胆碱与谷氨酸共价单层混合修饰玻碳电极的制作与表征及其测定亚硝酸根的分析应用

A choline and L-glutamic acid mixed monolayer covalently modified glassy carbon electrode (Ch-Glu/GCE) was fabricated and characterized by X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). It provided an excellent example of mixed covalent monolayer modification of carbon electrodes with alkanol and amino acid, and also a facile means for altering the interfacial architecture. The Ch-Glu/GCE displayed good catalytic activity toward the oxidation of nitrite anions. Differential pulse voltammetry was used for determination of nitrite at the Ch-Glu/GCE. The Ch-Glu/GCE showed higher capability for restraint of pollutions than a simple Ch modified electrode or a simple Glu modified electrode.     

Analytical applications of glassy carbon electrodes modified with multi-wall carbon nanotubes dispersed in polyethylenimine as detectors in flow systems

This work reports the advantages of using glassy carbon electrodes (GCEs) modified with multi-wall carbon nanotubes (CNT) dispersed in polyethylenimine (PEI) as detectors in flow injection and capillary electrophoresis. The presence of the dispersion of CNT in PEI at the electrode surface allows the highly sensitive and reproducible determination of hydrogen peroxide, different neurotransmitters (dopamine (D) and its metabolite dopac, epinephrine (E), norepinephrine (NE)), phenolic compounds (phenol (P), 3-chlorophenol (3-CP) and 2,3-dichlorophenol (2,3CP)) and herbicides (amitrol). Sensitivities enhancements of 150 and 140 folds compared to GCE were observed for hydrogen peroxide and amitrol, respectively. One of the most remarkable properties of the resulting electrode is the antifouling effect of the CNT/PEI layer. No passivation was observed either for successive additions (30) or continuous flow (for 30 min) of the compounds under investigation, even dopac or phenol. A critical comparison of the amperometric and voltammetric signal of these different analytes at bare- and PEI-modified glassy carbon electrodes and pyrolytic graphite electrodes is also included, demonstrating that the superior performance of CNT is mainly due to their unique electrochemical properties. Glassy carbon electrodes modified with CNT-PEI dispersion also show an excellent performance as amperometric detector in the electrophoretic separation of phenolic compounds and neurotransmitters making possible highly sensitive and reproducible determinations.     

Designing stable redox-active surfaces: chemical attachment of an osmium complex to glassy carbon electrodes prefunctionalized by electrochemical reduction of an in situ-generated aryldiazonium cation

The production of stable redox-active layers on electrode surfaces can lead to improvements in electronic device design. Enhanced stability can be achieved by pretreatment of electrode surfaces to provide surface chemical functional groups for covalent tethering of redox complexes. Herein, we describe pretreatment of glassy carbon electrodes to provide surface carboxylic acid groups by electro-reduction of an in situ-generated aryl diazonium salt from 3-(4-aminophenyl)propionic acid. This surface layer is characterized by attenuated total reflection infrared spectroscopy, atomic force microscopy, and electrochemical blocking studies. The surface carboxylic acid generated is then used to tether an osmium complex, [Os(2,2'-bipyridyl)2(4-aminomethylpyridine)Cl]PF6, to provide a covalently bound redox-active monolayer, E(0) ' of 0.29 V (vs Ag/AgCl in phosphate buffer, pH 7.4), on the pretreated glassy carbon electrode. The layer proves stable to pH, temperature, and storage conditions, retaining electroactivity for at least 6 months.     

Boron doped diamond and glassy carbon electrodes comparative study of the oxidation behaviour of cysteine and methionine

The electrochemical oxidation behaviour at boron doped diamond and glassy carbon electrodes of the sulphur-containing amino acids cysteine and methionine, using cyclic and differential pulse voltammetry over a wide pH range, was compared. The oxidation reactions of these amino acids are irreversible, diffusion-controlled pH dependent processes, and occur in a complex cascade mechanism. The amino acid cysteine undergoes similar three consecutive oxidation reactions at both electrodes. The first step involves the oxidation of the sulfhydryl group with radical formation, that undergoes nucleophilic attack by water to give an intermediate species that is oxidized in the second step to cysteic acid. The oxidation of the sulfhydryl group leads to a disulfide bridge between two similar cysteine moieties forming cysteine. The subsequent oxidation of cystine occurs at a higher potential, due to the strong disulfide bridge covalent bond. The electro-oxidation of methionine at a glassy carbon electrode occurs in two steps, corresponding to the formation of sulfoxide and sulfone, involving the adsorption and protonation/deprotonation of the thiol group, followed by electrochemical oxidation. Methionine undergoes a one-step oxidation reaction at boron doped diamond electrodes due to the negligible adsorption, and the oxidation also leads to the formation of methionine sulfone.     

Au/GCE电极对水中15种苯酚衍生物的测定

研究了15种不同取代基苯酚衍生物在纳米金/玻碳 (Au/GCE) 电极上的电化学响应. 测试表明：该电极对15种苯酚衍生物的电化学反应各呈现出不同程度的电催化作用;与GCE和平面金电极相比,苯酚衍生物的氧化峰电流均有所增加,氧化电位受待测物反应活性影响较大;水杨酸在Au/GCE电极上响应迅速,电流灵敏度是GCE电极的1.8倍;该电极可用于多种苯酚衍生物的痕量测定.     

在抗坏血酸存在下用L-赖氨酸修饰玻碳电极测定多巴胺

采用电化学氧化法制备了L-广赖氮酸单分子层修饰玻碳电极,研究了多巴胺（DA）和抗坏血酸（AA）在该电极上的电化学行为。结果表明,L-广赖氨酸单分子层修饰玻碳电极不仅能改善多巴胺和抗坏血酸的电化学行为,而且能将多巴胺和抗坏血酸二者在裸电极上的完全重叠的单氧化峰分开成为两个完全独立的氧化峰,循环伏安（CV）图上峰间距为507mV,差分脉冲伏安（DPV）图上峰间距为460mV,由此可实现在AA的共存下对样品中的DA进行选择性测定。     

Surface preparation of glassy carbon electrodes

Recent work on glassy carbon electrodes for various applications is reviewed. Activation of glassy carbon electrodes by different types of polishing, heat treatment, and electrochemical methods yields enhanced rates of electron transfer. Characterization of different glassy carbon surfaces by x-ray photoelectron spectroscopy shows that polished and electrochemically pretreated surfaces contain more oxygen on the surface than do unactivated surfaces; much of this oxygen is associated with phenolic groups. Causes of activation, characterization of glassy carbon by spectroscopic methods, and the role of surface cleanliness are summarized. For simple electron-transfer reactions, removal of contaminants from the electrode surface is important. For proton-coupled electrode reactions, specific interactions of reactants with catalytic groups created on the surface during polishing tend to play an important role in electrode activation     

In situ electrodeposition of Pt nanoclusters on glassy carbon surface modified by monolayer choline film and their electrochemical applications

Pt nanoclusters attached to the monolayer choline (Ch) modified glassy carbon surface were successfully synthesized by use of in situ cyclic voltammetry (CV) method. Field emission scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS) were used to characterize the properties of this modified electrode. It was demonstrated that Ch was immobilized onto the carbon surface forming a covalently planted Ch monolayer, which could induce the formation of Pt nanoclusters. The preliminary study found that the homogeneous nanostructured Pt/Ch film exhibited remarkable electrocatalytic activity towards the oxidation of methanol and nitrite.     

Direct RP‐HPLC determination of underivatized amino acids with online dual UV absorbance,fluorescence, and multiple electrochemical detection

The combined use of a dual‐UV detector, a fluorimetric one and of a multiple electrochemical (EC) detector equipped with a dual electrode, consisting of a conventional size 3 mm diameter glassy carbon electrode (GCE) and of a pair of 30 μm thick carbon microfibers, is proposed for the determination of 15 amino acids, two dipeptides and creatinine. This online coupling of the above detection modes could partially replace amino acid analysis by derivatization methods, since it solves problems concerning the direct detection of selected underivatized amino acids. Additionally, it was proved that the use of multiple‐detection allows positive peak identification in a single chromatographic run, yields more information for free amino acids and solves in some cases the problem of chromatographic resolution. In order to optimize the detection conditions of the underivatized amino acids and related compounds by different detectors, their detection characteristics were determined by adequate preliminary experiments. The electro‐oxidation characteristics of the underivatized compounds of interest were determined by hydrodynamic voltammetry using a flow cell with a macrodisc GCE and by ex‐situ voltammetry using both a GCE of conventional size and a carbon fiber disk microelectrode. Important practical advantages of microfiber and microdisk electrodes with respect to macroelectrodes were demonstrated.     

Fabrication of layer-by-layer modified multilayer films containing choline and gold nanoparticles and its sensing application for electrochemical determination of dopamine and uric acid

A novel electrochemical sensor has been constructed by use of a glassy carbon electrode (GCE) coated with a gold nanoparticle/choline (GNP/Ch). Electrochemical impedance spectroscopy (EIS), field emission scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of this modified electrode. It was demonstrated that choline was covalently bounded on the surface of glassy carbon electrode, and deposited gold nanoparticles with average size of about 100 nm uniformly distributed on the surface of Ch. Moreover, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with obviously reduction of overpotentials. For the ternary mixture containing DA, AA and UA, these three compounds can be well separated from each other, allowing simultaneously determination of DA and UA under coexistence of AA. The proposed method can be applied to detect DA and UA in real samples with satisfactory results.     

Dense monolayers of metal-chelating ligands covalently attached to carbon electrodes electrochemically and their useful application in affinity binding of histidine-tagged proteins

In this work, monolayers of metal complexes were covalently attached to the surface of carbon electrodes with the goal of binding monolayers of histidine-tagged proteins with a controlled molecular orientation and a maintained biological activity. In this novel method, which is simple, versatile, and efficient, the covalent attachment was accomplished in a single step by the electrochemical reduction of aryl diazonium ions that were substituted with a nitrilotriacetic (NTA) or an imminodiacetic (IDA) ligand at the para position. The transient aryl radicals that were generated in the reduction were grafted to the surfaces of glassy carbon, highly oriented pyrolitic graphite, and graphite-based screen-printed electrodes, producing dense monolayers of the ligands. The NTA- and IDA-modified electrodes were shown to efficiently chelate Cu(II) and Ni(II) ions. The presence of the metal was established using X-ray photoelectron spectroscopy and electrochemistry. Surface coverages of the ligands were indirectly determined from the electroactivity of the copper(II) complex formed on the electrode surface. Studies on the effect of electrodeposition time and potential showed that, at sufficiently negative potentials, the surface coverage reached a saturating value in less than 2 min of electrodeposition time, which corresponds to the formation of a close-packed monolayer of ligand on the electrode surface. Once loaded with a metal ion, the modified electrode was able to bind specifically to histidine-tagged proteins such as the horseradish peroxidase (His-HRP) or to an enhanced, recombinant green-fluorescent protein via its N-terminal hexahistidine tail. In the case of His-HRP, the amount of active enzyme specifically immobilized by metal-chelating binding was determined from the analysis of electrocatalytic currents using cyclic voltammetry. The electrochemical grafting makes it possible to accurately controlled and electronically address the amount of deposited ligand on the conductive surfaces of carbon electrodes with any size and shape.     

Improvement of alternariol monomethyl ether detection at gold electrodes modified with a dodecanethiol self-assembled monolayer

The electro-oxidation of alternariol monomethyl ether (AME), one of the main metabolites of the Alternaria genus mycotoxins, is studied at 1-dodecanethiol (DDT)-modified gold electrodes, in acetonitrile (ACN) – aqueous phosphate buffer solutions of different pH values, by using cyclic (CV) and square-wave (SWV) voltammetries. The AME voltammetric response at the bare electrode suffers from two drawbacks: it appears at potentials close to the onset of gold oxide formation, and it is hampered by a fouling of the electrode surface due to the accumulation of oxidized products. These shortcomings are circumvented by the use of DDT-coated electrodes, since the intervening monolayer inhibits gold oxide formation and surface passivation by the electrochemical products, without affecting the oxidation kinetics of AME significantly. Diagnostic criteria based on the voltammetric peak parameters show that the electrochemical behavior of AME at the modified electrode is mainly controlled by reactant diffusion from solution, with a weak adsorption of both the mycotoxin and its oxidation products at monolayer defects. Calibration curves were constructed from the AME square-wave voltammetric response and a detection limit of 9.1 × 10⁻⁸ mol dm⁻³ was determined, which is about three times smaller than a previous estimate at platinum and glassy carbon electrodes, and about fifty times smaller than the limit derived from measurements carried out at a polyphenol oxidase-modified carbon paste electrode.     

Photochromism and electrochemistry of a dithienylcyclopentene electroactive polymer

A bifunctional substituted dithienylcyclopentene photochromic switch bearing electropolymerisable methoxystyryl units, which enable immobilization of the photochromic unit on conducting substrates, is reported. The spectroscopic, electrochemical, and photochemical properties of a monomer in solution are compared with those of the polymer formed through oxidative electropolymerization. The electroactive polymer films prepared on gold, platinum, glassy carbon, and indium titanium oxide (ITO) electrodes were characterized by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The thickness of the films formed is found to be limited to several monolayer equivalents. The photochromic properties and stability of the polymer films have been investigated by UV/vis spectroscopy, electrochemistry, and XPS. Although the films are electrochemically and photochemically stable, their mechanical stability with respect to adhesion to the electrode was found to be sensitive to both the solvent and the electrode material employed, with more apolar solvents, glassy carbon, and ITO electrodes providing good adhesion of the polymer film. The polymer film is formed consistently as a thin film and can be switched both optically and electrochemically between the open and closed state of the photochromic dithienylethene moiety.     

Electrochemical detection of amino acids at carbon nanotube and nickel-carbon nanotube modified electrodes

The oxidation and enhanced detection of traditionally 'non-electroactive' amino acids at a single-wall carbon nanotube (SWNT) surface and at a nickel hydroxide film electrochemically deposited and generated upon the SWNT layer is reported. Different CNT are compared, with Nafion-dispersed SWNT offering the most favorable layer for constant-potential amperometric detection. Factors affecting the oxidation process, including the pH or applied potential, are assessed. The response of the SWNT-Nafion coated electrode compares favorably with that of copper and nickel disk electrodes under flow injection analysis (FIA) conditions. The electrodeposition of nickel onto the SWNT-Nafion layer (Ni-CNT) led to a dramatic enhancement of the analytical response (vs. that observed at the SWNT or nickel electrodes alone). The oxidative process at the Ni(OH)(2) layer has been studied and the increase in sensitivity rationalized. In the presence of amino acid the Ni-CNT layer undergoes an electrocatalytic process in which the amino acid reduces the newly formed NiO(OH) species. Furthermore, the attractive response of both the CNT and Ni-CNT layers has allowed these electrodes to be used for constant-potential FIA of various amino acids and indicates great promise for monitoring chromatographic effluents. Once again an improved signal was observed at the Ni-CNT electrode compared to nickel deposited upon a bare glassy carbon electrode (Ni-GC).     

Voltammetric oxidation of acetophenone derivatives and benzophenone in acetonitrile on a platinum and glassy carbon electrode

The voltammetric oxidation of five para-substituted acetophenone derivatives (containing nitro, chloro, bromo, methyl and hydroxyl groups as substituents) and that of benzophenone was studied on a platinum and glassy carbon electrode in acetonitrile media. Electrode passivation was observed in the case when all selected compounds are on a glassy carbon electrode; an oxidation peak appeared between 2.5 and 3 V. The voltammograms of 4′-hydroxyacetophenone showed an additional peak around 2 V, which may be associated with the oxidation of the phenol moiety. In the case of a platinum electrode, no relevant peaks appeared on the voltammograms, reflecting the absence of passivation. The use of a redox probe 1,4-dihydroxybenzene showed that the glassy carbon electrode, after cyclization in the solutions of the outlined compounds, has higher sensitivity towards the oxidation product (1,4-benzoquinone) of this compound.     

Electrochemical characteristics of conductive carbon cement as matrix for chemically modified electrodes

Conductive carbon cement (CCC) was evaluated as matrix material for the preparation of electrodes bulk-modified with electrocatalysts. For pure CCC electrodes the background current characteristics were examined. In acidic or neutral phosphate buffers the useful electrode potential range was from −0.3 to + 1.0 V vs. SCE, while in 0.1 mol 1⁻¹ NaOH it was from −0.3 to + 0.7 V. The electrochemical reversibility of CCC electrodes was examined by measuring the standard rate constants for the reduction of hexacyanoferrate (III) and the oxidation of hydroquinone, using cyclic voltammetry (CV) and rotating disk experiments. The reversibility of a CCC electrode was comparable with that of a freshly polished glassy carbon electrode and better than that of carbon paste electrodes. CCC was used as matrix for the preparation of electrodes bulk-modified with cuprous oxide and cobalt phthalocyanine (CoPC). With a Cu₂O-CCC electrode the oxidation potential of glucose, which shows sluggish kinetics at unmodified carbon electrodes, was strongly reduced. The kinetics of the mediated glucose oxidation has been studied with a rotating disk electrode. It was shown that at glucose concentrations higher than approximately 1 mmol l⁻¹ the electrochemical regeneration of the catalyst becomes rate-determining. The Cu₂O-CCC modified electrode has been applied with a constant potential in flow-injection analysis for the determination of glucose. The long-term stability of the electrode was studied; repeated injections of a glucose solution during a period of 6 h yielded a relative standard deviation of the peak height of 1.8% (n = 57). In CV experiments the electrocatalytic activity of CoPC was shown for the oxidation of various compounds such as penicillamine, hydrazine and bile acids. Application of the CoPC-CCC electrode for the detection of bile acids in flow-through detection with a constant or pulsed potential failed, due to a rapid deactivation of the electrode.     

Oxidation of phenol on RuO2–TiO2/Ti anodes

The oxidation of phenol on the RuO₂–TiO₂/Ti electrode has been studied by cyclic voltammetry, polarization measurements, electrochemical impedance spectroscopy and potentiostatic transients in H₂SO₄ and NaCl aqueous solutions. A reaction path with polymerization as the main reaction and side reactions after the initial step, similar to the reaction path on other electrode materials, is suggested. The formation of a phenoxy radical in a diffusion-controlled irreversible process is the initial step. The polymerization of phenoxy radicals leads to the formation of porous polyoxyphenylene film, strongly adherent to the electrode surface. The cyclic voltammetry measurements indicate side products, which could be, according to the literature, of quinone-like structure. Polyoxyphenylene film inhibits further oxidation of phenol, although complete electrode passivation was not observed. The presence of polyoxyphenylene film does not influence the pseudocapacitive behaviour of the electrode to a great extent, since the polyoxyphenylene film covers dominantly the coating surface, while active sites placed within coating cracks remain uncovered. The film seems to be permeable for hydrogen ions and water molecules.     

Solar-powered electrochemical oxidation of organic compounds coupled with the cathodic production of molecular hydrogen

A Bi-doped TiO2 anode, which is prepared from a mixed metal oxide coating deposited on Ti metal, is shown to be efficient for conventional water splitting. In this hybrid photovoltaic-electrochemical system, a photovoltaic (PV) cell is used to convert solar light to electricity, which is then used to oxidize a series of phenolic compounds at the semiconductor anode to carbon dioxide with the simultaneous production of molecular hydrogen from water/proton reduction at the stainless steel cathode. Degradation of phenol in the presence of a background NaCl electrolyte produces chlorinated phenols as reaction intermediates, which are subsequently oxidized completely to carbon dioxide and low-molecular weight carboxylic acids. The anodic current efficiency for the complete oxidation of phenolic compounds ranges from 3% to 17%, while the cathodic current efficiency and the energy efficiency for hydrogen gas generation range from 68% to 95% and 30% to 70%, respectively.     

Construction of an electrochemical sensor based on the electrodeposition of Au-Pt nanoparticles mixtures on multi-walled carbon nanotubes film for voltammetric determination of cefotaxime

Mixtures of gold-platinum nanoparticles (Au-PtNPs) are fabricated consecutively on a multi-walled carbon nanotubes (MWNT) coated glassy carbon electrode (GCE) by the electrodeposition method. The surface morphology and nature of the hybrid film (Au-PtNPs/MWCNT) deposited on glassy carbon electrodes is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode is used as a new and sensitive electrochemical sensor for the voltammetric determination of cefotaxime (CFX). The electrochemical behavior of CFX is investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable improvement in the oxidation peak current of CFX compared to glassy carbon electrodes individually coated with MWCNT or Au-PtNPs. Under the optimized conditions, the modified electrode showed a wide linear dynamic range of 0.004-10.0 μM with a detection limit of 1.0 nM for the voltammetric determination of CFX. The modified electrode was successfully applied for the accurate determination of trace amounts of CFX in pharmaceutical and clinical preparations.     

聚多巴胺/多壁碳纳米管/玻璃碳电极上多巴胺的电分析

基于多巴胺（DA）在多壁碳纳米管（MWCNTs）修饰玻璃碳（GC）电极上的电聚合,制得聚多巴胺(PDA)/MWCNTs/GC电极,并对该修饰电极进行了电化学阻抗谱 (EIS)和循环伏安法(CV)表征。 在该修饰电极上,DA呈现良好的电化学行为。在pH=7.4磷酸缓冲溶液中其氧化电流显著高于在裸电极上的响应,且能有效地抑制2.0 mmol/L抗坏血酸(AA)或K4Fe(CN)6的直接电化学响应,表明MWCNTs可增敏信号,且阳离子选择透过性PDA膜可抑制阴离子的电化学干扰。 采用CV实验检测DA,DA氧化的半微分伏安峰高(ipa-sd)与多巴胺浓度在0.08～1.76 μmol/L范围内呈线性关系,在无抗坏血酸和有0.5 mmol/L抗坏血酸共存时的线性回归方程分别为ipa-sd(μA/s1/2)=0.107+0.405c(μmol/L)（r2=0.986）和ipa-sd(μA/s1/2)=0.628+0.649c(μmol/L)(r2=0.992),检测限均为8.0×10-8 mol/L(S/N=3)。 该法用于盐酸多巴胺注射液中多巴胺的快速测定,结果满意。