Ion Gating Research Articles

High Resolving Power Electrospray Ionization Ion Mobility Spectrometer Based on Fourier Deconvolution Multiplexing.

The resolving power of the drift tube ion mobility spectrometry (IMS) is mainly dependent on the drift length, the drift voltage, the pulse width of an ion gate, and the pressure inside the drift tube. Electrospray ionization (ESI)-IMS is a highly sensitive and reliable technique for the detection and analysis of nonvolatile compounds, and high resolving power is necessary to separate structurally similar compounds. To improve the analytical performance of atmospheric pressure ESI-IMS, the Fourier deconvolution (FD) multiplexing technique is investigated as an effective and convenient means to improve the resolving power as well as the signal-to-noise ratio. By reducing the equivalent ion gate opening width to 5 μs using a typical Tyndall-Powell ion shutter, a high resolving power RP up to 170 can be achieved with a drift length of 12 cm and a drift voltage of 10 kV. Rhodamine 6G (R6G), sodium dodecyl sulfate (SDS), methacycline, oxytetracycline, and ractopamine were evaluated using the FD-ESI-IMS, and mixtures with similar ion mobility can be well separated without prolonging the drift length.

Binding kinetics of quaternary ammonium ions in Kcv potassium channels.

Kcv channels from plant viruses represent the autonomous pore module of potassium channels, devoid of any regulatory domains. These small proteins show very reproducible single-channel behavior in planar lipid bilayers. Thus, they are an optimum system for the study of the biophysics of ion transport and gating. Structural models based on homology modeling have been used successfully, but experimental structural data are currently not available. Here we determine the size of the cytosolic pore entrance by studying the blocker kinetics. Blocker binding and dissociation rate constants ranging from 0.01 to 1000 ms-1 were determined for different quaternary ammonium ions. We found that the cytosolic pore entrance of KcvNTS must be at least 11 Å wide. The results further indicate that the residues controlling a cytosolic gate in one of the Kcv isoforms influence blocker binding/dissociation as well as a second gate even when the cytosolic gate is in the open state. The voltage dependence of the rate constant of blocker release is used to test, which blockers bind to the same binding site.

2D Carbonaceous Materials for Molecular Transport and Functional Interfaces: Simulations and Insights.

ConspectusCarbon-based two-dimensional (2D) functional materials exhibit potential across a wide spectrum of applications from chemical separations to catalysis and energy storage and conversion. In this Account, we focus on recent advances in the manipulation of 2D carbonaceous materials and their composites through computational design and simulations to address how the precise control over material structure at the atomic level correlates with enhanced functional properties such as gas permeation, selectivity, membrane transport, and charge storage. We highlight several key concepts in the computational design and tuning of 2D structures, such as controlled stacking, ion gating, interlayer pillaring, and heterostructure charge transfer.The process of creating and adjusting pores within graphene sheets is vital for effective molecular separation. Simulations show the power of controlling the offset distance between layers of porous graphene in precisely regulating the pore size to enhance gas separation and entropic selectivity. This strategy of controlled stacking extends beyond graphene to include covalent organic frameworks (COFs) such as covalent triazine frameworks (CTFs). Experimental assembly of the layers has been achieved through electrostatic interactions, thermal transformation, and control of side chain interactions.Graphene can interface with ionic liquids in various forms to enhance its functionality. A computational proof-of-concept showcases an ion-gating concept in which the interaction of anions with the pores in graphene allows the anions to dynamically gate the pores for selective gas transport. Realization of the concept has been achieved in both porous graphene and carbon molecular sieve membranes. Ionic liquids can also intercalate between graphene layers to form interlayer pillaring structures, opening the slit space. Grand canonical Monte Carlo simulations show that these structures can be used for efficient gas capture and separation. Experiments have demonstrated that the interlayer space can be tuned by the density of the pillars and that, when fully filled with ionic liquids and forming a confined interface structure, the graphene oxide membrane achieves much higher selectivity for gas separations. Moreover, graphene can interface with other 2D materials to form heterostructures where interfacial charge transfers take place and impact the function. Both ion transport and charge storage are influenced by both the local electric field and chemical interactions.Fullerene can be used as a building block and covalently linked together to construct a new type of 2D carbon material beyond a one-atom-thin layer that also has long-range-ordered subnanometer pores. The interstitial sites among fullerenes form funnel-shaped pores of 2.0-3.3 Å depending on the crystalline phase. The quasi-tetragonal phases are shown by molecular dynamics simulations to be efficient for H2 separation. In addition, defects such as fullerene vacancies can be introduced to create larger pores for the separation of organic solvents.In conclusion, the key to imputing functions to 2D carbonaceous materials is to create new interactions and interfaces and to go beyond a single-atom layer. First-principles and molecular simulations can further guide the discovery of new 2D carbonaceous materials and interfaces and provide atomistic insights into their functions.

A modular, isolated high-voltage switch for application in ion mobility spectrometry

Ion mobility spectrometry is an emerging technology in trace gas analysis that has moved from typical safety and security applications to many other fields ranging from environmental and food quality monitoring to medicine and life sciences. Nevertheless, further dissemination, including the development of new instruments and the expansion into new fields of application requires the availability of the fundamental components of ion mobility spectrometers. For example, the electronics is essential for the analytical performance, but is only provided by specialized manufacturers due to specific requirements. In this paper, we present a modular, isolated high-voltage switch that can be operated at an isolated potential. The modular design enables tailoring its configuration to the required application. Each module can switch a voltage of up to 3 kV, and can be operated with an offset voltage of up to 7 kV. The switch has rise and fall times of less than 25 ns, making it suitable for a wide range of applications, e.g., in ion mobility spectrometry. Finally, the presented modular, isolated high-voltage switch was used in a push–pull configuration to generate the injection pulse of the ion gate. The new modular, isolated high-voltage switch shows similar performance compared to a commercially available high-voltage switch.

Determination of product ions emerged from dications by varying retarding electric field in reflectron time-of-flight mass spectrometer supported by ion trajectory simulations

Investigation of the metastable dissociations clarifies the characteristics of ionic states. Tandem mass spectrometry using an ion trap mass spectrometer, a time-of-flight mass spectrometer (TOF-MS), and the combination of those spectrometers were used for the analysis of metastable dissociation. However, investigation of the metastable dissociations of multiply charged ions is not straightforward because collision-induced charge transfer reactions to lose charges should be avoided. TOF-MS equipped with a reflectron (refTOF-MS) maintained under high vacuum condition is one of the suitable instruments. However, another difficulty arises due to the working principle of refTOF-MS: The product ions whose m/z is greater than that of multiply charged precursor ions can pass through a reflectron under the experimental conditions for detecting the product ions of a singly charged precursor ion. In this study, we report the ionization of decafluorobiphenyl (DFB) by femtosecond laser pulses and the determination of the product ions emerged from doubly charged precursor ions using a refTOF-MS. Detection of ions behind a reflectron by varying the retarding potential of a reflectron enables us to identify the m/z of product ions in two ways: measurement of the threshold retarding potential reflecting product ion; comparing the relative flight time of the product ions obtained by experiments and ion trajectory simulations. We have reported three and one metastable dissociation channels of DFB+ and DFB2+, respectively, by a conventional product ion analysis, that is the selection of a precursor ion and its product ions using an ion gate followed by the reflection and separation of them by a reflectron. In this study, we further identified the products that passed through a reflectron: charge transfer product of C2+; the product ion of C4F22+ which is a secondary product of DFB ion; the product ion of DFB2+. The detection of the product ions that passed through a reflectron expanded the measurable m/z range of product ions emerged from doubly charged precursor ions.

Development of an Ion Mobility Spectrometer Based on a Pulsed Photoelectric Effect Ionization Source.

Ion mobility spectrometry (IMS) is a compact and sensitive trace gas analysis instrument that ionizes the sample into ions for detection. Typically, an ion gate is used to cut the continuous ion beam into ion packets for separation and detection. However, commonly used ion gates suffer from complex structures or low ion transmission rates, making the gateless IMS a viable alternative. In this study, an IMS based on a pulsed photoelectric effect ionization source was designed. The photoelectrons were generated by irradiating a photoelectric material with a back-illuminated pulsed xenon lamp. This allows for low-energy photoelectron generation and the production of simple reactant ions (O2-(H2O)n) and thus negative product ions. The photoelectron current generated by this ionization source was analyzed, which can reach an intensity of a few microamperes and can be converted into an ion signal exceeding 10 nA. The introduction of the pulsed photoelectric effect ionization source makes it possible to generate separate ion packets and complete ion injection when a constant electric field is maintained in the ionization region. And with an assisted pulsed electric field in the ionization region, the resolving power of the system can be effectively improved to 1.85 times that of the constant electric field. The IMS developed in this study was used for the detection of common volatile hazardous chemicals, yielding effective results. The detection limit for phenol was below 1 ppb, and the dynamic response range exceeded 1 order of magnitude, which implies the potential applications of this IMS to detect substances with high electron affinity, such as explosives detection in public safety.

Enhancing the Performance of Tyndall-Powell Gate Ion Mobility Spectrometry by Combining Ion Enrichment, Discrimination Reduction, and Temporal Compression into a Single Gating Process.

The broad applications of ion mobility spectrometry (IMS) demand good sensitivity and resolving power for ion species with different reduced mobilities (K0). In this work, a new Tyndall-Powell gate (TPG) gating method for combining ion enrichment, mobility discrimination reduction, and temporal compression into a single gating process is proposed to improve IMS analysis performance. The two-parallel-grid structure and well-confined gate region of the TPG make it convenient to spatiotemporally vary the electric fields within and around the gate region. Under the new gating method, a potential wave is applied on TPG grid 1 to enrich ions within the ionization region adjacent to the TPG during the gate-closed state; meanwhile, a potential wave is applied on TPG grid 2 to enhance mobility discrimination reduction and temporal compression simultaneously during the gate-open state. For triethyl phosphate (TEP) and dimethyl methylphosphonate mixtures, product ion peaks within K0 of 1.9 to 1.1 cm2/V·s exhibit a 19-fold increase in ion current compared to the traditional TPG gating method, while maintaining a resolving power of 85. The estimated limit of detection for the TEP dimer is lowered from 8 ppb to 135 ppt. The new gating method can be applied to other TPG-based IMS systems to enhance their performance in analyzing complex samples.

A high-performance deep reservoir computer experimentally demonstrated with ion-gating reservoirs

While physical reservoir computing is a promising way to achieve low power consumption neuromorphic computing, its computational performance is still insufficient at a practical level. One promising approach to improving its performance is deep reservoir computing, in which the component reservoirs are multi-layered. However, all of the deep-reservoir schemes reported so far have been effective only for simulation reservoirs and limited physical reservoirs, and there have been no reports of nanodevice implementations. Here, as an ionics-based neuromorphic nanodevice implementation of deep-reservoir computing, we report a demonstration of deep physical reservoir computing with maximum of four layers using an ion gating reservoir, which is a small and high-performance physical reservoir. While the previously reported deep-reservoir scheme did not improve the performance of the ion gating reservoir, our deep-ion gating reservoir achieved a normalized mean squared error of 9.08 × 10−3 on a second-order nonlinear autoregressive moving average task, which is the best performance of any physical reservoir so far reported in this task. More importantly, the device outperformed full simulation reservoir computing. The dramatic performance improvement of the ion gating reservoir with our deep-reservoir computing architecture paves the way for high-performance, large-scale, physical neural network devices.

A coarse-grained Poisson–Nernst–Planck model for polyelectrolyte-modified nanofluidic diodes

Abstract Polyelectrolyte (PE)-modified synthetic nanopores have gained substantial research attention because molecular modification promotes ion gating and rectification. However, theoretical research on PE-modified nanopores is relatively scarce because it is difficult to establish an elaborate model for PEs, and it accordingly causes a trade-off between the computational resources needed and the accuracy. Therefore, an appropriate simulation method for the PE-modified nanopore is in high demand and still an enormous challenge. Herein, we report the simulation result of ion transport through PE-modified nanopores through a coarse-grained Poisson–Nernst–Planck method. By modeling the stuffed PE molecules as PE particles in a well-established continuum model, adequate computational accuracy can be achieved with acceptable computational cost. Based on this model, we study the ion transport in PE-modified nanofluidic diodes and reveal the PE around ion selectivity, which can explain the previous experimental works. Intriguingly, we found that the ion enrichment state in the nanofluidic diode is sensitive to steric hindrance and charge distribution near the heterojunction region. This property is critical for the ion transport behavior in the PE-modified nanofluidic diodes. Based on this property, we predict a heterogeneous structure that can realize the single molecule response to charged analytes. These findings provide insights for understanding the ion transport in PE-modified nanofluidic systems and bring inspiration to the design and optimization of high-performance chemical sensors.

Organic Synaptic Transistors with an Ultra‐Short‐Term Weight‐Reconstruction for Processing Multiple Types of Signals

AbstractAn organic synaptic transistor (OST) that utilizes a multiple‐annealing process and an ion gate to achieve significant reductions in operating voltage and increases in transconductance is demonstrated. The OST exhibits an ultra‐short‐term plasticity (USTP) with a maximum retention time of only 20.7 ms, which does not increase with the number and duration of spikes. This is the shortest retention time yet achieved by an ion‐gel‐regulated synaptic transistor. In addition, OST‐integrated array exhibits a tunable weight plasticity and a short weight refresh time for a stable image resetting in ample time of <0.2 s. It is also sensitive to the frequency and amplitude of electrical inputs; a low‐frequency suppression and a nonlinear amplitude gain enables OST‐constructed filter for use in processing multiple types of signals. This work is a step toward constructing high‐performance and multifunctional artificial intelligent systems.

Few- and single-molecule reservoir computing experimentally demonstrated with surface-enhanced Raman scattering and ion gating.

Molecule-based reservoir computing (RC) is promising for achieving low power consumption neuromorphic computing, although the information-processing capability of small numbers of molecules is not clear. Here, we report a few- and single-molecule RC that uses the molecular vibration dynamics in the para-mercaptobenzoic acid (pMBA) detected by surface-enhanced Raman scattering (SERS) with tungsten oxide nanorod/silver nanoparticles. The Raman signals of the pMBA molecules, adsorbed at the SERS active site of the nanorod, were reversibly perturbated by the application of voltage-induced local pH changes near the molecules, and then used to perform time-series analysis tasks. Despite the small number of molecules used, our system achieved good performance, including >95% accuracy in various nonlinear waveform transformations, 94.3% accuracy in solving a second-order nonlinear dynamic system, and a prediction error of 25.0 milligrams per deciliter in a 15-minute-ahead blood glucose level prediction. Our work provides a concept of few-molecular computing with practical computation capabilities.

Strategy to improve synaptic behavior of ion-actuated synaptic transistors—the use of ion blocking layer to improve state retention

Synaptic transistors (STs) with a gate/electrolyte/channel stack, where mobile ions are electrically driven across the solid electrolyte, have been considered as analog weight elements for neuromorphic computing. The current (ID) between the source and drain in the ST is analogously updated by gate voltage (VG) pulses, enabling high pattern recognition accuracy in neuromorphic systems; however, the governing physical mechanisms of the ST are not fully understood yet. Our previous physics-based simulation study showed that ion movement in the electrolyte, rather than the electrochemical reactions that occur in the channel, plays an important role in switching. In this study, we experimentally explore the properties of the HfOx electrolyte and show that by tuning the density of oxygen vacancies, it can assume the dual role of electrolyte and channel. We demonstrate analog synaptic behavior using a novel ST with a two-layer stack of CuOx/HfOx, where the CuOx is the gate and Cu ion reservoir, and the HfOx is the electrolyte and channel. To improve state retention and linearity, we introduce a Cu ion transport barrier in the form of a dense and stoichiometric Al2O3 layer. The CuOx/Al2O3/HfOx exhibits excellent state retention and improved potentiation and depression response. Energy dispersive spectroscopy mapping following potentiation confirms the role of the Al2O3 layer in confining the Cu ions in the HfOx layer. We also show that a two-step programming scheme can further enhance synaptic response and demonstrate high recognition accuracy on the Fashion-MNIST dataset in simulation.

Nonlinear frequency modulation for Fourier transform ion mobility mass spectrometry improves experimental efficiency

Through optimization of terminal frequencies and effective sampling rates, we have developed nonlinear sawtooth-shaped frequency sweeps for efficient Fourier transform ion mobility mass spectrometry (FT-IM-MS) experiments. This is in contrast to conventional FT-IM-MS experiments where ion gates are modulated according to a linear frequency sweep. Linear frequency sweeps are effective but can be hindered by the amount of useful signal obtained using a single sweep over a large frequency range imposed by ion gating inefficiencies, particularly small ion packets, and gate depletion. These negative factors are direct consequences of the inherently low gate pulse widths of high-frequency ion gating events, placing an upper bound on FT-IM-MS performance. Here, we report alternative ion modulation strategies. Sawtooth frequency sweeps may be constructed for the purpose of either extending high-SNR transients or conducting efficient signal-averaging experiments for low-SNR transients. The data obtained using this approach show high-SNR signals for a set of low-mass tetraalkylammonium salts (<1000 m/z) where resolving powers in excess of 500 are achieved. Data for low-SNR obtained for multimeric protein complexes streptavidin (53 kDa) and GroEL (800 kDa) also reveal large increases in the signal-to-noise ratio for reconstructed arrival time distributions.

Computational methods for unlocking the secrets of potassium channels: Structure, mechanism, and drug design

AbstractPotassium (K+) channels play vital roles in various physiological functions, including regulating K+ flow in cell membranes, impacting nervous system signal transduction, neuronal firing, muscle contraction, neurotransmitters, and enzyme secretion. Their activation and switch‐off are directly linked to diseases like arrhythmias, atrial fibrillation, and pain etc. Although the experimental methods play important roles in the studying the structure and function of K+ channels, they are still some limitations to enclose the dynamic molecular processes and the corresponding mechanisms of conformational changes during ion transport, permeation, and gating control. Relatively, computational methods have obvious advantages in studying such problems compared with experimental methods. Recently, more and more three‐dimensional structures of K+ channels have been disclosed based on experimental methods and in silico prediction methods, which provide a good chance to study the molecular mechanism of conformational changes related to the functional regulations of K+ channels. Based on these structural details, molecular dynamics simulations together with related methods such as enhanced sampling and free energy calculations, have been widely used to reveal the conformational dynamics, ion conductance, ion channel gating, and ligand binding mechanisms. Additionally, the accessibility of structures also provides a large space for structure‐based drug design. This review mainly addresses the recent progress of computational methods in the structure, mechanism, and drug design of K+ channels. After summarizing the progress in these fields, we also give our opinion on the future direction in the area of K+ channel research combined with the cutting edge of computational methods.This article is categorized under: Molecular and Statistical Mechanics &gt; Molecular Dynamics and Monte‐Carlo Methods Structure and Mechanism &gt; Computational Biochemistry and Biophysics Data Science &gt; Chemoinformatics

Ion Transport in Intelligent Nanochannels: A Comparative Analysis of the Role of Electric Field.

This research delves into investigating ion transport behavior within nanochannels, enhanced through modification with a negatively charged polyelectrolyte layer (PEL), aimed at achieving superior control. The study examines two types of electric fields─direct current and alternating current with square, sinusoidal, triangular, and sawtooth waveforms─to understand their impact on ion transport. Furthermore, the study compares symmetric (cylindrical) and asymmetric (conical) nanochannel geometries to assess the influence of overlapping electrical double layers (EDLs) in generating specific electrokinetic behaviors such as ionic current rectification (ICR) and ion selectivity. The research employs the finite element method to solve the coupled Poisson-Nernst-Planck and Navier-Stokes equations under unsteady-state conditions. By considering factors such as electrolyte concentration, soft layer charge density, and electric field type, the study evaluates ion transport performance in charged nanochannels, investigating effects on concentration polarization, electroosmotic flow (EOF), ion current, rectification, and ion selectivity. Notably, the study accounts for ion partitioning between the PEL and electrolyte to simulate real conditions. Findings reveal that conical nanochannels, due to improved EDL overlap, significantly enhance ion transport and related characteristics compared to cylindrical ones. For instance, under ηε = ηD = 0.8, ημ = 2, C0 = 20 mM, and NPEL/NA = 80 mol m-3 conditions, the average EOF for conical and cylindrical geometries is 0.1 and 0.008 m/s, respectively. Additionally, the study explores ion selectivity and rectification based on the electric field type, unveiling the potential of nanochannels as ion gates or diodes. In cylindrical nanochannels, the ICR remains at unity, with lower ion selectivity across waveforms compared to conical channels. Furthermore, rectification and ion selectivity trends are identified as Rf,square > Rf,DC > Rf,triangular > Rf,sinusoidal > Rf,sawtooth and Ssawtooth > Ssinusoidal > Striangular > SDC > Ssquare for conical nanochannels. Our study of ion transport control in nanochannels, guided by tailored electric fields and unique geometries, offers versatile applications in the field of Analytical Chemistry. This includes enhanced sample separation, controlled drug delivery, optimized pharmaceutical analysis, and the development of advanced biosensing technologies for precise chemical analysis and detection. These applications highlight the diverse analytical contributions of our methodology, providing innovative solutions to challenges in chemical analysis and biosensing.

Effects of metal work function and gate-oxide dielectric on super high frequency performance of a non-align junction DG-MOSFET based inverter in the sub-100 nm regime: a TCAD simulation analysis

ABSTRACT This paper presents simulation analysis of an inverter made from non-aligned double gate field effect transistors (NADGFETs) in Sub-100 nm regime. The inverter consists of n-channel NADGFET and p-channel NADGFET device with a channel length of 40 nm and 50% non-alignment between gate and source/drain. The response of the inverter was tested by a combination of gate dielectric constant (k) and metal work function (ϕ). Three gate dielectrics namely, SiO2 (k = 3.9), Si3N4 (k = 7.2), HfO2 (k = 24), and three metal work function namely tungsten (ϕ = 4.5 eV), molybdenum (ϕ = 4.75 eV), gold (ϕ = 5 eV), were considered in the NADGFET inverter. This paper defines a kϕ index as characterising parameter to explore the best response from inverter configuration with minimum propagation delay, and minimum power consumption at super-high frequency. The paper proposes to analyse the NADGNFET device, in term of ION current, ION/IOFF ratio, cut-off frequency, and gate delay. And observes that low k material with moderate metal work function gives best response. The work then simulates the inverter and group the results into voltage transfer curve (VTC), transient response, and power dissipation category. The result shows that when inverter was subjected to high frequency, all the kϕ combination responds good, however when the inverter was subjected to super-high frequency, the low value of kϕ combination performs well. Thus, the result concludes that SiO2-M2 combination will be best selection to get minimum propagation delay and dynamic power dissipation by the inverter. The test strategy presented in this paper on the basis of kϕ index can serve as benchmark to test inverter device at super-high frequency.

Enhancing ion mobility spectrometry performance through a programmable ion swarm shaping method based on Bradbury-Nielsen gates

The ion gate is a critical element in drift tube ion mobility spectrometry (IMS) as it directly influences the resolving power and sensitivity of the system. However, the conventional Bradbury-Nielsen gate (BNG) often leads to deformation of the ion swarm shape, resulting in reduced resolving power and significant discrimination effects. To address these limitations, we propose a novel method that incorporates a cutting phase following the gate opening. This approach effectively reduces trailing edge deformation, resulting in a maximum resolving power of over 100 and increased signal intensity. Additionally, this method maintains high resolving power even during longer gate opening times. Remarkably, this method not only significantly reduces the mobility discrimination effect but also enables the achievement of reverse discrimination by adjusting the duration of the cutting phase. Consequently, it demonstrates the potential to selectively amplify the peak height of target ions. Our method offers straightforward implementation across all IMS systems utilizing the BNG, thereby significantly improving system performance.

Charge-Dependent Metastable Dissociations of Multiply Charged Decafluorobiphenyl Formed by Femtosecond Laser Pulses.

Femtosecond laser ionization is a unique means to produce multiply charged organic molecules in the gas phase. The charge-dependent chemical reactions of such electron-deficient molecules are interesting from both fundamental and applied scientific perspectives. We have reported the production of quadruply charged perfluoroaromatics; however, they were so stable that we cannot obtain information about their chemical reactions. In general, it might be difficult to realize the conflicting objectives of observing multiply charged molecular ion themselves and their metastable dissociations. In this study, we report the first example showing metastable dissociations of several charge states within the measurable time range of a time-of-flight mass spectrometer. Metastable dissociations were analyzed by selecting a precursor ion with a Bradbury-Nielsen ion gate followed by time-of-flight analysis using a reflectron. We obtained qualitative information that triply and quadruply charged decafluorobiphenyl survived at least in the acceleration region but completely decomposed before entering a reflectron. In contrast, three dissociation channels for singly and one for doubly charged molecular ions were discriminated by a reflectron and determined with the help of ion trajectory simulations.

Reversible Switch in Charge Storage Enabled by Selective Ion Transport in Solid Electrolyte Interphase.

Solid-electrolyte interphases (SEIs) in advanced rechargeable batteries ensure reversible electrode reactions at extreme potentials beyond the thermodynamic stability limits of electrolytes by insulating electrons while allowing the transport of working ions. Such selective ion transport occurs naturally in biological cell membranes as a ubiquitous prerequisite of many life processes and a foundation of biodiversity. In addition, cell membranes can selectively open and close the ion channels in response to external stimuli (e.g., electrical, chemical, mechanical, and thermal), giving rise to "gating" mechanisms that help manage intracellular reactions. We wondered whether the chemistry and structure of SEIs can mimic those of cell membranes, such that ion gating can be replicated. That is, can SEIs realize a reversible switching between two electrochemical behaviors, i.e., the ion intercalation chemistry of batteries and the ion adsorption of capacitors? Herein, we report such SEIs that result in thermally activated selective ion transport. The function of open/close gate switches is governed by the chemical and structural dynamics of SEIs under different thermal conditions, with precise behaviors as conducting and insulating interphases that enable battery and capacitive processes within a finite temperature window. Such an ion gating function is synergistically contributed by Arrhenius-activated ion transport and SEI dissolution/regrowth. Following the understanding of this new mechanism, we then develop an electrochemical method to heal the SEI layer in situ. The knowledge acquired in this work reveals the possibility of hitherto unknown biomimetic properties of SEIs, which will guide us to leverage such complexities to design better SEIs for future battery chemistries.

Determination of Organic Acids in Cucumber Leaves by Solid Phase Extraction–Electrospray Ionization–Ion Mobility Spectrometry (SPE-ESI-IMS)

A solid phase extraction-electrospray ionization-ion mobility spectrometry (SPE-ESI-IMS) method was developed to determine six organic acids in cucumber leaves. The multiplexing IMS using correlation technique was adopted to optimize the signal-to-noise ratio (SNR) and resolution. 90% methanol/water was selected to be the solvent, the flow rate was 120 µL·h−1, the stop frequency of ion gate was 5000 Hz, the ion gate opening period was 0.1 ms, the air flow velocity was 2.0 L·min−1, the electrospray voltage was 3.5 kV, and the drift tube temperature was 90 °C. The cucumber leaves were treated with ultrasound in 50% methanol/water. The analytes were subsequently eluted from an SPE cartridge with 0.1 mol·L−1 HCl, and the extract was neutralized to pH 2–3 with ammonia before freeze-drying. SPE-ESI-IMS enabled the effective determination of citric acid, fumaric acid, lactic acid, malic acid, pyruvic acid, and succinic acid based upon the drift time. The limits of detection were from 0.008 µg·mL−1 to 0.2 µg·mL−1, and the recoveries of spiked samples were from 87.00% to 107.20%. The convenient, sensitive, and efficient developed SPE-ESI-IMS method may be applicable for the determination of organic acids in leaves.