Spectroelectrochemistry of tetracyanoquinodimethane modified electrodes

Thin films of a tetracyanoquinodimethane (TCNQ) oligomer adsorbed on optically transparent platinum electrodes have been studied using spectroelectrochemical techniques. In contact with aqueous electrolytes the electron aceptor sites in these modified electrodes are reduced to mixtures of the radical aion, TCNQ^?, the dimer radical anion, TCNQ^2?₂, the dimer dianion, TCNQ₂^2?, and the dianion, TCNQ^2∮. Electrolyte effects on the reduction process and the stability of the reduced films were studied. Both monovalent and divalent ions exhibited Nernstian potential dependence, and in the presence of Ca²⁺ ions the dianion state was stabilized. Counterion effects are suggested as the origin of variations in the wave shape in multcycle voltammograms.     

生物功能电极I: GOD修饰电极的电化学活性

以二环己基碳化二亚胺为活化剂将葡萄糖氧化酶(GOD)共价键接在玻碳电极上, 伏安实验观察到酶与电极基体的直接电子传递, 有观电子传递速度常数约为1s^-^1, 过程归因于全酶中辅基FAD的氧化还原转变。Ag^+离子的存在强烈地阻碍酶辅基的还原, 这与该离子抑制酶活性的机理可能有联系。Ag^+的抑制作用可由EDTA处理或电化学处理而解除, GOD电极对氧和苯醌的电还原有催化作用。测定了苯醌同还原态GOD的化学反应速度常数, 并讨论用苯醌代替氧作为生物电催化中的电子传递体的优点。     

血红素蛋白质-琼脂糖膜修饰电极的表征和电催化特性

利用琼脂糖(agarose)水凝胶将肌红蛋白(Mb)、血红蛋白(Hb)、辣根过氧化物酶(HRP)和过氧化氢酶(Cat)4种血红素蛋白质固定在裂解石墨电极表面,形成稳定的血红素蛋白质-agarose膜修饰电极.用紫外-可见和红外光谱及原子力显微法对血红素蛋白质-琼脂糖膜修饰电极进行了表征.紫外-可见和红外光谱显示,在琼脂糖凝胶中,血红素蛋白质保持原始构象.溶液的pH(3.0～10.0)可逆地改变血红素蛋白质的构象,从而影响其光谱性质.原子力显微图象表明血红素蛋白质与agarose水凝胶之间存在较强的作用.研究了血红素蛋白质催化还原O2、H2O2的机理.稳定的血红素蛋白质-agarose修饰电极能运用于H2O2的定量测定.     

Preventing inhibition of tyrosinase with modified electrodes

Wines, especially red wines, contain numerous biologically active compounds, the most important of which are polyphenols, whose nutritional importance is attributed to their antioxidant power. Because of this, the detection of the amount of phenolic compounds in red wines becomes extremely important. However, using free enzyme in the determination of phenolic compounds in wines cannot reflect the actual values since there are also naturally found inhibitors in red wines. In this study, benzoic acid, cinnamic acid, and sorbic acid were utilized to understand the behavior of immobilized polyphenol oxidase in the conducting polymer matrices toward inhibition. Cinnamic acid was found to be the most powerful inhibitor for both free and immobilized enzyme in copolymer matrix of poly(terephthalic acid bis-(2-thiophen-3-yl-ethyl) ester) (PTATE) with polypyrrole (PPy). In the case of immobilized enzyme in PPy matrix, it was observed that sorbic acid is a stronger inhibitor than cinnamic acid. The inhibitory effects of these inhibitors on PPO were compared with respect to both the structural differences of inhibitors and conducting polymer matrices.     

碳纳米材料在修饰电极领域的应用

碳纳米材料具有良好的力学、电学及化学性能等特点,被人们广泛研究,特别是具有大比表面积、高的电导率和良好生物相容性的碳纳米管和石墨烯更是研究的热点,在电化学领域显示出独特的优势.采用碳纳米材料修饰的电极具有高灵敏度、高选择性及优良的媒介作用.主要阐述了碳纳米材料在修饰电极领域中的应用,从功能及应用上重点探讨了近年来碳纳米管、石墨烯、富勒烯、纳米金刚石等碳纳米材料在修饰电极领域的研究进展.     

Carbon paste electrodes electrochemically modified with cyclodextrins

Cyclic voltammetry was used in order to obtain carbon paste electrodes (CPEs) modified with α- and β-cyclodextrins (CPE_α-CD, CPE_β-CD) in HClO₄ media as electrolyte. The modified CPEs were obtained by applying 30 potential cycles, thus forming on the substrate a film with electroactive characteristics; a rise in current for the anodic and cathodic peaks became apparent as the number of cycles increased. Such behaviour confirmed the CPE modification by the species mentioned. The CPE_α-CD and CPE_β-CD exhibited significant stability before various electrolytes. In order to evaluate the sort of modification attained on the CPEs, a study was conducted, varying the potential scan rate, that confirmed the CD's presence. The modified electrodes were used to determine Pb(II) ions in solution within the range from 1×10^–5 M up to 1×10^–3 M. The CPE_α-CD and CPE_β-CD electrochemical response was studied by means of anodic stripping voltammetry of the Pb(II) ions, thereby giving a linear relation between the current for the anodic peak as a function of Pb(II) concentration with r ²=0.996 for the CPE_β-CD and 0.992 for the CPE_α-CD. Electronic Publication     

Carbohydrates electrocatalytic oxidation using CNT-NiCo-oxide modified electrodes

A new sensor for an amplified electrochemical detection of carbohydrates is proposed, where carbohydrates are oxidized by CNT-NiCo-oxide composite in basic solutions. Cyclic voltammograms of the modified electrode show a stable and well defined redox couple in alkaline media due to the synergy of Ni(II)/Ni(III) system with Co(II)/Co(III). The modified electrode shows excellent electrocatalytic activity towards monosaccharides oxidation at reduced overpotential in alkaline solutions. Six monosaccharides were determined amperometrically at the surface of this modified electrode with high sensitivity over a wide range of concentrations, from 0.02 up to 12.12 mM. Low detection limit of 5 μM for glucose could be obtained.     

Clay modified electrodes: Part VI. Aluminum and silicon pillared clay-modified electrodes

Metal (Ru, Os, Fe) bipyridyl complexes and Ru(NH₃)³⁺₆ were incorporated into several montmorillonite clays and their aluminum and silicon-pillared analogues. Film concentrations and apparent diffusion coefficients were measured and compared by using spectrophotometry, cyclic voltammetry and chronocoulometry. The catalytic role of isomorphously substituted iron was evaluated and implicated by its effects on Ru(bpy)³⁺₃ voltammetric behavior. A model is proposed for charge transport within the novel silicon-pillared clay.     

Electrostatic-gated transport in chemically modified glass nanopore electrodes

Electrostatic-gated transport in chemically modified glass nanopore electrodes with orifice radii as small as 15 nm is reported. A single conical-shaped nanopore in glass, with a approximately 1 microm radius Pt disk located at the pore base, is prepared by etching the exposed surface of a glass-sealed Pt nanodisk. The electrochemical response of the nanopore electrode corresponds to diffusion of redox-active species through the nanopore orifice to the Pt microdisk. Silanization of the exterior glass surface with Cl(Me)(2)Si(CH(2))(3)CN and the interior pore surface with EtO(Me)(2)Si(CH(2))(3)NH(2) introduces pH-dependent ion selectivity at the pore orifice, a consequence of the electrostatic interactions between the redox ions and protonated surface amines. Nanopore electrodes with very small pore orifice radii (< approximately 50 nm) display anion permselectively at pH < 4, as demonstrated by electrochemical measurement of transport through the pore orifice. Ion selective transport vanishes at pH > 6 or when the pore radius is significantly larger than the Debye screening length, consistent with the observed ion selectivity resulting from electrostatic interactions. The ability to introduce different surface functionalities to the interior and exterior surfaces of glass nanopores is demonstrated using fluorescence microscopy to monitor the localized covalent attachment of 5- (and 6)-carboxytetramethylrhodamine succinimidyl ester to interior pore surfaces previously silanized with EtO(Me)(2)Si(CH(2))(3)NH(2).     

Stripping-voltammetric signals on carbon electrodes modified with mercury

Conditions for the formation of a stable and reproducible thin-film mercury microdrop cover on electrodes from carbon glass ceramics, carbon glass, and graphite are proposed. The influence of various factors on the parameters of signals from cadmium (II), lead (II), and copper (II) is studied by stripping voltammetry with linear, differential-pulse, sinusoidal, and square-wave potential sweep. The parameters of the stripping voltammetric experiment are optimized. The value of RSD in determining the specified modeling trace components did not exceed 15%. Approaches to the multicomponent stripping voltammetric analysis of waters are proposed.     

Cation and anion exchange on clay modified electrodes

Carbon paste electrodes modified with clay minerals were used for the study of ion-exchange properties of these clay minerals. Cation exchange of Cu(II) was studied by the dependence on the pH, ionic strength and the form of the minerals. The highest anionic exchange of Hg(II) acetates and chlorides was found on montmorillonites. Anionic exchange of Au(III) chloro complexes was found on montmorillonite, but their sorption is strongly influenced by other anions such as chlorides and thiocyanates. The results found are important with regard to the study of the anion-exchange properties of clay minerals. Received: 2 December 1999 / Accepted: 2 March 2000     

Graphite epoxy composite electrodes modified with bacterial cells

The modification of a graphite-epoxy composite electrode (GECE) with bacterial cells along with an analytical application are presented. Pseudomonas putida DSM 50026 was used as a biological component and the measurement was based on the respiratory activity of the cells. The optimization of working conditions of resulting biosensor (including pH and temperature) was conducted and the limit of detection was calculated as 7 microM phenol based on the signal to noise ratio. Then the system was applied for xenobiotic detection. Resulting sample signals were found to be very similar with the standard solutions having the same concentration while the recoveries of the spiked samples were close to 100%.     

Calixarene--poly(dithiophene)-based chemically modified electrodes

The stepwise synthesis of cone and partial cone 1,3-bridged n-propoxy-calix[4]crown ethers ("monomers" 2 and 3) with an electropolymerizable 2,2'-dithiophene-3-yl-hexylene functionality at the lower rim, is described. The potential of 2 and 3 as sensing agents for alkali metal ions was investigated by 1H NMR titration experiments with NaSCN and KSCN. The results obtained have confirmed that the presence of the heterocyclic subunit does not affect the well-known size-selectivity observed with calix[4]crowns. Monomers 2 and 3 were electropolymerized (Pt as a working electrode, CH2Cl2/CH3CN, Bu4NPF6) to produce the title chemically modified electrodes (CMEs). After coating with a PVC membrane containing a lipophylic cation exchanger, CMEs based on calix[4]-crown-5 2b (cone) and 3b (partial cone) were tested for the potentiometric recognition of alkali metal ions in aqueous solution. In agreement with NMR titration studies, a satisfactory potentiometric response in terms of K+/Na+ selectivity was obtained only with CME 2b (pK(K/Na) 1.51). The amperometric responses of PVC-uncoated CMEs were studied by cyclic voltammetry (CV) experiments in CH3CN solution. High Na- selectivity was found with the CME based on partial cone calix[4]crown-4 3a, and frequency response analysis (FRA) measurements support this finding.     

Electrocatalysis with monolayer modified highly organized macroporous electrodes

For the first time the inner surface of highly organized macroporous electrodes, obtained by electrodeposition of gold into the interstitial spaces of a self-assembled close packed array of latex beads, is modified with a monolayer of a catalyst. The combination of the increased specific surface area of these electrodes and the high catalytic rate constant of the redox mediator allows us to construct surfaces showing good electrocatalytic efficiency. As a model system the electrooxidation of NADH using nitrofluorenone mediators is studied.     

Electroanalysis of cationic species at membrane-carbon electrodes modified by polysaccharides. Bioaccumulation at microorganism-modified electrodes

Membrane-carbon electrodes modified with polysaccharides suspensions entrapped between a dialysis membrane and the carbon surface were used for electroanalysis of various cationic species. Cationic complexes of ruthenium and cobalt, metallic cations (Cu²⁺, Fe³⁺, UO₂²⁺) as well as methylviologen were considered. By investigating various parameters (concentration of the suspension, pH) binding of the cations by the polysaccharides was demonstrated. Comparison of cations uptake by different kinds of polysaccharides such as alginic acid, polygalacturonic acid, pectin, dextran and agar was performed. This study has been extended to natural biomaterials, alga and lichen, which are known to contain polysaccharides. The interest of the membrane–electrode strategy is described.     

Electrocatalytic oxidation of NADH at mesoporous carbon modified electrodes

The electrochemical oxidation of β-nicotinamine adenine dinucleotide (NADH) was investigated at a glassy carbon electrode modified with carbon mesoporous materials (CMM). Due to the large surface area and electro-catalytic properties of CMM, the overpotential of the electrodes toward the oxidation of NADH is decreased by 595 mV in aqueous solution at neutral pH. The anodic peak currents increase steadily with the concentration of NADH in the range from 2 µM to 1.1 mM, the detection limit being 1.0 µM at pH 7.2 and a potential of +0.3 V vs. SCE. The apparent Michaelis-Menten constant is ～21.5 μM. The results enable NADH to be sensed at a low potential and are promising with respect to the design of dehydrogenase-based amperometric biosensors.