Preparation of Carbon Nanotubes/Neutral Red Composite Film Modified Electrode and Its Catalysis on Rutin

Neutral red was directly electropolymerized onto the carbon nanotubes modified electrode. A polymerized neutral red/carbon nanotubes composite film was characterized by scanning electron micrograph (SEM) and cyclic voltammetry (CV). Well‐defined voltammetric responses are observed for [Fe(CN)₆]^4?/3? on the composite film modified glassy carbon electrode. And it's found that this modified electrode has good catalysis on the redox of rutin. Differential pulse voltammetry method was used to determinate the concentration of rutin and obtain a linear equation between the current and concentration in a certain range. The modified electrode is satisfied with us for its good sensibility and stability.     

Effect of hydroxypropyl-β-cyclodextrin on the electrochemical oxidation and polymerization of 3,4-ethylenedioxythiophene

The electrochemical oxidation of 3,4-ethylenedioxythiophene (EDOT) on platinum is studied in electrolyte solutions containing hydroxypropyl-β-cyclodextrin (HP-β-CD). HP-β-CD is found to increase the solubility of EDOT up to a concentration of 0.026 M in aqueous solutions. Addition of HP-β-CD (0.1 M) produces a slight red shift of the EDOT main absorption band from 254.9 to 257.7 nm and an increase of the HP-β-CD concentration decreases the absorption coefficient, _max to 6150 l mol⁻¹ cm⁻¹ in the UV–vis region, indicating complex formation. The cyclic voltammetric response of EDOT in 0.1 M aqueous LiClO₄ solutions consists of an ill-defined wave (P₁) and an adsorption peak (P₂). Contrary to the case of oxidation in acetonitrile medium, a post-peak is observed in the voltammograms of EDOT electro-oxidation in aqueous LiClO₄ solutions due to the adsorption of the oxidized EDOT species. A gradual reduction of the peak current of P₂ with increasing [HP-β-CD] and its total disappearance at high [HP-β-CD] suggest complex formation between HP-β-CD and EDOT√⁺ and also the peak P₂ to be due to adsorption of EDOT√⁺ species. The experiments intended to show the effect of ‘pre-adsorbed’ HP-β-CD on EDOT oxidation led to the conclusion that adsorbed HP-β-CD also solubilizes EDOT at the electrode surface. The CV behaviour of EDOT in HP-β-CD is discussed in comparison with that in sodium dodecylsulfate micellar solutions. Addition of increasing amounts of HP-β-CD shifts P₁ positively and P₂ negatively while also suppressing P₂ totally and reducing the peak current of P₁ to a significant extent. At a higher concentration of HP-β-CD, viz. 0.05 M, a peak appears at 1.29 V as a result of the above two opposing effects of CD on the peak potentials of P₁ and P₂. This resultant peak (P_composite) is more positive relative to the position of P₁ observed in the absence of HP-β-CD. The positive shift of the peak and peak current reduction indicate that EDOT (or an oxidized EDOT species) possibly interacts with the outer nucleophilic part of HP-β-CD. The electro-oxidation processes occurring at P₁ and P₂ are explained using an oligomeric approach, in which the electrochemical reactions are coupled to chemical reactions or adsorption of the oxidized species. Potential cycling of the platinum electrode in solutions containing 0.026 M EDOT+0.05 M HP-β-CD+0.1 M LiClO₄ between −0.5 and 1.2 V yields an adherent and smooth polymer film of poly(ethylenedioxythiophene), as shown in the SEM examination. In situ resistance measurements carried out with the polymer films in the electroactive region show a minimum resistance in the potential range of 0.3–0.4 V. Even the electrochemically-reduced films are found to possess some residual electrical conductivity.     

Comparison of biosensors based on entrapment of cholesterol oxidase and cholesterol esterase in electropolymerized films of polypyrrole and diaminonaphthalene derivatives for amperometric determination of cholesterol

Cholesterol amperometric biosensors constructed with enzymes entrapped in electropolymerized layers of polypyrrole and poly-naphthalene derivative polymers are compared. The biosensors are based on entrapment of cholesterol oxidase and/or cholesterol esterase in monolayer or multilayer films electrochemically synthesised from pyrrole, 1,8-diaminonaphthalene (1,8-DAN), and 1,5-diaminonaphthalene (1,5-DAN) monomers. Seven configurations were assayed and compared, and different analytical properties were obtained depending on the kind of polymer and the arrangement of the layers. The selectivity properties were evaluated for the different monolayer and bilayer configurations proposed as a function of the film permeation factor. All the steps involved in the preparation of the biosensors and determination of cholesterol were carried out in a flow system. Sensitivity and selectivity depend greatly on hydrophobicity, permeability, compactness, thickness, and the kind of the polymer used. In some cases a protective outer layer of non-conducting poly(o-phenylenediamine) polymer improves the analytical characteristics of the biosensor. A comparative study was made of the analytical performance of each of the configurations developed. The biosensors were also applied to the flow-injection determination of cholesterol in a synthetic serum.     

Synthesis and Electrochemical Characterization of a New Electropolymerizable Hydrophilic Viologen Designed for Enzyme Wiring

A new viologen derivative functionalized by an electropolymerizable pyrrole group via a long hydrophilic spacer has been synthesized. This redox monomer has been electrochemically characterized both for its presence in organic and in aqueous media. Its electrooxidation in both solvents leads to the formation of a polymeric film exhibiting the regular electrochemical behaviour of the viologen groups. The electropolymerization process was applied to the immobilization of isocitrate dehydrogenase as an enzyme model. An electrical connection between the redox polymer and the immobilized enzyme molecules has been observed in the presence of oxoglutarate and CO₂.     

Polypyrrole films electrosynthesized on stainless steel grid from saccharinate aqueous solution and its behaviour toward acetone vapor

The electrochemical behaviour of stainless steel electrode in 0.1 M sodium saccharinate solution in the absence and the presence of the monomer were investigated using several electrochemical techniques such as cyclic voltammetry, galvanostatic and potentiostatic. The XPS analysis was used to study the elementary composition of the obtained polymer and to estimate the doping level of the PPy obtained under this electrolytic conditions. Moreover, the characterization of the coating was achieved by SEM, IR and Raman. In this context, samples of PPy in oxidized and reduced state synthesized galvanostatically on stainless steel grid were used to investigate the behaviour of the polymer toward acetone vapor.     

Lead Determination by Anodic Stripping Voltammetry Using a p‐Phenylenediamine Modified Carbon Paste Electrode

Carbon paste electrodes were modified by mixing appropriate amounts of the monomers o‐phenylendiamine, p‐phenylendiamine and m‐phenylendiamine (o‐PD, p‐PD and m‐PD) into a graphite powder‐paraffin oil matrix. The electropolymerization of the incorporated phenylendiamine was then carried out in a carbon paste electrode in acidic medium by cyclic voltammetry between ?0.30 V and +0.90 or under constant potential. The modified carbon paste electrodes (MCPEs) obtained by this electropolymerization method were found to be useful for trace determination of Pb²⁺ in aqueous solutions. Lead(II) was first preconcentrated on the modified electrodes by complexation with the modifier, and the electrode was then transferred to an electrochemical cell. The best results in terms of sensitivity and detection limit were obtained with poly p‐phenylenediamine (poly (p‐PD)). For a 10‐min preconcentration time, the calibration plot was linear from 5×10^?8 mol L^?1 to 10^?5 mol L^?1, with r²=0.999 and relative standard deviation equal to 5%. However, the lowest lead concentration that could be detected was 10^?9 mol L^?1. Interference from metal ions like Cd(II), Hg(II), Zn(II), Fe(II) and Cu(II) was also studied.     

Amperometric cholesterol biosensors based on the electropolymerization of pyrrole and the electrocatalytic effect of Prussian-Blue layers helped with self-assembled monolayers

Three cholesterol biosensor configurations based on the formation of a layer of Prussian-Blue (PB) on a Pt electrode for the electrocatalytic detection of the H₂O₂ generated during the enzymatic reaction of cholesterol with cholesterol oxidase (ChOx) were constructed. The enzyme was entrapped within a polypyrrole (PPy) layer electropolymerized onto the PB film. The influence of the formation of self-assembled monolayers (SAMs) on the Pt surface on the adherence and stability of the PB layer and the formation of an outer layer of nafion (Nf) as a means of improving selectivity were both studied. A comparative study was made of the analytical properties of the biosensors corresponding to the three configurations named: Pt/PB/PPy-ChOx, Pt/SAM/PB/PPy-ChOx and Pt/SAM/PB/PPy-ChOx/Nf. The sensitivity (from 600 to 8500 nA mM⁻¹ cm⁻²) and selectivity of the developed biosensors permitted the determination of the cholesterol content in reference and synthetic serum samples. The detection limit for the Pt/SAM/PB/PPy-ChOx/Nf biosensor was 8 μM. Formation of the SAM on the electrode surface and covering with a Nf film considerably improved the stability and lifetime of the biosensor based on the catalytic effect of the PB layer (as the PB layer was retained longer on the electrode), and the Nf layer protects the enzyme from the external flowing solutions. Lifetime is up to 25 days of use. The formation of the SAM also has an effect on the charge transfer and the formation of the PB layer.     

Oxidation of a PPy-modified tantalum electrode

A tantalum electrode on which polypyrrole (PPy) had been previously formed by electropolymerization was galvanostatically electrolyzed in an aqueous solution of 0.01 wt% phosphoric acid. This process contains the irreversible oxidation of a PPy film, the decomposition of solvent, and the formation of Ta₂O₅ by the reaction of OH^? coming through the PPy film, with Ta electrodes. A three layer-structure (PPy/Ta₂O₅/Ta) was confirmed by electron spectroscopy for chemical analysis (ESCA). A PPy film containing CIO₄^? as dopant [PPy(CIO₄^?)] was significantly deteriorated in comparison with PPy(TsO^?) at the electrolysis. Therefore, the (PPy(TsO^?)/Ta₂O₅/Ta) system showed better electrical characteristics as a capacitor than the (PPy(CIO₄^?)/Ta₂O₅/Ta) system showed better electrical characteristics as a capacitor than the (PPy(ClO₄^?)/Ta₂O₅/Ta) system.     

Formation of PPy/Ta2O5/Ta structure by electropolymerization

Electropolymerization of pyrrole on tantalum (Ta) electrodes was carried out in buffer solutions (0.04 M phosphoric acid, 0.04 M acetic acid, 0.04 M boric acid and 0.2 M sodium hydroxide) containing 0.1 M sodium ptoluenesulfonate (TsONa) under galvanostatic conditions and it was found that a polypyrrole (PPy) and a tantalum oxide (Ta₂O₅) layer are formed on a Ta electrode by an electrochemical oxidation process. The conditions of this simultaneous formation were studied in respect to current density (i_d), pyrrole concentration ([Py]), pH and the amount of electricity. Under certain conditions ([Py] = 0.25 M, pH = 1.8, i_d = 10–20 mA cm^?2, the amount of electricity = 1 C), 6–8 μm thick PPy films were efficiently formed on homogeneous 30–50 nm thick Ta₂O₅ layers. The PPy film showed a high electrical conductivity (110 s cm^?1), adhered well and covered the Ta₂O₅ layer. The resulting PPy/Ta₂O₅/Ta system is therefore proved to have excellent properties as a capacitor.     

Electrochemically Deposited Polymer‐Coated Gold Electrodes Selective for 2,4‐Dichlorophenoxyacetic Acid

Electropolymerized membranes on gold electrodes doped with 2,4‐dichlorophenoxyacetic acid (2,4‐D) were prepared from a solution containing resorcinol, o‐phenylenediamine and 2,4‐D. Fourier Transform Infrared (FTIR) spectroscopy was used to evaluate the incorporation and interaction of 2,4‐D with the polymer matrix prior to and after the sensing experiments. The FTIR data indicate that 2,4‐D does not leach appreciably from the polymer matrix under experimental conditions employed for the sensing studies. The electrochemical current response for 2,4‐D is compared for the doped polymer‐coated and control polymer‐coated electrode. The response of the doped polymer‐electrode was dependent on increasing concentrations of 2,4‐D and 2,4‐dichlorophenol while unresponsive to benzoic acid.