Electrochemical study on oxidation of ofloxacin at nano-ZnS/poly (Styrene sulfonic acid sodium salt) modified electrode and its interaction with calf thymus DNA

A PSS/nano-ZnS thin film modified electrode has been fabricated on the surface of glassy carbon electrode (GCE). In pH 5.0 phosphate buffer solution (PBS), Ofloxacin (OFX) appeared as an anodic peak with the peak potential of 1.28 V at PSS/nano-ZnS film modified electrode. In comparison with a bare GCE or a nano-ZnS modified electrode, the PSS/nano-ZnS film modified electrode exhibited an enhanced effectiveness for the oxidation of OFX. Cyclic voltammetry (CV) coupled with fluorescence and UV-vis absorbance spectra techniques were used to study the interaction of OFX with Calf thymus DNA (ctDNA). The interaction of OFX and ctDNA could result in a considerable decrease in the peak currents and positively shift in the peak potential, as well as changes of fluorescence, UV-Vis adsorption spectra. All acquired data showed that the new adduct between OFX and ctDNA was formed. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 3, pp. 289–295. The article is published in the original.     

Green Synthesis of Silver Nanoparticles Using Ionic Liquid and Application for the Detection of Dissolved Oxygen

The electrochemical synthesis of silver nanoparticles (nano‐Ag) has been successfully carried out on glassy carbon electrode (GCE) and indium tin oxide electrode (ITO) using 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMT) as green electrolytes. Further the electrodeposited nano‐Ag modified ITO electrode has been examined using atomic force microscopy (AFM), and X‐ray diffraction studies (XRD). The electrodeposited Ag nanoparticles on ITO were found in the size range of 5 to 35 nm. The nano‐Ag film modified GCE was further coated with nafion (Nf) and BMT (1 : 1 ratio) mixture and found to be stable in BMT and in pH 7 phosphate buffer solution (PBS). The nano‐Ag/BMT‐Nf film modified GCE successfully applied for the oxygen reduction reaction in neutral pH (pH 7.0 PBS). The proposed film modified GCE successfully reduces the over potential and show well defined reduction peaks for the detection of dissolved oxygen using cyclic voltammetry (CV) and rotating disc voltammetry (RDE). The film also applied for the detection of dissolved oxygen using electrochemical impedance spectroscopic studies (EIS).     

Electrochemical and Spectroelectrochemical Studies on Pyridoxine Hydrochloride Using a Poly(methylene blue) Modified Electrode

The electrochemical redox processes of pyridoxine hydrochloride (VB₆) at a poly(methylene blue) film modified glass carbon electrode (PMBE) in a phosphate buffer solution (PBS, pH 8.0) were studied by cyclic voltammetry. The VB₆ electrode reaction with quasi‐reversible characteristics was diffusion‐controlled at low scan rates and adsorption‐controlled at high scan rates. The anodic peak current positive to 0.6 V (vs. SCE) was found to be proportional to the concentration of VB₆ in the range of 0.010 to 1.03 mg?mL^?1 with a detection limit of 1.34 μg mL^?1. Fluorescence and UV‐vis absorption spectroelectrochemical measurements suggest that the pyridine ring was not destroyed over the potential range from ?0.8 to 1 V (vs. SCE), and the electrocatalytic generation of pyridoxal was anodically started at 0.57 V.     

A Novel Electrochemical Method for the Analysis of Hydrogen Peroxide with the Use of a Glassy Carbon Electrode Modified by a Prussian Blue/Copper‐Gold Bimetallic Nanoparticles Hybrid Film

A novel Prussian blue/copper‐gold bimetallic nanoparticles hybrid film modified electrode was prepared by electrochemical deposition on a glassy carbon electrode (PB/Cu‐AuNPs/GCE). Morphology and electrochemistry of this electrode were studied by UV‐vis spectroscopy, scanning electron microscopy, X‐ray diffraction, cyclic voltammetry and electrochemical impedance spectroscopy. The sensor showed significantly better electrocatalytic activity for the reduction of hydrogen peroxide in comparison with the single PB/GCE and PB/AuNPs/GCE. This was attributed to the synergistic effect of PB and Cu‐Au bimetallic nanoparticles. Also, the sensor demonstrated an overall high level of performance for the analysis of H₂O₂ in the concentration range from 0.002 to 0.84 mM.     

Electrocatalysis of Hemoglobin in ZnO Nanoparticle/Ionic Liquid Composite Film Modified Glassy Carbon Electrode

A nanobiocompatible composite containing hemoglobin (Hb), ZnO nanoparticles (nano‐ZnO) and ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) was fabricated and further modified on the glassy carbon electrode (GCE). The electrochemical behaviours of Hb in the composite film were carefully studied and a pair of quasi‐reversible redox peaks appeared in pH 7.0 phosphate buffer solution, which was attributed to the electrode reaction of Hb heme Fe(III)/Fe(II) redox couple. The presences of nano‐ZnO and BMIMPF₆ in the film can retain the bioactivity of Hb and greatly enhance the direct electron transfer of Hb. The immobilized Hb showed high stability and good electrocatalytic ability to the reduction of hydrogen peroxide and O₂.     

Voltammetric Determination of 2′‐Deoxyadenosine and Adenine in Urine of Patients with Hepatocellular Carcinoma Using Fullerene‐C60‐modified Glassy Carbon Electrode

A fullerene‐C₆₀‐modified glassy carbon electrode has been examined for the simultaneous determination of 2′‐deoxyadenosine (2′‐dAdo) and adenine in human blood and urine using Osteryoung square‐wave voltammetry (OSWV) at pH 7.2. Compared to bare glassy carbon electrode (GCE), the modified electrode displays a shift of the oxidation potential in the negative direction with significant increase in the peak current for both the analytes. At modified electrode well‐defined anodic peaks at potential of 1248 mV and 994 mV are observed for 2′‐dAdo and adenine respectively. Linear calibration curves were obtained within the concentration range 10 nM to 100 μM for both the compounds in 0.1 M phosphate buffer solution (PBS) with the limit of detection 0.8×10^?8 M and 0.95×10^?8 M for 2′‐dAdo and adenine respectively. The analytical utility of the present method is demonstrated by quantitative detection of 2′‐dAdo and adenine in human urine of normal subjects as well as in patients with hepatocellular carcinoma. Interfering effect of some coexisting metabolites has also been reported.     

Voltammetric Determination of Bisphenol A Using an Acetylene Black‐Dihexadecyl Hydrogen Phosphate Composite Film‐Modified Electrode

Abstract

Herein, acetylene black (AB) was easily dispersed into water in the presence of dihexadecyl hydrogen phosphate (DHP), resulting in a stable and homogeneous AB‐DHP suspension. Then, an AB‐DHP composite film coated glassy carbon electrode (GCE) was constructed after evaporation of water. The electrochemical behavior of bisphenol A was investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV). Compared with the unmodified GCE, the AB‐DHP film‐modified GCE not only significantly enhances the oxidation peak current of bisphenol A but also lowers the oxidation overpotential, suggesting that AB‐DHP film‐modified GCE has great potential in sensitive determination of bisphenol A. Based on this, a sensitive and simple electrochemical method was developed after optimization of the experimental parameters such as supporting electrolyte, the amount of AB‐DHP, scan rate, and accumulation time. The linearity is over the range form 2.0×10^?8 to 5.0×10^?6 mol l^?1, and the detection limit is 6.0×10^?9 mol l^?1. Finally, this method was successfully employed to determine bisphenol A in waste water samples.     

Enhanced Oxidation of Simvastatin at a Multi‐Walled Carbon Nanotubes‐Dihexadecyl Hydrogen Phosphate Composite Modified Glassy Carbon Electrode and the Application in Determining Simvastatin in Pharmaceutical Dosage Forms

A sensitive electrochemical method for the determination of simvastatin (SV) was established, based on the enhanced oxidation of SV at a multi‐walled carbon nanotubes‐dihexadecyl hydrogen phosphate composite modified glassy carbon electrode (MWNTs‐DHP/GCE). The voltammetric studies showed that MWNTs instead of DHP or GCE could effectively catalyze the oxidation of SV. The dependence of oxidation current on SV concentration was explored under optimal conditions, which exhibited a good linear relationship in the range of 1.0×10^?7–7.5×10^?6 M. The detection limit of SV was also examined and a low value of 5.0×10^?8 M was obtained for 5 min accumulation (σ=3). This electrode was applied to the detection of SV in drug forms and the results were in accordance with those obtained by UV spectroscopy.     

Electrochemical Behaviors of Resveratrol and Its Interaction with DNA

Electrochemical behavior of resveratrol was studied in Britton‐Robinson (B‐R) buffer solution (pH = 4.0) at glassy carbon electrode (GCE) using cyclic voltammetry (CV). Resveratrol showed an irreversible anodic peak at 0.570 V which was involving one electron and one proton. Also, the interaction of resveratrol with double‐stranded fish sperm DNA was investigated by linear sweep voltammetry (LSV) and UV‐vis spectra. The results showed that peak potentials shifted to more positive value and peak currents decreased in electrochemical experiment and the maximum absorption decreased with red shift in UV‐vis spectra experiment with the addition of DNA, indicating the resveratrol interacted with DNA by intercalating into the double helix of DNA. Besides, the binding of resveratrol with DNA, analyzed in terms of the cooperative Hill model, yields the association constant K_a = 3.18 × 10⁵ and a Hill coefficient m = 1.06.     

Electrochemical Characteristics of Poly(<Emphasis Type="Italic">o</Emphasis>-Aminobenzoic Acid) Modified Glassy-Carbon Electrode and Its Electrocatalytic Activity towards Oxidation of Epinephrine

Poly(o-aminobenzoic acid) (o-ABA) film is deposited on glassy-carbon electrode (GCE) by electropolymerization in pH 7.0 phosphate buffer solution (PBS). Electrochemical behavior of modified electrode is investigated by electrochemical impedance spectroscopy (EIS), different pulse voltammetry (DPV), and cyclic voltammetry (CV). The results indicate that there is a greater resistance during the electron transfer process in poly(o-ABA) film than in bare GCE for the redox of [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻. Further research indicates that epinephrine (EP) can be strongly absorbed on the surface of the poly(o-ABA) film-modified electrode. The modified electrode shows an excellent electrocatalytical activity on EP oxidation. The EP cathodic peak potential shifts negatively with a slope of −53.5 mV/pH, indicating that equal amounts of proton and electron are involved in the electrode reaction process. In pH 7.0 PBS, the peak current of EP and the concentration has a linear relationship from 0 to 65 μM by amperometric current-time curve. __________ From Elektrokhimiya, Vol. 41, No. 9, 2005, pp. 1059–1065. Original English Text Copyright ? 2005 by Cheng, Jin, Zhang. The text was submitted by the authors in English.     

对苯二胺在血红蛋白/聚L-谷氨酸/玻碳修饰电极上的可逆氧化

采用电聚合法在玻碳电极(GCE)表面得到导电性能良好的聚L-谷氨酸(PGA)薄膜,通过共价键合法将血红蛋白(Hb)固定于电极表面得到稳定且具有催化活性的Hb/PGA/GCE修饰电极,将其用于对苯二胺(PPD)的可逆氧化。 修饰电极交流阻抗及血红蛋白直接电化学实验表明,血红蛋白成功地固定于电极表面,保持良好的电催化活性,能有效催化H₂O₂的还原。 PPD在电极上表现为受吸附控制的准可逆氧化还原反应,I_p,a/I_p,c约为1.02,电极没有明显的钝化现象。 氧化还原峰电流与PPD的浓度均呈良好的线性关系,I_p,a(μA)=3.124+0.705c_PPD(mmol/L)(r=0.9973)。 H₂O₂的存在使PPD氧化还原峰型更对称,可逆性更好,表明体系中PPD氧化与过氧化酶催化途径一致。     

Sensitive Determination of Clomipramine at Poly‐ABSA/Pt Nano‐Clusters Modified Glassy Carbon Electrode

Abstract

Clomipramine, an important tricylic antidepressant drug with low redox activity, was effectively electrocatalyzed on poly‐aminobenzene sulfonic acid/Pt nano‐clusters modified glassy carbon electrode (i.e., poly‐ABSA/Pt/GCE) and generated a sensitive anodic peak at about 0.80 V in pH 8.1 PBS. ABSA was electropolymerized on the surface of GCE modified with Pt nano‐clusters. Pt nanoparticles provide a 3 D and conductive structure for the polymer immobilization. The resulting sensor exhibited a considerable enhancement in voltammetric response characteristics: extending the linear range and lowering the detection limit. The anodic peak current of clomipramine was linear with its concentration over two concentration intervals, viz., 1.0×10^?7～4.0×10^?6 M and 4.0×10^?6～4.0×10^?5 M, with the detection limit of 1.0×10^?9 M (S/N=3). This method was successfully applied to the determination of clomipramine in drug tablets and proved to be reliable compared with UV.     

Direct Electrochemistry and Electrocatalysis Behaviors of Glucose Oxidase Based on Hyaluronic Acid-Carbon Nanotubes-Ionic Liquid Composite Film

Multi‐walled carbon nanotubes (MWNTs) were dispersed in the ionic liquid [BMIM][BF₄] to form a uniform black suspension. Based on it, a novel glucose oxidase (GOx)‐hyaluronic (HA)‐[BMIM][BF₄]‐MWNTs/GCE modified electrode was fabricated. UV‐vis spectroscopy confirmed that GOx immobilized in the composite film retained its native structure. The experimental results of EIS indicated MWNTs, [BMIM][BF₄] and HA were successfully immobilized on the surface of GCE and [BMIM][BF₄]‐MWNTs could obviously improve the diffusion of ferricyanide toward the electrode surface. The experimental results of CV showed that a pair of well‐defined and quasi‐reversible peaks of GOx at the modified electrode was exhibited, and the redox reaction of GOx at the modified electrode was surface‐confined and quasi‐reversible electrochemical process. The average surface coverage of GOx and the apparent Michaelis‐Menten constant were 8.5×10⁻⁹ mol/cm² and 9.8 mmol/L, respectively. The cathodic peak current of GOx and the glucose concentration showed linear relationship in the range from 0.1 to 2.0 mmol/L with a detection limit of 0.03 mmol/L (S/N=3). As a result, the method presented here could be easily extended to immobilize and obtain the direct electrochemistry of other redox enzymes or proteins.     

Direct Electron Transfer of Horseradish Peroxidase in Gellan Gum–Hydrophilic Ionic Liquid Gel Film

A new composite film of microbial exocellular polysaccharide‐gellan gum (GG) and hydrophilic room temperature ionic liquid 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate (BMIMBF₄) was firstly used as an immobilization matrix to entrap horseradish peroxidase (HRP), and its properties were studied by UV/vis spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that BMIMBF₄ could promote the electron transfer between HRP and electrode surface, and the existence of GG could successfully immobilize BMIMBF₄ on the electrode surface with improved stability. HRP–BMIMBF₄–GG/GCE exhibited a pair of well‐defined and quasireversible cyclic voltammetric peaks in 0.1 M pH 7.0 phosphate buffer solutions at 1.8 V/s, which was the characteristic of HRP Fe(III)/Fe(II) redox couples. The formal potentials (E°′) was ?0.368 V (vs. SCE) and the peak‐to‐peak potential separation (ΔE_P) was 0.058 V. The peak currents were five times as large as those of HRP–GG/GCE. The average surface coverage (Γ*) and the apparent Michaelis‐Menten constant (K_m) were 4.5×10^?9 mol/cm² and 0.67 μM, respectively. The electron transfer rate constant was estimated to be 15.8 s^?1. The proposed electrode showed excellent electrocatalytic activity towards hydrogen peroxide (H₂O₂). The linear dynamic range for the detection of H₂O₂ was 0.05–0.5 μM with a correlation coefficient of 0.9945 and the detection limit was estimated at about 0.02 μM (S/N=3). BMIMBF₄–GG composite film was promising to immobilize other redox enzymes or proteins and attain their direct electrochemistry.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin in Lipid Film Incorporated with Room‐Temperature Ionic Liquid

A facile phospholipid/room‐temperature ionic liquid (RTIL) composite material based on dimyristoylphosphatidylcholine (DMPC) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim]PF₆) was exploited as a new matrix for immobilizing protein. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were adopted to characterize this composite film. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. UV‐vis absorbance spectra showed that Hb still maintained its heme crevice integrity in this composite film. By virtue of the Hb/DMPC/[bmim]PF₆ composite film‐modified glassy carbon electrode (GCE), a pair of well‐defined redox peaks of Hb was obtained through the direct electron transfer between protein and underlying GCE. Moreover, the reduction of O₂ and H₂O₂ at the Hb/DMPC/[bmim]PF₆ composite film‐modified GCE was dramatically enhanced.     

Electrocatalytic Oxidation and Determination of Norepinephrine at Poly(Cresol Red) Modified Glassy Carbon Electrode

A glassy carbon electrode (GCE) was modified with electropolymerized films of cresol red in pH 5.6 phosphate buffer solution (PBS) by cyclic voltammetry (CV). The modified electrode shows an excellent electrocatalytic effect on the oxidation of norepinephrine (NE). The peak current increases linearly with the concentration of NE in the range of 3×10^?6–3×10^?5 M by the differential pulse voltammetry. The detection limit was 2×10^?7 M. The modified electrode can also separate the electrochemical responses of norepinephrine and ascorbic acid (AA). The separation between the anodic peak potentials of NE and AA was 190 mV by the cyclic voltammetry. And the responses to NE and AA at the modified electrode were relatively independent.     

Electrochemical Surface Structuring with Polyaniline Wrapped Hb for Hydrogen Peroxide Biosensing

Through the electrodeposition of aniline with hemoglobin (Hb) on zincoxide‐gold colloidal sols (ZnO‐AuNPs) modified indium oxide electrode, a hydrogen peroxide (H₂O₂) biosensor was constructed. Polyaniline (PANI) form a nano‐cage wrapped Hb, which provided a comfortable and stable site for the immobization of Hb. UV‐vis spectrum was employed to characterize Hb retained original structure in the resulting Hb‐PANI/ZnO‐AuNPs membrane. Electrochemical investigation of the biosensor showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa= ‐0.139 V and E_pc = ‐0.238 V (vs. SCE) in 0.1 M pH 7.0 phosphate buffer solution at the scan rate of 100 mV/s. The biosensor displayed a fast response time (<3 s) and broad linear response to H₂O₂ in the range from 1.5 μM to 1.7 mM with a detection limit of 0.8 μM (S/N = 3).     

Voltammetric Determination of Adrenaline Using a Poly(1‐Methylpyrrole) Modified Glassy Carbon Electrode

A voltammetric method using a poly(1‐methylpyrrole) modified glassy carbon electrode was developed for the quantification of adrenaline. The modified electrode exhibited stable and sensitive current responses towards adrenaline. Compared with a bare GCE, the modified electrode exhibits a remarkable shift of the oxidation potentials of adrenaline in the cathodic direction and a drastic enhancement of the anodic current response. The separation between anodic and cathodic peak potentials (ΔEp) for adrenaline is 30 mV in 0.1 M phosphate buffer solution (PBS) at pH 4.0 at modified glassy carbon electrodes. The linear current response was obtained in the range of 7.5 × 10^?7 to 2.0 × 10^?4 M with a detection limit of 1.68 × 10^?7 M for adrenaline by square wave voltammetry. The poly(1‐methypyrrole)/GCE was also effective to simultaneously determine adrenaline, ascorbic acid and uric acid in a mixture and resolved the overlapping anodic peaks of these three species into three well‐defined voltammetric peaks in cyclic voltammetry. The modified electrode has been successfully applied for the determination of adrenaline in pharmaceuticals. The proposed method showed excellent stability and reproducibility.     

Electrochemistry and Electrocatalysis of a Nafion/Nano‐CaCO3/Hb Film Modified Carbon Ionic Liquid Electrode Using BMIMPF6 as Binder

In this paper a room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) was used as binder for the construction of carbon ionic liquid electrode (CILE) and a new electrochemical biosensor was developed for determination of H₂O₂ by immobilization of hemoglobin (Hb) in the composite film of Nafion/nano‐CaCO₃ on the surface of CILE. The Hb modified electrode showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa and E_pc as ?0.265 V and ?0.470 V (vs. SCE). The formal potential (E°′) was got by the midpoint of E_pa and E_pc as ?0.368 V, which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The peak to peak separation was 205 mV in pH 7.0 Britton–Robinson (B–R) buffer solution at the scan rate of 100 mV/s. The direct electrochemistry of Hb in the film was carefully investigated and the electrochemical parameters of Hb on the modified electrode were calculated as α=0.487 and k_s=0.128 s^?1. The Nafion/nano‐CaCO₃/Hb film electrode showed good electrocatalysis to the reduction of H₂O₂ in the linear range from 8.0 to 240.0 μmol/L and the detection limit as 5.0 μmol/L (3σ). The apparent Michaelis–Menten constant (K_M^app) was estimated to be 65.7 μmol/L. UV‐vis absorption spectroscopy and FT‐IR spectroscopy showed that Hb in the Nafion/nano‐CaCO₃ composite film could retain its native structure.     

The determination of adrenaline on the porous gold film modified glassy carbon electrode

A simple method has been developed to prepare porous Au film-modified glassy carbon electrode (PAu/GCE). By using a simple electrodeposition process, a dense porous Au (PAu) film possessing good adhesion, large surface area, and mechanical integrity, was obtained. The surface characterization studies confirm that the formation of porous film constituted of Au nanoparticles. It was found, from the CV studies, that the prepared PAu modified electrode shows excellent catalytic activity for the electro-oxidation of adrenaline (AD) in a neutral medium. As to the electrochemical response of redox of adrenaline/adrenalinequinone couple in 0.1 M pH 7.0 phosphoate buffer solution (PBS), at the PAu/GCE, the anodic peak potential E _pa shifted by 50 mV negatively in the negative direction, compared to that on the Au film modified glassy carbon electrode (Au/GCE), indicating the extraordinary activity of PAu in electrocatalysis for the oxidation process of AD. The application of the modified electrode for the determination of AD in pharmaceutical preparations indicates that the PAu/GCE has good sensitivity and reproducibility.