Shigeru Amemiya

• University of Pittsburgh

The nuclear pore complex (NPC) is the proteinous nanopore that solely regulates molecular transport between the nucleus and cytoplasm of a eukaryotic cell. Hypothetically, the NPC utilizes the hydrophobic barriers based on the repeats of phenylalanine–glycine (FG) units to selectively and efficiently transport macromolecules. Herein, we quantitativ...

The nuclear pore complex (NPC) plays imperative biological and biomedical roles as the sole gateway for molecular transport between the cytoplasm and nucleus of eukaryotic cells. The proteinous nanopore, however, can be blocked by arginine-containing polydipeptide repeats (DPRs) of proteins resulting from the disordered C9orf72 gene as a potential...

The nuclear pore complex (NPC) is a proteinaceous nanopore that solely and selectively regulates the molecular transport between the cytoplasm and nucleus of a eukaryotic cell. The ∼50 nm-diameter pore of the NPC perforates the double-membrane nuclear envelope to mediate both passive and facilitated molecular transport, thereby playing paramount bi...

Scanning electrochemical microscopy (SECM) has emerged as a powerful method to quantitatively investigate the transport of molecules and ions across various biological membranes as represented by living cells. Advantageously, SECM...

Herein, we feature our recent efforts toward the development and application of nanoelectrochemistry at liquid/liquid interfaces, which are also known as interfaces between two immiscible electrolyte solutions (ITIES). Nanopipets, nanopores, and nanoemulsions are developed to create the nanoscale ITIES for the quantitative electrochemical measureme...

Herein, we describe our recent studies on the molecular mechanism of adsorption-coupled electron transfer (ACET). ACET is ubiquitous and crucial in many important electrode reactions to generate irreversibly adsorbed products in electrodeposition and electrointercalation and reversibly adsorbed intermediates in electrocatalysis and photoelectrocata...

Here, we demonstrate for the first time that the mechanism of adsorption-coupled electron-transfer (ACET) reactions can be identified experimentally. The electron transfer (ET) and specific adsorption of redox-active molecules are coupled in many electrode reactions with practical importance and fundamental interest. ACET reactions are often repres...

The electron transfer and specific adsorption of a redox-active molecule are coupled in many important electrode reactions. Herein, we report a theoretical framework for the voltammetric discrimination of the concerted and non-concerted mechanisms of adsorption-coupled electron-transfer (ACET) reactions. In the concerted mechanism, an oxidant in th...

Scanning electrochemical microscopy (SECM) enables the high‐resolution imaging and measurement of electrochemical, chemical, and biological reactions at various interfaces. The power of SECM originates from the versatility based on the highly accurate and precise positioning of a micrometer‐ or nanometer‐sized ultramicroelectrode tip near the surfa...

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....

Herein, we advance our fundamental understanding of hydrogen electrochemistry as crucial energy technology by challenging the century-long paradigm that Volmer, Heyrovsky, and Tafel reactions are elementary. We identify and resolve the theoretical controversy of this phenomenological model to argue that each reaction must be stepwise not concerted...

This chapter is concerned with studies of heterogeneous electron transfer (ET) at carbon electrodes when redox‐active molecules can be reversibly and specifically adsorbed on the electrode surfaces. It introduces progress in theory of adsorption‐coupled ET and its experimental assessment at carbon electrodes. Adsorption‐coupled ET is ubiquitous in...

Ferrocene derivatives are considered as representative outer‐sphere redox couples that do not specifically interact with the electrode surface. It, however, is highly challenging to unambiguously prove their outer‐sphere character experimentally. Herein, we employ quantitative cyclic voltammetry to assess whether ferrocene carboxylates and sulfonat...

Scanning electrochemical microscopy (SECM) enables high-resolution imaging by examining the amperometric response of an ultramicroelectrode tip near a substrate. Spatial resolution, however, is compromised for non-flat substrates, where distances from a tip far exceed the tip size to avoid artifacts caused by the tip–substrate contact. Herein, we p...

The nuclear pore complex (NPC) is a large protein nanopore that solely mediates molecular transport between the nucleus and cytoplasm of a eukaryotic cell. There is a long-standing consensus that selective transport barriers of NPC are exclusively based on hydrophobic repeats of phenylalanine and glycine (FG) of nucleoporins. Herein, we reveal expe...

The nuclear pore complex (NPC) solely mediates molecular transport between the nucleus and cytoplasm of a eukaryotic cell to play important biological and biomedical roles. It, however, is not well understood chemically how this biological nanopore selectively and efficiently transports various substances including small molecules, proteins, and RN...

Reversible and specific adsorption of redox-active molecules from the electrolyte solution to the electrode surface is an important process and is often diagnosed by cyclic voltammetry (CV). The entire voltammogram, however, is rarely analyzed quantitatively, thereby completely missing or incorrectly extracting inherent information about adsorption...

Electrochemical measurements with unprecedentedly high sensitivity, selectivity, and kinetic resolution have been enabled by a pair of electrodes separated by a nanometer-wide gap. The fabrication of nanogap electrodes, however, requires extensive nanolithography or nanoscale electrode positioning, thereby preventing the full exploration of this po...

Applications of conducting carbon materials for highly efficient electrochemical energy devices require a greater fundamental understanding of heterogeneous electron-transfer (ET) mechanisms. This task, however, is highly challenging experimentally, because an adsorbing carbon surface may easily conceal its intrinsic reactivity through adventitious...

High temporal resolution of fast-scan cyclic voltammetry (FSCV) is widely appreciated in fundamental and applied electrochemistry to quantitatively investigate rapid dynamics of electron transfer and neurotransmission using ultramicroelectrodes (UMEs). Faster potential scan, however, linearly increases the background current, which must be subtract...

Electron-beam (E-beam) deposition of carbon on a gold substrate yields a very flat (0.43 nm of root-mean-square roughness), amorphous carbon film consisting of a mixture of sp2 and sp3 hybridized carbon with sufficient conductivity to avoid ohmic potential error. E-beam carbon (eC) has attractive properties for conventional electrochemistry, includ...

Electrodeposition is an important approach that can produce functional compound materials by assembling multiple species at the electrode surface. However, a fundamental understanding of the electrodeposition mechanism has been limited by its complexity and is often gained only through ex-situ studies of deposited materials. Here we report on the f...

Clean surfaces of conducting carbon materials are highly demanded for fundamental and applied electrochemistry to mechanistically understand and practically utilize their intrinsic reactivity. In this presentation, we will discuss about the nanoelectrochemical characterization of clean carbon surfaces to gain novel insights into heterogeneous elect...

Nanoscale scanning electrochemical microscopy (SECM) is a powerful scanning probe technique that enables high-resolution imaging of chemical processes at single nanometer-sized objects. However, it has been a challenging task to quantitatively understand nanoscale SECM images, which requires to accurately characterize the size and geometry of nanoe...

Herein, we assess general impact of heterogeneous self-exchange reaction (HSER) on electrochemical measurement to comment on a recent report by Unwin and co-workers, particularly about their interpretations of our nanogap voltammograms.1 In ref. 1, they proposed a model to imply that a HSER caused anomalous asym-metry of nanogap voltammograms based...

Carbon materials are tremendously important as electrode materials in both fundamental and applied electrochemistry. Recently, significant attention has been given not only to traditional carbon materials, but also to carbon nanomaterials for various electrochemical applications in energy conversion and storage as well as sensing. Importantly, many...

The high ion selectivity of potentiometric and optical sensors based on ionophore-based polymeric membranes is thermodynamically limited. Here, we report that the voltammetric selectivity of thin ionophore-based polymeric membranes can be kinetically improved by several orders of magnitude in comparison with their thermodynamic selectivity. The kin...

Formation of a nanometer-wide gap between tip and substrate electrodes by scanning electrochemical microscopy (SECM) enables voltammetric measurement of ultrafast electron-transfer kinetics. Herein, we demonstrate the advantage of SECM-based nanogap voltammetry to assess the cleanness of the substrate surface in solution by confirming that airborne...

The capability to detect multianalyte ions in their mixed solution is an important advantage of voltammetry with an ionophore-based polymeric membrane against the potentiometric and optical counterparts. This advanced capability is highly attractive for the analysis of physiological ions at millimolar concentrations in biological and biomedical sam...

The intrinsic wettability of graphitic materials, such as graphene and graphite, can be readily obscured by airborne hydrocarbon within 5-20 min of ambient air exposure. We report a convenient method to effectively preserve a freshly prepared graphitic surface simply through a water treatment technique. This approach significantly inhibits the hydr...

Nanoscale scanning electrochemical microscopy (SECM) has emerged as a powerful electrochemical method that enables the study of interfacial reactions with unprecedentedly high spatial and kinetic resolution. In this work, we develop carbon nanoprobes with high electrochemical reactivity and well-controlled size and geometry based on chemical vapor...

High electrochemical reactivity is required for various energy and sensing applications of graphene grown by chemical vapor deposition (CVD). Herein, we report that heterogeneous electron transfer can be remarkably fast at CVD-grown graphene electrodes that are fabricated without using the conventional poly(methyl methacrylate) (PMMA) for graphene...

Selective ion-ionophore complexation in a polymeric membrane is crucial to various sensing applications. In this work, we report on a novel voltammetric approach based on a thin polymeric membrane to determine the stoichiometry and overall formation constant of an ion-ionophore complex. With this approach, a ~1.6 µm-thick ionophore-doped membrane c...

Cation-exchange extraction of polypeptide protamine from water into an ionophore-based polymeric membrane has been hypothesized as the origin of a potentiometric sensor response to this important heparin antidote. Here, we apply ion-transfer voltammetry not only to confirm protamine extraction into ionophore-doped polymeric membranes but also to re...

Highly oriented pyrolytic graphite (HOPG) is an important electrode material as a structural model of graphitic nanocarbons such as graphene and carbon nanotubes. Here, we apply scanning electrochemical microscopy (SECM) to quantitatively demonstrate that the electroactivity of the HOPG basal surface can be significantly lowered by the adsorption o...

Here we report on ion-transfer voltammetry of perfluoroalkyl sulfonates and carboxylates at the interface between a plasticized polymer membrane and water to enable the ultrasensitive detection of these persistent environmental contaminants with adverse health effects. The ion-transfer cyclic voltammograms of the perfluoroalkyl oxoanions are obtain...

Ultrasensitive ion-selective electrode measurements based on stripping voltammetry are an emerging sensor technology with low- and sub-nanomolar detection limits. Here, we report on stripping voltammetry of down to 0.1 nM Ca(2+) by using a thin-polymer-coated electrode and demonstrate the advantageous effects of the divalent charge on sensitivity....

Efficient delivery of therapeutic macromolecules and nanomaterials into the nucleus is imperative for gene therapy and nanomedicine. Nucleocytoplasmic molecular transport, however, is tightly regulated by the nuclear pore complex (NPC) with the hydrophobic transport barriers based on phenylalanine and glycine repeats. Herein, we apply scanning elec...

Here we review the recent applications of ion transfer (IT) at the interface between two immiscible electrolyte solutions (ITIES) for electrochemical sensing and imaging. In particular, we focus on the development and recent applications of the nanopipet-supported ITIES and double-polymer-modified electrode, which enable the dynamic electrochemical...

Glass-sealed Pt electrodes with submicrometer and nanometer size have been successfully developed and applied for nanoscale electrochemical measurements such as scanning electrochemical microscopy (SECM). These small electrodes, however, are difficult to work with because they often lose a current response or give a low SECM feedback in current-dis...

The nuclear pore complex (NPC) is the proteinaceous nanopore that solely mediates molecular transport across the nuclear envelope between the nucleus and cytoplasm of a eukaryotic cell. Small molecules (<40 kDa) diffuse through the large pore of this multiprotein complex. A passively impermeable macromolecule tagged with a signal peptide is chapero...

The inexpensive and disposable electrode based on a double-polymer-modified pencil lead is proposed for upper-division undergraduate instrumental laboratories to enable the highly sensitive detection of perchlorate. Students fabricate and utilize their own electrodes in the 3–4 h laboratory session to learn important concepts and methods of electro...

Here, we report on the first application of an ionophore-doped double-polymer electrode for ion-transfer stripping voltammetry (ITSV) to explore the nanomolar limit of detection (LOD) and multiple-ion detectability. We developed a theoretical model for ITSV at a thin ionophore-doped membrane on the solid supporting electrode to demonstrate that its...

Here we report on the unprecedentedly high resolution imaging of ion transport through single nanopores by scanning electrochemical microscopy (SECM). The quantitative SECM image of single nanopores allows for the determination of their structural properties, including their density, shape, and size, which are essential for understanding the permea...

In this article, we introduce the principle of scanning electrochemical microscopy (SECM) and its applications as a powerful electrochemical method for material characterization. The principle of SECM is based on the use of a micrometer- or nanometer-sized ultramicroelectrode as the scanning chemical probe of electrons, ions, and molecules that are...

The control of a nanometer-wide gap between tip and substrate is critical for nanoscale applications of scanning electrochemical microscopy (SECM). Here, we demonstrate that the stability of the nanogap in ambient conditions is significantly compromised by the thermal expansion and contraction of components of an SECM stage upon a temperature chang...

Here, we report on the first electrochemical study that reveals the kinetics and molecular level mechanism of heterogeneous ion-ionophore recognition at plasticized polymer membrane/water interfaces. The new kinetic data provide greater understanding of this important ion-transfer (IT) process, which determines various dynamic characteristics of th...

The monitoring of heparin and its derivatives in blood samples is important for the safe usage of these anticoagulants and antithrombotics in many medical procedures. Such an analytical task is, however, highly challenging due to their low therapeutic levels in the complex blood matrix, and it still relies on classical, indirect, clot-based assays....

Here we report on a generalized theory for scanning electrochemical microscopy to enable the voltammetric investigation of a heterogeneous electron-transfer (ET) reaction with arbitrary reversibility and mechanism at the macroscopic substrate. In this theory, we consider comprehensive nanoscale experimental conditions where a tip is positioned at a...

We report on a novel theory and experiment for scanning electrochemical microscopy (SECM) to enable quasi-steady-state voltammetry of rapid electron transfer (ET) reactions at macroscopic substrates. With this powerful approach, the substrate potential is cycled widely across the formal potential of a redox couple while the reactant or product of a...

We report on the application of scanning electrochemical microscopy (SECM) to the measurement of the ion-selective permeability of porous nanocrystalline silicon membrane as a new type of nanoporous material with potential applications in analytical, biomedical, and biotechnology device development. The reliable measurement of high permeability in...

Here we report on the novel application of scanning electrochemical microscopy (SECM) to enable spatially resolved electrochemical characterization of individual single-walled carbon nanotubes (SWNTs). The feedback imaging mode of SECM was employed to detect a pristine SWNT (approximately 1.6 nm in diameter and approximately 2 mm in length) grown h...

Finite element simulations of ion transfer (IT) reactions at the nanopipet-supported interface between two immiscible electrolyte solutions (ITIES) were carried out, and the numerical results were generalized in the form of an analytical approximation. The developed theory is the basis of a new approach to kinetic analysis of steady-state voltammog...

Steady-state voltammetry at the pipet-supported liquid/liquid interface has previously been used to measure kinetics of simple and facilitated ion transfer (IT) processes. Recently, we showed that the conventional experimental protocol and data analysis produce large uncertainties in kinetic parameters of rapid IT processes extracted from pipet vol...

Subnanomolar limits of detection (LODs) are obtained for stripping voltammetry based on ion transfer at the interface between the aqueous sample and the thin polymeric membrane supported with a solid electrode. It has been predicted theoretically that a lower LOD can be obtained for a more lipophilic analyte ion, which can be preconcentrated at a h...

Heparin and low-molecular-weight heparin are voltammetrically extracted across 1,2-dichloroethane/water interfaces for the detection of these highly sulfated polysaccharides widely used as anticoagulants/antithrombotics in many medical procedures. A new heparin ionophore, 1-[4-(dioctadecylcarbamoyl)butyl]guanidinium, is the first to enable the volt...

Nanowires with nanometer-scale gaps are an emerging class of nanomaterials with potential applications in electronics and optics. Here, we demonstrate that the feedback mode of scanning electrochemical microscopy (SECM) allows for spatially resolved detection of a nanogap on the basis of its electrical conductivity. A gapped nanoband is used as a m...

Scanning electrochemical microscopy (SECM) is developed as a powerful approach to electrochemical characterization of individual one-dimensional (1D) nanostructures under unbiased conditions. 1D nanostructures comprise high-aspect-ratio materials with both nanoscale and macroscale dimensions such as nanowires, nanotubes, nanobelts, and nanobands. F...

Here we report on remarkably high lipophilicity of perfluoroalkyl carboxylate and sulfonate. A lipophilic nature of this emerging class of organic pollutants has been hypothesized as an origin of their bioaccumulation and toxicity. Both carboxylate and sulfonate, however, are considered hydrophilic while perfluroalkyl groups are not only hydrophobi...

A highly sensitive analytical method is required for the assessment of nanomolar perchlorate contamination in drinking water as an emerging environmental problem. We developed the novel approach based on a voltammetric ion-selective electrode to enable the electrochemical detection of "redox-inactive" perchlorate at a nanomolar level without its el...

This review describes work done in scanning electrochemical microscopy (SECM) since 2000 with an emphasis on new applications and important trends, such as nanometer-sized tips. SECM has been adapted to investigate charge transport across liquid/liquid interfaces and to probe charge transport in thin films and membranes. It has been used in biologi...

Electrochemically controlled molecular recognition of a synthetic heparin mimetic, Arixtra, at nitrobenzene/water microinterfaces was investigated to obtain a greater understanding of interfacial recognition and sensing of heparin and its analogues with biomedical importance. In contrast to unfractionated heparin, this synthetic pentasaccharide tha...

We report on a simple, quantitative relationship between structure and permeability of a novel ultrathin nanoporous membrane based on nanocrystalline silicon. Large permeability of the free-standing nanomembrane to Ru(NH3)63+, O2, or 1,1'-ferrocenedimethanol, which was able to be measured for the first time by employing scanning electrochemical mic...

Cyclic voltammetry at micropipet electrodes is applied to the kinetic study of ion transfer at liquid/liquid interfaces. Simple and facilitated transfer of an ion that is initially present outside a tapered pipet was simulated by the finite element method, enabling complete analysis of the resulting transient cyclic voltammogram (CV) with a sigmoid...

The chapter emphasizes on potentiometric ion-selective electrodes. Potentiometric ion-selective electrodes (ISEs) belong to one of the most important groups of chemical sensors. The application of ISEs has evolved to a well-established routine analytical technique in many fields, including clinical and environmental analysis, physiology, and proces...

The theory of the feedback mode of scanning electrochemical microscopy is extended for probing heterogeneous electron transfer at an unbiased conductor. A steady-state SECM diffusion problem with a pair of disk ultramicroelectrodes as a tip and a substrate is solved numerically. The potential of the unbiased substrate is such that the net current f...

A novel, solid-supported voltammetric ion-selective electrode to detect anticoagulant/antithrombotic heparin at polarizable poly(vinyl chloride) (PVC) membrane/water interfaces was developed. An approximately 3-4.5-microm-thick PVC membrane plasticized with 2-nitrophenyl octyl ether was supported on a gold electrode modified with a poly(3-octylthio...

Recent applications of scanning electrochemical microscopy (SECM) to studies of single biological cells are reviewed. This scanning probe microscopic technique allows the imaging of an individual cell on the basis of not only its surface topography but also such cellular activities as photosynthesis, respiration, electron transfer, single vesicular...

Local feedback mode is introduced as a novel operation mode of scanning electrochemical microscopy (SECM) for electrochemical characterization of a single one-dimensional (1D) nanostructure, for example, a wire, rod, band, and tube with 1-100-nm width and micrometer to centimeter length. To demonstrate the principle, SECM feedback effects under dif...

Heparin, a highly negatively charged polysaccharide, which has been used widely as an anticoagulant and antithrombotic, was detected by ion-transfer voltammetry at the interface between 1,2-dichloroethane and an aqueous buffer solution or undiluted blood plasma. Quaternary ammoniums with different numbers of methyl and long alkyl groups were examin...

In interphase eukaryotic cells, molecular transport between the cytoplasm and the nucleus is mediated by the nuclear pore complex (NPC), which perforates the double-membraned nuclear envelope (NE). Local permeability of the NE at large intact nuclei (approximately 400 microm in diameter) isolated from Xenopus laevis oocytes was studied by scanning...

Cyclic voltammetry and chronoamperometry at micropipet electrodes were applied to study the phase transfer of polypeptide protamine facilitated by complexation with charged ionophore dinonylnaphthalenesulfonate (DNNS) at polarized water/1,2-dichloroethane (DCE) interfaces, i.e., sDNNS(-) (DCE) + protamine(n+) (aq) right harpoon over left harpoon pr...

Chronoamperometry was carried out at liquid/liquid interfaces supported at the tip of micropipet electrodes for direct determination of the diffusion coefficient of a species in the outer solution. The diffusion coefficient was used for subsequent determination of the transferred charges per species from the diffusion-limited steady-state current....

Selectively etched optical fibers were used as a new template material of conical ultramicroelectrodes, which are suitable for use as a probe in scanning electrochemical microscopy (SECM). Multistep index optical fibers with high-GeO2-doped core surrounded by two cladding layers were etched in a NH4F/HF solution for reproducible construction of tap...

Using natural polypeptide protamines as the illustrating example, we observed the phase transfer of biological polyions at polarized interfaces between two immiscible electrolyte solutions (ITIES) for the first time by micropipet voltammetry. Analysis of the limiting currents indicates that each protamine carries 20 positive charges as expected fro...

A generalized model that describes apparently "non-Nernstian" equilibrium responses of ionophore-based ion-selective electrodes (ISEs) is presented. It is formulated for primary and secondary ions of any charges that enter the membrane phase and independently form complexes with the ionophore, respectively. Equations for the phase boundary potentia...

Ionophore-free ion exchanger electrodes were found to exhibit quite a high selectivity for the creatininium ion; however, measurements in diluted urine samples revealed large emf drifts. Potentiometric, chromatographic, NMR, and mass spectrometric evidence did not reveal any major cationic interfering agents, and anionic interfering agents cannot t...

Ring ultramicroelectrodes, which are of particular interest as probes for scanning electrochemical microscopy (SECM), combined with near-field scanning optical microscopy, were investigated. Theoretical SECM tip current-distance (approach) curves for a ring electrode were calculated by numerical (finite element) analysis. The SECM curves obtained w...

The origin of the non-Nernstian potentiometric anion response behavior exhibited by several metalloporphyrin-based liquid/polymeric membrane electrodes is examined. UV-visible spectrophotometry of organic-phase solutions and thin plasticized PVC films containing In(III) and Ga(III) octaethylporphyrins suggests that, in the absence of preferred axia...

Voltammetric ion-selective micropipet electrodes for use in scanning electrochemical microscopy (SECM) for detection of potassium ion were fabricated. These used pulled borosilicate capillaries with tip orifice radii of 0.7-20 mu m with silanized inner walls filled with a solution of 10 mM valinomycin and 10 mM ETH 500 in dichloroethane. The electr...

The influence of ionic sites on the selectivities of ionophore-based ion-selective electrodes (ISEs) is described on the basis of a phase boundary potential model. The discussion presented here is significantly more general than previous ones. It is formulated for primary and interfering ions of any charges and it is valid for ISEs based on electri...

The principles of scanning electrochemical microscopy (SECM) and its application to studies of electron transfer at the interface between two immiscible electrolyte solutions are reviewed. The results of SECM measurements with a number of redox couples at the bare liquid | liquid interface or an interface with a lipid monolayer suggest that the ele...

Potentiometric selectivity coefficients, K-A,B(pot), have been collected for ionophore-based ion-selective electrodes (ISEs) for inorganic cations reported from 1988-1997. In addition to numerical values of K-A,B(pot), together with the methods and conditions for their determination, response slopes, linear concentration ranges, chemical compositio...

The use of the scanning electrochemical microscope (SECM) to probe the kinetics of charge-transfer processes at bilayer lipid membranes (BLM) is presented. Analysis of the SECM tip response demonstrates that an unmodified BLM behaves as an insulator, whereas a BLM doped with iodine shows some positive feedback. The SECM technique thus allows one to...

A numerical model is developed for the SECM feedback mode for the case of irreversible electron transfer (ET) processes at the interface between two immiscible electrolyte solutions (ITIES). In this application, a redox-active species is electrogenerated by the reduction/oxidation of the oxidized/reduced form of a couple at an ultramicroelectrode (...

The potentiometric responses of ion-selective electrodes (ISEs) based on electrically charged receptors and hydrogen-bonding neutral receptors were investigated experimentally and theoretically on the basis of the phase boundary potentials at liquid/liquid interfaces. Neutral derivatives of nucleobases were synthesized and applied to ISEs for nucle...

An ion-selective electrode for acetate based on (α,α,α,α)-5,10,15,20-tetrakis[2-(4-fluorophenylureylene)phenyl]porphyrin as an ionophore that has no metal center and forms hydrogen bonds to the analyte is described. At pH 7.0 (0.1 M HEPES-NaOH buffer), the electrode based on this ionophore and cationic sites (50 mol % relative to the ionophore) res...

Selective binding of electroinactive analytes to electrodes that are chemically modified with receptors can be used to control heterogeneous redox reactions of electroactive species. The latter are in this context often called markers because their use allows the indirect determination of the electroinactive analytes with the inherent possibility f...