of this blockade phenomenon we found that the Open and Closed states of the graphene nanochannels for water transport could be switched according to external electric-field intensities, and electroosmotic flow could further enhance the water transport. These findings might have potential applications in designing and fabricating controllable valves in lab-on-chip nanodev...

Exact solutions and physical analogies for unidirectional flows

Unidirectional flow is the simplest phenomenon of fluid mechanics. Its mathematical description, the Dirichlet problem for Poisson's equation in two dimensions with constant forcing, arises in many physical contexts, such as the torsion of elastic beams, first solved by de Saint-Venant for complex shapes. Here, the literature is unified and extended by identifying seventeen physical analogies for unidirectional flow and describing their common mathematical structure. Besides classical analogies in fluid and solid mechanics, applications are discussed in stochastic processes (first passage in two dimensions), pattern formation (river growth by erosion), and electrokinetics (ion transport in nanochannels), which also involve Poisson's equation with non-constant forcing. Methods are given to construct approximate geometries that admit exact solutions, by adding harmonic functions to quadratic forms or by truncating eigenfunction expansions. Exact solutions for given geometries are also derived by conformal mapping. We prove that the remarkable geometrical interpretation of Poiseuille flow in an equilateral triangular pipe (the product of the distances from an interior point to the sides) is only shared by parallel plates and unbounded equilateral wedges (with the third side hidden behind the apex). We also prove Onsager reciprocity for linear electrokinetic phenomena in straight pores of arbitrary shape and surface charge, based on the mathematics of unidirectional flow.