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Serotonin, a monoamine neurotransmitter, is important in both the central nervous system (CNS) and the peripheral nervous system. Malfunction of serotonin signaling leads to various disorders. We studied serotonin signaling from serotonergic neurons inside the ventral nerve cord of Drosophila melanogaster. Serotonergic neurons and stimulated release were visualized and achieved with mCherry and channelrhodopsin‐2 (an optogenetically transfected ion channel), respectively, and two electrochemical techniques quantified serotonin release and vesicular content. Mean vesicular serotonin content released during exocytosis from these neurons was 84 %, considerably higher than reported in previous studies regarding octopamine (4.5 %) and glutamate release (31 %). Serotonin content within all vesicles is uniformly changed when serotonin concentration is inhibited or enhanced. However, serotonin release exhibits two Gaussian distributions: higher frequency of small release events, and similar or slightly higher frequency of large events, resulting in differential release fractions ranging from partial (13–18 %) to full (100 %) release after treatment with agents to either enhance or diminish release. This is the first example of consistent full exocytotic release events we have observed in any system. We suggest one pool of vesicles can release significantly diverse fractions of transmitter load during exocytosis, a potentially novel pathway to regulate exocytosis and neuronal signaling. [ABSTRACT FROM AUTHOR]

Mediated processes using a solid material, often called "solid booster", have been proposed to increase the energy density in redox flow batteries (RFB). The strategy alters the energy storage in the dissolved redox species to a solid active material placed in a compartment of the device. Understanding the reaction kinetics of the dissolved redox mediator and the solid booster is crucial for proposing feasible pairs of solid boosters and dissolved redox mediators. We demonstrate a nanoelectrochemical methodology to monitor the reaction between the dissolved species in solution and the solid active material electrodeposited in recessed carbon nanoelectrodes. Our strategy overcomes issues inherent to standard methodologies, such as mass transport limitation, and evaluation of the intrinsic reactivity of the solid material. As a proof of concept, Prussian blue was electrodeposited in a recessed carbon nanoelectrode and used as a confined‐solid material platform to evaluate the reaction between the reduced form of Prussian blue and triiodide, I3- ${{{\rm I}}_{3}^{-}}$. A high conversion rate of the solid booster was observed in the presence of μM concentrations of the dissolved redox species. The proposed nanoelectrode was successfully employed as a potentiometric sensor to monitor the evolution of the reaction with the dissolved active species. [ABSTRACT FROM AUTHOR]

Nanopores play essential roles in biological processes, such as ion channels and pumps in cellular membranes, and in technological applications such as DNA sequencing. Advancements in nanofabrication techniques have enabled the routine integration of nanopores into solid-state devices, resulting in a plethora of analytical applications. This review explores recent developments in nanopore-enabled electrochemical systems, which have transcended traditional resistive pulse sensing to offer novel capabilities in single-entity studies, stimulus-responsive gating, and point-of-care diagnostics. We highlight recent studies on the design and utility of nanopore electrode arrays, which serve as nanocontainers capable of isolating and analyzing single entities, and extend the discussion to hierarchically organized, stimulus-responsive systems that regulate species transport across nanopores, enriching analytes for ultrasensitive detection. In addition, we review the utilization of probe-assisted nanopore sensing, demonstrating its efficacy in selectively binding and detecting target molecules and ions. Finally, we outline future directions for nanopore-based systems to enhance robustness, achieve high-throughput analysis, and incorporate artificial intelligence for materials design and data analysis, promising transformative impacts on diagnostics and biological research.

Abstract Mediated processes using a solid material, often called “solid booster”, have been proposed to increase the energy density in redox flow batteries (RFB). The strategy alters the energy storage in the dissolved redox species to a solid active material placed in a compartment of the device. Understanding the reaction kinetics of the dissolved redox mediator and the solid booster is crucial for proposing feasible pairs of solid boosters and dissolved redox mediators. We demonstrate a nanoelectrochemical methodology to monitor the reaction between the dissolved species in solution and the solid active material electrodeposited in recessed carbon nanoelectrodes. Our strategy overcomes issues inherent to standard methodologies, such as mass transport limitation, and evaluation of the intrinsic reactivity of the solid material. As a proof of concept, Prussian blue was electrodeposited in a recessed carbon nanoelectrode and used as a confined‐solid material platform to evaluate the reaction between the reduced form of Prussian blue and triiodide, I3- . A high conversion rate of the solid booster was observed in the presence of μM concentrations of the dissolved redox species. The proposed nanoelectrode was successfully employed as a potentiometric sensor to monitor the evolution of the reaction with the dissolved active species.

Single-entity electrochemistry, which employs electrolysis during the collision of single particles on ultramicroelectrodes, has witnessed significant advancements in recent years, enabling the observation and characterization of individual particles. Information on a single aqueous droplet (e.g., size) can also be studied based on the redox species contained therein. Dopamine, a redox-active neurotransmitter, is usually present in intracellular vesicles. Similarly, in the current study, the electrochemical properties of neurotransmitters in submicron droplets were investigated. Because dopamine oxidation is accompanied by proton transfer, unique electrochemical properties of dopamine were observed in the droplet. We also investigated the electrochemical properties of the adsorbed droplets containing DA and the detection of oxidized dopamine by the recollision phenomenon. [ABSTRACT FROM AUTHOR]

The in‐depth study of single cells requires the dynamically molecular information in one particular nanometer‐sized organelle in a living cell, which is difficult to achieve using current methods. Due to high efficiency of click chemistry, a new nanoelectrode‐based pipette architecture with dibenzocyclooctyne at the tip is designed to realize fast conjugation with azide group‐containing triphenylphosphine, which targets mitochondrial membranes. The covalent binding of one mitochondrion at the tip of the nanopipette allows a small region of the membrane to be isolated on the Pt surface inside the nanopipette. Therefore, the release of reactive oxygen species (ROS) from the mitochondrion is monitored, which is not interfered by the species present in the cytosol. The dynamic tracking of ROS release from one mitochondrion reveals the distinctive "ROS‐induced ROS release" within the mitochondria. Further study of RSL3‐induced ferroptosis using nanopipettes provides direct evidence for supporting the noninvolvement of glutathione peroxidase 4 in the mitochondria during RSL3‐induced ROS generation, which has not previously been observed at the single‐mitochondrion level. Eventually, this established strategy should overcome the existing challenge of the dynamic measurement of one special organelle in the complicated intracellular environment, which opens a new direction for electroanalysis in subcellular analysis. [ABSTRACT FROM AUTHOR]

Summary: High-entropy alloys are claimed to possess superior stability due to thermodynamic contributions. However, this statement mostly lies on a hypothetical basis. In this study, we use on-line inductively coupled plasma mass spectrometer to investigate the dissolution of five representative electrocatalysts in acidic and alkaline media and a wide potential window targeting the most important applications. To address both model and applied systems, we synthesized thin films and carbon-supported nanoparticles ranging from an elemental (Pt) sample to binary (PtRu), ternary (PtRuIr), quaternary (PtRuIrRh), and quinary (PtRuIrRhPd) alloy samples. For certain metals in the high-entropy alloy under alkaline conditions, lower dissolution was observed. Still, the improvement was not striking and can be rather explained by the lowered concentration of elements in the multinary alloys instead of the synergistic effects of thermodynamics. We postulate that this is because of dissolution kinetic effects, which are always present under electrocatalytic conditions, overcompensating thermodynamic contributions.

Summary: Efficient and sustainable amino acid synthesis is essential for industrial applications. Electrocatalytic reductive amination has emerged as a promising method, but challenges such as undesired side reactions and low efficiency persist. Herein, we demonstrated a lignin-derived catalyst for alanine synthesis. Carbon nanosheets (CNSs) were synthesized from lignin via a template-assisted method and doped with nitrogen and sulfur to boost reductive amination and suppress side reactions. The resulting N,S-co-doped carbon nanosheets (NS-CNSs) exhibited outstanding electrochemical performance. It achieved a maximum alanine Faradaic efficiency of 79.5%, and a yield exceeding 1,199 μmol h−1 cm−2 on NS-CNS, with a selectivity above 99.9%. NS-CNS showed excellent durability during long-term electrolysis. Kinetic studies including control experiments and theoretical calculations provided further insights into the reaction pathway. Moreover, NS-CNS catalysts demonstrated potential in upgrading real-world polylactic acid plastic waste, yielding value-added alanine with a selectivity over 75%.

MXene, a family of two-dimensional (2D) transition metal carbides and nitrides, has intriguing electrochemical energy storage and electrocatalysis applications. Introducing the electronic metal-support interaction (EMSI) effect is one effective strategy to optimize the catalytic efficiency for MXene-based composites. However, most of the studies concentrate on optimizing the performance of metals rather than supported substrates by using this strategy. In this work, we mainly investigate the influence of an EMSI effect on the performance of the supported substrate (Ti3C2Tx MXene). Detailed scanning electrochemical microscopy and numerical simulations results reveal that the charge distribution on the Ti3C2Tx basal plane (approximate 100 nm-radius) surrounding Au nanoparticles (20 nm-radius) was significantly enhanced as a result of —O being the majority surface functional group on Ti3C2Tx that was attached to Au nanoparticle, and the related hydrogen evolution reaction (HER) activity was much better than that of the unaffected Ti3C2Tx basal plane, which even can be comparable to that of Au. This finding will be helpful for designing new strategies to enhance the overall catalytic performance of various MXene-based composites. [ABSTRACT FROM AUTHOR]

Single-entity electrochemistry, which employs electrolysis during the collision of single particles on ultramicroelectrodes, has witnessed significant advancements in recent years, enabling the observation and characterization of individual particles. Information on a single aqueous droplet (e.g., size) can also be studied based on the redox species contained therein. Dopamine, a redox-active neurotransmitter, is usually present in intracellular vesicles. Similarly, in the current study, the electrochemical properties of neurotransmitters in submicron droplets were investigated. Because dopamine oxidation is accompanied by proton transfer, unique electrochemical properties of dopamine were observed in the droplet. We also investigated the electrochemical properties of the adsorbed droplets containing DA and the detection of oxidized dopamine by the recollision phenomenon.

Molybdenum disulfide (MoS2) is considered as one of the most promising non‐noble‐metal catalysts for hydrogen evolution reaction (HER). To achieve practical application, introducing sulfur (S) vacancies on the inert basal plane of MoS2 is a widely accepted strategy to improve its HER activity. However, probing active sites at the nanoscale and quantitatively analyzing the related electrocatalytic activity in electrolyte aqueous solution are still great challenges. In this work, utilizing high‐resolution scanning electrochemical microscopy, optimized electrodes and newly designed thermal drift calibration software, the HER activity of the S vacancies on an MoS2 inert surface is in situ imaged with less than 20‐nm‐radius sensitivity and the HER kinetic data for S vacancies, including Tafel plot and onset potential, are quantitatively measured. Additionally, the stability of S vacancies over the wide range of pH 0−13 is investigated. This study provides a viable strategy for obtaining the catalytic kinetics of nanoscale active sites on structurally complex electrocatalysts and evaluating the stability of defects in different environments for 2D material‐based catalysts. [ABSTRACT FROM AUTHOR]

We report enhanced electrochemical detection of single water-in-oil emulsion droplets using the nano-impact method. To detect the emulsion droplets, the water molecules in the droplets were directly oxidized (i.e., water splitting) without additional electroactive species when the droplets collided with the ultramicroelectrode. The water molecules in the emulsion droplet cannot be directly electrolyzed in an organic solvent because the emulsifier does not require a hydrophobic electrolyte. To enhance the signal intensity, the electrochemistry of sub-microscale single droplets was investigated considering the charge neutrality and limiting reagent. Therefore, effective electrolysis of the droplets was achieved. Approximately 10% of water molecules in the droplet (55.6 M H2O) were oxidized based on calculations from the electrochemical peak analysis and DLS measurements. [ABSTRACT FROM AUTHOR]

Sodium ion capacitors (SICs) are designed to deliver both high energy and power densities at low cost. Electric double-layer capacitive cathodes are typically used in these devices, but they lead to very limited capacity. Herein, we apply a pseudocapacitive layered ferric vanadate (Fe-V-O) as cathode to construct non-aqueous SICs with both high energy and power densities. The Fe-V-O nanosheets cathode displays remarkable rate capability and cycling stability. The pseudocapacitive sodium storage mechanism of Fe-V-O, with over 83% of total capacity from capacitive contribution, is confirmed by kinetics analysis and ex situ characterizations. The capacitive-adsorption mechanism of hard carbon (HC) anode is demonstrated, and it delivers excellent rate capability. Based on as-synthesized materials, the assembled HC//Fe-V-O SIC delivers a maximum energy density of 194 Wh kg-1 and power density of 3,942 W kg-1. Our work highlights the advantages of pseudocapacitive cathodes for achieving both high energy and power densities in sodium storage devices.

Semiconductor nanomaterials and nanostructured interfaces have important technological applications, ranging from fuel production to electrosynthesis. Their photocatalytic activity is known to be highly heterogeneous, both in an ensemble of nanomaterials and within a single entity. Photoelectrochemical imaging techniques are potentially useful for high-resolution mapping of photo(electro)catalytic active sites; however, the nanoscale spatial resolution required for such experiments has not yet been attained. In this article, we report photoreactivity imaging of two-dimensional MoS 2 photocatalysts by two modes of photoscanning electrochemical microscopy (photo-SECM): diffusion and tunneling-based modes. Diffusion-based (feedback mode) photo-SECM is used to map the electron transfer and hydrogen evolution rates on mixed-phase MoS 2 nanosheets and MoS 2 chemical vapor deposition (CVD)-grown triangles. An extremely high resolution of photoelectrochemical imaging (about 1-2 nm) by the tunneling mode of the photo-SECM is demonstrated.

Nucleation is a fundamentally important step in electrochemical phase transition reactions, e.g., in electrodeposition, which is pertinent for emerging battery technology, nanoparticle synthesis, and many industrial processes. Surface defects have been suggested to enhance nucleation rates. However, directly quantifying the nucleation rates at specific surface sites is challenging due to the ensemble averaging effect in bulk measurements. Herein, we report the measurement of rates and energetics of electronucleation across the model surface of highly oriented pyrolytic graphite (HOPG). Specifically, scanning electrochemical cell microscopy (SECCM) is used to confine the nucleation spatially in the nanoscale cell, allowing one nucleation event to be measured at one time. The scanning capability further allows the mapping of Ag nucleation at the step edge vs basal plane. A stochastic model is developed to extract the nucleation rate and energetics from voltammetric experiments. We observed a ∼57 mV difference in the median nucleation overpotential between the step edge and basal plane, corresponding to a ∼12 kJ mol -1 difference in the nucleation energy barrier. The voltammetric method to measure the nucleation rate explored here can be extended to understand the heterogeneity of nucleation rates in other electrochemical nucleation systems, e.g., metal anode batteries.

N-doped graphene oxides (GO) are nanomaterials of interest as building blocks for 3D electrode architectures for vanadium redox flow battery applications. N- and O-functionalities have been reported to increase charge transfer rates for vanadium redox couples. However, GO synthesis typically yields heterogeneous nanomaterials, making it challenging to understand whether the electrochemical activity of conventional GO electrodes results from a sub-population of GO entities or sub-domains. Herein, single-entity voltammetry studies of vanadyl oxidation at N-doped GO using scanning electrochemical cell microscopy (SECCM) are reported. The electrochemical response is mapped at sub-domains within isolated flakes and found to display significant heterogeneity: small active sites are interspersed between relatively large inert sub-domains. Correlative Raman-SECCM analysis suggests that defect densities are not useful predictors of activity, while the specific chemical nature of defects might be a more important factor for understanding oxidation rates. Finite element simulations of the electrochemical response suggest that active sub-domains/sites are smaller than the mean inter-defect distance estimated from Raman spectra but can display very fast heterogeneous rate constants >1 cm s -1 . These results indicate that N-doped GO electrodes can deliver on intrinsic activity requirements set out for the viable performance of vanadium redox flow battery devices., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Summary: Green self-powered devices based on biodegradable materials have attracted widespread attention. Here, we propose the construction of the transient biotriboelectric nanogenerator (TENG) using green-in-green bionanocompoites. The green-in-green nanocomposites, cellulose nanocrystal (CNC)/polyhydroxybutyrate (PHB), are prepared with a high-pressure molding method. The CNC promotes the degradation and enhances the dielectric constant of CNC/PHB. It further allows for the significant improvement of the triboelectric output of CNC/PHB-based TENG. The voltage output and current output of CNC/PHB-based TENG are 5.7 and 12.5 times higher than those of pristine PHB-based TENG, respectively. Also, the bio-TENG exhibits admirable signal stability in over 20000 cycles. Despite the high hardness of CNC/PHB, a soft but simple-structured arch sensor is successfully assembled using CNC/PHB-based TENG. It can attain the precise real-time monitoring of various human motions. This study may provide new insights into the design/fabrication of green functional materials, and initiate the next wave of innovations in eco-friendly self-powered devices.

Nanoelectrochemistry allows for the investigation of the interaction of per‐ and polyfluoroalkyl substances (PFASs) with silver nanoparticles (AgNPs) and the elucidation of the binding behaviour of PFASs to nanoscale surfaces with high sensitivity. Mechanistic studies supported by single particle collision electrochemistry (SPCE), spectroscopic and density functional theory (DFT) calculations indicate the capability of polyfluorooctane sulfonic acid (PFOS), a representative PFAS, to selectively bind and induce aggregation of AgNPs. Single‐particle measurements provide identification of the "discrete" AgNPs agglomeration (e.g. 2–3 NPs) formed through the inter‐particles F−F interactions and the selective replacement of the citrate stabilizer by the sulfonate of the PFOS. Such interactions are characteristic only for long chain PFAS (‐SO3−) providing a means to selectively identify these substances down to ppt levels. Measuring and understanding the interactions of PFAS at nanoscale surfaces are crucial for designing ultrasensitive methods for detection and for modelling and predicting their interaction in the environment. [ABSTRACT FROM AUTHOR]

Heterogeneous bubble nucleation is one of the most fundamental interfacial processes ranging from nature to technology. There is excellent evidence that surface topology is important in directing heterogeneous nucleation; however, deep understanding of the energetics by which nanoscale architectures promote nucleation is still challenging. Herein, we report a direct and quantitative measurement of single-bubble nucleation on a single silica nanoparticle within a microsized droplet using scanning electrochemical cell microscopy. Local gas concentration at nucleation is determined from finite element simulation at the corresponding faradaic current of the peak-featured voltammogram. It is demonstrated that the criteria gas concentration for nucleation first drops and then rises with increasing nanoparticle radius. An optimum nanoparticle radius around 10 nm prominently expedites the nucleation by facilitating the special topological nanoconfinements that consequently catalyze the nucleation. Moreover, the experimental result is corroborated by our theoretical calculations of free energy change based on the classic nucleation theory. This study offers insights into the impact of surface topology on heterogenous nucleation that have not been previously observed. [ABSTRACT FROM AUTHOR]

Single entity electrochemistry is employed to gain insights into ion solvation in solvent mixtures. To this end, the time required for the oxidation of individual indicator nanoparticles to sparingly soluble products is used to probe ionic diffusion, and hence gain new insights into the solvation properties of solvent mixtures. Herein, water‐ethanol or water‐methanol mixtures of different compositions are analyzed following this new approach, using silver nanoparticle oxidation in the presence of chloride and iodide as a complementary indicator reaction. For increasing concentrations of the bulkier alcohol molecules in the mixtures with water, an increasing content of alcohol molecules in the halide's solvation shell is detected by the observation of hindered halide diffusion. The extent of this solvent replacement is shown to scale with the charge density of the ions and the experimental results are rationalized with respect to literature‐derived thermodynamic data, highlighting the ability of single entity electrochemistry to explore solvation in solvent mixtures. [ABSTRACT FROM AUTHOR]

Scanning electrochemical cell microscopy (SECCM) is increasingly applied to determine the intrinsic catalytic activity of single electrocatalyst particle. This is especially feasible if the catalyst nanoparticles are large enough that they can be found and counted in post-SECCM scanning electron microscopy images. Evidently, this becomes impossible for very small nanoparticles and hence, a catalytic current measured in one landing zone of the SECCM droplet cannot be correlated to the exact number of catalyst particles. We show, that by introducing a ruler method employing a carbon nanoelectrode decorated with a countable number of the same catalyst particles from which the catalytic activity can be determined, the activity determined using SECCM from many spots can be converted in the intrinsic catalytic activity of a certain number of catalyst nanoparticles. [ABSTRACT FROM AUTHOR]

We report enhanced electrochemical detection of single water-in-oil emulsion droplets using the nano-impact method. To detect the emulsion droplets, the water molecules in the droplets were directly oxidized (i.e., water splitting) without additional electroactive species when the droplets collided with the ultramicroelectrode. The water molecules in the emulsion droplet cannot be directly electrolyzed in an organic solvent because the emulsifier does not require a hydrophobic electrolyte. To enhance the signal intensity, the electrochemistry of sub-microscale single droplets was investigated considering the charge neutrality and limiting reagent. Therefore, effective electrolysis of the droplets was achieved. Approximately 10% of water molecules in the droplet (55.6 M H2O) were oxidized based on calculations from the electrochemical peak analysis and DLS measurements.

Understanding the oxidation/reduction dynamics of secondary microparticles formed from agglomerated nanoscale primary particles is crucial for advancing electrochemical energy storage technologies. In this study, the behavior of individual copper hexacyanoferrate (CuHCF) microparticles is explored at both global and local scales combining scanning electrochemical microscopy (SECM), for electrochemical interrogation of a single, but global-scale microparticle, and optical microscopy monitoring to obtain a higher resolution dynamic image of the local electrochemistry within the same particle. Chronoamperometric experiments unveil a multistep oxidation/reduction process with varying dynamics. On the one hand, the global SECM analysis enables quantifying the charge transfer as well as its dynamics at the single microparticle level during the oxidation/reduction cycles by a redox mediator in solution. These conditions allow mimicking the charge storage processes in these particles when they are used as solid boosters in redox flow batteries. On the other hand, optical imaging with sub-particle resolution allows the mapping of local conversion rates and state-of-charge within individual CuHCF particles. These maps reveal that regions of different material loadings exhibit varying charge storage capacities and conversion rates. The findings highlight the significance of porous nanostructures and provide valuable insights for designing more efficient energy storage materials., (© 2024 The Authors. Small published by Wiley‐VCH GmbH.)

The transport of molecules and ions through biological nanopores is governed by interaction networks among restricted ions, transported molecules, and residue moieties at pore inner walls. However, identification of such weak ion fluctuations from only few tens of ions inside nanopore is hard to achieve owing to electrochemical measurement limitations. Here, we developed an advanced frequency method to achieve qualitative and spectral analysis of ion interaction networks inside a nanopore. The peak frequency fm reveals the dissociation rate between nanopore and ions; the peak amplitude am depicts the amount of combined ions with the nanopore after interaction equilibrium. A mathematical model for single‐molecule frequency fingerprint achieved the prediction of interaction characteristics of mutant nanopores. This single‐molecule frequency fingerprint is important for classification, characterization, and prediction of synergetic interaction networks inside nanoconfinement. [ABSTRACT FROM AUTHOR]

The nuclear pore complex (NPC) is the proteinaceous nanopore that solely mediates the transport of both small molecules and macromolecules between the nucleus and cytoplasm of a eukaryotic cell to regulate gene expression. In this personal account, we introduce recent progress in our nanoelectrochemical study of molecular transport through the NPC. Our work represents the importance of chemistry in understanding and controlling of NPC‐mediated molecular transport to enable the efficient and safe delivery of genetic therapeutics into the nucleus, thereby fundamentally contributing to human health. Specifically, we employ nanoscale scanning electrochemical microscopy to test our hypothesis that the nanopore of the NPC is divided by transport barriers concentrically into peripheral and central routes to efficiently mediate the bimodal traffic of protein transport and RNA export, respectively, through cooperative hydrophobic and electrostatic interactions. [ABSTRACT FROM AUTHOR]

Summary: Electrosynthesis is to use electricity to drive chemical reactions for chemical synthesis and is potentially a green approach to fuel and energy sustainability. Nanostructured catalysts play an important role in promoting electrochemical reactions under green chemistry conditions. This perspective first provides a brief tutorial on electrosynthesis and the roles the nanocatalysts play in the synthesis. It then outlines the common strategies used to develop nanocatalysts for hydrogen evolution reaction, CO2 reduction reaction, and biomass upgrading. The perspective further summarizes the current methodologies that have been developed for scaling-up synthesis of nanocatalysts, which will be essential for the electrosynthesis to become a viable industry approach.

Electrochemical AFM is a powerful tool for the real‐space characterization of catalysts under realistic electrochemical CO2 reduction (CO2RR) conditions. The evolution of structural features ranging from the micrometer to the atomic scale could be resolved during CO2RR. Using Cu(100) as model surface, distinct nanoscale surface morphologies and their potential‐dependent transformations from granular to smoothly curved mound‐pit surfaces or structures with rectangular terraces are revealed during CO2RR in 0.1 m KHCO3. The density of undercoordinated copper sites during CO2RR is shown to increase with decreasing potential. In situ atomic‐scale imaging reveals specific adsorption occurring at distinct cathodic potentials impacting the observed catalyst structure. These results show the complex interrelation of the morphology, structure, defect density, applied potential, and electrolyte in copper CO2RR catalysts. [ABSTRACT FROM AUTHOR]

Nanoscale scanning electrochemical probe microscopy started to elucidate the heterogeneity of electrocatalytic activity at electrode surfaces. However, understanding the heterogeneity in product selectivity, another crucial aspect of interfacial reactivity, remains challenging. Herein, we introduce a method combining scanning electrochemical microscopy (SECM) and scanning electrochemical cell microscopy (SECCM) to enable the spatially resolved mapping of both activity and selectivity in electrocatalysis. A dual-channel nanopipette probe was developed: one channel for activity mapping and the other for product detection with a high collection efficiency (>95%) and sensitivity. Simultaneous mapping of activity and selectivity in the oxygen reduction reaction (ORR) is demonstrated. Combined with colocalized crystal orientation mapping, we uncover the local electrocatalytic performance of ORR at different facets on polycrystalline Pt and Au. The high-resolution selectivity mapping enabled by our method with colocalized structural characterization can provide structure-activity-selectivity relationships that are often unavailable in ensemble measurement, holding promise for understanding key structural motifs controlling interfacial reactivity.

Artificial van der Waals heterostructures, obtained by stacking two-dimensional (2D) materials, represent a novel platform for investigating physicochemical phenomena and applications. Here, the electrochemistry at the one-dimensional (1D) edge of a graphene sheet, sandwiched between two hexagonal boron nitride (hBN) flakes, is reported. When such an hBN/graphene/hBN heterostructure is immersed in a solution, the basal plane of graphene is encapsulated by hBN, and the graphene edge is exclusively available in the solution. This forms an electrochemical nanoelectrode, enabling the investigation of electron transfer using several redox probes, e.g., ferrocene(di)methanol, hexaammineruthenium, methylene blue, dopamine and ferrocyanide. The low capacitance of the van der Waals edge electrode facilitates cyclic voltammetry at very high scan rates (up to 1000 V s -1 ), allowing voltammetric detection of redox species down to micromolar concentrations with sub-second time resolution. The nanoband nature of the edge electrode allows operation in water without added electrolyte. Finally, two adjacent edge electrodes are realized in a redox-cycling format. All the above-mentioned phenomena can be investigated at the edge, demonstrating that nanoscale electrochemistry is a new application avenue for van der Waals heterostructures. Such an edge electrode will be useful for studying electron transfer mechanisms and the detection of analyte species in ultralow sample volumes., (© 2023 The Authors. Small published by Wiley‐VCH GmbH.)

Summary: The carbon-free production of hydrogen from water splitting holds grand promise for the critical energy and environmental challenges. Herein, few-atomic-layers iron (FeFAL) anchored on GaN nanowire arrays (NWs) is demonstrated as a highly active hydrogen evolution reaction catalyst, attributing to the spatial confinement and the nitrogen-terminated surface of GaN NWs. Based on density functional theory calculations, the hydrogen adsorption on FeFAL:GaN NWs is found to exhibit a significantly low free energy of −0.13 eV, indicative of high activity. Meanwhile, its outstanding optoelectronic properties are realized by the strong electronic coupling between atomic iron layers and GaN(10ī0) together with the nearly defect-free GaN NWs. As a result, FeFAL:GaN NWs/n+-p Si exhibits a prominent current density of ∼ −30 mA cm−2 at an overpotential of ∼0.2 V versus reversible hydrogen electrode with a decent onset potential of +0.35 V and 98% Faradaic efficiency in 0.5 mol/L KHCO3 aqueous solution under standard one-sun illumination.

At the most fundamental level, the behavior of tissue is governed by the activity of its single cells. A detailed examination of single-cell biology is necessary in order to gain a deeper understanding of disease progression. While single-cell genomics and transcriptomics are mature due to robust amplification strategies, the metabolome is difficult to quantify. Nanoelectrochemical techniques stand poised to quantify single-cell metabolism as a result of the fabrication of nanoelectrodes, which allow one to make intracellular electrochemical measurements. This article is concerned with intracellular nanoelectrochemistry, focusing on the sensitive and selective quantification of various metabolites within a single, living cell. We will review the strong literature behind this field, discuss the potential deleterious effects of passing charge inside cells, and provide future outlooks for this promising avenue of inquiry. We also present a mathematical relationship based on Faraday's Law and bulk electrolysis theory to examine the consumption of analyte within a cell due to passing charge at the nanotip. Graphical abstract [ABSTRACT FROM AUTHOR]

Label-free biosensing has been the dream of scientists and biotechnologists as reported by Vollmer and Arnold (Nat Methods 5:591–596, 2008). The ability of examining living cells is crucial to cell biology as noted by Fang (Int J Electrochem 2011:460850, 2011). Chemical measurement with electrodes is label-free and has demonstrated capability of studying living cells. In recent years, nanoelectrodes of different functionality have been developed. These nanometer-sized electrodes, coupled with scanning electrochemical microscopy (SECM), have further enabled nanometer spatial resolution study in aqueous environments. Developments in the field of nanoelectrochemistry have allowed measurement of signaling species at single cells, contributing to better understanding of cell biology. Leading studies using nanoelectrochemistry of a variety of cellular signaling molecules, including redox-active neurotransmitter (e.g., dopamine), non-redox-active neurotransmitter (e.g., acetylcholine), reactive oxygen species (ROS), and reactive nitrogen species (RNS), are reviewed here. [ABSTRACT FROM AUTHOR]

The use of renewable energy by means of electrochemical techniques by converting H2O, CO2 and N2 into chemical energy sources and raw materials, is the basis for securing a future sustainable "green" energy supply. Some weaknesses and inconsistencies in the practice of determining the electrocatalytic performance, which prevents a rational bottom‐up catalyst design, are discussed. Large discrepancies in material properties as well as in electrocatalytic activity and stability become obvious when materials are tested under the conditions of their intended use as opposed to the usual laboratory conditions. They advocate for uniform activity/stability correlations under application‐relevant conditions, and the need for a clear representation of electrocatalytic performance by contextualization in terms of functional investigation or progress towards application is emphasized. [ABSTRACT FROM AUTHOR]

The catecholamines, mainly dopamine (DA), are present in the cellular cytosol with low abundance, while, play key roles in various neurodegenerative disorders. Here, platinized nanocavity carbon electrodes are employed to analyze cytosolic catecholamines in a single living PC12 cell, which is not easily quantified using the classic electrodes. The confined structure and excellent conductivity in the platinized nanocavity accelerate the electron transfer of the DA, resulting in a low detection limit down to 50 nM. The sensitivity of DA detection is improved to be 10.73 pA mM−1 nm−1 in the response range of 50 nM–100 μM, which guarantees quantitative analysis of cytosolic catecholamines with low abundance. Eventually, the platinized nanocavity electrode is employed to detect cytosolic catecholamines in a single PC12 cell without an obvious interruption of cellular catecholamine level. The cytosolic catecholamines in a single PC12 cell is measured in situ to be 0.1 μM, which is achieved for the first time at the single cell level using the electrochemical method. The results demonstrate that the nanocavity electrode with a high sensitivity could offer a promising means to dynamically track catecholamines in a single cell. The low abundant cytosolic catecholamines in a single PC12 cell are successfully quantified with high sensitivity using a platinized nanocavity carbon electrodes with the confined structure and excellent conductivity. [Display omitted] • Accurate measurement of fluctuation of the cytosolic catecholamines is critical to deeply understand their roles in various neurodegenerative disorders. • The platinized nanocavity electrodes with the confined structure are employed to analyze the low abundant cytosolic catecholamines in a single living PC12 cell. • The cytosolic catecholamines in a single PC12 cell is measured in situ to be 0.1 μM, which is achieved for the first time at the single cell level using the electrochemical method. [ABSTRACT FROM AUTHOR]

Nanopore techniques are experiencing a gallop since it walked out the notebook and show its charm on the science arena. The nanoscale pore offers a single-molecule resolution with a label-free and high-selective manner for the research of molecular structures, molecular dynamics, single-molecule reactions and for a variety of applications in biophysics and bionanotechnology. In this review, we introduce the construction of three types of nanopore platforms along with the latest progress in DNA sensing, structure and dynamics analysis of peptides/proteins, and the detection of redox reactions with new sensing mechanisms. Then, we depict nanopore data processing methods which provide an insight of data mining under the background of big data. We could fully expect the great impact of nanopore techniques on not only for DNA sequencing and sensing applications, but also in protein sequencing and clinical diagnostics. [ABSTRACT FROM AUTHOR]

Blocking electrochemistry, a subfield of single-entity electrochemistry, enables in-situ sizing of redox-inactive particles. This method exploits the adsorptive impact of individual insulating particles on a microelectrode, which decreases the electrochemically active surface area of the electrode. Against the background of an electroactive redox reaction in solution, each individual impacting particle results in a discrete current drop, with the magnitude of the drop corresponding to the size of the blocking particle. One significant limitation of this technique is "edge effects", resulting from the inhomogeneous flux of the redox species' diffusion due to increased mass transport to the edge of the disk electrode surface. "Edge effects" cause increased errors in size detection, resulting in poor analytical precision. Here, we use computational simulations to demonstrate that inhomogeneous diffusional edge flux of quasi-reversible redox species is mitigated at lowered overpotentials. This phenomenon is further illustrated experimentally by lowering the applied potential such that the system is operating under a kinetically-controlled regime instead of a diffusion-limited regime, which mitigates edge effects and increases particle sizing precision significantly. In addition, we found this method to be generalizable, as the precision enhancement is not limited to geometrically spherical particles but also occurs for cubic particles. This work presents a simple, novel methodology for edge effect mitigation with general applicability across different particle types. [ABSTRACT FROM AUTHOR]

Abstract: Lithium (Li) dendrite formation is one of the major hurdles limiting the development of Li‐metal batteries, including Li‐O2 batteries. Herein, we report the first observation of the dendrite‐free epitaxial growth of a Li metal up to 10‐μm thick during charging (plating) in the LiBr‐LiNO3 dual anion electrolyte under O2 atmosphere. This phenomenon is due to the formation of an ultrathin and homogeneous Li2O‐rich solid‐electrolyte interphase (SEI) layer in the preceding discharge (stripping) process, where the corrosive nature of Br− seems to give rise to remove the original incompact passivation layer and NO3− oxidizes (passivates) the freshly formed Li surface to prevent further reactions with the electrolyte. Such reactions keep the SEI thin (<100 nm) and facilitates the electropolishing effect and gets ready for the epitaxial electroplating of Li in the following charge process. [ABSTRACT FROM AUTHOR]

Abstract: An activation step is essential for yielding nitrogen‐doped mesoporous carbon (NMCs) oxygen reduction reaction (ORR) electrocatalysts from biomass. Though many solely KOH or ZnCl2 activated carbon materials have been synthesized with fine ORR activity, there a deep discussion of activated‐carbon‐based electrocatalysts obtained from different activation processes is still lacking. In this paper, we systemically compare radish‐derived NMCs that underwent different activation processes, and reveal the relationship between structure and activity of these activated carbons. We showed that though ZnCl2 is not an effective porogen compared with KOH, owing to a more open pore structure along with effective preservation of nitrogen heteroatoms, ZnCl2 assisted activated carbon could show significantly improved ORR activity, with an onset potential of 0.91 V (vs. RHE), close to benchmark Pt/C catalysts and even better extended operation stability and stronger tolerance to methanol crossover compared with commercial Pt/C catalysts. Thus we proved that ZnCl2 assisted activation is better than exclusively self‐activation or KOH assisted activation in preparing biomass‐derived ORR catalysts. [ABSTRACT FROM AUTHOR]

Abstract: In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size‐ and shape‐controlled ligand‐free Cu nanocubes during CO2 electroreduction (CO2RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X‐ray absorption fine‐structure spectroscopy and X‐ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuOx species observed were found to lead to a suppression of the selectivity for multi‐carbon products (i.e. C2H4 and ethanol) versus CH4. A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of CuI species under CO2RR in the former samples. Both factors are held responsible for the higher C2/C1 product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO2RR selectivity. [ABSTRACT FROM AUTHOR]

Studying electrocatalytic metal nanoparticles (NPs) at the single particle level is highly desirable to unfold their structure-function correlation. In this report, we present the fabrication and spectroelectrochemistry characteristics of light-scattering single Au NP at the tip of an electrochemically etched sharp tungsten (W)electrode. Au NPs with a tunable particle size (≥60 nm) can be obtained at the W tips by adjusting the Au electrodeposition conditions. Catalyzed electrogenerated chemiluminescence (ECL) from Tris(2,2′-bipyridine) ruthenium (II) (Ru(bpy) 3 2+ )/Tri- n -propylamine (TPrA) system at single Au NP electrode shows an increase in its intensity with Au NP particle size in the range of 300 nm–500 nm. The potential application of these single Au NP electrodes in the studies of electrocatalytic reaction and spectroelectrochemistry at the nanometer scale is demonstrated using dark-field scattering (DFS) spectroelectrochemistry method. The decrease in DFS intensity upon oxidation of hydrazine at the single Au NP electrode is attributed to the formation of low-refraction-index N 2 near the surface of the Au NP to decrease its light scattering cross-section. Single Au NP electrode presented in this work would help improve instrument capability of scanning electrochemical microscope (SECM) and near-field scanning optical microscope (NSOM) techniques for ultrasensitive electrochemical analysis. [ABSTRACT FROM AUTHOR]

Novel electronic detection techniques are being increasingly sought as components of highly scalable technologies for high-throughput biosensing applications. Among the techniques being considered, electrochemical detection offers an attractive alternative. Advancement in nanoscale electrochemistry makes this an opportune moment to consider the prospects of its integration with CMOS processes. This paper focuses on the new properties and challenges that emerge from the downscaling of electrode dimensions, focusing, in particular, on redox-cycling-based approaches to nanoscale electrochemical devices. We explore the possibilities of interfacing arrays of such devices with CMOS process technology to create highly parallelized integrated platforms. We cite selective examples to provide a qualitative overview of the general design constraints that attend any system-level integration process. We also discuss several challenges that limit the scalability of such platforms and that need to be overcome to create reliable and robust CMOS-integrated electrochemical biosensing platforms.

Long, straight mesoscale silver wires have been fabricated from AgNO3 electrolyte via electrodeposition without the help of templates, additives, and surfactants. Although the wire growth speed is very fast due to growth under non-equilibrium conditions, the wire morphology is regular and uniform in diameter. Structural studies reveal that the wires are single-crystalline, with the [112] direction as the growth direction. A possible growth mechanism is suggested. Auger depth profile measurements show that the wires are stable against oxidation under ambient conditions. This unique system provides a convenient way for the study of self-organization in electrochemical environments as well as for the fabrication of highly-ordered, single-crystalline metal nanowires.