Amperometric enzyme electrodes in analytical chemistry

Summary An overview is given of works on the construction and application of amperometric enzyme electrodes for the determination of metabolites in biological solutions. The following electrodes are dealt with: monoenzyme and polyenzyme electrodes involving amperometric detection of hydrogen peroxide, bienzyme electrodes with oxidase-peroxidase, electrodes based on organic metals and chemically modified electrodes, dehydrogenase electrodes, amperometric hydrolase electrodes and highly sensitive electrodes involving chemical amplification. Biocatalytic stripping and macrokinetic behaviour of the electrodes are discussed.

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Amperometrische Enzymelektroden in der analytischen Chemie

     

Floating electrode dielectrophoresis

In practice, dielectrophoresis (DEP) devices are based on micropatterned electrodes. When subjected to applied voltages, the electrodes generate nonuniform electric fields that are necessary for the DEP manipulation of particles. In this study, electrically floating electrodes are used in DEP devices. It is demonstrated that effective DEP forces can be achieved by using floating electrodes. Additionally, DEP forces generated by floating electrodes are different from DEP forces generated by excited electrodes. The floating electrodes' capabilities are explained theoretically by calculating the electric field gradients and demonstrated experimentally by using test-devices. The test-devices show that floating electrodes can be used to collect erythrocytes (red blood cells). DEP devices which contain many floating electrodes ought to have fewer connections to external signal sources. Therefore, the use of floating electrodes may considerably facilitate the fabrication and operation of DEP devices. It can also reduce device dimensions. However, the key point is that DEP devices can integrate excited electrodes fabricated by microtechnology processes and floating electrodes fabricated by nanotechnology processes. Such integration is expected to promote the use of DEP devices in the manipulation of nanoparticles.     

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.     

不同浸润性多孔电极表面的气泡行为

采用氢气模板法制备了具有多孔结构的电极; 通过改变电镀电流密度和电镀时间实现了电极表面多孔结构孔径和分布的控制; 通过改变表面化学组成有效调控了电极表面的浸润性质. 比较了具有不同微观结构和表面化学组成的电极在给定条件下电解水过程中气泡的产生及行为机制. 实验结果表明: 相对于亲水的多孔电极, 疏水的多孔电极表面能够黏附气泡, 更易倾向于形成稳定的气膜; 多孔结构对于亲水电极表面气泡行为的影响比对疏水电极表面气泡行为的影响更为显著; 与没有多孔结构的亲水电极相比, 具有多孔结构的亲水电极表面产生的气泡数量多, 速率快; 与较小孔径的多孔亲水电极相比, 较大孔径的多孔亲水电极表面产生气泡速率快且黏附气泡数量少. 该研究结果为微气泡减阻电极的设计提供了理论依据.     

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.     

ITO-free transparent conductive films based on carbon nanomaterials with metal grid for liquid crystal displays

Carbon nanomaterials with metal grids were used as transparent conductive electrodes for liquid crystal displays (LCDs) to develop an indium tin oxide (ITO)-free device. We prepared LCDs with CNTs and graphene electrodes; however, the working voltage of the device with the CNT electrodes was high. The device with graphene electrodes had good performance, but not as good as devices with ITO electrodes. To improve the device performance, we applied a metal grid to the carbon nanomaterial to create low sheet-resistance transparent electrodes. The device with the graphene and metal grid transparent electrodes had a threshold voltage as low as 0.23 V/µm, which is similar to that of typical LCDs with ITO electrodes. The results show that a hybrid transparent conductive film with graphene and metal grid could be an alternative to ITO for developing ITO-free LCDs.     

Hydrogel-based flexible micro-reference electrodes for use in alkaline and neutral pH solutions

Two types of nonbreakable, flexible micro-reference electrodes filled with gel-electrolytes were prepared for use in solutions with alkaline and neutral pH. The electrodes are intended for electrochemical measurements, in which chloride-free conditions are important. Due to the flexible, bendable construction of the electrodes, electrochemical experiments at locations difficult to access with common reference electrodes are enabled. Hg|HgO-type electrodes were prepared from amalgamated Au wires, followed by oxidation of the amalgam, which is mounted in a PTFE tube filled with 0.1M NaOH solution immobilized in a PAA-g-PEO gel. The potential of this type of electrode was found to be 0.162?±?0.002 V (SHE) at room temperature. Cu|CuSO₄ electrodes, consisting of a Cu wire immersed in a saturated CuSO₄ solution jellied with gelatin, showed a stable open-circuit potential of 0.312?±?0.001 V (SHE). Further characterization of the electrodes was performed in terms of electrochemical impedance spectroscopy and micro-polarization measurements. As an alternative to the flexible electrodes, rigid electrodes in glass enclosure were fabricated in analogy to the flexible-type electrodes.     

Exploring the electrocatalytic sites of carbon nanotubes for NADH detection: an edge plane pyrolytic graphite electrode study

The electrocatalytic properties of multi-walled carbon nanotube modified electrodes toward the oxidation of NADH are critically evaluated. Carbon nanotube modified electrodes are examined and compared with boron-doped diamond and glassy carbon electrodes, and most importantly, edge plane and basal pyrolytic graphite electrodes. It is found that CNT modified electrodes are no more reactive than edge plane pyrolytic graphite electrodes with the comparison with edge plane and basal plane pyrolytic graphite electrodes allowing the electroactive sites for the electrochemical oxidation of NADH to be unambiguously determined as due to edge plane sites. Using these highly reactive edge plane sites, edge plane pyrolytic graphite electrodes are examined with cyclic voltammetry and amperometry for the electroanalytical determination of NADH. It is demonstrated that a detection limit of 5 microM is possible with cyclic voltammetry or 0.3 microM using amperometry suggesting that edge plane pyrolytic graphite electrodes can conveniently replace carbon nanotube modified glassy carbon electrodes for biosensing applications with the relative advantages of reactivity, cost and simplicity of preparation. We advocate the routine use of edge plane and basal plane pyrolytic graphite electrodes in studies utilising carbon nanotubes particularly if 'electrocatalytic' properties are claimed for the latter.     

Bioinspired superwettable electrodes towards electrochemical biosensing

Superwettable materials have attracted much attention due to their fascinating properties and great promise in several fields. Recently, superwettable materials have injected new vitality into electrochemical biosensors. Superwettable electrodes exhibit unique advantages, including large electrochemical active areas, electrochemical dynamics acceleration, and optimized management of mass transfer. In this review, the electrochemical reaction process at electrode/electrolyte interfaces and some fundamental understanding of superwettable materials are discussed. Then progress in different electrodes has been summarized, including superhydrophilic, superhydrophobic, superaerophilic, superaerophobic, and superwettable micropatterned electrodes, electrodes with switchable wettabilities, and electrodes with Janus wettabilities. Moreover, we also discussed the development of superwettable materials for wearable electrochemical sensors. Finally, our perspective for future research is presented.

The recent progress of superhydrophilic/phobic electrodes, superaerophilic/phobic electrodes, superwettable patterned electrodes, Janus wettability electrodes and wettability switchable electrodes in electrochemical biosensing is reviewed.     

Schiff碱型和仲胺型双冠醚II: 用双冠醚作载体的PVC膜钾离子选择性电极

用六个含二个苯并-15-冠-5单元的席夫碱型和仲胺型新型双冠醚作载体制备了钾离子选择性PVC膜电极,并研究了它们的电极行为,这些电极对所有的其它碱金属和碱土金属离子展现出显著的钾离子选择性,可期望有一定的应用价值.     

Use of disposable gold working electrodes for cation chromatography-integrated pulsed amperometric detection of sulfur-containing amino acids

We have prepared disposable thin-film gold working electrodes on polymeric substrates. Our microfabrication process allows for inexpensive and reproducible mass production of such electrodes. We utilize this new type of electrode in flow-through electrochemical cells to replace the conventional non-disposable gold working electrodes for integrated pulsed amperometric detection (IPAD) of compounds separated by high-performance cation-exchange chromatography. Using two S-containing amino acids (homocysteine and cysteine) as test compounds, we have modified a previously reported waveform for optimum performance with disposable gold electrodes. With the help of the same two test substances we have characterized the analytical performance of disposable gold electrodes under the new conditions. Compared to non-disposable working electrodes, the disposable working electrodes generated equal or better results in the limit of detection, linearity of calibration and reproducibility. When used with a new IPAD waveform, the disposable electrodes functioned reproducibly for 3 days. At the end of the specified usage period of 3 days, the disposable electrodes are simply replaced. Reconditioning by polishing is thus no longer required.     

聚萘二胺修饰电极对痕量物质的检测

综述了聚萘二胺修饰铂电极、玻碳电极和碳糊电极用于检测痕量银离子、铅离子、亚硝酸根及硝酸根阴离子、过氧化氢、葡萄糖和胆甾醇等方面的研究成果，列举了这些电极的优异探测性能，并指出该类电极有望发展成为性能优异的检测电极和传感器。引用文献14篇。     

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.     

Long-term stability of glass electrodes in aqueous media

The stability of the potential of glass electrodes has been studied. The potential changes only slightly during the hydration of freshly etched electrodes. With glass electrodes previously used in alkaline solutions, structural transformations within the gel-layer give rise to large potential drifts in neutral or acidic test solutions. In alkaline solutions all glass electrodes are attacked, especially the low-temperature type, and the potential changes with time. Drying hydrated electrodes affects the stability only slightly. Alternating transfers between acidic and basic solutions decrease the stability. Recommendations for precise measurements with glass electrodes are given.     

Analytical quality solid-state composite reference electrode manufactured by injection moulding

An injection moulding method was used for fabricating solid-state reference electrodes (Ag/AgCl type) based on a polymer/inorganic salt composite. In this method, a silver/silver chloride wire was placed inside a mould into which the mixture of polymer and inorganic salt was injected. The obtained solid-state composite reference electrodes were extensively tested to study the influence of different parameters such as solution composition, the concentrations and mobility of ions and pH on the potential stability of the electrodes. These experiments revealed that the composite reference electrodes are insensitive to the matrix effect, have excellent potential readings stability and considerably reduced leakage of inorganic salt. The composite reference electrodes were compared favourably to high-quality commercial reference electrodes. It was concluded that the composite reference electrodes obtained by injection moulding are of analytical quality allowing for continuous, prolonged and intensive usage.     

锌铋合金电极在溶胶电解液中的电化学行为

锌电极的自腐蚀速率, 持续放电下的阳极溶解速率和电极钝化的难易程度是碱性电池性能的重要电化学参数. 本文应用线性极化、恒流放电等电化学实验方法研究了电解液中添加Carbopol树脂以及电极中添加Bi对锌电极电化学行为的影响. 并应用金相显微镜和环境扫描电子显微镜(ESEM)对锌电极和锌铋合金电极浸蚀及放电后的形貌进行了表征. 结果表明: 电解液中添加适量的Carbopol树脂可明显提高电极的极化电阻, 显著降低电极的自腐蚀速率; 阳极的溶解电位出现不同程度的正移, 阳极过电位显著增大且大电流密度放电时较明显促进电极钝化. 锌电极中添加一定量的Bi对改善电极表面氧化物膜的沉积形貌和电极表面固液界面的传质条件, 减小电极的自腐蚀速率, 抑制电极自腐蚀等方面具有显著作用.     

Polycrystalline and monocrystalline antimony, iridium and palladium as electrode material for pH-sensing electrodes

Different ways of making pH-sensing electrodes from monocrystalline or polycrystalline antimony, iridium and palladium have been investigated. Monocrystalline antimony and iridium are superior to the polycrystalline elements with respect to reproducibility between electrodes and stability of the electrode potential over long periods of time. No good palladium/palladium oxide electrode could be obtained by electrochemical oxidation and the thermal preparation method could not take advantage of the properties of the monocrystalline palladium. Therefore, only polycrystalline palladium was used to study this type of electrodes. The different electrodes were compared with respect to the manner of preparation, the pH-response (reproducibility and time response) and the effect that different complexing ligands present in the measuring solutions may have on the electrode response. Also, the redox-response of the electrodes and the effect of different oxygen pressures on the electrode potentials were studied. The monocrystalline antimony electrodes have the best reproducibility and long-term stability but also respond to complexing ligands and to variations in the oxygen pressure. Monocrystalline iridium electrodes can be obtained by continuously cycling the potential between -0.25 and +1.25 V (SCE) in 0.5M sulphuric acid. They do not respond to the complexing ligands tested, and have fairly good long-term stability, but the reproducibility between electrodes is inferior to that of the monocrystalline antimony electrodes. Polycrystalline antimony and iridium electrodes were inferior to the monocrystalline ones. The properties of the palladium electrodes were similar to those of the iridium ones.     

Electrochemical Determination of Uric Acid,Dopamine and Tryptophan at Zinc Hexacyanoferrate Clay Modified Electrode

A Cameroonian smectite clay has been transformed into Zn²⁺ homoionic form and then used to prepare film modified glassy carbon electrodes and carbon paste electrodes. These electrodes containing Zn²⁺ were exploited to prepare a mixed valence zinc hexacyanoferrate (ZnHCF). Cyclic voltammetry has been employed to monitor the in situ growth of ZnHCF on clay modified electrodes. Although interesting electrocatalytic properties toward UA were observed with these modified electrodes, the modified carbon paste electrodes were the most suitable for dopamine, uric acid and tryptophan detection and exhibited for these analytes extended linear range, high sensitivities, selectivity and low limit.     

Screen Printed Electrodes and Screen Printed Modified Electrodes Benefit from Insonation

The synergy of power ultrasound with screen printed electrodes and screen printed modified electrodes is shown to be possible and beneficial. Proof‐of‐concept is shown for the anodic stripping voltammetry of lead at screen printed electrodes and screen printed calomel modified electrodes offering shorter deposition times and increased sensitivity.     

电滴定分析的新方法

利用示波极谱图上切口的出现或消失来指示滴定终点的示波极谱滴定法具有终点直观、操作简便和抗干扰能力强等优点。但该法要求试剂(滴定剂、被滴物或指示剂)能在示波极谱图上产生敏锐切口才能应用。