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The nonuniform diffusion profile to the edge of many multifunctional microelectrodes has the potential to give rise to distortions in its imaging capability, reducing the spatial accuracy of the techniques they are used in. In this work, numerical simulations are used to predict these distortions for dual-barrel electrodes used in the combined feedback/ generation-collection mode of scanning electrochemical microscopy imaging a model substrate. The sensitivity of this distortion to tip-substrate distance, electrolyte composition, and size and shape of a reactive substrate feature are discussed. Multifunctional microelectrodes have promising applications in the field of high-speed electrochemical imaging, allowing local in situ measurements of kinetics, pH, and topography to be performed consecutively rather than concurrently.1,2 The challenges associated with aligning microscopy techniques are eliminated by integrating multiple electrodes (probes) into the same sensor. A broad range of multifunctional probe geometries have been fabricated, including modified AFM tips,3-5 crescent moons,6-8 multibarrel, 9-14 and disk15,16 geometries, that are suitable for tandem techniques involving scanning electrochemical microscopy (SECM),14,17 scanning ion conductance microscopy (SICM), 2 , 6-8 ,10-13,17 scanning dropl e t methods (SDM),9,10,15,18 atomic force microscopy (AFM),1,3,4,19,20 and others.15 These techniques have been used to study substrates such as nanoparticles and nanocrystals,10,11,13,18 corroding materials,5,21 single-membrane pores,3,4,8,17 and biological samples.12,14,16,19 Despite this extensive development in multifunctional microelectrodes, the relationship between probe shape and response remains underdeveloped for multifunctional microelectrodes outside of discussions of probe size. [ABSTRACT FROM AUTHOR]

The damage to a metal is significantly enhanced when simultaneously exposed to a corrosive solution and a cyclic mechanical stress. However, decoupling the contributions from each damage mechanisms is difficult. Localised electrochemical techniques, in particular scanning electrochemical microscopy (SECM), scanning electrochemical cell microscopy (SECCM), scanning kelvin probe force microscopy (SKPFM), and scanning vibrating electrode technique (SVET), can be advantageous when determining corrosion fatigue damage mechanisms and local phenomena, such as the transition between a corrosion pit and a fatigue crack. The recent corrosion fatigue literature is reviewed to highlight the usefulness of each localised electrochemical technique and how they can contribute to advancing the corrosion fatigue field. [Display omitted] [ABSTRACT FROM AUTHOR]

The article offers information on the recent trends in scanning probe techniques that are useful in understanding magnesium alloy corrosion.

The cytotoxicity of menadione on hepatocytes was studied by using the substrate generation/tip collection mode of scanning electrochemical microscopy by exposing the cells to menadione and detecting the menadione-S-glutathione conjugate (thiodione) that is formed during the cellular detoxication process and is exported from the cell by an ATP-dependent pump. This efflux was electrochemically detected and allowed scanning electrochemical microscopy monitoring and imaging of single cells and groups of highly confluent live cells. Based on a constant flux model, ∼6 × 106 molecules of thiodione per cell per second are exported from monolayer cultures of Hep G2 cells. [ABSTRACT FROM AUTHOR]

The uptake of menadione (2-methyl-1,4-naphthoquinone), which is toxic to yeast cells, and its expulsion as a glutathione complex were studied by scanning electrochemical microscopy. The progression of the in vitro reaction between menadione and glutathione was monitored electrochemically by cyclic voltammetry and correlated with the spectroscopic (UV-visible) behavior. By observing the scanning electrochemical microscope tip current of yeast cells suspended in a menadione-containing solution, the export of the conjugate from the cells with time could be measured. Similar experiments were performed on immobilized yeast cell aggregates stressed by a menadione solution. From the export of the menadione-glutathione conjugate detected at a 1-μm-diameter electrode situated 10 μm from the cells, a flux of about 30,000 thiodione molecules per second per cell was extracted. Numerical simulations based on an explicit finite difference method further revealed that the observation of a constant efflux of thiodione from the cells suggested the rate was limited by the uptake of menadione and that the efflux through the glutathione-conjugate pump was at least an order of magnitude faster. [ABSTRACT FROM AUTHOR]

Mussel byssus offers bio‐inspired designs for advanced adhesives, coatings, and supramolecular hydrogels. Solidification of secreted proteins into mechanically robust fibers is triggered by a pH jump from acidic fluid condensates to basic seawater conditions driving protein crosslinking by metal coordination with 3,4‐dihydroxyphenylalanine (DOPA). Knowledge of the dynamic and localized pH changes during secretion is currently lacking. Yet, this information is crucial for controlling the gelation and properties of mussel‐inspired DOPA‐modified materials. Here, an iridium oxide‐based pH microsensor combining high mechanical stability and spatial resolution is used to measure the acidic pH during byssus secretion and to map mussel‐inspired hydrogels revealing compositional heterogeneity resulting in mechanically distinct regions. Within the hydrogel, high pH values >12 are measured which are detrimental to DOPA due to its strong propensity for oxidation, which adversely alters gel properties. This demonstrates the need to improve preparation methods of mussel‐inspired adhesive materials to more closely mimic native processes. [ABSTRACT FROM AUTHOR]

Scanning electrochemical microscopy (SECM) is an electroanalytical scanning probe technique capable of imaging substrate topography and local reactivity with high resolution. Since its inception in 1989, it has expanded into a wide variety of research areas including biology, corrosion, energy, kinetics, instrumental development, and surface modification. In the past 25 years, over 1800 peer-reviewed publications have focused on SECM, including several topical reviews. However, these reviews often omit key details, forcing readers to search the literature. In this review, we provide a comprehensive summary of the experimental parameters (e.g., solvents, probes, and mediators) used in all SECM publications since 1989, irrespective of the application. It can be used to rapidly assess experimental possibilities and make an informed decision about experimental design. In other words, it is a practical guide to SECM. [ABSTRACT FROM AUTHOR]

In scanning electrochemical microscopy (SECM), an approach curve performed in feedback mode involves the downward displacement of a microelectrode toward a substrate while applying a bias to detect dissolved electroactive species at a diffusion-limited rate. The resulting measured current is said to be at steady state. In order to reduce the required measurement time, the approach velocity can be increased. In this paper, we investigate experimentally and theoretically the combination of diffusion and convection processes related to a moving microdisk electrode during feedback approaches. Transient modeling and numerical simulations with moving boundaries are performed, and the results are compared to the experimental approach curves obtained in aqueous solution. The geometry and misalignment of the microelectrode influence the experimental approach curves recorded at high approach velocities. The effects are discussed through the decomposition of the current into transient diffusional, radial convectional, and axial convectional contributions. Finally a ready-to-use expression is provided to rapidly evaluate the maximal approach velocity for steady state measurements as a function of the microelectrode geometry and the physical properties of the media. This expression holds for the more restrictive case of negative feedback as well as other modes, such as SECM approach curves performed at substrates displaying first order kinetics. [ABSTRACT FROM AUTHOR]

The development of a reproducible procedure for the fabrication of Pt disk-shaped microelectrodes with characteristic dimensions ranging from 50 nm to 1 μm in diameter was carried out using a laser pulling technique. The governing physical phenomena involved in their fabrication are discussed, and the importance of adding a critical quartz thinning step in the general procedure is demonstrated. The preparation of the microelectrodes involves sealing a platinum wire inside a quartz tubing using a pipet puller, thinning the composite material (platinum/quartz assembly), and laser pulling it to obtain two microelectrodes. The resulting microelectrodes display reproducible well-controlled geometry, which is important to downstream quantitative scanning electrochemical studies and imaging. Mechanical polishing of the microelectrode is required and remains the critical step in the fabrication of nanometer size electrodes. Following production, the microelectrodes are characterized by electron microscopy, scanning electrochemical microscopy, and cyclic voltammetry. Development of these microelectrodes is motivated by their subsequent application to electrocatalysis and their potential in theoretical study because of their well-defined geometry. [ABSTRACT FROM AUTHOR]

The article reports on the use of scanning electrochemical microscopy (SECM) as an analytical technique to monitor electrochemical activity of a surface. The fundamental element of SECM is a small-scale electrode that serves as high spatial resolution, recording alterations in electrochemical potential having remarkable sensitivity and mobile probe. SECM measurements fuse with other biosensing techniques can conduct multiple experiments on a living project.

The design of stable redox active liposomes where the organometallic electroactive pendent was covalently bound to the phospholipid headgroup through a phospholipase D (PLD)-catalyzed transphosphatidylation reaction between a choline-bearing phospholipid and a primary alcohol containing a ferrocene derivative is reported. The functionalization of a liposome surface with this organometallic redox phospholipid allowed the study of membrane-bound electrochemical reactions, which are important in the design of redox-sensitive liposome delivery systems. [ABSTRACT FROM AUTHOR]

The fabrication and characterization of novel micropipet probes for use in scanning electrochemical microscopy (SECM) are described. These can be used to dispense small (pL) amounts of a solution while monitoring the electrochemical response at a substrate and at a ring electrode tip on the micropipet probe. The probes were constructed by insulating gold-coated borosilicate micropipets with electrophoretic paint and exposing a ring electrode at the tip by heat treatment. Characterization of the probes was performed using scanning electron microscopy, cyclic voltammetry, and SECM approach curve experiments. Routine construction of tips with diameters of the order of 3 μm was possible using this technique. The probes exhibited stable steady-state currents and positive and negative feedback approach curves that agreed with those predicted by theory. Demonstrative SECM imaging experiments were performed using a picodispenser to continuously dispense an electroactive solution (ferrocenemethanol) to the SECM cell while the probe was located within a few micrometers of a Pt substrate surface. Oxidation of the dispensed electroactive solution was performed at the substrate, and feedback currents were measured at the probe tip by holding the gold ring at a reducing potential. This mode of tip-dispensing SECM was used to obtain images of a platinum substrate electrode while monitoring both the substrate current and the feedback current at the probe. [ABSTRACT FROM AUTHOR]

Challenges facing enzyme-based electrochemical sensors include substrate specificity, batch to batch reproducibility, and lack of quantitative metrics related to the effect of enzyme immobilization. We present a quick, simple, and general approach for measuring the effect of immobilization and cross-linking on enzyme activity and substrate specificity. The method can be generalized for electrochemical biosensors using an enzyme that releases hydrogen peroxide during its catalytic cycle. Using as proof of concept RgDAAO-based electrochemical biosensors, we found that the Michaelis-Menten constant (Km) decreases post immobilization, hinting at alterations in the enzyme kinetic properties and thus substrate specificity. We confirm the decrease in Km electrochemically by characterizing the substrate specificity of the immobilized RgDAAO using chronoamperometry. Our results demonstrate that enzyme immobilization affects enzyme substrate specificity and this must be carefully evaluated during biosensor development. [ABSTRACT FROM AUTHOR]

Scanning electrochemical microscopy (SECM) has recently been reported as a convenient technique to characterize the apparent diffusion coefficients in porous media (D ⋆) such as lithium-ion battery electrodes. The technique relies on hemispherical diffusion at the probe in the presence and absence of porous media. However, transition towards cylindrical diffusion follows as the diffusion layer becomes comparable to the media thickness, gradually limiting direct correlation between D ⋆ and the SECM probe steady state current. In this work, we examine the experimental parameters that define this transitional frontier using simulations. A best practice thickness criterium is derived that ensures that the measured steady state current is ≳ 90% of that found in the ideal hemispherical case. Below this thickness limit the response was found to follow an empirical formulation with only two variables. Fundamentally, this quantifies diffusion in the transition regime between hemispherical and cylindrical transport. Practically, this correction formulation may be included into standard steady-state current expression to account for the deviation from hemispherical transport in "thin" electrodes. The analysis consolidates SECM as a reliable tool to characterize liquid phase mass transport within porous films over wide range of thicknesses, including films supported on blocking substrates, like lithium-ion battery electrodes. [Display omitted] • Scanning electrochemical microscopy (SECM) porous media electrolyte transport. • Thin/thick threshold for SECM measurement of lithium-ion battery electrodes. • Empirical expressions for SECM analysis of high power thin electrodes. [ABSTRACT FROM AUTHOR]

Scanning electrochemical microscopy (SECM) is increasingly applied to study and image live cells. Quantitative analyses of biological systems, however, still remain challenging. In the presented study, single human adenocarcinoma cervical cancer cells are electrochemically investigated by means of SECM. The target cell's electrochemical response is observed over time under the influence of green tea catechins (GTC), which are suggested to offer chemopreventive and therapeutic effects on cancer. The electrochemical response of living target cells is measured experimentally and quantified in an apparent heterogeneous rate constant by using a numerical model, based on forced convection during high speed SECM imaging. The beneficial effect of GTC on cancer cells could be confirmed by SECM, and the presented study shows an alternative approach toward unraveling the mechanisms involved during inhibition of carcinogenesis. [ABSTRACT FROM AUTHOR]

Abstract: The chemical modification of an sp2 hybridized carbon surface in a controllable manner is very challenging but also crucial for many applications. An inverse electron demand Diels–Alder (IEDDA) reaction using microcontact printing technique is introduced to spatially control the modification of a highly ordered pyrolytic graphite (HOPG) surface under ambient conditions. The covalent modification was characterized by Raman spectroscopy, XPS, and SECM. Tetrazine derivatives can effectively react with an HOPG surface and with microcontact printing methods resulting in spatially patterned surfaces being produced with micrometer‐scale resolution. [ABSTRACT FROM AUTHOR]

Electrogenerated chemiluminescence (ECL) based sensors have the intrinsic advantage of having zero theoretical background signal, derived from the electrochemical initiation of the luminescence process. Since the limit of detection (LOD) for sensors is defined as three times the noise of the background over the sensitivity of the system, further improvement to an ECL based detection limit is tied to improving sensitivity. Enhancing ECL sensitivity can be achieved through optimizing the mechanistic or kinetic performance of the reagents. While the mechanism for many luminophore-coreactant pairs have been established, the kinetics for the competing homogeneous reactions responsible for photon emission have not been directly resolved. This is due to the difficulty in experimentally probing and isolating a single homogeneous reaction while multiple simultaneous heterogeneous and homogeneous reactions are occurring. Combining the techniques of spectroelectrochemistry and finite element modeling, we monitor the homogeneous reactions for the coreactant pair, tris(2,2'-bipyridine)ruthenium(II) (Ru(BPY)32+) and tripropylamine (TPA). Corresponding trends found in the experimental absorbance and theoretical concentration profiles demonstrated that the reaction between Ru(BPY)33+ and TPA• intermediates proceeds significantly faster than the other available pathways. The identification of the oxidized intermediates as the dominant electron transfer pathway implies that the screening of luminophore and coreactant pairs that increase the stability of these kinetically labile intermediates would increase ECL sensitivity and ultimately performance. [ABSTRACT FROM AUTHOR]

Cancer cells can develop multidrug resistance (MDR) after prolonged exposure to chemotherapeutic drugs, which is a severe impediment to successful treatment. MDR is typically associated with transmembrane proteins mediating efflux of administered drugs, thereby keeping their intracellular concentration below the threshold required to kill cells. Although expression assays based on flow cytometry and immunostaining have shown that multidrug resistance-associated protein 1 (MRP1) is prevalent in many cancer types, the functional activity of this efflux pump is more difficult to elucidate, especially at the single-cell level. Herein, we report the measurement of MRP1 functional activity in individual cancer cells using scanning electrochemical microscopy (SECM). Cells were cultured onto plastic substrates containing selective adhesion sites. Optical microscopy and SECM revealed that cells adapt to the underlying surface, while MRP1 functional activity increases once the dimensions of the adhesive islands become smaller than those of the cell itself. Time-lapse SECM imaging revealed a suitable window of 30 min to complete each measurement before the cell undergoes blebbing, which is associated with a considerable increase in functional activity. Distinct cell populations were produced by performing a doxorubicin drug challenge on two parental cell lines (e.g., wild-type HeLa cells and MRP1-overexpressing HeLa-R cells). Expression and functional activity of MRP1 were determined using flow cytometry and SECM, and our findings show that these parameters do not directly correlate. This suggests that functional activity may represent a powerful indicator of a cancer cell's response to chemotherapeutic treatment and should improve our understanding of efflux mechanisms based on MRP1. [ABSTRACT FROM AUTHOR]

A new type of flow platform for electrochemical and spectroelectrochemical measurements is presented. Finite element method simulations confirm that the hydrodynamic profile within the device is not turbulent and provides an analytical platform for the investigation of homogeneous kinetics, radical lifetimes, and reaction mechanisms. The modular "plug and play" configuration of the platform allows one to carry out electrochemistry and spectroscopy individually or simultaneously. Specific demonstrations of electroanalytical measurements using the flow system platform includes voltammetric analysis of organometallic compounds and quantitative analysis of ascorbic acid in commercial orange juice samples. Combined spectroelectrochemical demonstrations include electrochemical luminescence of ruthenium compounds and ligand exchange reactions of iron complexes using UV-vis spectroscopy. [ABSTRACT FROM AUTHOR]

We present herein localized galvanostatic and potentiodynamic measurements on lithium iron phosphate (LFP) particles, using the combination of a scanning micropipette contact method (SMCM) and scanning electron microscopy (SEM). The proposed technique allows small substrate areas (∼10 μm in diameter) decorated with LFP particles to be probed within a lithium electrolyte solution in organic carbonate solvents (0.1 M LiClO 4 in propylene carbonate in the present study). SEM images of the scanned area allow the correlation of each electrochemical response to the number, and volume of the probed particles. Under favorable conditions, single particles are found within the measurement areas, thus enabling the determination of single particle properties in an anaerobic environment without the additional complications arising from the presence of binders and electronically conductive fillers. The ability to analyze a material with complementary experimental techniques at the single particle level should create new opportunities for fundamental studies and for the quality control of granular materials. [ABSTRACT FROM AUTHOR]

Controlled payload release is one of the key elements in the creation of a reliable drug delivery system. We report the discovery of a drug delivery vessel able to transport chemotherapeutic agents to target cancer cells and selectively trigger their release using the electrochemical activity of a ferrocene-modified phospholipid. Supported by in vitro assays, the competitive advantages of this discovery are (i) the simple one step scalability of the synthetic process, (ii) the stable encapsulation of toxic drugs (doxorubicin) during transport, and (iii) the selective redox triggering of the liposomes to harness their cytotoxic payload at the cancer site. Specifically, the redox-modified giant unilamellar vesicle and liposomes were characterized using advanced methods such as scanning electrochemical microscopy (SECM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and fluorescent imaging. [ABSTRACT FROM AUTHOR]

Six cyclometalated iridium(III) phenanthroimidazole complexes with different modifications to the imidazole phenanthroline ligand exhibit enhanced luminescence when bound to guanine (G-) quadruplex DNA sequences. The complexes bind with low micromolar affinity to human telomeric and c-myc sequences in a 1:1 complex:quadruplex stoichiometry. Due to the luminescence enhancement upon binding to G-quadruplex DNA, the complexes can be used as selective quadruplex indicators. In addition, the electrogenerated chemiluminescence of all complexes increases in the presence of specific G-quadruplex sequences, demonstrating potential for the development of an ECL-based G-quadruplex assay. [ABSTRACT FROM AUTHOR]

Six cyclometalated iridium(III) phenanthroimidazole complexes with different modifications to the imidazole phenanthroline ligand exhibit enhanced luminescence when bound to guanine (G-) quadruplex DNA sequences. The complexes bind with low micromolar affinity to human telomeric and c-myc sequences in a 1:1 complex:quadruplex stoichiometry. Due to the luminescence enhancement upon binding to G-quadruplex DNA, the complexes can be used as selective quadruplex indicators. In addition, the electrogenerated chemiluminescence of all complexes increases in the presence of specific G-quadruplex sequences, demonstrating potential for the development of an ECL-based G-quadruplex assay. [ABSTRACT FROM AUTHOR]

The work presented here describes the development and characterization of platinum-mercury hemispherical nanoelectrodes for the spatially resolved quantitative detection of manganese cations. The electrochemical probes were made by electrodeposition of metallic mercury from a mercuric ion solution onto Pt/quartz laser-pulled concentric disk nanoelectrodes (with disk radii ranging from 3 to 500 nm). The nanoelectrodes were characterized by steady-state voltammetry, scanning electrochemical microscopy, environmental scanning electron microscopy, energy-dispersive X-ray spectroscopy and calibrated with respect to the concentration of Mn 2+ ions using anodic stripping voltammetry. The fully characterized probes were employed for the quantitative detection of Mn 2+ . The technique has been used to evaluate the impact of a novel approach for mitigating the undesirable consequences of manganese dissolution in Li-ion batteries. [ABSTRACT FROM AUTHOR]

The corrosion of an AM50 Mg alloy was studied in ethylene glycol using electrochemical and electron microscopy techniques. Switching from H 2 O to ethylene glycol, it was shown that the corrosion of the AM50 alloy was significantly suppressed thereby slowing H 2 evolution. The corrosion of the AM50 alloy was mapped using scanning electrochemical microscopy in the feedback mode. Ferrocenemethanol can be used to expose the reactive anodic areas on the Mg alloy. These studies confirmed that studies in ethylene glycol can be used to elucidate reaction features obscured by rapid corrosion in H 2 O without significantly altering the mechanism and damage morphology. [ABSTRACT FROM AUTHOR]

A simple, fast, and reproducible method for the fabrication of disk ultramicroelectrodes (UMEs) with controlled geometry is reported. The use of prepulled soda-lime glass capillaries allows one to bypass the irreprodudble torchsealing and experimentally challenging tip-sharpening steps used in conventional fabrication protocols. A micron-sized electroactive wire is sealed inside this capillary producing UMEs with a highly reproducible geometry. Total fabrication time (l h) and experimental difficulty are significantly reduced. Disk UMEs with various diameters and cores were fabricated, including carbon fiber (7 and 11 μm), gold (10 and 25 μm), platinum (10 and 25 μm), silver (25 μm), and mercury (25 μm). The ratio of the insulating sheath to the electroactive core of the UMEs was 2.5-3.6. Silver UMEs were also used to produce a Ag/AgCl microreference electrode. This general fabrication method can readily be applied to other electroactive cores and could allow any research group to produce high quality disk UMEs, which are a prerequisite for quantitative scanning electrochemical microscopy. [ABSTRACT FROM AUTHOR]

The site-specific incorporation oftransition-metal complexes withinDNA duplexes, followed by their immobilization on a gold surface,was studied by electrochemistry to characterize their ability to mediatecharge. Cyclic voltammetry, square-wave voltammetry, and control experimentswere carried out on fully matched and mismatched DNA strands thatare mono- or bis-labeled with transition-metal complexes. These experimentsare all consistent with the ability of the metal centers to act asa redox probe that is well coupled to the DNA π-stack, allowingDNA-mediated charge transport. [ABSTRACT FROM AUTHOR]

Quantitative in-situ and localized analytical methods that can monitor Mg 2+ release are central to probe the impact of the microstructure on magnesium alloy corrosion. As such, a potentiometric micro-Mg 2+ ion-selective membrane electrode is fabricated, calibrated, characterized and used to selectively monitor the Mg 2+ release from different cast Mg AM50 alloys during corrosion. We demonstrate that the local Mg 2+ release is tied to the alloy microstructure and its aluminum distribution, indicating a possibility of optimization of the base material corrosion properties. [ABSTRACT FROM AUTHOR]

Maintaining a well-defined tip-to-substrate separation is a critical area of development in scanning electrochemical microscopy (SECM). One technique that provides topographic data independently to the electrochemical measurement is shear force (SF) SECM. SF measurements are highly sensitive to factors including the tip-to-substrate separation, experimental solution, and probe geometry. We present a procedure for the fabrication of highly reproducible electrochemical probes with an active electrode disc with radii between 3nm to 190nm. A systematic study of the SF characteristics of these nano electrodes provides details on how to achieve the highest sensitivity and stability of SF signals, and maximize the number of SF sensitive frequencies. A new methodology to identify SF sensitive frequencies without needing to immerse the probes in solution or approach the surface is presented. Furthermore, we demonstrate that the greatest source of error in achieving reproducible SF behavior lies in the positioning of the piezo electric components and the piezo-nano electrode interface. [ABSTRACT FROM AUTHOR]

Highlights: [•] Detection of local flux of H2 for the analysis of the corrosion behavior of microstructural features. [•] SECM maps and approach curves measurement showed time-dependent change of the corrosion process. [•] Numerical simulations revealed a continual change in the size of active site and the local flux of H2 formation. [ABSTRACT FROM AUTHOR]

At the synapse, D-serine is an endogenous co-agonist for the N-methyl-D-aspartate receptor (NMDAR). It plays an important role in synaptic transmission and plasticity and has also been linked to several pathological diseases such as schizophrenia and Huntington's. The quantification of local changes in n-serine concentration is essential to further understanding these processes. We report herein the development of a disk-shaped amperometric enzymatic biosensor for detection of D-serine based on a 25 μm diameter platinum disk microelectrode with an electrodeposited poly-m-phenylenediamine (PPD) layer and an K gracilis D-amino acid oxidase (RgDAAO) layer. The disk-shaped D-serine biosensor is 1-5 orders of magnitude smaller than previously reported probes and exhibits a sensitivity of 276 μA cm-2 mM-1 with an in vitro detection limit of 0.6 μM. We demonstrate its usefulness for in vivo applications by measuring the release of endogenous D-serine in the brain of Xenopus laevis tadpoles. [ABSTRACT FROM AUTHOR]

Abstract: Scanning electrochemical microscopy (SECM) is increasingly applied to study and image live cells. To reduce the overall analysis time during live cell SECM measurements and maintain cell viability, the microelectrode scan rate can be increased. The use of increasing microelectrode scan rates is challenging because our understanding of the downstream convection effects is tied to the ill-defined topography of the imaged live cells. The present study investigates the effect of forced convection on the microelectrode current during SECM imaging of live cells, model non-planar substrates and planar surfaces. Experimentally, we demonstrate that during constant height imaging, the normalized peak current observed during line scans on all three substrates scales linearly with the microelectrode velocity. This quasi-linear relationship is corroborated by finite element simulations of non-planar substrates, which further reveal that the slope is closely related to the electrochemical activity of the substrate. [Copyright &y& Elsevier]

A model showing one metallic nanoparticle (MNP) surrounded by TMVCPs, with a large portion of the nanoparticle surface remaining exposed to the environment and accessible by small reactants. The resulting MNPs thus exhibited high catalytic activity towards 4-nitrophenol reduction and allyl alcohol hydrogenation. [Display omitted] • Successful formation of metallic nanoparticles (MNPs) on a bulky protein under environmental-benign synthetic conditions. • MNPs showed exceptional catalytic activities towards 4-nitrophenol reduction and unsaturated alcohol hydrogenation. • Molecular dynamic simulation was employed to study the assembly patterns of the protein on the Pd NP surface. • The high catalytic activity was attributed to the limited passivation of bulk protein over the nanoparticle surface. • This study may stimulate more research on employing natural ligands to protect nanomaterials for heterogeneous catalysis. Bio-nano hybrid materials feature eco-friendly synthesis, various self-assembly patterns and numerous possibilities for surface functionalization. With these unique advantages, biological scaffolds have been regarded as green alternatives to fabricate metallic nanomaterials. Herein, a bulky tobacco mosaic virus coat protein (TMVCP) was employed as a versatile template to synthesize metallic nanoparticles at room temperature. These materials exhibited exceptional performance for organic transformations under green conditions. Remarkably, while Au NPs showed rapid kinetics in pollutant 4-nitrophenol reduction, Pd NPs demonstrated superior catalytic activity towards hydrogenation of unsaturated alcohols. The enhanced performance is likely related to the protein. To ascertain the protein structure-function effect on the catalytic performance, an in-depth analysis was performed for a TMVCP-Pd NP system via molecular dynamic (MD) simulations. Our results suggest that due to minimal passivation of bulky protein, a large portion of the Pd NP surface remains approachable for the reactants, thus resulting in high reaction rate. [ABSTRACT FROM AUTHOR]

The emergence of resistance to multiple unrelated chemotherapeutic drugs impedes the treatment of several cancers. Although the involvement of ATP-binding cassette transporters has long been known, there is no in situ method capable of tracking this transporter-related resistance at the single-cell level without interfering with the cell's environment or metabolism. Here, we demonstrate that scanning electrochemical microscopy (SECM) can quantitatively and noninvasively track multidrug resistance-related protein 1-dependent multidrug resistance in patterned adenocarcinoma cervical cancer cells. Nonresistant human cancer cells and their multidrug resistant variants are arranged in a side-by-side format using a stencil-based patterning scheme, allowing for precise positioning of target cells underneath the SECM sensor. SECM measurements of the patterned cells, performed with ferrocenemethanol and [Ru(NH3)6]3+ serving as electrochemical indicators, are used to establish a kinetic "map" of constant-height SECM scans, free of topography contributions. The concept underlying the work described herein may help evaluate the effectiveness of treatment administration strategies targeting reduced drug efflux. [ABSTRACT FROM AUTHOR]

The effect of the insulator-mixed-material edge on the galvanic corrosion rate of magnesium alloy (AE44)-mild steel (MS) couple is experimentally studied using scanning vibrating electrode technique (SVET), profilometry, and classical electrochemistry. The local and average corrosion rates estimated from the experimental depth of anodic attack profile of AE44-MS couple are validated by 2D and 3D corrosion numerical models. Our study demonstrates experimentally and theoretically that the presence of the insulator edge increases the local current density, which enhances the corrosion rate. The extent of the local corrosion rate enhancement and its effect on the overall corrosion rate of the mixed material is discussed and depends on the mixed material's geometry and the edge type. [ABSTRACT FROM AUTHOR]

Abstract: Two different surface derivation procedures have been used to modify glassy carbon electrodes based on the electrochemical reduction of diazonium cations in situ generated from the nitro precursor. The first sequential procedure completely reduces the nitro group into the corresponding amine, which is further diazotized in situ. This unique sequential procedure allows surface derivatization by species having extended conjugation as illustrated by the use of a p-nitrophenylethynyl benzene precursor. The second concerted procedure yields the diazonium cation in situ by the conversion of the nitro group into the corresponding amine in presence of all reagents required for the diazotization reaction. The major advantage of this “one-pot” procedure is that the diazonium cation is generated locally in close proximity to the electrode surface by rapid diazotization of the electrogenerated amine. The in situ production of diazonium cations and subsequent surface attachment is monitored using a p-nitrophenylethynyl benzene precursor bearing a catechol group. Surface coverages are determined from the cyclic voltammograms of the surface-confined catechol groups. A comparative study of the surface coverage values obtained for redox surfaces prepared with different conditions, allows optimization of the “one pot” procedure, leading to an efficient surface modification. [Copyright &y& Elsevier]

Abstract: Cancer cell multidrug resistance is a molecular signature that highly influences the outcome of chemotherapy treatment and for which there is currently no robust method to monitor in vitro its activity. Herein, we demonstrate that ferrocenemethanol (FcCH2OH) and its oxidized form ([FcCH2OH]+) affect the redox state of cancer cells. Specifically, the interaction of FcCH2OH with the glutathione couple (GSH/GSSG) is shown in human adenocarcinoma cervical cancer cells HeLa and a multidrug resistant variant overexpressing the multidrug resistant associated protein 1 (MRP1) using bioanalytical techniques, such as flow cytometry and fluorescence microscopy. It is further demonstrated that the differential response to FcCH2OH in multidrug-resistant cells is in part due to MRP1''s unspecific efflux. Scanning electrochemical microscopy confirmed the interaction between FcCH2OH and the cells, and the differential response was observed to depend on MRP1 expression. This newly established relation between FcCH2OH/[FcCH2OH]+, GSH/GSSG and multidrug resistance in human cancer cells enables than the acquisition of scanning electrochemical microscopy images. [Copyright &y& Elsevier]

The present shear-force constant-distance scanning electrochemical microscope regulates tip-to-substrate distance using a phase-controlled feedback mechanism that is more sensitive than the amplitude-controlled constant-distance scanning electrochemical microscopes. Phase control responds faster to frequency perturbation and presents enhance sensitivity during distance curves under constant-distance mode. [ABSTRACT FROM AUTHOR]

This work combines two industrially friendly processing methods in order to create wear resistant and solid-lubricating composite coatings potentially suitable for high load applications. Layered composite coatings were fabricated over wrought stainless steel 444 (SS444) by compression molding a mixture of solid lubricant polymer, polytetrafluoroethylene (PTFE, 80 wt%), and wear resistant polymer, polyimide (PI, 20 wt%), onto iron aluminide (Fe 3 Al) thermal spray coatings without the need of either primers or adhesives. The fabrication process consisted of three main steps: deposition of the Fe 3 Al thermal spray coating onto a SS444 substrate and transfer into a metal mold; transfer, compress, and sinter mixed polymeric powder onto the thermal spray coating; and finally, sample cooling to room temperature. This method takes advantage of the high surface roughness of thermal spray coatings, which increases mechanical adhesion of slippery PTFE to the underlying metallic material. Coatings were produced with and without a small amount of graphite (5 wt%) to analyze its impact on sliding and wear properties. Unlike current coating technologies, the thickness of the coatings presented herein can be easily and quickly tailored by varying the amount of polymer powder added to the mold prior to compression or by grinding after fabrication. We produced and analyzed coatings ~1.3 mm in total thickness that portray coefficient of frictions ~0.1, similar to pure PTFE. The calculated wear rates for both coatings with and without graphite are an order of magnitude lower than what has been previously reported for coatings of similar composition. The influence of graphite on wear properties was found to be minimal due to the high content of self-lubricating PTFE yet can act as a way to lower material costs and increase the coatings load capacity. [Display omitted] • PTFE/PI films were deposited on Fe3Al thermal spray coatings using compression molding to produce composite coatings. • The coating method is simple and enables scalable production of polymer coatings with tailorable thicknesses. • No primer or adhesive layer was needed due to the roughness of thermal spray coatings and the addition of PI. • The well-adhered coatings were self-lubricating and portrayed wear rates two orders of magnitude lower than pure PTFE. • The addition of graphite in the polymer layer did not change tribological performance and could lower material costs. [ABSTRACT FROM AUTHOR]

The present work uses a scanning electrochemical microscopy technique to study systems containing the membrane-bound reaction center protein (RC) from the purple photosynthetic bacteria Rhodobacter spheroides to chromatophores (spherical reorganization of cell membrane following its mechanical rupture) and liposomes (reconstituted membrane systems at lower degree of complexity). Scanning electrochemical microscopy is a useful tool to investigate redox processes involving a RC, because the effective heterogeneous rate constants for the redox reaction with different mediators can be measured. The technique is also able to provide information on the role of the outer cell membrane permeation on the kinetics of the electron-transfer processes and to obtain more insight into the nature of the species involved. [ABSTRACT FROM AUTHOR]

Scanning electrochemical microscopy (SECM) allows imaging and analysis of a variety of biological samples, such as living cells. Up to now, it still remains a challenge to successfully decouple signals related to topography and reactivity. Furthermore, such delicate samples require careful adjustment of experimental parameters, such as scan velocity. The present study proposes a method to extract a substrate's kinetic rate by numerical modeling and experimental high speed constant height SECM imaging. This is especially useful for the determination of substrates with unknown surface reaction kinetics and large topographical features. To make this approach applicable to soft cell samples, which cannot be imaged at high velocity, a nonlinear fit strategy is presented to obtain kinetic rate values also under slow scan velocity conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pulse field gradient nuclear magnetic resonance (PFG-NMR) measurement of electrolyte transport. • Proof of concept measurement on the impact dissolved gasses on D Li + . • CO 2(g) has no measurable effect on the solution phase Li+ diffusion coefficient. Electrolyte decomposition in Li-ion batteries (LIB) and its entailing gas evolution significantly impacts cell performance. CO 2 is one of the most abundantly evolved gases from common LIB electrolytes and could potentially affect Li+ solution transport during LIB operation. To this end, a comparative analysis of the Li+ diffusion coefficient (D Li + ) which governs mass transport is required. Herein a methodology is established to saturate common battery electrolytes with a soluble gas without introducing other contaminants, so as to determine D Li + in saturated and unsaturated samples. As a proof of concept, the values of D Li + are determined in 1 M LiPF 6 and 1 M LiClO 4 in ethylene carbonate (EC):dimethyl carbonate (DMC) with and without dissolved CO 2 , confirmed by gas chromatography–mass spectrometry (GC–MS). The results obtained by pulse field gradient nuclear magnetic resonance (PFG-NMR) diffusion measurements agree for both electrolytes; saturating the electrolyte with CO 2 has no measurable effect on D Li + and therefore does not hinder Li+ mass transport. [ABSTRACT FROM AUTHOR]

In suit and dynamic reaction monitoring platform for chiral cysteine. • A customizable optoelectronically functionally coupled microelectrode was designed. • A novel chiral sensor based on microelectrode breaks the traditional template for electrochemical analysis. • The first developed a platform for EC-SERS studies the electrochemical reaction mechanism of cysteine enantiomers. • The proposed method provides ultra-high sensitivity and low detection limits for the detection of D-Cys. A novel concept for the development of chiral sensor is proposed based on electrochemical phase transformation of silver nanoparticles (Ag NPs), which is shown for in situ photoelectric cooperative analysis mode. To demonstrate this, self-assembled Ag NPs on gold microelectrode (Ag-Au ME) serve as the sensing platform for chiral cysteine (D/L-Cys) detection. Through differences in the specific binding force, the system was validated with efficient synergistic electrochemical redox reactions and complexation of D/L-Cys with silver ions, and a novel sensing mode was developed based on the shift of oxidation peak potential of silver ions. In the proposed assay procedure, the simple principle of electrochemical phase transformation of Ag NPs, which can be monitored by electrochemical-surface enhanced Raman scattering (EC-SERS), was used as an in situ , rapid, dynamic analysis strategy for improving the detection sensitivity. Moreover, the proposed assay strategy with satisfactory sensitivity up to 74.88 μA μM−1 cm−2 was achieved, the limit of detection (LOD) is reduced to nanomolar level (8.7 nM) for D-Cys. Going beyond the conventional chiral biosensing, more importantly, the elaborate dynamic coupling of multiple mechanisms in a micro/nanoscale interface may provide a new approach for future highly sensitive biosensing. [ABSTRACT FROM AUTHOR]

CO 2 reduction offers an attractive alternative green synthetic route for ethylene, especially where CO 2 could be sourced from industrial exhausts and in combination with green power sources. However, practical applications are currently limited due to the unfortunately low selectivity of cathode materials towards ethylene. This work uses polymers with intrinsic microporosity (PIMs) to improve the performance of copper gas diffusion electrodes for CO 2 reduction to ethylene. We report an improved selectivity and activity towards ethylene with the addition of a thin PIMs layer, which is seen as improved Faradaic efficiency, increased stability and a shift in the reduction to lower overpotential. This improvement is highly dependent on the thickness of the added polymer layer, with too thick a layer having a detrimental impact on the hydrophobicity of the gas diffusion layer. With a compromise in loading, PIMs can be used to enhance the activity and selectivity of catalysts for targeted CO 2 reduction to ethylene. Image 10694 • Gas diffusion electrodes allow CO 2 reduction to ethylene, but selectivity is low. • Polymers with intrinsic microporosity can increase ethylene production. • Using too much polymer has a detrimental impact. • A compromise polymer thickness increases ethylene yield and electrode stability. [ABSTRACT FROM AUTHOR]