Interfacing cytochrome c to electrodes with a DNA – carbon nanotube composite film

Multi-walled carbon nanotube (MWCNT) is successfully immobilized on the surface of platinum electrode by mixing with DNA. The DNA/MWCNT modified electrodes are characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Further research indicates that cytochrome c can strongly adsorbed on the surface of the modified electrode, and forms an approximate monolayer. The immobilized MWCNT can promote the redox of horse heart cytochrome c which gives reversible redox peaks with a formal potential of 81 mV vs SCE.     

Electrochemical impedance analysis of methanol oxidation on carbon nanotube-supported Pt and Pt-Ru nanoparticles

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are employed to investigate methanol oxidation reactions on single-walled carbon nanotube-supported platinum (Pt) and platinum–ruthenium (Pt-Ru) nanoparticles. EIS and CV measurements show consistent results: Pt catalyst supported on single-walled carbon nanotubes possesses higher catalytic activity for methanol oxidation than that on carbon black. Additionally, semicircles in the second quadrant of the Nyquist diagrams are observed for methanol oxidation on all types of catalytic nanoparticles when applying an electrical potential of 600 mV, which indicates the occurrence of negative resistance during electrocatalytic methanol oxidations. However, all impedance spectra show positive resistance at other electrode potentials (e.g., 300, 400, and 800 mV). Electrocatalytic characteristics of all catalysts are further analyzed by equivalent circuit simulations. We propose that intermediate coverage on the catalyst surface and subsequently the oscillation of nonlinear electrochemical methanol oxidations lead to the occurrence of negative resistance at 600 mV.     

A novel nano-sized bionic function interface for enhancing the ability of red blood cells to carry oxygen

A nano-sized bionic function interface was prepared by immobilizing red blood cells onto a silver electrode, which was modified with cysteamine and colloidal gold. Scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize its surface. Cyclic voltammograms in phosphate buffer solution of pH?7.0 exhibited a pair of redox peaks for oxygen at -378 and -207 mV, respectively. The reduction peak currents at -378 mV were linearly proportional to the oxygen concentration in the range from 12.6 µM to 1.39 mM. Cyclic voltammetry also indicated that the functional surface enhanced the ability of red blood cells to transport oxygen.     

Direct Electrochemical Determination of Glyphosate at Copper Phthalocyanine/Multiwalled Carbon Nanotube Film Electrodes

A copper phthalocyanine/multiwalled carbon nanotube film‐modified glassy carbon electrode has been used for the determination of the herbicide glyphosate (Gly) at ?50 mV vs. SCE by electrochemical oxidation using differential pulse voltammetry (DPV). Cyclic voltammetry and electrochemical impedance spectroscopy showed that Gly is adsorbed on the metallic centre of the copper phthalocyanine molecule, with formation of Gly‐copper ion complexes. An analytical method was developed using DPV in pH 7.4 phosphate buffer solution, without any pretreatment steps: Gly was determined in the concentration range of 0.83–9.90 μmol L^?1, with detection limit 12.2 nmol L^?1 (2.02 μg L^?1).     

Sum frequency generation spectroscopy and double-layer capacitance studies of the 1-butyl-3-methylimidazolium dicyanamide-platinum interface

The orientation of the cation and the anion of 1-butyl-3-methylimidazolium dicyanamide at the platinum-liquid interface, using sum frequency generation (SFG) spectroscopy is reported. Sum frequency spectra at two different polarizations and different potentials are recorded, and analysis of polarization-dependent spectra is performed to estimate the orientation of the dicyanamide anion and the alkyl and ring moieties in the cation as a function of the potential applied to the platinum electrode. In addition, cyclic voltammetry and electrochemical impedance spectroscopy are conducted. A model of the double-layer structure at the electrified interface is presented from the analysis of capacitance and SFG data.     

Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at thick-film gold electrodes

Cyclic voltammetric and electrochemical impedance spectroscopic investigations of screen-printed, thick-film gold electrodes reveal significant differences when compared with conventional polished gold disk electrodes of comparable size. The rough and porous structure of the thick-film electrode surface leads to an actual electrode area which is increased six-fold compared to polished disk electrodes. Due to the catalytic properties of these surface structures it is possible to perform the electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) at relatively low overpotentials, i.e. +0.145 V vs. SCE. By operating electrodes at this potential, electrode fouling processes and interference from electroactive species, e.g. acetaminophen, are minimized. An amperometric glucose sensor based on polymer matrix-entrapped glucose dehydrogenase with a working potential of +0.145 V vs. SCE was successfully incorporated into a flow injection analysis (FIA) system.     

The redox chemistry of the covalently immobilized native and low-pH forms of yeast iso-1-cytochrome c

Cyclic voltammetry experiments were carried out on native Saccharomyces cerevisiae iso-1-cytochrome c and its C102T/N62C variant immobilized on bare polycrystalline gold electrode through the S-Au bond formed by a surface cysteine. Experiments were carried out at different temperatures (5-65 degrees C) and pH values (1.5-7). The E degrees ' value at pH 7 (+370 mV vs SHE) is approximately 100 mV higher than that for the protein in solution. This difference is enthalpic in origin and is proposed to be the result of the electrostatic repulsion among the densely packed molecules onto the electrode surface. Two additional electrochemical waves are observed upon lowering the pH below 5 (E degrees ' = +182 mV) and 3 (E degrees ' = +71 mV), which are attributed to two conformers (referred to as "intermediate" and "acidic", respectively) featuring an altered heme axial ligation. This is the first determination of the reduction potential for low-pH conformers of cytochrome c in the absence of denaturants. Since the native form of cytochrome c can be restored, bringing back the pH to neutrality, the possibility offered by this transition to reversibly modulate the redox potential of cytochrome c is appealing for bioelectronic applications. The immobilized C102T/N62C variant, which differs from the native protein in the orientation of the heme group with respect to the electrode, shows very similar reduction thermodynamics. For both species, the rate constant for electron transfer between the heme and the electrode increases for the acidic conformer, which is also found to act as a biocatalytic interface for dioxygen reduction.     

铂电极上吡啶吸附及其取向的现场红外反射吸收光谱研究

用电化学和现场红外反射吸收光谱方法研究了Pt电极上吡啶的吸附取向。结果表明,在-0.80～0.80 V(vs SCE)范围内皆存在吡啶吸附,在较负电势下(约-0.80～-0.20 V),吡啶环可能以2种方式吸附于电极表面上,随电势变正(约-0.20～0.80V)由垂直取向向平躺取向转变,该平躺吸附降低了电极表面及其附近水分子结构的有序性。     

铂电极上苯和苯磺酸吸附定向的现场红外反射吸收光谱电化学方法研究

本文用现场红外反射吸收光谱电化学方法和循环伏安法研究铂电析上苯和苯磺酸的吸附定向。对于苯/铂势系, 电势在-0.6至0.0V(相对饱和甘汞电极)内, 苯主要以垂直方式吸附; 在0.0至0.8V内则主要以平躺方式吸附。对于苯磺酸/铂体系,电势在-0.4V至0.0V内, 苯磺酸分子中的苯环主要呈垂直吸附且SO~3H基团远离电极表面; 在0.0至1.0V内则主要以倾斜平躺方式吸附, SO~3H基团通过其中的两个氧原子吸附于电极表面上。     

Potential oscillations during the electrochemical treatment of white liquor

Potential oscillations during the electrochemical treatment of white liquor are reported on. White liquor in the kraft process is composed mainly of sodium sulfide, sodium hydroxide, and sodium carbonate. Cyclic voltammetry, linear galvanic voltammetry, and galvanostatic techniques are used to characterize the behavior of the potential oscillations. The amplitude of the harmonic potential oscillations is between −150 and 750 mV (SCE). The behavior of the potential oscillations strongly depends on the applied current density, temperature, and mass transfer. Electrochemical impedance spectroscopy is employed to study the origin of the oscillations during the electrochemical treatment of the white liquor on the Ti/Ta₂O₅-IrO₂ electrodes. Negative faradaic impedance is observed in the potential range of the potential oscillation amplitudes, and equivalent circuits are designed to fit the experimental impedance spectra. The potential oscillations are caused by the synergic effect of sulfur formation/removal and oxygen evolution in the high-potential range. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 617–626. The text was submitted by the authors in English.     

Ultrasensitive potentiometric immunosensor based on SA and OCA techniques for immobilization of HBsAb with colloidal Au and polyvinyl butyral as matrixes

A novel potentiometric immunosensor for detection of hepatitis B surface antigen (HBsAg) has been developed by means of self-assembly (SA) and opposite-charged adsorption (OCA) techniques to immobilize hepatitis B surface antibody (HBsAb) on a platinum electrode. A cleaned platinum electrode was first pretreated in the presence of 10% HNO3 and 2.5% K2CrO4 solution and held at -1.5 V (vs SCE) for 1 min to make it negatively charged and then immersed in a mixing solution containing hepatitis B surface antibody, colloidal gold (Au), and polyvinyl butyral (PVB). Finally, HBsAb was successfully immobilized onto the surface of the negatively charged platinum electrode modified nanosized gold and PVB sol-gel matrixes. The modified procedure was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The immobilized hepatitis B surface antibody exhibited direct electrochemical behavior toward hepatitis B surface antigen (HBsAg). The performance and factors influencing the performance of the resulting immunosensor were studied in detail. More than 95.7% of the results of the human serum samples obtained by this method were in agreement with those obtained by enzyme-linked immunosorbent assays (ELISAs). The resulting immunosensor exhibited fast potentiometric response (<3 min) to HBsAg. The detection limit of the immunosensor was 2.3 ng.mL(-1), and the linear range was from 8 to 1280 ng.mL(-1). Moreover, the studied immunosensor exhibited high sensitivity, good reproducibility, and long-term stability (>6 months).     

Electrochemistry and electrocatalytic properties of mixed assemblies of horseradish peroxidase, poly(diallyl dimethylammonium chloride) and gold nanoparticles on a glassy carbon electrode

Poly(diallyldimethylammonium chloride), gold nanoparticles (Au-NPs; 2–5 nm) and horseradish peroxidase (HRP) were alternately self-assembled on a glassy carbon electrode. Due to the conducting wire effect of the Au-NPs, the HRP undergoes direct electrochemistry with a small peak-to-peak separation of 33 mV and a formal potential of ?0.370 V (versus SCE). The reaction involves a single electron transfer coupled to a one-proton transfer reaction. Electrochemical impedance spectroscopy and cyclic voltammetry also were applied to characterize the self-assembly process and to study the electrochemical behavior of the immobilized HRP. Its good electrocatalytic response to the reduction of hydrogen peroxide resulted in a novel third-generation biosensor for this species.     

A Graphite‐Polyurethane Composite Electrode for the Analysis of Furosemide

A graphite‐polyurethane composite electrode has been used for the determination of furosemide, a antihypertensive drug, in pharmaceutical samples by anodic oxidation. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrooxidation process at +1.0 V vs. SCE over a wide pH range, with the result that no adsorption of analyte or products occurs, unlike at other carbon‐based electrode materials. Quantification was carried out using cyclic voltammetry, differential pulse voltammetry, and square‐wave voltammetry. Linear ranges were determined (up to 21 μmol L^?1 with cyclic voltammetry) as well as limits of detection (0.15 μmol L^?1 by differential pulse voltammetry). Four different types of commercial samples were successfully analyzed. Recovery tests were performed which agreed with those obtained by spectrophotometric evaluation. The advantages of this electrode material for repetitive analyzes, due to the fact that no electrode surface renewal is needed owing to the lack of adsorption, are highlighted.     

Surface metal modifiers for methanol electrooxidation on platinum; silver and mercury

The catalytic activity of platinum surfaces towards methanol electrooxidation can be modified by the deposition of a second metal using different methodologies. There is little information about the catalytic performance of polycrystalline platinum modified by silver and mercury adatoms using spontaneous and electrochemical deposition methods. Cyclic voltammetrics have been performed to compare the current vs potential profiles of modified platinum surfaces in acid solution at room temperature. The inhibition of the hydrogen adatom voltammetric profile by foreign metal adatoms on platinum was used to calculate the degree of surface coverage by the metal. Poisoning effects were checked by anodic stripping experiments of methanol residues on the modified platinum surfaces at adsorption potentials in the hydrogen electrosorption region using a micro flux cell. Methanol solution oxidation was also evaluated at slow scan rates of up to 0.8 vs reversible hydrogen electrode (RHE) on the platinum-modified surfaces. The comparison between the amounts of carbon-monoxide-type residues and the solution oxidation of methanol was analysed to check for their utility as catalytic surfaces for direct methanol fuel cells. Dedicated to Professor Dr. Algirdas Vaskelis on the occasion of his 70th birthday.     

钛基纳米多孔金电极对甲醛氧化的电催化活性

采用水热法制备了钛基纳米金微粒修饰电极(Au/Ti)。扫描电镜图表明纳米金颗粒粒径大约为300 nm,在钛基体表面构成三维多孔网状结构。运用循环伏安,电位阶跃和交流阻抗等电化学技术研究了碱性介质中甲醛在Au/Ti电极上的电氧化行为。循环伏安图显示,甲醛在Au/Ti上的起始氧化电位在-0.90 V左右,相对于多晶金电极提前大约0.2 V,交流阻抗测试表明,甲醛在Au/Ti电极上电氧化表现出低的电荷传递电阻。研究结果表明钛基纳米金微粒修饰电极对甲醛氧化具有良好的电催化活性。     

Direct electrodeposition of gold nanoparticles onto indium tin oxide film coated glass: Application to the detection of arsenic(III).

Gold nanoparticle modified indium tin oxide (ITO) film coated glass electrodes were prepared for the first time through direct electrochemical deposition from 0.5 M H2SO4 containing 0.1 mM HAuCl4. The resulting electrode surfaces were characterized with AFM. Cyclic voltammetry and linear sweep voltammetry (LSV) of arsenic(III) on the modified electrodes were performed. After optimization, a LOD of 5 +/- 0.2 ppb was obtained with 60 s deposition at -0.6 V (vs. SCE) in 1 M HNO3 using LSV.     

IrO2电极在4-氯苯酚水溶液中的电化学活性

研究了在4-氯苯酚(简称氯酚)电化学稳定窗口内氯酚对Ti基IrO2电极在酸性水溶液中电化学活性的影响. 循环伏安(CV)与电化学阻抗谱(EIS)测试均显示, 几乎在整个氯酚的电化学稳定电位区间内, 氯酚对氧化物电极均起到活化作用. 以金属Ir电极为对比试样的测试结果却显示, 由于氯酚易于在金属表面吸附, 氯酚在其电化学稳定窗口内对金属电极的活性产生抑制作用. 基于氯酚对上述两类电极电化学行为影响的差异, 提出活性氧化物自身在上述电位区间内发生从低价态到高价态的转变, 进而用于氧化去除吸附在电极表面的有机分子, 可能是氯酚对IrO2电极造成活化的主要原因.     

中性介质中L-丝氨酸在Pt电极上解离吸附和氧化的原位FTIR研究

运用电化学循环伏安(CV)和原位红外反射光谱(in situ FTIRS)研究了中性介质中L-丝氨酸在Pt电极上的解离吸附和氧化过程. 结果表明, 在中性溶液中, 以两性离子形式存在的丝氨酸可以在很低的电位下(-0.6 V, vs. SCE)在Pt电极表面发生解离吸附, 生成强吸物种一氧化碳(COL)、(COB)和氰负离子(CN-). 研究结果还表明, 当电位低于0.7 V(vs. SCE)时, CN-能稳定存在于电极表面, 抑制丝氨酸的进一步反应. 在更高电位时则主要为丝氨酸分子的氧化过程.     

Development and characterization of a new conducting carbon composite electrode

A new conducting composite flexible material prepared from cellulose acetate (CA) polymer and graphite has been developed and used for the fabrication of electrodes, which were then characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) was used to provide information concerning the morphology of the composite electrode surface. The potential window, background currents and capacitance were evaluated by cyclic voltammetry in the pH range from 4.6 to 8.2. The voltammetry of model electroactive species demonstrates a close to reversible electrochemical behaviour, under linear diffusion control. The electroactive area of the composite electrodes increases after appropriate electrode polishing and electrochemical pre-treatment. The electrodes were used as substrate for the electropolymerisation of the phenazine dye neutral red, for future use as redox mediator in electrochemical biosensors. The composite electrodes were also successfully used for the amperometric detection of ascorbate at 0.0 V vs. SCE, and applied to the measurement of ascorbate in Vitamin C tablets; the sensor exhibits high sensitivity and a low detection limit of 7.7 μM. Perspectives for use as a versatile, mechanically flexible and robust composite electrode of easily adaptable dimensions are indicated.     

绿脓杆菌Pseudomonas aeruginosa BTE-1直接电催化特征

本文研究厌氧条件下产电绿脓杆菌P. aeruginosa BTE-1的电化学催化特征。研究结果表明,P. aeruginosa BTE-1菌株在厌氧条件下,不能分泌可充当电子介体的绿脓菌素,但可通过在电极表面形成生物膜呈现了直接电催化性能。P. aeruginosa BTE-1在电极表面形成生物膜与其在特定电极电位下向电极传递电子的过程直接相关,适宜的电位为+0.2 V (vs. SCE),电位过高可能会损害P. aeruginosa BTE-1细胞。室温范围内升高温度可增强P. aeruginosa BTE-1生物膜电催化活性,但过高的温度(>60℃)会抑制生物膜电催化活性。循环伏安曲线显示,在厌氧条件下形成的P. aeruginosa BTE-1生物膜,具有与典型产电菌株G. sulfurreducens相近的氧化还原电位(-0.4 V~ -0.2 V vs. SCE)。P. aeruginosa BTE-1生物膜可电催化酵母抽取物和葡萄糖,但不能电催化醋酸盐。