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。     

聚苯胺葡萄糖氧化酶电极的催化过程

用电化学方法固定在直径为0.5mm铂丝上的聚苯胺(PANI)葡萄糖(GOD)电极对葡萄糖有催化氧化作用.在0～-0.6V(vs.SCE)的电极范围内,在电极的循环伏安曲线上观察到与葡萄糖浓度有关的氧的还原峰和GOD还原态的氧化峰,用此GOD还原态的氧化峰电流可定量检测葡萄糖的浓度。本文提出在PANI电极上存在着酶反应氧化还原电荷直接传递的可能性。     

生物功能电极(Ⅴ)─葡萄糖氧化酶在环糊精聚合物中的固定化

将葡萄糖氧化酶(GOD)固定在α-环糊精聚合物中,而电子传递体分子被包含在环糊精腔穴中。固定化酶膜的FTIR测定表明,GOD与环糊精聚合物发生共价连接。制备了含电子传递体的不同GOD酶电极并比较了它们的性能。含四硫代富瓦烯的酶电极具有良好的电流响应特性,可望成为第二代葡萄糖酶电极的新构型。     

介体型酶电极二级催化反应速度常数的测定

采用开路驰豫法，测定了以二茂铁及其衍生物作为电子传递体的介体型酶电极的均相二级催化反应速度常数，结果表明二甲氨基甲基二茂铁，在绝氧条件下对于酶的再生反应具有高的催化活性，是一种性能优良的电子传递体．此外，讨论了开路弛豫法在酶电极研究中的适用条件及各种因素对该方法测定结果的影响．     

二氢辅酶的电催化氧化: I: α-萘甲酰尼罗蓝修饰电极性能研究

新的电子传递中间体α-萘甲酰尼罗蓝(NNB)能强烈吸附在石墨上以构成修饰电极。在-0.5V至+0.6V(vs. SCE)电位区内, 固定化的NNB表观出相当可逆的氧化还原行为, 总反应中有2个电子和2个质子参加。在pH7.0缓冲溶液中其表面标准电位E°'为-170mV, 表观电子传递常数kg为3s^-^1。NNB对还原辅酶NADH的电化学氧化有明显催化作用, 可使氧化过电位降低550mV。NADH的电催化遵循EC机理, 催化反应步骤为速度决定步骤, 其速度常数为3×10^3dm^3.mol^-^1.s^-^1。NNB在中性和弱碱性介质中的稳定性优于其它电子传递中间体, 是有前途的电催化剂。     

二氢辅酶的电催化氧化: I: α-萘甲酰尼罗蓝修饰电极性能研究

新的电子传递中间体α-萘甲酰尼罗蓝(NNB)能强烈吸附在石墨上以构成修饰电极。在-0.5V至+0.6V(vs. SCE)电位区内, 固定化的NNB表观出相当可逆的氧化还原行为, 总反应中有2个电子和2个质子参加。在pH7.0缓冲溶液中其表面标准电位E°'为-170mV, 表观电子传递常数kg为3s^-^1。NNB对还原辅酶NADH的电化学氧化有明显催化作用, 可使氧化过电位降低550mV。NADH的电催化遵循EC机理, 催化反应步骤为速度决定步骤, 其速度常数为3×10^3dm^3.mol^-^1.s^-^1。NNB在中性和弱碱性介质中的稳定性优于其它电子传递中间体, 是有前途的电催化剂。     

环糊精聚合物与苯醌的分子包合作用及其在酶电极中的应用

研究了水溶性环糊精预聚合物的存在对苯醌/氢醌体系在铂电极上氧化还原行为的影响, 根据伏安曲线讨论了该预聚合物与苯醌的分子包合作用。环糊精预聚合物与戊二醛缩聚反应而形成的不溶性聚合物膜用于葡萄糖氧化酶的固定化, 以制得新型的第二代葡萄糖电极。由于分子包合作用, 作为电子受体的苯醌在含酶的环糊精聚合物膜中具有较高的浓度, 从而加速了固定化酶的电子传递。测定了酶电极上BQ反应的动力学参数。     

电化学活化玻碳电极上葡萄糖氧化酶的吸附与直接电化学

利用循环伏安法和SNIFTIRS法研究了葡萄糖氧化酶(GOD)在经电化学活化的玻碳(GC)电极上的吸附与直接电化学行为。GC电极经活化后对GOD的吸附大为增强。吸附速度与吸附量同GC电极活化时高电位氧化时间、GOD浓度、溶液pH值及通氮搅拌有关。SNIFTIRS实验表明,GOD可能主要吸附于活化新生石墨结构晶棱或晶面上。表面微晶石墨结构可能为吸附GOD同GC电报的直接电子传递场所。     

氯过氧化物酶-聚L-赖氨酸/GC电极的电化学特性

应用电化学方法在玻碳电极上修饰聚L-赖氨酸膜,以1-乙基-(3-二甲基氨基丙基)碳二亚胺盐酸盐做交联剂,固定氯过氧化物酶.修饰电极的循环伏安曲线呈现一对可逆的氧化还原峰,表明聚L-赖氨酸能够很好地促进氯过氧化物酶在电极表面的直接电子传递,这是一个受吸附控制并伴随有质子转移的准可逆电子传递过程.该电极有很好的稳定性,并能显著地电催化氧的电化学还原反应.     

基于钯纳米颗粒修饰直立碳纳米管电极的电化学葡萄糖生物传感器

将电化学氧化生成的Pd(Ⅳ)离子配合到直立碳纳米管(ACNTs)上, 使其还原为纳米颗粒(Pb nps), 从而制得Pd nps-ACNTs纳米复合物电极, 经过葡萄糖氧化酶(GOD)进一步修饰后, 制成GOD/Pds nps/ACNTs酶电极, 通过测量GOD和葡萄糖酶促反应中产生的H₂O₂含量, 进而监测葡萄糖浓度. 实验结果表明, 电极表面大量Pd纳米颗粒的存在显著提高了传感器的检测灵敏度, 使酶电极具有响应时间短(<5 s)及检测电位低(<0.4 V)等优点.     

The instructive redox behaviour of 4‐ferrocenylcatechol on nanocrystalline titanium dioxide electrodes

An investigation into the redox behaviour of 4‐ferrocenylcatechol bound to nanocrystalline TiO₂ electrodes identified a limitation to the use of catechol as an electron‐transfer facilitating anchoring group. 4‐Ferrocenylcatechol was adsorbed to transparent nanocrystalline TiO₂ electrodes. UV–visible spectra of the modified electrode were recorded in an acetonitrile‐electrolyte solution. At an applied potential of + 0.45 mV (vs Ag/AgCl/Cl^?) the ferrocenyl group oxidized to the ferrocenium cation and the catecholate group oxidized to the benzoquinone form. Subsequent application of a potential of 0 V reduced the ferrocenium to ferrocene but, owing to the irreversibility of the catechol oxidation in aprotic solvents, benzoquinone is not reduced to catecholate and subsequently desorbs and is lost due into solution. Electrochromic switching of the ferrocenyl electrochromophore on TiO₂ with aprotic electrolyte is, therefore, irreversible. Copyright © 2006 John Wiley & Sons, Ltd.     

Organic interlayers for oxygen reducing electrodes based on bilirubin oxidase and MWCNT modified gold

Electrochemical properties of bilirubin oxidase (BOD) and multi-walled carbon nanotubes (MWCNT) modified gold electrodes were characterised by linear sweep voltammetry. For enhancement of the direct electron transfer of BOD an interlayer of different aromatic compounds was introduced between the adsorbed or covalently bound enzyme and the MWCNTs. By usage of pyrroloquinoline quinone (PQQ) an increased catalytic oxygen current was observed. The reduction process starts at a potential of +500 mV vs. Ag/AgCl, 1 M KCl. The peak current density in unstirred solution could be determined with about 500 μA/cm². A reduction of the diffusion layer thickness by stirring enhances the current density up to 1600 μA/cm² (at +250 mV).     

环糊精聚合物的分子包合作用及在酶电极中的应用

伏安法用于研究环糊精预聚合物的分子包合作用．红外光谱实验表明环糊精预聚合物与戊二醛缩聚生成的聚合物带有悬挂的羰基,后者能使葡萄糖氧化酶共价固定化．由于分子包合作用,电子受体可存储在含酶的环糊精聚合物膜中,从而提高了酶膜中电子受体的浓度又减少了电子受体的用量．用ＴＴＦ等作电子受体,可实现酶和电子受体在环糊精聚合物中的同时固定化．环糊精聚合物膜中的组成和膜厚度可以控制,为酶电极的基础研究工作提供了方便．     

Direct electron transfer reactions between human ceruloplasmin and electrodes

In an effort to find conditions favouring bioelectrocatalytic reduction of oxygen by surface-immobilised human ceruloplasmin (Cp), direct electron transfer (DET) reactions between Cp and an extended range of surfaces were considered. Exploiting advances in surface nanotechnology, bare and carbon-nanotube-modified spectrographic graphite electrodes as well as bare, thiol- and gold-nanoparticle-modified gold electrodes were considered, and ellipsometry provided clues as to the amount and form of adsorbed Cp. DET was studied under different conditions by cyclic voltammetry and chronoamperometry. Two Faradaic processes with midpoint potentials of about 400 mV and 700 mV vs. NHE, corresponding to the redox transformation of copper sites of Cp, were clearly observed. In spite of the significant amount of Cp adsorbed on the electrode surfaces, as well as the quite fast DET reactions between the redox enzyme and electrodes, bioelectrocatalytic reduction of oxygen by immobilised Cp was never registered. The bioelectrocatalytic inertness of this complex multi-functional redox enzyme interacting with a variety of surfaces might be associated with a very complex mechanism of intramolecular electron transfer involving a kinetic trapping behaviour.     

Electrocatalytic reduction of oxygen on the surface of glassy carbon electrodes modified with plumbagin

The preparation and electrochemical characterization of glassy carbon electrodes modified with plumbagin were investigated by employing cyclic voltammetry, chronoamperometry and rotating disc electrode techniques. The cyclic voltammograms of the electroreduction of oxygen showed an enhanced current peak at approximately −0.289 V in air-saturated phosphate buffer pH = 7 and scan rate 10 mV s⁻¹. The thermodynamic and kinetic parameters of the reduction of oxygen at glassy carbon have been evaluated using cyclic voltammetry. The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The obtained values of E°′ (V vs. Ag/AgCl), the apparent electron transfer rate constant k_s (s⁻¹), heterogeneous rate constant for the reduction of O₂ at the surface of the modified electrode k_h (M⁻¹ s⁻¹) and α (charge transfer coefficient of oxygen) were as follows: −0.146, 23.4, 9.9 × 10³ and 0.57, respectively. In addition, plumbagin exhibited strong catalytic activity toward the reduction of H₂O₂.     

Facile Fabrication of a Graphene‐based Electrochemical Biosensor for Glucose Detection

A simple and effective glucose biosensor based on immobilization of glucose oxidase (GOD) in graphene (GR)/Nafion film was constructed. The results indicated that the immobilized GOD can maintain its native structure and bioactivity, and the GR/Nafion film provides a favorable microenvironment for GOD immobilization and promotes the direct electron transfer between the electrode substrate and the redox center of GOD. The electrode reaction of the immobilized GOD shows a reversible and surface‐controlled process with the large electron transfer rate constant (k_s) of 3.42±0.08 s^?1. Based on the oxygen consumption during the oxidation process of glucose catalyzed by the immobilized GOD, the as‐prepared GOD/GR/Nafion/GCE electrode exhibits a linear range from 0.5 to 14 mmol·L^?1 with a detection limit of 0.03 mmol·L^?1. Moreover, it displays a good reproducibility and long‐term stability.     

Modeling the surface phenomena in carbon paste electrodes by low frequency impedance and double-layer capacitance measurements

Impedance and capacitance studies have been performed with covalently coupled Glucose oxidase (GOD) enzyme, covalently coupled flavin adenine dinucleotide (FAD), reconstituted GOD enzyme and blank carbon paste electrodes to study the changes in the electrochemical interfacial properties. Impedance studies were performed using a low frequency impedance technique and the electrochemical surface capacitance was measured by a pulse technique. We have attempted to fit the experimental values to an equivalent circuit model. The Randles' cell circuit with Warburg impedance modeled well the experimental values and the behavior of the enzyme electrodes. The individual components of the model were calculated and the parameters were explained. The blank paste electrode showed a constant phase element behavior.     

Direct Electrochemistry of Glucose Oxidase at a Gold Electrode Modified with Graphene Nanosheets

In this work, we report the direct electrochemistry of glucose oxidase (GOD) observed at a gold electrode modified with graphene nanosheets. Initially, graphene nanosheets were synthesized and conjugated to the enzyme GOD and immobilized on to a gold electrode surface. Cyclic voltammetry was then performed using Gold-Graphene-GOD modified electrodes in a pH 7.2 phosphate buffered saline (PBS). A pair of well-defined redox peaks was obtained for GOD with the reduction peak centered at +180 mV and a peak separation of 70 mV in PBS under physiological conditions. Moreover, the electron transfer rate of GOD redox reaction was greatly enhanced and the peak potential was found to be pH dependent at the graphene-GOD surface. Further, the performance of the Gold-Graphene-GOD was found to be stable and excellent under physiological conditions indicating the possibility of employing this platform for real time analysis. The observed results indicated that the 2D-graphene holds great promise for conjugation ability with a variety of enzymes. Further, our results also confirmed that graphene is capable of holding the enzyme GOD in a favorable position and retains its original structure and functionality that are essential for biosensing.     

Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube‐Modified Electrodes

The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)‐modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH 7.4 phosphate buffer solutions (PBS) with the formal potential of about ?455 mV (vs. Ag/AgCl) and shows a surface‐controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0 mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD.