Cholesterol oxidase biosensor based on a glassy carbon electrode modified with Nafion and methyl viologen

Cholesterol oxidase biosensor has been constructed by using bovine serum albumin and glutaraldehyde as cross linker to immobilize cholesterol oxidase and cholesterol esterase on a glassy carbon electrode modified with Nafion and methyl viologen. The biosensor has been used to determine total cholesterol in blood. The linear range of the determination is 2.5×10~7 to 1.0×10-4 mol/L. The detection limit is about 5.0×10~8 mol/L. The response time is 12 s. This biosensor has the advantage of high selectivity, sensitivity and short response time.     

A study of uricase biosensor based on a glassy carbon electrode modified with Nafion and methyl viologen

A uricase biosensor was constructed by using bovine serum albumin and glutaraldehyde as cross linker to immobilize uricase on a glassy carbon electrode modified with Nafion and methyl viologen (MV). A linear response of uric acid in serum was observed in a range of 1.0·10^–3 to 5.0·10^–6 mol/1 and the response time is 25 s. This biosensor has the advantage of high sensitivity, fast response as compared with previous sensors and low interferences.     

Electrochemical behavior of methyl viologen at graphite electrodes modified with Nafion sol–gel composite

Electrodes were prepared by spin-coating spectroscopic graphite rods with a Nafion doped sol. Coating solutions consisting of Nafion:TEOS (tetraethoxysilane) ratios of 3:1 and 4:1 gave smooth films on the electrode surface. These modified electrodes were evaluated and compared with Nafion modified and bare spectroscopic graphite electrodes using methyl viologen (MV²⁺) as a representative cationic electroactive probe. Substantial partitioning of MV²⁺ into the Nafion:sol–gel matrix to the electrode surface was observed by cyclic voltammetry and square wave voltammetry. Cyclic voltammograms of MV²⁺ in 0.1 M NaCl at Nafion:sol–gel 4:1 modified electrodes showed a reversible reduction to MV⁺ with E^0′=−0.695 V vs. Ag/AgCl. Results of scan rate variation showed the wave to be characterized by semi-infinite diffusion for scan rates in the range 50–500 mV/s. Slowing the scan rate below 50 mV/s resulted in a transition to thin-layer behavior. MV²⁺ partitioned much more quickly into the sol–gel-Nafion modified electrodes compared to pure Nafion modified electrodes. Reversibility of the MV²⁺-loaded modified Nafion-doped sol–gel coatings on electrodes was obtained by soaking in 1 M NaCl solution. Concentration calibration plots for MV²⁺ at the sol–gel-Nafion modified electrodes were nonlinear. Substantial enhancement of current signal at low concentrations was observed by square wave voltammetry.     

Electrocatalytic reduction of dioxygen at the surface of glassy carbon electrodes modified by calix[6]arene-methyl viologen

The preparation and electrochemical characterization of glassy carbon electrodes modified with calixarene-methyl viologen (MV) were investigated. The intermolecular complex of calix[6]arene and MV has an electrocatalytic effect on oxygen reduction. The cyclic voltammograms of the electroreduction of oxygen showed an enhanced current peak at approximately −0.60 V in air-saturated phosphate buffer. The experimental parameters were optimized and the mechanism of the catalytic process was discussed.     

Conductometric nitrate biosensor based on methyl viologen/Nafion/nitrate reductase interdigitated electrodes

A highly sensitive, fast and stable conductometric enzyme biosensor for determination of nitrate in water is reported for the first time. The biosensor electrodes were modified by methyl viologen mediator mixed with nitrate reductase (NR) from Aspergillus niger by cross-linking with glutaraldehyde in the presence of bovine serum albumin and Nafion^® cation-exchange polymer. The process parameters for the fabrication of the enzyme electrode and various experimental variables such as pH, the enzyme loading and time of immobilization in glutaralaldehyde vapor were investigated with regard to their influence on sensitivity, limit of detection, dynamic range and operational and storage stability. The biosensor can reach 95% of steady-state conductance value in about 15 s. Linear calibration in the range of 0.02 and 0.25 mM with detection limits of 0.005 mM nitrate was obtained with a signal-to-noise ratio of 3. When stored in 5 mM phosphate buffer (pH 7.5) at 4 °C, the sensor showed good stability over 2 weeks.     

Determination of dissolved oxygen by catalytic reduction on Nafion-methyl viologen chemically modified electrode

A small size Nafion-methyl viologen chemically modified electrode (Nafion-MV CME) together with a small size electrolytic cell were constructed for the purpose of dissolved oxygen (DO) determination. The catalytic reduction of DO on Nafion-MV CME results in fast and sensitive DO determination. The mechanism of such detection is also considered.     

Catalysis of dioxygen reduction at soluble polyaniline modified electrode

A reflux-treatment of soluble polyaniline (SPA) in dimethylformamide (DMF) containing CoCl₂ yields an active catalyst for dioxygen reduction which can be adsorbed on the electrode surface firmly. The catalytic reduction of dioxygen at the glassy carbon (GC) electrode modified by the catalyst was studied with cyclic voltammetry (CV), rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE). The kinetic process of dioxygen reduction at the modified electrode was analyzed with a new RRDE theory dealing with a nondiffusion-controlled process on ring electrode. The rate constants for each scheme of dioxygen reduction were calculated, showing that only 2-electron reduction to H₂O₂ was conducted at the modified electrode. The effect of solution acidity on the electrocatalytic behaviour for dioxygen reduction was investigated. A possibility of initiating catalytic activity for dioxygen reduction was explored with ESCA method.     

Photocatalytic reduction of methyl viologen and water in the presence of zinc porphyrins

Several insoluble zinc porphyrins with N-methylpyridyl and n-nonyl meso-substituents are suggested as photocatalysts for a photocatalytic system (photocatalyst-Pt/TiO₂-electron donor) of water reduction.

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(-Pt/TiO₂- ) - N- - -.

     

Electrocatalytic reduction of dioxygen on a glassy carbon electrode modified with adsorbed cobaloxime complex.

The preparation and electrochemical properties of a glassy carbon (GC) electrode modified with cobaloxime complex were investigated. The complex of the type [CoIII(DO)(DOH)pn)Cl2] where (DO)(DOH)pn = N2,N2'-propanediylbis-2,3-butanedione-2-imine-3-oxime) was adsorbed irreversibly and strongly on the surface of preanodized glassy carbon electrode. Electrochemical behavior and stability of modified GC electrode were investigated by cyclic voltammetry. The electrocatalytic reduction of dioxygen has been studied using this modified glassy carbon electrode by cyclic voltammetry, chronoamperometry and rotating disk electrode voltammetry as diagnostic techniques. The modified electrode showed excellent eletrocatalytic ability for the reduction of dioxygen to hydrogen peroxide in acetate buffer (pH 4.0) with overpotential 1.0 V lower than the plain glassy carbon electrode. The formal potential for this modified electrode is not shifted to more negative potentials by repeated reduction-oxidation cycles in oxygen-saturated supporting electrolyte solution. The apparent electron transfer rate constant (kS), the transfer coefficent (alpha) and the catalytic rate constant of O2 reduction at a GC modified electrode were determined by cyclic voltammetry and rotating disk electrode voltammetry and were found to be around 2.6 s(-1), 0.33 and 2.25 x 10(4) M(-1) s(-1). Based on the results, a catalytic mechanism is proposed and discussed.     

The kinetics of the reduction of methyl viologen and 9,10-anthraquinone-2-sulfonate by the benzopinacol anion

The reduction of methyl viologen (MV²⁺) and 9,10-anthraquinone-2-sulfonate (AQS) by the benzopinacol anion in 50% (v/v) propan-2-ol/water was investigated spectroscopically. The rate constants for these reactions were found to be 12.9 ± 0.2 and 0.23 ± 0.01 M^?1 s^?1, respectively. © John Wiley & Sons, Inc.     

Electrochemical reduction of dioxygen on Alizarin modified glassy carbon electrode in acidic medium

The catalytic behaviour of glassy carbon electrode modified by 1,2-dihydroxy antraquinone (Alizarin) was investigated. The electrocatalytic ability of modified electrode for the reduction of dioxygen was examined by cyclic voltammetry and rotating disk electrode (RDE) voltammetry techniques. The Alizarin modified glassy carbon electrode possesses excellent electrocatalytic abilities for dioxygen reduction over potential 400 mV lower than at the bare glassy carbon electrode. Hydrodynamic studies were performed to determine the heterogeneous rate constant for the reduction of O₂ at the surface of modified electrode. It was determined by Koutecky-Levich plot. The apparent diffusion coefficient of O₂ in O₂ saturated acidic solutions was estimated by using Levich equation. Studies show the involvement of four electrons in dioxygen reduction at the surface of this modified electrode.     

Exploring the impact of Nafion modifier on electrocatalytic CO2 reduction over Cu catalyst

Nafion as a universal polymer ionomer was widely applied for nanocatalysts electrode preparation.However, the effect of Nafion on electrocatalytic performance was often overlooked, especially for CO₂ electrolysis. Herein, the key roles of Nafion for CO₂RR were systematically studied on Cu nanoparticles(NPs) electrocatalyst. We found that Nafion modifier not only inhibit hydrogen evolution reaction(HER) by decreasing the accessibility of H₂O from electrolyte to Cu...     

Selective recognition of methyl viologen by an endo-functionalized naphthobox

Highly selective binding of structurally similar substrates is common for biomolecular recognition, but is often challenging to realize in synthetic hosts. Herein, we report highly selective binding of methyl viologen over other analogues by an endo-functionalized naphthobox. X-ray single crystal structure and Density Functional Theory (DFT) calculations revealed that the endo-functionalized groups in the cavity of the naphthobox is important for the high binding selectivity through the formation of multiple CH???N, CH???π, and π???π interactions with methyl viologen.     

Self-assembly of molybdophosphate on a glassy carbon electrode covalently modified with choline and electrocatalytic reduction of iodate.

Choline can be covalently grafted on glassy carbon electrodes using cyclic voltammetric method, forming a stable cationic monolayer-modified electrode (Ch/GCE). Keggin-type molybdophosphate anions, alpha-PMo(12)O(40)(3-), then were self-assembled on the Ch/GCE through electrostatic interactions for fabrication of an electrochemical sensor, which is denoted as alpha-PMo(12)/Ch/GCE. This two-layer modified electrode was carefully characterized by cyclic voltammetry and X-ray photoelectron spectroscopy. It was found that the sensor exhibits strong electrocatalytic activity and sensitivity toward the reduction of IO(3)(-). The content of IO(3)(-) in a table salt was determined with satisfactory results. The sensor is promising as an electrochemical sensor for the detection of IO(3)(-).     

Enhancement of bioelectrochemical dioxygen reduction with oxygen-enriching materials

Bioelectrochemical dioxygen reduction reaction (ORR) catalyzed by multi-copper oxidases (MCOs) is a process of paramount importance occurring at the cathode of enzymatic biofuel cells (EBFCs), which is an energy harvester that holds promise of self-sustained implantable and wearable medical devices. The MCO biocathode is, however, frequently the limiting factor of a working EBFC. Besides the operational stability issue, enzymatic biocathodes are largely constrained by the relatively low solubility of dioxygen in aqueous solution. As an emerging topic, we here review the introduction of dioxygen-enriching materials to the cathodic bioelectrode for overcoming the dioxygen supply limitation, leading to improved ORR performance.     

化学修饰电极的研究XVIII,四苯基钴卟啉化学修饰玻碳电极的热处理及其对氧的催化还原

本文研究四苯基钴卟啉化学修饰玻碳电极的热处理,经热处理的这种电极[(PCo/GC)h]具有对氧催化还原的异常高的稳定性和活性.在纯O2饱和的0.05mol.L^-^1H2SO4溶液中经循环伏安(CV)扫描3000次(100mV/s),其催化活性未见明显降低.研究了热处理温度(500-1000℃)对(PCo/GC)h电极电催化性能的影响.用紫外可见光谱对热处理产物的结构进行了分析.用CV法及旋转圆盘电极研究了O2在(PCo/GC)h电极上电催化反应动力学,测定了速率常数.在该电极上O2的还原反应为二电子还原成H2O2的不可逆过程.     

Direct electrocatalytic reduction of p-nitrophenol at room temperature ionic liquid modified electrode

Direct electrochemical reduction ofp-nitrophenol （PNP） was investigated on a room temperature ionic liquid N-butylpyridinium hexafluorophosphate （BPPF6） modified carbon paste electrode （CILE）. The cathodic peak potential was positively shifted and the peak currents were increased compared to that obtained on traditional carbon paste electrode （CPE）. The results indicated that the presence of ionic liquid BPPF6 on the electrode surface showed excellent catalytic ability to the electrochemical reduction of PNP. The electrochemical behaviors of PNP on the CILE were investigated by cyclic voltammetry and the conditions such as the scan rate, the buffer pH, the substrate concentration were optimized. The electrochemical parameters were further calculated with the results of the electron transfer number （n）, the charge-transfer coefficient （α） and the surface concentration （Гr） as 1.76, 0.37 and 2.47 × 10^-9 mol/cm^2, respectively, for the selected reductive peak. The results indicated that PNP showed an irreversible adsorption-controlled electrode process on the CILE.