Ionic Circuits Research Articles

Photosensitive ion channels in layered MXene membranes modified with plasmonic gold nanostars and cellulose nanofibers

Ion channels transduce external stimuli into ion-transport-mediated signaling, which has received considerable attention in diverse fields such as sensors, energy harvesting devices, and desalination membrane. In this work, we present a photosensitive ion channel based on plasmonic gold nanostars (AuNSs) and cellulose nanofibers (CNFs) embedded in layered MXene nanosheets. The MXene/AuNS/CNF (MAC) membrane provides subnanometer-sized ionic pathways for light-sensitive cationic flow. When the MAC nanochannel is exposed to NIR light, a photothermal gradient is formed, which induces directional photothermo-osmotic flow of nanoconfined electrolyte against the thermal gradient and produces a net ionic current. MAC membrane exhibits enhanced photothermal current compared with pristine MXene, which is attributed to the combined photothermal effects of plasmonic AuNSs and MXene and the widened interspacing of the MAC composite via the hydrophilic nanofibrils. The MAC composite membranes are envisioned to be applied in flexible ionic channels with ionogels and light-controlled ionic circuits.

Application of iontophoresis in ophthalmic practice: an innovative strategy to deliver drugs into the eye

Delivery of drugs to special locations of ocular lesions, while minimizing systemic and local toxic effects, is recognized as a critical challenge in the ophthalmic practice. The special anatomy and physiology barriers within the eyeball entail effective drug delivery systems. Emerging attempts in drug delivery has led to developments in ocular iontophoresis, which acts as a noninvasive technology to enhance drug penetration using a small electric current. This technique offers greater flexibility to deliver desired drug dose in a controlled and tolerable manner. In previous studies, this technique has been testified to deliver antibiotics, corticoid, proteins and other gene drugs into the eye with the potency of treating or alleviating diverse ophthalmological diseases including uveitis, cataract, retinoblastoma, herpes simplex and cytomegalovirus retinitis (CMVR), etc. In this review, we will introduce the recent developments in iontophoresis device. We also summarize the latest progress in coulomb controlled iontophoresis (CCI), hydrogel ionic circuit (HIC) and EyeGate II delivery system (EGDS), as well as overview the potential toxicity of iontophoresis. We will discuss these factors that affect the efficacy of iontophoresis experiments, and focus on the latest progress in its clinical application in the treatment of eye diseases.

A Highly Efficacious Electrical Biofilm Treatment System for Combating Chronic Wound Bacterial Infections.

Biofilm infection has a high prevalence in chronic wounds and can delay wound healing. Current treatment using debridement and antibiotic administration imposes a significant burden on patients and healthcare systems. To address their limitations, a highly efficacious electrical antibiofilm treatment system is described in this paper. This system uses high-intensity current (75mA cm-2 ) to completely debride biofilm above the wound surface and enhance antibiotic delivery into biofilm-infected wounds simultaneously. Combining these two effects, this system uses short treatments (≤2h) to reduce bacterial count of methicillin-resistant S.aureus (MRSA) biofilm-infected ex vivo skin wounds from 1010 to 105.2 colony-formingunits(CFU) g-1 . Taking advantage of the hydrogel ionic circuit design, this system enhances the in vivo safety of high-intensity current application compared to conventional devices. The in vivo antibiofilm efficacy of the system is tested using a diabetic mouse-based wound infection model. MRSA biofilm bacterial count decreases from 109.0 to 104.6 CFU g-1 at 1 day post-treatment and to 103.3 CFU g-1 at 7 days post-treatment, both of which are below the clinical threshold for infection. Overall, this novel technology provides a quick, safe, yet highly efficacious treatment to chronic wound biofilm infections.

PH-Regulated Ionic Diode Based on an Asymmetric Shaped Multiple-Layer Polymer Membrane

Smart artificial ion channels with tunable properties have wide applications in many fields to achieve ion transport manipulation. Most reported artificial ions are constructed with vertical structures, limiting the further integration of ionic diodes into complex iontronic systems. Inspired by the asymmetric concentration polarization induced by the asymmetric geometry of nanochannels, a novel method is developed to construct horizontally arranged and pH-regulated ionic diodes in nanofluidic chips by self-assembling pH-responsive polymers. The effects of the fabrication and operation parameters on the performance of the ionic diode are systematically investigated. The current rectification ratio of the ionic diode can be modulated flexibly by regulating the pH conditions of the working fluid. An ionic diode bridge circuit for rectifying alternating current signals is built in a single nanofluidic chip and demonstrated, highlighting the feasibility of the ionic diode for complex iontronic system integration. The method presented in this paper provides a promising platform for the development of smart nanofluidic iontronic devices with widespread applicability in biological analysis, sensing, and logic computing.

An Aqueous Analog MAC Machine.

Using ions in aqueous milieu for signal processing, like in biological circuits, may potentially lead to a bioinspired information processing platform. Studies, however, have focused on individual ionic diodes and transistors rather than circuits comprising many such devices. Here a 16×16 array of new ionic transistors is developed in an aqueous quinone solution. Each transistor features a concentric ring electrode pair with a disk electrode at the center. The electrochemistry of these electrodes in the solution provides the basis for the transistor operation. The ring pair electrochemically tunes the local electrolytic concentration to modulate the disk's Faradaic reaction rate. Thus, the disk current as a Faradaic reaction to the disk voltage is gated by the ring pair. The 16×16 array of these transistors performs analog multiply-accumulate (MAC) operations, a computing modality hotly pursued for low-power artificial neural networks. This exploits the transistor's operating regime where the disk current is a multiplication of the disk voltage and a weight parameter tuned by the ring pair gating. Such disk currents from multiple transistors are summated in a global reference electrode to complete a MAC task. This ionic circuit demonstrating analog computing is a step toward sophisticated aqueous ionics.

Brain Wave-Like Signal Modulator by Ionic Nanochannel Rectifier Bridges.

Smart modulation of bioelectric signals is of great significance for the development of brain-computer interfaces, bio-computers, and other technologies. The regulation and transmission of bioelectrical signals are realized through the synergistic action of various ion channels in organisms. The bionic nanochannels, which have similar physiological working environment and ion rectification as their biological counterparts, can be used to construct ion rectifier bridges to modulate the bioelectric signals. Here, the artificial smart ionic rectifier bridge with light response is constructed by anodic aluminum oxide (AAO)/poly (spiropyran acrylate) (PSP) nanochannels. The output ion current of the rectifier bridge can be switched between "ON" and "OFF" states by irradiation with UV and visible (Vis) light, and the conversion efficiency (η) of the system in "ON" state is ≈70.5%. The controllable modulation of brain wave-like signal can be realized by ionic rectifier bridge. The ion transport properties and processes of ion rectifier bridges are explained using theoretical calculations based on Poisson-Nernst-Planck (PNP) equations. These findings have significant implications for the understanding of the intelligent ionic circuit and combination of artificial smart ionic channels to organisms, which provide new avenues for development of intelligent ion devices.

Ionic diode desalination: Combining cationic Nafion™ and anionic Sustainion™ rectifiers

Microscale ionic rectifier effects are commonly observed in devices based on semipermeable ionomer coated on an array of microholes with potential applications in alternating current (AC) driven desalination and/or electroosmotic pumping. The efficiency of devices is dependent on ionic diode switching speed, the rectification ratio, and the design of materials and the ionic circuit. Here, a new circuit is proposed based on coupling in parallel (i) a cationic diode based on the cation conductor Nafion and (ii) an anionic diode based on the anion conducting Sustainion. With an alternating driving voltage, a net desalination effect is observed without any moving parts and without significant side reactions. Experimentally, a 4-electrode configuration and a 2-electrode configuration are compared. The ionic diode desalination system is shown to work with only two carbon mat driver electrodes, but the performance in particular at higher ionic strengths (>10 mM) still needs to be improved. Based on the experimental prototype, the current/power efficiency are investigated and challenges for future improvements are discussed.

Flexible Ionic Diodes with High Rectifying Ratio and Wide Temperature Tolerance

AbstractSoft iontronics expand the toolbox of bio‐integrated or bio‐interfaced devices, owing to their natural resemblance with living systems; however, the development for analogous integrated ionic circuits is immature due to the difficulty of fabricating fundamental ionic logic elements. Among these, ionic diodes have motivated great endeavors for their unique ionic current rectifying characteristics. Nonetheless, it is still challenging to achieve high‐performance ionic diodes; also, most reported aqueous solution‐based ionic diodes fail to work at extreme temperatures, seriously hindering their practical uses. This work reports a highly rectifying, temperature‐tolerant, and flexible hydrogel ionic diode enabled by an ethylene glycol/water binary solvent system. The ionic diodes exhibit outstanding dehydration resistance to high temperatures (100 °C) and anti‐freezing performance at low temperatures (−20 °C). Rectification ratios as high as 1201 (with 0% ethylene glycol content) and 566 (with 40% EG content) are achieved, which are distinctly advantageous over most previous reports. A flexible four‐diode bridge full‐wave rectifier circuit is then fabricated, and its integration with the triboelectric nanogenerator for effective biomechanical energy harvesting is demonstrated. This work is believed to open up new insights for the development of future bio‐interfaced applications.

Bipolar Modulation of the Ionic Circuit for Generic Organic Photoelectrochemical Transistor Logic and Sensor

AbstractPhotonic (bio)electronic circuits and devices have been an enduring goal in modern photonics and electronics. Organic photoelectrochemical transistor (OPECT) interfacing light with biological world creates a substantial opportunity to this end due to the immense light−bio−matter interplay. Through modulating the invisible ionic circuit of organic electrochemical transistor (OECT) with a bipolar electrode (BPE) accommodating different semiconductor combinations, the unique photonic electronics toward logic and sensor applications are realized. Six combinations of BPEs are produced by the representative n‐type CdS/TiO2 and p‐type BiOI/NiO semiconductors, and the corresponding photonic characteristics and operation rationale are systematically investigated and explained. Designation of opto‐logic circuits and feasibility as a sensory platform are subsequently demonstrated. This work not only represents new photonic bioelectronics but also provides a generic mechanism for the design and development of advanced opto‐logics and bio‐analytics.

Photoswitchable Binary Nanopore Conductance and Selective Electronic Detection of Single Biomolecules under Wavelength and Voltage Polarity Control.

We fabricated photoregulated thin-film nanopores by covalently linking azobenzene photoswitches to silicon nitride pores with ∼10 nm diameters. The photoresponsive coatings could be repeatedly optically switched with deterministic ∼6 nm changes to the effective nanopore diameter and of ∼3× to the nanopore ionic conductance. The sensitivity to anionic DNA and a neutral complex carbohydrate biopolymer (maltodextrin) could be photoswitched "on" and "off" with an analyte selectivity set by applied voltage polarity. Photocontrol of nanopore state and mass transport characteristics is important for their use as ionic circuit elements (e.g., resistors and binary bits) and as chemically tuned filters. It expands single-molecule sensing capabilities in personalized medicine, genomics, glycomics, and, augmented by voltage polarity selectivity, especially in multiplexed biopolymer information storage schemes. We demonstrate repeatedly photocontrolled stable nanopore size, polarity, conductance, and sensing selectivity, by illumination wavelength and voltage polarity, with broad utility including single-molecule sensing of biologically and technologically important polymers.

Modulation of ionic current behaviors based on a dual-channel micro/nano-pipette with ternary-form-charged model

• Ternary-Formed-Charged model is proposed for simulation of ionic behaviors of a dual-channel pipette such as a resistor, diodes, and a bipolar junction transistor. • The uneven distribution and location of surface charge density are confirmed to cause asymmetric bipolar junction transistor behavior and pseudo-bipolar junction transistor behavior. • Scale ratio of radius of the pipette to liquid bridge and the effect of surface charge at the interface between liquid bridge and air is evaluated. Dual-channel micro- or nanopipettes can be used to perform various ionic current behaviors such as a resistor, diodes, and a bipolar junction transistor (BJT) via chemical modification. These ionic current devices could be modulated by charge pattern of modification, pH, size and scale ratio of pipette to the liquid bridge, whose intrinsic mechanism is indistinct. Herein, a universal Ternary-Form-Charged (TFC) model is proposed, in which the pipettes contain three individual tunable regions with different scale, location, surface charge density while ions can flux across the charged liquid bridge connected with them. Based on the TFC model, we could obtain three basic ionic behaviors mentioned above of dual-channel pipettes and demonstrate that these basic ionic behaviors of dual-channel pipette are dependent on the number of transition zone. Transformation from the BJT behavior to a pseudo-BJT behavior is attributed to a narrow middle charged region or a thick liquid bridge. Asymmetric BJT behavior is also observed under asymmetric distribution of location and quantity of surface charge density. Furthermore, we provide the approximate size of liquid bridge: 5–8 nm and 15–20 nm for dual-channel nanopipette and micropipette, respectively. In short, the TFC model and our simulation results shed light on the mechanism of dual-channel pipette based ionic circuits and provide a useful guide to design, modify and develop novel applications of dual-channel pipettes in nanofluidic sensors.

Correlation between Transient Response and Neuromorphic Behavior in Organic Electrochemical Transistors

AbstractThe factors controlling the neuromorphic response of organic electrochemical transistors (OECTs) are examined. In these devices, the gate voltage is used to supply the pre‐synaptic input, while the drain current is taken as the post‐synaptic output. The behavior of devices made from polymer blends of a mixed conductor (PEDOT:PSS) and an ion conductor (PSSNa) is analyzed. The experimental results highlight that the post‐synaptic response timescale depends on the size of ion in the electrolyte. Modeling shows that the neuromorphic response is controlled by the transient response of the ionic circuit of the OECT. These insights on device response time pave the way for a more rational design of OECT‐based neuromorphic devices.

Development of multifunctional nanopipettes for controlled intracellular delivery and single-entity detection.

The intracellular delivery of biomolecules and nanoscale materials to individual cells has gained remarkable attention in recent years owing to its wide applications in drug delivery, clinical diagnostics, bio-imaging and single-cell analysis. It remains a challenge to control and measure the delivered amount in one cell. In this work, we developed a multifunctional nanopipette - containing both a nanopore and nanoelectrode (pyrolytic carbon) at the apex - as a facile, minimally invasive and effective platform for both controllable single-cell intracellular delivery and single-entity counting. While controlled by a micromanipulator, the baseline changes of the nanopore ionic current (I) and nanoelectrode open circuit potential (V) help to guide the nanopipette tip insertion and positioning processes. The delivery from the nanopore barrel can be facilely controlled by the applied nanopore bias. To optimize the intracellular single-entity detection during delivery, we studied the effects of the nanopipette tip geometry and solution salt concentration in controlled experiments. We have successfully delivered gold nanoparticles and biomolecules into the cell, as confirmed by the increased scattering and fluorescence signals, respectively. The delivered entities have also been detected at the single-entity level using either one or both transient I and V signals. We found that the sensitivity of the single-entity electrochemical measurement was greatly affected by the local environment of the cell and varied between cell lines.

Bidirectional Light-Driven Ion Transport through Porphyrin Metal–Organic Framework-Based van der Waals Heterostructures via pH-Induced Band Alignment Inversion

Bidirectional Light-Driven Ion Transport through Porphyrin Metal–Organic Framework-Based van der Waals Heterostructures via pH-Induced Band Alignment Inversion

Light‐Fueled Organic Photoelectrochemical Transistor for Probing Membrane Protein in an H‐Cell

AbstractThough great advances are achieved in the area of organic electrochemical transistor (OECT) biosensors, general issues of shared electrolyte by the channel and gate electrode remain unsolved. On the other hand, to date binding‐free OECT detection of cellular membrane proteins is not reported. On the basis of the advanced technique of organic photoelectrochemical transistor (OPECT), herein the H‐cell‐supported OPECT device that can easily circumvent the issues of abovementioned shared electrolyte and its application toward binding‐free detection of membrane alkaline phosphatase (ALP) of HeLa cells is demonstrated. In such a configuration, usage of a Nafion perfluorinated membrane equipped H‐cell can well retain the ionic circuit of the device but prevent the diffusion of various molecules and minimize the possible interference. In the detection, ALP catalytic chemistry enables the sensitization of the TiO2 nanotubes electrode, triggering enhanced de‐doping of the poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) and thus resulting in altered channel currents proportionate to the membrane ALP. This work not only provides a new perspective for binding‐free detection of membrane protein but also represents a general protocol for H‐cell‐supported OECT/OPECT biosensors with enhanced accuracy.

A Hydrogel Ionic Circuit Based High-Intensity Iontophoresis Device for Intraocular Macromolecule and Nanoparticle Delivery.

Iontophoresis is an electrical-current-based, noninvasive drug-delivery technology, which is particularly suitable for intraocular drug delivery. Current ocular iontophoresis devices use low current intensities that significantly limit macromolecule and nanoparticle (NP) delivery efficiency. Increasing current intensity leads to ocular tissue damage. Here, an iontophoresis device based on a hydrogel ionic circuit (HIC), for high-efficiency intraocular macromolecule and NP delivery, is described. The HIC-based device is capable of minimizing Joule heating, effectively buffering electrochemical (EC) reaction-generated pH changes, and absorbing electrode overpotential-induced heating. As a result, the device allows safe application of high current intensities (up to 87mA cm-2 , more than 10 times higher than current ocular iontophoresis devices) to the eye with minimal ocular cell death and tissue damage. The high-intensity iontophoresis significantly enhances macromolecule and NP delivery to both the anterior and posterior segments by up to 300 times compared to the conventional iontophoresis. Therapeutically effective concentrations of bevacizumab and dexamethasone are delivered to target tissue compartments within 10-20min of iontophoresis application. This study highlights the significant safety enhancement enabled by an HIC-based device design and the potential of the device to deliver therapeutic doses of macromolecule and NP ophthalmic drugs within a clinically relevant time frame.

Geometric Tailoring of Macroscale Ti3C2Tx MXene Lamellar Membrane for Logic Gate Circuits.

Constructing nanofluidic diode nanochannels with an asymmetric structure for logic gate circuits has attracted extensive research interests. Currently, the preparation of a geometrically asymmetric nanochannel relies on cost-effective material-processing methods and has been hard to scale up, limiting the development of nanofluidic research. Herein, we introduce the idea of geometric tailoring to cut the MXene lamellar membrane in different shapes and investigate the ion transport behavior systematically. The ion rectification can be regulated by adjusting geometric factors such as the asymmetric ratio and height of the trapezoidal membrane. On the basis of the above-mentioned research on rectification characteristics, we further optimized the trapezoidal membrane into a triangular membrane on the macroscopic level and successfully applied it to logic circuits, realizing the logic operations of "AND" and "OR". It is worth mentioning that the shape of a macrocut triangular membrane is exactly the same as the symbol of an electronic diode, and the conduction and cutoff directions of the ionic current are also exactly the same as those of electronic diodes. Our finding provides a facile and general strategy for fabricating a macroscale geometric asymmetry nanochannel-based two-dimensional lamellar membrane and shows the potential applications in complex highly integrated ionic circuits.

Hydrogel Ionotronics with Ultra‐Low Impedance and High Signal Fidelity across Broad Frequency and Temperature Ranges

AbstractIonotronics, emerging devices that couple gel ionic conductors and electronic circuits, have shown great promise as stretchable alternatives with multi‐functionalities to conventional rigid devices, ranging from energy harvesting to sensing, displaying, and actuation. However, current hydrogel ionotronics’ performances are still unsatisfactory: i) upon high alternating current frequency (> 1000 Hz), the ionic conductivity dominates but is rather low and drops further drastically as temperature decreases; ii) upon low frequency (< 1000 Hz), the unstable and high impedance at the electrode/hydrogel interface dominates unfavorably but has been overlooked previously. To remedy these issues, herein, a systematic strategy is proposed by employing a highly ionically‐conductive anti‐freezing hydrogel and electronically‐conductive porous polymer films with high electrical‐double‐layer capacitance as electrodes to connect the hydrogel and metal leads. The hydrogel has an ultra‐high conductivity, while being transparent, stretchable, and easily prepared by one‐step photo‐gelation. Meanwhile, the conducting polymer electrodes realize a stable and low interfacial impedance and improved voltage tolerance, enabling much higher fidelity of ion‐electron signal transduction than using gold electrodes. This strategy can be applied to construct various ionotronics for broad applications, including triboelectric nanogenerators, touch panels, displays, soft robotics, and multifunctional electronics with broad operational frequency and temperature ranges.

Ionic Diode Based on an Asymmetric‐Shaped Carbon Black Nanoparticle Membrane

AbstractBioinspired ionic diodes are widely explored to mimic the controllable ion transport of biological ion channels. However, due to their vertical structures, the integration of conventional ionic diodes into complex ionic circuits is still a challenge. Here, a horizontal ionic diode is developed based on an asymmetric nanochannel network membrane (NCNM) constructed from carbon black nanoparticles. The rectification of ionic current is achieved through the asymmetric concentration polarization of ions at two ends of the asymmetric NCNM. The rectification ratio of the NCNM ionic diode can be modified flexibly by changing the working fluid and the geometry of the NCNM. It is found that with the presence of cationic surfactant in the working fluid, the rectification ratio increases more than 30 times from 3.03 to 109.77. Advanced functions of the developed ionic component, including working as an ionic transistor for current switching and integrating into an ionic diode bridge on a single nanofluidic chip for rectifying alternating current signals, are also demonstrated in this paper. The horizontally arranged NCNM ionic diode possesses the advantages of easy fabrication and integration that can be practically applied in the development of ionic electronics and biocomputing.

Harnessing Ionic Power from Equilibrium Electrolyte Solution via Photoinduced Active Ion Transport through van-der-Waals-Like Heterostructures.

Nanofluidic ion transport through van der Waals heterostructures, composed of two or more types of reconstructed 2D nanomaterials, gives rise to fascinating opportunities for light-energy harvesting, due to coupling between the optoelectronic properties of the layered constituents and ion transport in between the atomic layers. Here, a photoinduced active ion transport phenomenon through transition metal dichalcogenides (TMDs)-based van-der-Waals-like multilayer heterostructures is reported for harnessing ionic power from equilibrium electrolyte solution. The binary heterostructure comprises sequentially stacked 2D-WS2 and 2D-MoS2 multilayers with sub-1 nm interlayer spacing. Upon visible-light illumination, a net ionic flow is initiated through the Janus membrane, suggesting a directional cationic transport from WS2 to MoS2 part. The transport mechanism is explained in terms of a photovoltaic effect due to type II band alignment of WS2 /MoS2 heterostructures. The driving mechanism can be generally applied to a variety of heterogeneous TMD membranes with type II semiconductor heterojunctions. In equilibrium ionic solutions, the maximum ionic photoresponse approaches ≈21 µAcm-2 and ≈45mV under one sun equivalent excitation. Under optimized conditions, the harvested power density reaches 2mWm-2 . The proof-of-concept demonstration of photonic-to-ionic power generation within angstrom-scale confinement anticipates potential for light-controlled ionic circuits, artificial photosynthesis, and biomimetic energy conversion.