Ruthenium and ruthenium dioxide-modified graphite-ethylene/propylene/diene and graphite-Teflon composite electrodes as amperometric flow detectors. Application to the determination of methionine

The flow injection amperometric performance of solid composite graphite electrodes with ethylene/propylene/diene (EPD) or Teflon as binding agents, and with Ru or RuO2 particles as electrocatalytic modifiers has been compared. Both, Ru and RuO2 modified electrodes exhibited electrocatalytic properties on the methionine oxidation process in alkaline media. The electrodes composition and the hydrodynamic and chemical variables were optimized. Graphite-EPD (GEPD) electrodes showed a better analytical performance than graphite-Teflon (GPTFE) electrodes. Furthermore, a better sensitivity, repeatability and reproducibility was observed for RuO2-GEPD electrodes when compared with Ru-GEPD electrodes. At an applied potential of +0.50 V, a detection limit for methionine of 4.8x10(-5) mol L(-1), similar to those reported in the literature for other RuO2-modified electrodes, was obtained. The analytical applicability of RuO2-GEPD electrodes was demonstrated by determining methionine in a complex pharmaceutical formulation.     

Combination pH electrodes of special design: Temperature characteristics and performance in poorly-buffered waters

The performance of 5 combination pH electrodes with special design features has been assessed. Two electrodes were intended for measurements in low-conductivity waters, two were designed to have a rapid and stable temperature response and one electrode shared both features. The performance in low-conductivity waters was either poor or merely acceptable; better results have been obtained with separate glass and reference electrodes. The electrodes designed to have good temperature response were better in this respect than conventional combination electrodes, but the same or better performance can be obtained by use of separate glass and remote-junction reference electrodes. It should be noted that the temperature coefficients of these combination electrodes were the same as for almost all pH electrodes: any improvement was only in the rate and stability of response.     

Analytical performance characteristics of thin and thick film amperometric microcells

The analytical performance of amperometric microcells with different electrode geometries is compared for enzyme activity measurements. The microcells were fabricated with thin film photolithography or thick film screen-printing in four different designs. The cells made with the thin film process used flexible substrate with microelectrode array or a circular, disk-shaped working electrode. The screen-printed working electrodes had semicircle or disk shape on ceramic chips. Putrescine oxidase (PUO) activity measurement was used as a model. The determination of PUO activity is important in the clinical diagnosis of premature rupture of the amniotic membrane. An electropolymerized m-phenylenediamine size-exclusion layer was used to eliminate common interferences. The size exclusion layer revealed also to be advantageous in protecting the electrodes from fouling by putrescine (enzyme substrate). The electrode fouling of bare electrodes was insignificant for screen-printed electrodes, but very severe for electroplated platinum working electrodes. The microelectrode array electrodes demonstrated smaller RSD and higher normalized sensitivities for hydrogen peroxide and PUO activity. All the other electrodes were demonstrating comparable analytical performances.     

Analytical performance characteristics of thin and thick film amperometric microcells

The analytical performance of amperometric microcells with different electrode geometries is compared for enzyme activity measurements. The microcells were fabricated with thin film photolithography or thick film screen-printing in four different designs. The cells made with the thin film process used flexible substrate with microelectrode array or a circular, disk-shaped working electrode. The screen-printed working electrodes had semicircle or disk shape on ceramic chips. Putrescine oxidase (PUO) activity measurement was used as a model. The determination of PUO activity is important in the clinical diagnosis of premature rupture of the amniotic membrane. An electropolymerized m-phenylenediamine size-exclusion layer was used to eliminate common interferences. The size exclusion layer revealed also to be advantageous in protecting the electrodes from fouling by putrescine (enzyme substrate). The electrode fouling of bare electrodes was insignificant for screen-printed electrodes, but very severe for electroplated platinum working electrodes. The microelectrode array electrodes demonstrated smaller RSD and higher normalized sensitivities for hydrogen peroxide and PUO activity. All the other electrodes were demonstrating comparable analytical performances.     

Recent advances in graphite powder-based electrodes

Graphite powder-based electrodes have the electrochemical performance of quasi-noble metal electrodes with intrinsic advantages related to the possibility of modification to enhance selectivity and their easily renewable surface, with no need for hazardous acids or bases for their cleaning. In contrast with commercial electrodes, for example screen-printed or sputtered-chip electrodes, graphite powder-based electrodes can also be fabricated in any laboratory with the form and characteristics desired. They are also readily modified with advanced materials, with relatively high reproducibility. All these characteristics make them a very interesting option for obtaining a large variety of electrodes to resolve different kinds of analytical problems. This review summarizes the state-of-the-art, advantages, and disadvantages of graphite powder-based electrodes in electrochemical analysis in the 21st century. It includes recent trends in carbon paste electrodes, devoting special attention to the use of emergent materials as new binders and to the development of other composite electrodes. The most recent advances in the use of graphite powder-modified sol–gel electrodes are also described. The development of sonogel–carbon electrodes and their use in electrochemical sensors and biosensors is included. These materials extend the possibilities of applications, especially for industrial technology-transfer purposes, and their development could affect not only electroanalytical green chemistry but other interesting areas also, for example catalysis and energy conversion and storage.     

Disposable Injection‐Moulded Cell‐on‐a‐Chip Microfluidic Devices with Integrated Conducting Polymer Electrodes for On‐Line Voltammetric and Electrochemiluminescence Detection

This work reports the construction and characterization of plastic electrochemical micro‐flow‐cells with integrated injection‐moulded polymer electrodes. The three electrodes (working, auxiliary, and reference) were fabricated by injection‐moulding from a conducting grade of polystyrene loaded with carbon fibers. On‐chip reference electrodes were prepared by coating one of the conducting polymer electrodes with a Ag/AgCl layer (implemented either by e‐beam evaporation of Ag followed by electrochemical formation of AgCl or by applying a Ag/AgCl paste). Working electrodes were either polymer electrodes coated with Au by e‐beam evaporation or bare conducting polymer electrodes. The electrodes were integrated into the micro‐flow‐cells by an over‐moulding process followed by ultrasonic welding. The devices were characterized by optical and electrochemical techniques. Studies by cyclic voltammetry (CV), anodic stripping voltammetry (ASV) and electrochemiluminescence (ECL) demonstrate ‘proof–of‐principle’ of the micro‐flow‐cells as electrochemical sensors.     

Ion-selective electrodes and enzyme electrodes in environmental and clinical studies.

Electrodes have been developed for the assay of glucose, urea, amino acids, uric acid, phosphate, nitrate and perchlorate. The electrodes for the organic compounds are enzyme electrodes which are prepared by chemically immobilizing an enzyme over the outside of a conventional ion-selective electrode. These electrodes will be discussed in depth. The progress and the development of the electrodes that show sensitivity and selectivity for phosphate, nitrate and perchlorate will be outlined. The basis of these sensors is a complex of a transition metal of either an analog of thiourea or an organic chelator, such as 1,10-phenanthraline. Such electrodes respond linearly to phosphate, nitrate or perchlorate, and show selectivity over sulphate, halides and acetate. The linear range of all these electrodes is approx. 10(-1)-10(-5) M with a near Nernstian slope and a reproducibility of 1%. The electrodes are stable and can be used continuously.     

Microwave activation of the electro-oxidation of glucose in alkaline media

The oxidation of glucose is a complex process usually requiring catalytically active electrode surfaces or enzyme-modified electrodes. In this study the effect of high intensity microwave radiation on the oxidation of glucose in alkaline solution at Au, Cu, and Ni electrodes is reported. Calibration experiments with the Fe(CN)(6)(3-/4-) redox system in aqueous 0.1 M NaOH indicate that strong thermal effects occur at both 50 and 500 microm diameter electrodes with temperatures reaching 380 K. Extreme mass transport effects with mass transport coefficients of k(mt) > 0.01 m s(-1)(or k(mt) > 1.0 cm s(-1)) are observed at 50 microm diameter electrodes in the presence of microwaves. The electrocatalytic oxidation of glucose at 500 microm diameter Au, Cu, or Ni electrodes immersed in 0.1 M NaOH and in the presence of microwave radiation is shown to be dominated by kinetic control. The magnitude of glucose oxidation currents at Cu electrodes is shown to depend on the thickness of a pre-formed oxide layer. At 50 microm diameter Au, Cu, or Ni electrodes microwave enhanced current densities are generally higher, but only at Au electrodes is a significantly increased rate for the electrocatalytic oxidation of glucose to gluconolactone observed. This rate enhancement appears to be independent of temperature but microwave intensity dependent, and therefore non-thermal in nature. Voltammetric currents observed at Ni electrodes in the presence of microwaves show the best correlation with glucose concentration and are therefore analytically most useful.     

Integration of Layered Redox Proteins and Conductive Supports for Bioelectronic Applications

Integration of redox enzymes with an electrode support and formation of an electrical contact between the biocatalysts and the electrode is the fundamental subject of bioelectronics and optobioelectronics. This review addresses the recent advances and the scientific progress in electrically contacted, layered enzyme electrodes, and discusses the future applications of the systems in various bioelectronic devices, for example, amperometric biosensors, sensoric arrays, logic gates, and optical memories. This review presents the methods for the immobilization of redox enzymes on electrodes and discusses the covalent linkage of proteins, the use of supramolecular affinity complexes, and the reconstitution of apo-redox enzymes for the nanoengineering of electrodes with protein monolayers of electrodes with protein monolayers and multilayers. Electrical contact in the layered enzyme electrode is achieved by the application of diffusional electron mediators, such as ferrocene derivatives, ferricyanide, quinones, and bipyridinium salts. Covalent tethering of electron relay units to layered enzyme electrodes, the cross-linking of affinity complexes formed between redox proteins and electrodes functionalized with relay-cofactor units, or surface reconstitution of apo-enzymes on relay-cofactor-functionalized electrodes yield bioelectrocatalytic electrodes. The application of the functionalized electrodes as biosensor devices is addressed and further application of electrically "wired" enzymes as catalytic interfaces in biofuel cells is discussed. The organization of sensor arrays, self-calibrated biosensors, or gated bioelectronic devices requires the microstructuring of biomaterials on solid supports in the form of ordered micro-patterns. For example, light-sensitive layers composed of azides, benzophenone, or diazine derivatives associated with solid supports can be irradiated through masks to enable the patterned covalent linkage of biomaterials to surfaces. Alternatively, patterning of biomaterials can be accomplished by noncovalent interactions (such as in affinity complexes between avidin and a photolabeled biotin, or between an antibody and a photoisomerizable antigen layer) to provide a means of organizing protein microstructures on surfaces. The organization of patterned hydrophilic/hydrophobic domains on surfaces, by using photolithography, stamping, or micromachining methods, allows the selective patterning of surfaces by hydrophobic, noncovalent interactions. Photoactivated layered enzyme electrodes act as light-switchable optobioelectronic systems for the amperometric transduction of recorded photonic information. These systems can act as optical memories, biomolecular amplifiers, or logic gates. The photoswitchable enzyme electrodes are generated by the tethering of photoisomerizable groups to the protein, the reconstitution of apo-enzymes with semisynthetic photoisomerizable cofactor units, or the coupling of photoisomerizable electron relay units.     

All-solid-state planar miniature ion-selective chloride electrode

All-solid-state ion-selective electrodes with plastic membrane (poly(vinyl chloride) (PVC), bis(2-ethylhexyl) sebacate (DOS), methyltri-n-tetradecylammonium chloride (MTTACl)), a conducting poly(pyrrole) (PPy) film doped either with chloride ions (PPyCl) or hexacyanoferrate(II) ions (PPyFeCN), and glassy carbon (GC) or screen-printed graphite layer (S-PG) as an inner electric contact were investigated. All the electrodes show close to Nernstian response, but their lifetimes vary. The at least 2-months lifetime of screen-printed electrodes is only achieved for the electrodes containing PPyFeCN (cation-exchanging film). Shorter lifetime of other screen-printed electrodes, i.e. without PPy, or with PPyCl (anion-exchanging film), was attributed to the diffusion of anionic products of the hydrolysis of organic components of the graphite paste used to prepare the electric contact. The properties of miniature, screen-printed electrodes comprising PPyFeCN solid contact, were comparable to those ion-selective electrodes with PPy solid contact (regardless the ion-exchanging characteristic of the polymer) deposited on GC electric contact.     

Fabrication and characterisation of nanometre-sized platinum electrodes for voltammetric analysis and imaging

A simple procedure is described for the fabrication of micrometre to nanometre scale Pt electrodes. These electrodes are prepared by etching a fine Pt wire, which is subsequently coated with an electrophoretic paint, deposited anodically or cathodically. The electrodes are characterised by scanning electron microscopy and steady-state linear sweep voltammetry. Voltammetric measurements of the oxidation of aqueous ferrocyanide at electrodes with effective radii varying from 1 μm to 10 nm show the expected increase in irreversibility with increasing mass transport rate. The electrodes are shown to be particularly promising as imaging probes for scanning electrochemical microscopy.     

Degradation of Phenol by Hydroxyl Radicals on Different Coating Lead Dioxide Electrodes

Lead dioxide electrodes on Ti substrates were prepared by thermal-deposition or electro-deposition. The amount of hydroxyl radicals generated at the electrodes prepared by the above-mentioned two methods was compared with that at the electrodes mingled with Bi or La prepared by electro-deposition. The experimental results indicate that the highest concentration of hydroxyl radicals generated by thermal-deposition, electro-deposition mingled with nothing, electro-deposition mingled with Bi or La was 0.781, 1.048, 1.838 or 2.044 μmol/L, respectively. When phenol was electrolyzed on the four electrodes at a current density of 30 mA/cm2, the removal efficiency of phenol after electrolysis for 1.5 h was 87.30%, 93.55%, 97.95% or 98.70%, TOC removal efficiency after electrolysis for 5 h was 86.76%, 94.26%, 98.53% or 99.60%, respectively. Through the degradation experiments of phenol, the amount of hydroxyl radicals was responsible for the removal efficiency of phenol. The electro-catalytic characteristics were investigated by SEM, the generation amount of hydroxyl radicals, the degradation degree of phenol and the stability and conductivity of the electrodes were also investigated. The experimental results indicate that the four electrodes all show good electro-catalytic characteristics; the electro-catalytic characteristics of the electrode mingled with La were superior to those of the other three ones, and the electrochemical degradation of phenol followed one-step reaction dynamics.     

Inexpensive device for measurements with ion-selective and pH electrodes

The design and construction of a simple device for measuring ionic concentrations (or pH) with ion-selective electrodes are described. The automated system includes a special electronic circuit with an operational amplifier, a signal conditioner and a personalcomputer. A digital multimeter can be used if automation is not required. The results obtained in tests with iodide-, chloride- and nitrate-selective electrodes and glass electrodes show very good agreement with those obtained with sophisticated commercial apparatus.     

Bulk Nanostructuring of Janus-Type Metal Electrodes

The stable deposition of reactive nanostructures on metal electrodes is a key process for modern technologies including energy conversion/ storage, electrocatalysis or sensing. Here a facile, scalable route is reported, which allows the bulk nanostructuring of copper foam electrodes with metal, metal oxide or metal hydroxide nanostructures. A concentration-gradient driven synthetic approach enables the fabrication of Janus-type electrodes where one face features Cu(OH)₂ nanowires, while the other face features CuO nanoflowers. Thermal or chemical conversion of the nanostructured surfaces into copper oxide or copper metal is possible whilst retaining the respective nanostructure morphologies. As proof of concept, the functionalized electrodes are promising in electrocatalytic water oxidation and water reduction reactions.     

钯氧化物的电化学与光电子能谱

不少研究者曾分别利用金属钯的表面化学氧化、电化学氧化或喷涂钯氧化物层等方法制备钯氧化物pH电极,已有的工作表明:制备条件对电极的pH响应范围、响应速度和重现性均有明显影响。因此,在继续寻找最佳制备条件的同时有必要对决定电极性能的因素进行深入的研究.本文旨在通过比较由两种方法制得的钯氧化物电极的组成和伏安行为,探讨影响电极pH敏感性能的因素。     

Recent Advances in Nanomaterial‐Modified Pencil Graphite Electrodes for Electroanalysis

Pencil graphite electrodes (PGEs) have several advantages over other carbon‐based or commercial metal electrodes, including widespread availability, very low cost, and ease of modification. To make the best use of PGEs in electroanalysis, significant recent advances in the development of different nanomaterial‐PGEs have been observed. The literature published up to mid‐2015 is summarized in the present review, with a focus on the various methodologies used to readily modify graphite pencil electrodes using nanomaterials. This review also touches on the surface characterization of these electrodes and their potential applications in a variety of electrochemical detection applications. The review outlines the scope for further research in this area and discusses the importance of surface modifications of conventional PGE electrodes using nanomaterials or a combination of nanomaterials and electroactive polymers.     

Instrumental configurations for the determination of sub-micromolar concentrations of electroactive species with carbon,gold and platinum microdisk electrodes in static and flow-through cells

Microelectrodes should provide a greater analytical sensitivity than electrodes of conventional size. However, the detection of micromolar or lower concentrations with microdisk electrodes requires measurement of femtoamp currents, which is outside the range of most commercially available instrumentation. The novel use of a picoammeter or femto-ammeter as a current amplifier permits commercial instrumentation to be used with microdisk electrodes. Such instrumentation incorporating a picoammeter or femtoammeter is limited by the relatively slow rise time; this places restrictions on scan rates in all voltammetric techniques and on pulse widths in transient techniques such as differential pulse and square wave voltammetry. Because of the small currents, the ohmic (iR) drop is very small and polarization of the reference electrode is unimportant; thus a two-electrode format without a potentiostat can be used. Consequently, a microprocessor-based function generator and data storage system, in conjunction with a pico- or femto-ammeter, is satisfactory in providing inexpensive, versatile and very sensitive instrumentation for voltammetric detection with microdisk electrodes. Convenient methods for fabricating platinum, gold and carbon microdisk electrodes for use in stationary and flowing solution configurations are also presented.     

十种以碱性染料制备的PVC膜ReO4-离子选择电极——碱性染料结构对ReO4-电极性能的影响

本文以不同碱性染料制备了十种PVC膜ReO₄^-离子选择电极,测试和比较了它们的性能,筛选出六种较优者,并根据其差别初步探讨了碱性染料结构对ReO₄^-电极性能的影响.     

Enzyme electrode for L-amino acids and glucose

New electrodes based on chemically bound enzymes are described for glucose and L-amino acids. The decrease in the dissolved oxygen content during the enzyme reaction is measured polarographically. The electrodes are stable for at least 4 months and give a response in less than 1 min. These electrodes are more sensitive than the hydrogen peroxide-based electrodes described previously, because the unstable peroxide can be consumed in several ways such as catalase decomposition or reaction with other products.     

Differential labeling of closely spaced biosensor electrodes via electrochemical lithography

Electrochemical biosensors offer the promise of exceptional scalability and parallelizability. To achieve this promise, however, will require the development of new methods for the differential labeling of closely spaced electrodes with specific biomolecules such as DNA or proteins. Here we report a simple, highly selective method for passivating and differentially labeling closely separated gold electrodes with oligonucleotides or other biomolecules. Analogous to photolithography, where a light-sensitive resist is selectively removed to expose specific surfaces to further modification, we passivate gold electrodes with a self-assembled alkanethiol monolayer that protects them from modification. The monolayer is then electrochemically desorbed at relatively low potentials, allowing for the subsequent labeling of the now exposed array element with a specific sensing biomolecule. The observed passivation is highly efficient: using a C11-OH monolayer as the passivating agent, we do not observe any detectable cross-contamination of adjacent electrodes (95 microm separation) upon labeling with a stem-loop DNA probe. Critically, the conditions employed are sufficiently gentle that depassivation reduces the DNA load on adjacent electrodes by only approximately 1%, allowing for the sequential labeling of multiple, closely spaced electrodes. This technology paves the way for labeling multiple array elements sequentially without observable cross-contamination in a fast and controlled manner.