Surface modification of a planar electrochemical microcell

The fabrication of a three-electrode electrochemical microcell in which the working electrode is selectively modified with poly (vinylferrocene) (PVFer) is described for use as a chemical sensor. The microcell was characterized by cyclic voltammetric and differential-pulse voltammetric techniques and the behaviour of the PVFer-modified platinum electrode in contact with 0.1 M KCl is reported. The mediating properties of the PVFer film are demonstrated for this cell by using the oxidation of ascorbic acid, a process which is shown to be slow at the corresponding bare platinum microelectrode.     

Carbon nanotubes/alizarin red S–poly(vinylferrocene) modified glassy carbon electrode for selective determination of dopamine in the presence of ascorbic acid

A modified electrode was fabricated by electrochemical formation of poly(vinylferrocene) on the multi-wall carbon nanotube-alizarin red S matrix covered glassy carbon electrode. A higher electrochemical activity was obtained to the electrocatalytic oxidation of dopamine. The electrode surface was characterized electrochemically and spectroscopically. Poly(vinylferrocene) (PVF) in electrode was used as an electron transfer mediator in the electrochemical oxidation of compounds due to its perfect reversible redox properties. Multi-wall carbon nanotubes (MWCNTs) / alizarin red S (ARS)–PVF electrode was used to the determination of dopamine in the presence of ascorbic acid in 0.1 M sulphate buffer solution at pH 7. The performance of the MWCNTs/ARS–PVF electrode was evaluated by DPV and amperometry.     

无皂高分子纳米胶乳粒子的制备与稳定

在微波辐照下,以过硫酸钾(KPS)为引发剂,丙酮水溶液(质量比1∶ 1)为分散介质,进行了苯乙烯(ST)和其它共聚单体:甲基丙烯酸甲酯(MMA)、甲基丙烯酸丁酯(BMA)、丙烯酸乙酯(EA)及顺丁烯二酸酐(BDA)的无皂乳液聚合,得到了稳定的纳米胶乳粒子.讨论了共聚单体的种类和浓度对粒子水化半径的影响.增加配方中亲水性单体含量,使引发反应中引发剂的消耗量增加,粒子表面电荷密度增大,同时亲水性增加,油水界面张力减小,粒子变得稳定,有利于小粒子的生成.粒子的大小随亲水性单体的含量呈曲线关系,曲线上有最低点.     

Styrene Miniemulsion Polymerization: Incorporation of N-Alkanes

Summary: In this work, the incorporation of alkane hydrocarbons in poly(styrene-co-methacrylic acid) particles via miniemulsion polymerization was investigated. The reactions were performed at 80 °C for 4 hours, using benzoyl peroxide as oil-soluble initiator. The effects of different concentrations of a hydrophilic co-monomer (methacrylic acid) and different types and concentrations of alkanes, namely n-hexadecane, n-octane and n-heptane were evaluated. Miniemulsion stability at room temperature and reaction kinetics were monitored, as well as the particles size and morphology. Results show the viability of encapsulation of alkanes in miniemulsion polymerizations, especially of alkanes with intermediate chain lengths (e.g. n-hexadecane). When short chain alkanes are incorporated the miniemulsions become less stable, due to their lower hydrophobicity. Based on monomer droplet size distribution data, it was determined that the best concentration of hydrophilic co-monomer for the studied system was 1.0 wt%.     

The development of redox-modified electrodes as charge-accumulating devices for use in higher sensitivity detection systems

Electrochemical methods can be applied in a number of ways as detection systems for competitive immunoassays, especially through the use of redox-labelled antigens. To overcome the problem of detection of such conjugates at low concentration, a system is described in which a poly(vinylferrocene)-modified glassy carbon electrode is used to accumulate charge from solution glucose/glucose oxidase via the intermediacy of a redox-labelled antigen, cycled repeatedly between the enzyme and the electrode. The charge accumulated by the electrode is measured electrochemically by returning the electrode to its original potential and integrating the resulting current-time transient. The charge is proportional to the concentration of redox-labelled antigen in solution and to the charge-accumulation time. In this way 1,1'-dimethylferrocene-ethan-1-ol-2-amine was reproducibly detected to 0.9 nM, with a 10 min incubation period. The 8-ferrocenyl conjugate of theophylline was characterised as a model system for possible application in a higher sensitivity electrochemical immunoassay.     

Electrochemical reversibility of vinylferrocene monolayers covalently attached on H-terminated p-Si(100)

A reversible electrochemical behavior is demonstrated on a specially prepared redox-functionalized H-Si(100) surface, obtained via an extra-mild grafting procedure from vinylferrocene. The results of a detailed XPS and electrochemical characterization of the resulting hybrid are reported and discussed to propose it as a reference system for high-quality electroactive monolayers on Si. The investigated ferrocene derivative bears a functional group suitable for a mild route to covalent anchoring on Si, which is based on a photoinduced reaction with visible light under an inert atmosphere. Electrochemical reversibility is shown by sharp symmetric voltammograms on freshly prepared p-Si electrodes. Anodic oxide growth is responsible for the progressive degradation of the electrochemical response. Still, fast electron transfer to the surface redox species is maintained during several thousands cycles.     

Poly (ethylene terephthalate) thermo-mechanical and thermo-oxidative degradation mechanisms

¹H NMR and MALDI-TOF MS measurements were used to study the thermo-mechanical and thermo-oxidative degradation mechanisms of bottle-grade PET (btg-PET). In the thermo-oxidative degradation, the concentration of low molar mass compounds increased with time and the main products were cyclic and linear di-acid oligomers. In the thermo-mechanical degradation, the main-chain scission reactions affect the stability of the cyclic oligomers. One of the most important bottle-grade PET co-monomers is diethylene glycol (DEG), which is a “reactive site” in the thermal degradation of btg-PET. The DEG co-monomer was shown to be the precursor to colour changes in btg-PET, owing to the attack by molecular oxygen on the methylenic protons adjacent to the ether oxygen atoms of DEG. This behaviour was observed in the thermo-oxidative degradation process in which the degradation of DEG causes the release of hydroxyl radicals in the polymeric matrix, thereby producing mono- and di-hydroxyl substituted species. This was also observed in the thermo-mechanical degradation process.     

Preparation of hydrophilic molecularly imprinted polymers for tetracycline antibiotics recognition

Hydrophilic molecularly imprinted polymers(MIPs) were prepared using tetracycline as template,methacrylic acid as monomer and glycidilmethacrylate as pro-hydrophilic co-monomer.Compared with common MIPs,the imprinting effect and adsorption amounts of hydrophilic MIPs for tetracycline(TC) were greatly improved in water media.Furthermore,the electrochemical sensor fabricated by modifying hydrophilic MIPs on glassy carbon electrode was developed for the determination of TC in foodstuff samples.     

Construction of a Novel Glucose Biosensor Based on Covalent Immobilization of Glucose Oxidase on Poly(glycidyl methacrylate‐co‐vinylferrocene)

A novel glucose biosensor was constructed via direct covalent attachment of glucose oxidase onto epoxy group containing polymeric electron transfer mediator, Poly(glycidyl methacrylate‐co‐vinylferrocene). A copolymer of glycidyl methacrylate (GMA) and vinylferrocene (VFc) with different molar ratios has been prepared by free radical copolymerization. These copolymers have been utilized as polymeric mediators for amperometric glucose sensing. The catalytic electrochemistry of the enzyme electrode with the copolymer was investigated. Copolymer acts as an electron transfer mediator between the redox center of Glucose oxidase (GOx) and the electrode. The stability, reusability, pH and temperature response of the biosensor as well as its kinetic parameter have also been studied.     

Safety improvement of lithium ion batteries by organo-fluorine compounds

Thermal stability, electrochemical oxidation stability and charge/discharge characteristics of natural graphite powder were investigated by mixing of five fluoro-carbonates with 1 mol/L LiClO₄–EC/DEC/PC (1:1:1 vol.). DSC study revealed that thermal stability of the electrolyte solution was improved by mixing of fluoro-carbonates by 10.0–33.3 vol.%. Electrochemical oxidation stability was also improved. Oxidation currents for Pt electrode significantly decreased by mixing of fluoro-carbonates. In the fluoro-carbonate-mixed electrolyte solutions, electrochemical reduction of PC decreased with increasing concentration of fluoro-carbonate and current density. As a result, first coulombic efficiency for natural graphite electrode increased, that is, irreversible capacity decreased in the fluoro-carbonate-mixed solutions.     

纳米银/石墨烯修饰电极测定青蒿素

本文建立一种新型的青蒿素传感器。首先,在玻碳电极上滴涂氧化石墨,通过电化学方法将氧化石墨还原为石墨烯,然后,在石墨烯上沉积纳米银得到石墨烯/纳米银修饰电极,它作为检测青蒿素的电化学传感器。用此电极对青蒿素进行测定,并通过循环伏安法、差分脉冲伏安法、交流阻抗法等研究其电化学行为。该修饰电极在测定青蒿素溶液时,表现出较正的还原电位和较大的峰电流等优势;对其实验条件如电解质溶液的p H、应用电势等进行了探查,该电化学传感器在青蒿素溶液浓度范围为1.0×10-8~3.0×10-5mol/L时与其还原峰电流呈现良好的线性关系,最低检出限为1.2×10-9mol/L(S/N=3)。此外,对该传感器的稳定性和重现性等也进行了研究,获得令人满意的结果。     

Macromolecule–metal complexes exhibiting phase transition

A copolymer gel prepared from N-isopropyl-acrylamide (NIPA) and vinylferrocene (VF) exhibits volume phase transition. The phase transition can be controlled electrochemically, and electrochemical behavior of the gel can be controlled thermally. A copolymer of NIPA and VF, which is not crosslinked, also possesses similar characteristics. Those polymer and gel can be applied to enzyme electrodes. © 1997 John Wiley & Sons, Ltd.     

Polymer films on electrodes: Part II. Film structure and mechanism of electron transfer with electrodeposited poly(vinylferrocene)

The structure and properties of electrodeposited poly(vinylferrocene) (PVF) films on platinum electrodes (PVF/Pt) were examined by electron microscopy, X-ray photoelectron spectroscopy, various electrochemical techniques and measurements of the film resistance. The data were consistent with a mechanism in which the polymer films are permeable to dis-solved reactants. A theoretical treatment of this situation for chronoamperometry is presented. The oxidation and reduction of a variety of dissolved reactants with redox potentials far removed from that of the PVF/PVF⁺ system at PVF/Pt occurred by diffusion of the electroactive species through the polymer film and subsequent reaction at the platinum surface.     

Polymer films on electrodes: Part III. Digital simulation model for cyclic voltammetry of electroactive polymer film and electrochemistry of poly(vinylferrocene) on platinum

The electrochemistry of electrodeposited poly(vinylferrocene) (PVF) and poly(vinylferrocene acrylonitrile) (PVFAN) films on platinum electrodes was studied in acetonitrile solutions using perchlorate or p-toluenesulfonate as the counter ion by cyclic voltammetry. A model is proposed for the cyclic voltammetric behavior of polymeric films on electrode surfaces. The model incorporates non-equivalent redox sites with interconversion between such sites, electron-transfer kinetics at substrate/film interface and diffusion within the film. Parameters are obtained which yield a good fit to the experimental results.     

Colon-specific devices based on methacrylic functionalized Tween monomer networks: Swelling studies and in vitro drug release

Colon-targeted delivery devices based on methacrylic functionalized Tween monomer networks, useful for 5-FU or Ferulic acid site-specific release, were synthesized. The basic design consists of methacrylic functionalized Tween monomer-based networks prepared with or without acrylic acid as co-monomer. The swelling behaviour and loaded drugs release from these gels was studied as a function of pH. The devices showed a strong pH-dependent swelling behaviour, allowing a maximum release at pH 7.4. The acrylic acid introduction increased the polymeric gels pores size, as evidenced by the loading efficiency increase, but also reduced the amount of released drug in basic media compared to analogous network not containing the co-monomer. This behaviour, already found in the matrix swelling, could be attributed to a slower hydrolysis kinetics of the ester bond in functionalized Tween monomers, which implies a reduced ability to absorb water from a basic medium, resulting in a lower capacity to release the loaded drug.Since our device possesses a maximum drug release in the media at pH 7.4, it could be used for colon-targeted drug delivery of both 5-FU and Ferulic acid.     

Adsorption of methylmethacrylate-vinylferrocene copolymers at the solution/solid interface

A series of methylmethacrylate–vinylferrocene random copolymers was synthesized and characterized. Their adsorption from toluene and chloroform was measured onto pyrogenic silicas. The level of adsorption depended on the solvent, the surface area of the adsorbent, and the copolymer composition. Thus, an inverse adsorption-solubility relationship for toluene and chloroform was observed. However, in solvents such as tetrahydrofuran, 2-butanone, and cyclobutanone, which have strong interaction with silica, this trend was not evident. The compositional dependence of the adsorption of these copolymers in toluene and chloroform is similar. Initially, adsorption tends to increase with the vinylferrocene content in the polymer, and at equimolar copolymer compositions the adsorption reaches a maximum which is followed by a decrease in the adsorption values at high vinylferrocene contents. Gel permeation chromatography(GPC) measurements allowed us to conclude that high molecular weight polymer was preferentially adsorbed.     

Voltammetric determination of antibacterial drug gemifloxacin in solubilized systems at multi-walled carbon nanotubes modified glassy carbon electrode

A sensitive electroanalytical method for determination of gemifloxacin in pharmaceutical formulation has been investigated on the basis of the enhanced electrochemical response at multi-walled carbon nanotubes modified glassy carbon electrode in the presence of CTAB. Solubilized system of different surfactants including SDS, Tween-20 and CTAB were taken for the study of electrochemical behaviour of gemifloxacin at modified electrode. The reduction peak current increases in the presence of CTAB while other surfactants show opposite effect. The modified electrode exhibits catalytic activity, high sensitivity, stability and is applicable over wide range of concentration for the determination of gemifloxacin. The mechanism of electrochemical reduction of gemifloxacin has been proposed on the basis of CV, SWV, DPV and coulometeric techniques. The proposed squarewave voltammetric method shows linearity over the concentration range 2.47-15.5 μg/mL. The achieved limits of detection (LOD) and quantification (LOQ) are 0.90 ng/mL and 3.0 ng/mL respectively.     

同多酸和杂多酸修饰微电极的电化学研究——Ⅳ.1:2-磷钼杂多酸薄膜修饰碳纤维微电极的制备和电化性质

本文报道了1:12-磷铜杂多酸(PMo_(12)薄膜修饰碳纤维(CF)微电极的制备及其电化学性质。采用简单,快速的浸渍吸附制备的PMo_(12)薄膜修饰CF电极在酸性介质中具有很高的稳定性和氧化还原活性,电解质溶液的pH值和扫描电位范围对PMo_(12)膜的稳定性和电化学性质产生较大的影响。另一方面,PMo_(12)薄膜修饰CF微电极对酸性水溶液中的PMo_(12)和氯酸根离子(ClO)_3~-)的电催化还原作用也进行了描述。     

Nickel-Zeolite modified carbon paste electrode as electrochemical sensor for hydrogen peroxide

In the present work, nickel-zeolite modified carbon paste electrode (Ni-ZMCPE) was prepared. The electrochemical behaviour of hydrogen peroxide at the surface of modified electrode was investigated by cyclic voltammetry and chronoamperometry in 0.1 M NaOH supporting electrolyte. The electrochemical characterization of Ni-ZMCPE exhibits redox behavior of Ni(III)/Ni(II) couple in alkaline medium. It has been shown that Ni-ZMCPE improves efficiency of the modified electrode toward hydrogen peroxide electrooxidation (It wasn’t remarkable different on ZMCPE and CPE in the presence and absence of hydrogen peroxide). Moreover, the effects of various parameters such as effect of different percents of Ni-Z to graphite, effect of pH and hydrogen peroxide concentration on the electrooxidation of hydrogen peroxide as well as stability of the Ni-ZMCPE have also been investigated. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of hydrogen peroxide in the range 0.03–0.1 and 0.3–6 mM with amperometric method. The detection limit (S/N = 3) was also estimated to be 1 μM.     

Voltammetric Determination of Metronidazole Using a Sensor Based on Electropolymerization of α‐Cyclodextrin over a Carbon Paste Electrode

An electrochemical sensor for metronidazole (MTZ) was built via the surface modification of a carbon paste electrode (CPE) by a film obtained through electropolymerization of α‐cyclodextrin (CPE_α‐CD). The CPE_α‐CD was characterized by cyclic voltammetry (CV) and atomic force microscopy (AFM), by both techniques was demonstrated that the polymer film is coating the electrode surface. The electroreduction behaviour of MTZ in HClO₄ media as a supporting electrolyte was studied by differential‐pulse voltammetric (DPV) technique. The DPV electrochemical process was observed to be diffusion controlled and irreversible. Under optimal conditions, the peak current was proportional to MTZ concentration in the range of 0.5 to 103.0 μM with a detection limit of 0.28±0.02 μM. The method was successfully applied to quantify of MTZ in pharmaceutical formulations. In addition, this proposed MTZ sensor exhibited good reproducibility, long‐term stability and fast current response.