Biomimetic multifunctional nanochannels based on the asymmetric wettability of heterogeneous nanowire membranes

In-Situ Gas Permeation-Driven Ionic Current Rectification of Heterogeneously Charged Nanopore Arrays

Ionic diodes provide ionic current rectification (ICR), which is useful for micro-/nanofluidic devices for ionic current-mediated applications. However, the modulation of ICR is not fully developed, and current challenges include limited active control and localized modulation for further multiplexing of micro-/nanofluidic ionic diodes. Herein, a microfluidic device integrated with particle-assembly-based ionic diodes (PAIDs) and a gas-flow channel above them is presented. Exploiting in-situ gas permeation through a polymeric film, precise control over the physiochemical conditions of the nanopores within the PAIDs, leading to the modulation of ICR is demonstrated. The investigation not only characterizes the rectification properties of the PAIDs but also unveils their capacitor-like behavior and the ability to actively modulate ICR using various gas flows. Furthermore, the reversible modulation of ICR through dynamic switching of gas-dissolved solutions, enabling ion-signal amplification is showcased. This pioneering approach of in situ gas-permeation offers programmable manipulation of ion transport along PAIDs, thereby positioning ionic diodes as versatile nanofluidic components. Looking ahead, the development of multiplexed PAIDs in an addressable manner on a chip holds promise for practical applications across diverse fields, including ion signaling, ion-based logic, chemical reactors, and (bio)chemical sensing.

Nanoarchitectonics for Electrospun Membranes with Asymmetric Wettability

Membranes with asymmetric wettability have attracted significant interest by virtue of their unique transport characteristics and functionalities arising from different wetting behaviors of each membrane surface. The cross-sectional wettability distinction enables a membrane to realize directional liquid transport or multifunction integration, resulting in rapid advance in applications, such as moisture management, fog collection, oil-water separation, and membrane distillation. Compared with traditional homogeneous membranes, these membranes possess enhanced transport performance and higher separation efficiency owing to the synergistic or individual effects of asymmetric wettability. This Review covers the recent progress in fabrication, transport mechanisms, and applications of electrospun membranes with asymmetric wettability and provides a perspective on future development in this important area.

Anisotropic Janus materials: from micro-/nanostructures to applications

Janus materials have led to great achievements in recent years owing to their unique asymmetric structures and properties. In this review, recent advances of Janus materials including Janus particles and Janus membranes are summarized, and then the microstructures and applications of Janus materials are emphasized. The asymmetric wettability of Janus materials is related to their microstructures; hence, the microstructures of Janus materials were analyzed, compared and summarized. Also presented are current and potential applications in sensing, drug delivery, oil-water separation and so on. Finally, a perspective on the research prospects and development of Janus materials in more fields is given.

Interfacial Super-Assembly of Ordered Mesoporous Carbon-Silica/AAO Hybrid Membrane with Enhanced Permselectivity for Temperature- and pH-Sensitive Smart Ion Transport

Nanofluidic devices have been widely used for diode-like ion transport and salinity gradients energy conversion. Emerging reverse electrodialysis (RED) nanofluidic systems based on nanochannel membrane display great superiority in salinity gradient energy harvesting. However, the imbalance between permeability and selectivity limits their practical application. Here, a new mesoporous carbon-silica/anodized aluminum (MCS/AAO) nanofluidic device with enhanced permselectivity for temperature- and pH-regulated energy generation was obtained by interfacial super-assembly method. A maximum power density of 5.04 W m^-2 is achieved, and a higher performance can be obtained by regulating temperature and pH. Theoretical calculations are further implemented to reveal the mechanism for ion rectification, ion selectivity and energy conversion. Results show that the MCS/AAO hybrid membrane has great superiority in diode-like ion transport, temperature- and pH-regulated salinity gradient energy conversion.

Roles of energy dissipation and asymmetric wettability in spontaneous imbibition dynamics in a nanochannel

HYPOTHESIS

The imbibition dynamics is controlled by energy dissipation mechanisms and influenced by asymmetric wettability in a nanochannel. We hypothesize that the imbibition dynamics can be described by a combined model of the Lucas-Washburn equation and the Cox-Voinov law considering velocity-dependent contact angles.

METHODS

Molecular dynamics simulations are utilized to investigate the imbibition dynamics. A wide range of wetting conditions is achieved via adjusting the liquid-solid interaction parameters, and the spontaneous imbibition processes are quantified and compared.

FINDINGS

The critical condition for the occurrence of spontaneous imbibition is analyzed from a surface energy perspective. The analyses of energy conversion and dissipation indicate that the viscous dissipation is dominant during spontaneous imbibition. The classical Lucas-Washburn equation is modified with the Cox-Voinov law considering the effect of the dynamic contact angle and an effective equilibrium contact angle. We show that the proposed theory well captures the imbibition dynamics embodied in the growth of imbibition length as well as the transient interface shape and velocity for both the symmetric and asymmetric wetting conditions. In nanochannels with asymmetric wettability, the imbibition length difference between the sidewalls and interface oscillations increases with wetting disparity. Our findings deepen the understanding of imbibition dynamics on the nanoscale, and provide a theoretical reference for relevant applications.

Miniaturized Salinity Gradient Energy Harvesting Devices

Harvesting salinity gradient energy, also known as "osmotic energy" or "blue energy", generated from the free energy mixing of seawater and fresh river water provides a renewable and sustainable alternative for circumventing the recent upsurge in global energy consumption. The osmotic pressure resulting from mixing water streams with different salinities can be converted into electrical energy driven by a potential difference or ionic gradients. Reversed-electrodialysis (RED) has become more prominent among the conventional membrane-based separation methodologies due to its higher energy efficiency and lesser susceptibility to membrane fouling than pressure-retarded osmosis (PRO). However, the ion-exchange membranes used for RED systems often encounter limitations while adapting to a real-world system due to their limited pore sizes and internal resistance. The worldwide demand for clean energy production has reinvigorated the interest in salinity gradient energy conversion. In addition to the large energy conversion devices, the miniaturized devices used for powering a portable or wearable micro-device have attracted much attention. This review provides insights into developing miniaturized salinity gradient energy harvesting devices and recent advances in the membranes designed for optimized osmotic power extraction. Furthermore, we present various applications utilizing the salinity gradient energy conversion.

Improved osmotic energy conversion in heterogeneous membrane boosted by three-dimensional hydrogel interface

The emerging heterogeneous membranes show unprecedented superiority in harvesting the osmotic energy between ionic solutions of different salinity. However, the power densities are limited by the low interfacial transport efficiency caused by a mismatch of pore alignment and insufficient coupling between channels of different dimensions. Here we demonstrate the use of three-dimensional (3D) gel interface to achieve high-performance osmotic energy conversion through hybridizing polyelectrolyte hydrogel and aramid nanofiber membrane. The ionic diode effect of the heterogeneous membrane facilitates one-way ion diffusion, and the gel layer provides a charged 3D transport network, greatly enhancing the interfacial transport efficiency. When used for harvesting the osmotic energy from the mixing of sea and river water, the heterogeneous membrane outperforms the state-of-the-art membranes, to the best of our knowledge, with power densities of 5.06 W m^-2. The diversity of the polyelectrolyte and gel makes our strategy a potentially universal approach for osmotic energy conversion.

A high rectification ratio nanofluidic diode induced by an “ion pool”

Inspired by functionalized biological ion channels, artificial channels were prepared to mimic the natural ones. The key concept behind the rectifying phenomena in nanochannels is the construction of asymmetric restrictive nanochannels. Here, we prepared nanoporous oxidized polyvinyl alcohol (PVA) and WO₃ composite coatings on hourglass-shaped anodic aluminum oxide (AAO) nanochannel surfaces. Accordingly, a special “ion pool” is formed between the homogeneous junction in the middle of the AAO and the nanoporous PVA/WO₃ film-covered AAO surface and its two ends are greatly nano-confined. Ion enrichment and ion depletion occur in the “ion pool” and are dependant on the applied voltage polarity. A rectification ratio of 458, which is in accordance with the highest value found in previous reports, was obtained from the cooperative effects of the two small open ends of the “ion pool”. Furthermore, this value is enhanced to about 2000 under constant voltage. An excellent pH-sensitive rectification property, with a single rectification direction from acidic to basic conditions, has also been demonstrated.

Nanoporous polyvinyl alcohol (PVA)/WO₃ composite coatings were prepared onto the hourglass-shaped AAO nanochannels surface, and an “ion pool” is formed. A rectification ratio of 2000 was obtained with constant voltage enhancement.

Engineering Smart Nanofluidic Systems for Artificial Ion Channels and Ion Pumps: From Single-Pore to Multichannel Membranes

Biological ion channels and ion pumps with intricate ion transport functions widely exist in living organisms and play irreplaceable roles in almost all physiological functions. Nanofluidics provides exciting opportunities to mimic these working processes, which not only helps understand ion transport in biological systems but also paves the way for the applications of artificial devices in many valuable areas. Recent progress in the engineering of smart nanofluidic systems for artificial ion channels and ion pumps is summarized. The artificial systems range from chemically and structurally diverse lipid-membrane-based nanopores to robust and scalable solid-state nanopores. A generic strategy of gate location design is proposed. The single-pore-based platform concept can be rationally extended into multichannel membrane systems and shows unprecedented potential in many application areas, such as single-molecule analysis, smart mass delivery, and energy conversion. Finally, some present underpinning issues that need to be addressed are discussed.

Biomolecule-Functionalized Solid-State Ion Nanochannels/Nanopores: Features and Techniques

Solid-state ion nanochannels/nanopores, the biomimetic products of biological ion channels, are promising materials in real-world applications due to their robust mechanical and controllable chemical properties. Functionalizations of solid-state ion nanochannels/nanopores by biomolecules pave a wide way for the introduction of varied properties from biomolecules to solid-state ion nanochannels/nanopores, making them smart in response to analytes or external stimuli and regulating the transport of ions/molecules. In this review, two features for nanochannels/nanopores functionalized by biomolecules are abstracted, i.e., specificity and signal amplification. Both of the two features are demonstrated from three kinds of nanochannels/nanopores: nucleic acid-functionalized nanochannels/nanopores, protein-functionalized nanochannels/nanopores, and small biomolecule-functionalized nanochannels/nanopores, respectively. Meanwhile, the fundamental mechanisms of these combinations between biomolecules and nanochannels/nanopores are explored, providing reasonable constructs for applications in sensing, transport, and energy conversion. And then, the techniques of functionalizations and the basic principle about biomolecules onto the solid-state ion nanochannels/nanopores are summarized. Finally, some views about the future developments of the biomolecule-functionalized nanochannels/nanopores are proposed.

Janus Membranes: Creating Asymmetry for Energy Efficiency

Membranes are recognized as a key component in many environment and energy-related applications, but conventional membranes are challenged to satisfy the growing demand for ever more energy-efficient processes. Janus membranes, a novel class with asymmetric properties on each side, have recently emerged and represent enticing opportunities to address this challenge. With an inner driving force arising from their asymmetric configuration, Janus membranes are appealing for enhancing energy efficiency in a variety of membrane processes by promoting the desired transport. Here, the fundamental principles to prepare Janus membranes with asymmetric surface wettability and charges are summarized, and how they work in conventional and unconventional membrane processes is demonstrated.

Robust Sandwich-Structured Nanofluidic Diodes Modulating Ionic Transport for an Enhanced Electrochromic Performance

Biomimetic solid-state nanofluidic diodes have attracted extensive research interest due to the possible applications in various fields, such as biosensing, energy conversion, and nanofluidic circuits. However, contributions of exterior surface to the transmembrane ionic transport are often ignored, which can be a crucial factor for ion rectification behavior. Herein, a rational design of robust sandwich-structured nanofluidic diode is shown by creating opposite charges on the exterior surfaces of a nanoporous membrane using inorganic oxides with distinct isoelectric points. Potential-induced changes in ion concentration within the nanopores lead to a current rectification; the results are subsequently supported by a theoretical simulation. Except for providing surface charges, functional inorganic oxides used in this work are complementary electrochromic materials. Hence, the sandwich-structured nanofluidic diode is further developed into an electrochromic membrane exhibiting a visual color change in response to redox potentials. The results show that the surface-charge-governed ionic transport and the nanoporous structure facilitate the migration of Li+ ions, which in turn enhance the electrochromic performance. It is envisioned that this work will create new avenues to design and optimize nanofluidic diodes and electrochromic devices.

BiFACIAL ( Biomimetic Freestanding Anisotropic Catechol- Interfaces with Asymmetrically Layered) Films as Versatile Extracellular Matrix Substitutes

Biological naïve extracellular matrices (ECMs) exhibit anisotropic functions in their physical, chemical, and morphological properties. Representative examples include anisotropic skin layers or blood vessels simultaneously facing multiphasic environments. Here, anisotropically multifunctional structures called BiFACIAL ( biomimetic freestanding anisotropic catechol- interfaces with asymmetrically layered) films were developed simply by contacting two polysaccharide solutions of heparin-catechol (Hep-C) and chitosan-catechol (Chi-C). Such anisotropic characters were due to controlling catechol cross-linking by alkaline pH, resulting in a trimodular structure: a rigid yet porous Hep-C exterior, nonporous interfacial zone, and soft/highly porous Chi-C interior. The anisotropic features of each layer, including the porosity, rigidity, rheology, composition, and ionic strength, caused the BiFACIAL films to show spontaneously biased stimuli responses and differential behaviors against biological substances (e.g., blood plasma). The films could be created in situ in live animals and imitated the structural/functional aspects of the representative anisotropic tissues (e.g., skin and blood vessels), providing valuable ECM-like platforms for the creation of favorable environments or for tissue regeneration or disease treatment by effectively manipulating cellular behaviors.

Bioinspired smart asymmetric nanochannel membranes

Bioinspired smart asymmetric nanochannel membranes (BSANM) have been explored extensively to achieve the delicate ionic transport functions comparable to those of living organisms. The abiotic system exhibits superior stability and robustness, allowing for promising applications in many fields. In view of the abundance of research concerning BSANM in the past decade, herein, we present a systematic overview of the development of the state-of-the-art BSANM system. The discussion is focused on the construction methodologies based on raw materials with diverse dimensions (i.e. 0D, 1D, 2D, and bulk). A generic strategy for the design and construction of the BSANM system is proposed first and put into context with recent developments from homogeneous to heterogeneous nanochannel membranes. Then, the basic properties of the BSANM are introduced including selectivity, gating, and rectification, which are associated with the particular chemical and physical structures. Moreover, we summarized the practical applications of BSANM in energy conversion, biochemical sensing and other areas. In the end, some personal opinions on the future development of the BSANM are briefly illustrated. This review covers most of the related literature reported since 2010 and is intended to build up a broad and deep knowledge base that can provide a solid information source for the scientific community.

Highly Efficient Gating of Electrically Actuated Nanochannels for Pulsatile Drug Delivery Stemming from a Reversible Wettability Switch

Many ion channels in the cell membrane are believed to function as gates that control the water and ion flow through the transitions between an inherent hydrophobic state and a stimuli-induced hydration state. The construction of nanofluidic gating systems with high gating efficiency and reversibility is inspired by this hydrophobic gating behavior. A kind of electrically actuated nanochannel is developed by integrating a polypyrrole (PPy) micro/nanoporous film doped with perfluorooctanesulfonate ions onto an anodic aluminum oxide nanoporous membrane. Stemming from the reversible wettability switch of the doped PPy film in response to the applied redox potentials, the nanochannels exhibit highly efficient and reversible gating behaviors. The optimized gating ratio is over 10⁵ , which is an ultrahigh value when compared with that of the existing reversibly gated nanochannels with comparable pore diameters. Furthermore, the gating behavior of the electrically actuated nanochannels shows excellent repeatability and stability. Based on this highly efficient and reversible gating function, the electrically actuated nanochannels are further applied for drug delivery, which achieves the pulsatile release of two water-soluble drug models. The electrically actuated nanochannels may find potential applications in accurate and on-demand drug therapy.

Nanochannels as molecular check valves

A molecular check valve is a nanomachine that enables unidirectional molecular transport. In this work, we report a novel molecular check valve fabricated by asymmetric modification of a silica nanoporous membrane (SNM) consisting of parallel nanochannels with a diameter of 2-3 nm. Asymmetric modification refers to the thermal deposition of hydrophobic polydimethylsiloxane (PDMS) only on one side of the SNM to generate hydrophobic nanoorifices. Such an asymmetric nanostructure, designated as PDMS-SNM, could synergistically exert a hydrophobic force on the molecules by PDMS nanoorifices and an electrostatic force by naked silica nanochannels, resulting in unidirectional molecular transport under specific circumstances. Typically, only positively charged molecules were able to transport across the PDMS-SNM from the PDMS nanoorifice side, while backward transport from the other side was prohibited. In the former case, positively charged molecules were subject to electrostatic attraction from naked silica channels, which could exceed the hydrophobic rejection from PDMS nanoorifices to pull the molecule across the PDMS-SNM. However, in the latter case the electrostatic attraction is no longer a driving force to overcome the hydrophobic rejection from PDMS nanoorifices to promote the molecular transport. On the other hand, the PDMS-SNM based molecular check valve can be shut down to prevent any molecular transport from either side of the PDMS-SNM under certain conditions, such as a high salt concentration or an appropriate pH (e.g., pH 3). We believe that it could be applied to convert natural fluctuation energy into directed motion, as well as to prevent backward transport in batteries and fuel cells.

3D Porous Hydrogel/Conducting Polymer Heterogeneous Membranes with Electro-/pH-Modulated Ionic Rectification

Heterogeneous membranes composed of asymmetric structures or compositions have enormous potential in sensors, molecular sieves, and energy devices due to their unique ion transport properties such as ionic current rectification and ion selectivity. So far, heterogeneous membranes with 1D nanopores have been extensively studied. However, asymmetric structures with 3D micro-/nanoscale pore networks have never been investigated. Here, a simple and versatile approach to low-costly fabricate hydrogel/conducting polymer asymmetric heterogeneous membranes with electro-/pH-responsive 3D micro-/nanoscale ion channels is introduced. Due to the asymmetric heterojunctions between positively charged nanoporous polypyrrole (PPy) and negatively charged microscale porous hydrogel poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)), the membrane can rectify ion transmembrane transport in response to both electro- and pH-stimuli. Numerical simulations based on coupled Poisson and Nernst-Plank equations are carried out to explain the ionic rectification mechanisms for the membranes. The membranes are not dependent on elaborately fabricated 1D ion channel substrates and hence can be facilely prepared in a low-cost and large-area way. The hybridization of hydrogel and conducting polymer offers a novel strategy for constructing low-cost, large-area and multifunctional membranes, expanding the tunable ionic rectification properties into macroscopic membranes with micro-/nanoscale pores, which would stimulate practical applications of the membranes.

Biomimetic Voltage-Gated Ultrasensitive Potassium-Activated Nanofluidic Based on a Solid-State Nanochannel

In living organism, voltage-gated potassium channels play a crucial role and are largely responsible for various vital movements. For life science, it is significant and challenging to imitate and control the potassium ion transportation with a convenient artificial system. Here, we reported a voltage-gated ultrasensitive potassium-activated nanofluidic system using a 4'-aminobenzo-18-crown-6 molecule-functionalized funnel-shaped solid-state nanochannel. The switchlike property between open and closed states can be tuned freely by reversible immobilization and the release of potassium ions. By virtue of good reversibility and excellent stability, this system can potentially be applied in controlled drug release and biosensors.

Sequential Vapor Infiltration Treatment Enhances the Ionic Current Rectification Performance of Composite Membranes Based on Mesoporous Silica Confined in Anodic Alumina

Ionic current rectification of nanofluidic diode membranes has been studied widely in recent years because it is analogous to the functionality of biological ion channels in principle. We report a new method to fabricate ionic current rectification membranes based on mesoporous silica confined in anodic aluminum oxide (AAO) membranes. Two types of mesostructured silica nanocomposites, hexagonal structure and nanoparticle stacked structure, were used to asymmetrically fill nanochannels of AAO membranes by a vapor-phase synthesis (VPS) method with aspiration approach and were further modified via sequence vapor infiltration (SVI) treatment. The ionic current measurements indicated that SVI treatment can modulate the asymmetric ionic transport in prepared membranes, which exhibited clear ionic current rectification phenomenon under optimal conditions. The ionic current rectifying behavior is derived from the asymmetry of surface conformations, silica species components, and hydrophobic wettability, which are created by the asymmetrical filling type, silica depositions on the heterogeneous membranes, and the condensation of silanol groups. This article provides a considerable strategy to fabricate composite membranes with obvious ionic current rectification performance via the cooperation of the VPS method and SVI treatment and opens up the potential of mesoporous silica confined in AAO membranes to mimic fluid transport in biological processes.

Gated Molecular Transport in Highly Ordered Heterogeneous Nanochannel Array Electrode

In biology, all protein channels share a common feature of containing narrow pore regions with hydrophobic functional groups and selectivity filter regions abundant with charged residues, which work together to account for fast and selective mass transport in and out of cells. In this work, an ultrathin layer of polydimethylsiloxane (PDMS) was evaporated on the top orifices of charged silica nanochannels (2-3 nm in diameter and 60 nm in length) vertically attached to the electrode surface, and the resulting structure is designated as heterogeneous silica nanochannels (HSNs). As evidenced by voltammetric studies, the transport of ionic species in these HSNs was controlled by both hydrophobic rejection and electrostatic force arising from the top PDMS layer and from the bottom silica nanochannels, respectively. Anionic species encountered both hydrophobic rejection and electrostatic repulsion forces, and thus, their transport was strongly prohibited, while the transport of cationic species was permitted once the electrostatic attraction exceeded the hydrophobic rejection. Moreover, the magnitude of hydrophobic force could be regulated by the PDMS layer thickness, and that of the electrostatic force can be modulated by the salt concentration, solution pH, or applied voltage. It was demonstrated that the HSNs could be activated from an OFF state (no ion can transport) to an ON state (only cation transport occurs) by decreasing the salt concentration, increasing the solution pH, or applying negative voltages.

Asymmetric Multifunctional Heterogeneous Membranes for pH- and Temperature-Cooperative Smart Ion Transport Modulation

Asymmetric multifunctional heterogeneous membranes are demonstrated by combing a block copolymer polystyrene-block-poly(N,N-dimethylaminoethylmethacrylate) membrane with a track-etched porous poly(ethylene terephthalate) membrane. This hybrid membrane is capable of integrating pH- and temperature-cooperative high-performance ionic rectification, highly efficient cation gating, and excellent stability and controllability, which allows broad application in biosensing, energy conversion, and filtration.

"Uphill" cation transport: A bioinspired photo-driven ion pump

Biological ion pumps with active ionic transport properties lay the foundation for many life processes. However, few analogs have been produced because extra energy is needed to couple to this "uphill" process. We demonstrate a bioinspired artificial photo-driven ion pump based on a single polyethylene terephthalate conical nanochannel. The pumping process behaving as an inversion of zero-volt current can be realized by applying ultraviolet irradiation from the large opening. The light energy can accelerate the dissociation of the benzoic acid derivative dimers existing on the inner surface of nanochannel, which consequently produces more mobile carboxyl groups. Enhanced electrostatic interaction between the ions traversing the nanochannel and the charged groups on the inner wall is the key reason for the uphill cation transport behavior. This system creates an ideal experimental and theoretical platform for further development and design of various stimuli-driven and specific ion-selective bioinspired ion pumps, which anticipates wide potential applications in biosensing, energy conversion, and desalination.

Smart Gating Multi-Scale Pore/Channel-Based Membranes

Smart gating membranes are important and promising in membrane science and technology. Rapid progress in developing smart membranes is transforming technology in many different fields, from energy and environmental to the life sciences. How a specific smart behavior for controllable gating of porous membranes can be obtained, especially for nano- and micrometer-sized multi-scale pore/channel-based membrane systems is addressed.

Biomimetic Solid-State Nanochannels: From Fundamental Research to Practical Applications

In recent years, solid-state smart nanopores/nanochannels for intelligent control of the transportation of ions and molecules as organisms have been extensively studied, because they hold great potential applications in molecular sieves, nanofluidics, energy conversion, and biosensors. To keep up with the fast development of this field, it is necessary to summarize the construction, characterization, and application of biomimetic smart nanopores/nanochannels. These can be classified into four sections: the fabrication of solid-state nanopores/nanochannels, the functionalization methods and materials, the mechanism explanation about the ion rectification, and the practical applications. A brief conclusion and outlook for the biomimetic nanochannels is provided, highlighting those that could be developed and integrated into devices for use in tackling current and the future problems including resources, energy, environment, and health.

A Biomimetic Voltage-Gated Chloride Nanochannel

A novel biomimetic voltage-gated chloride nanochannel is described. This artificial nanochannel can realize reversible switching between the "on" and "off" states upon addition and removal of Cl(-) and can realize the selective and directional transport of Cl(-) driven by voltage. Moreover, it also has high sensitivity, good selectivity, responsive switchability, and good stability.

Colloidal Synthesis of Lettuce-like Copper Sulfide for Light-Gating Heterogeneous Nanochannels

Lettuce-like CuxS micron particles were successfully prepared by a colloidal hot-injection method, and the preliminary evaluation of the light-gating artificial ionic nanochannels designed using these particles was also demonstrated. A likely underlying mechanism behind the formation of the lettuce architecture was tentatively proposed via monitoring the evolution process. These particles are hydrophobic and possess a high surface area that can readily absorb the light-responsive 1,3,3-trimethylindolino-6'-nitrobenzopyrylospiran (Spiro) molecules. Finally, the heterogeneous nanochannels were constructed by spin-coating the preprepared CuxS particles loaded with Spiro onto the commercially available anodic alumina (AAO) substrate. The AAO-CuxS/Spiro heterogeneous nanochannels "close" under illumination of ultraviolet light (365 nm) and then "open" by visible light irradiation, which exhibits a regulated ionic transport property with good responsive switchability and stability.

A Bioinspired Multifunctional Heterogeneous Membrane with Ultrahigh Ionic Rectification and Highly Efficient Selective Ionic Gating

A bioinspired multifunctional heterogeneous membrane composed of a block copolymer (PS-b-P4VP) membrane and a porous anodic alumina membrane is fabricated. The ionic rectification is so strong that the maximum ratio is ≈489, and the chemical actuation of the anion or cation gate from the "OFF" to the "ON" state promotes a 98.5% increase in the channel conductance.

pH- and light-regulated ion transport in hourglass shaped Al2O3 nanochannels patterned with N719 and APTES

An investigation of the pH- and light-regulated ion rectification properties of symmetric and asymmetric Al₂O₃ nanochannels patterned with N719 and APTES at designated positions.

Fabrication of hydrogel-coated single conical nanochannels exhibiting controllable ion rectification characteristics

Herein, we report novel, interesting hydrogel-composited nanochannel devices with regulatable ion rectification characteristics.