Irreversible Electrode Process Research Articles

The direct electrochemical detection of Salmonella paratyphi A

A novel biosensor based on the direct electrochemistry of Salmonella paratyphi A immobilized on pretreated glassy carbon electrode (PGCE) was established. It was essential that the trans-membrane and trans-wall direct electron transfer of guanine (G) in DNA strand inside viable Salmonella paratyphi A was captured by microwave irradiation for melting double-stranded DNA（dsDNA） into single-stranded DNA (ssDNA). When the microwave irradiation condition reached 100 W for 9 s, the oxidation peak current reached maximal levels in pH 6.0 phosphate buffer solution (PBS). Meanwhile the typical surface controlled and irreversible electrode process of G was revealed by cyclic voltammetry (CV) with participation of 2 protons and 2 electrons respectively. In addition, A linear relationship for the oxidation current of G with the logarithm of Salmonella paratyphi A concentration was established with the range from 2.10 × 103 to 2.10 × 106 CFU ∙ mL−1. The rapid quantification of viable Salmonella paratyphi A was achieved based on the direct electrochemical biosensor.

Direct electrochemistry & enzyme characterization of fresh tobacco RNA

The direct electrochemistry of fresh tobacco RNA on the surface of the pretreated glassy carbon electrode (PGCE) is researched. Tobacco RNA immobilized at PGCE shows good electrochemical activity in 0.10 M pH 7.5 phosphate buffer solution. The typical surface-controlled & irreversible electrode process of tobacco RNA was achieved by cyclic voltammetry and differential pulse voltammetry with the participation of two electrons and two protons, providing a paradigm for the direct electrochemical study of RNA. In addition, cyclic voltammetry and amperometry techniques are employed to demonstrate that tobacco RNA displays the characteristics of peroxidase and exhibits excellent electrocatalytic oxidation to H2O2. The electrochemical H2O2 sensor based on the RNA exhibits a good response, which shows a range of 5.0 × 10−6–2.5 × 10−4 M with a low detection limit of 1.7 × 10−6 M (S/N = 3).

The direct electrochemistry of viable Escherichia coli

• Microwave irradiation can melt dsDNA into ssDNA in E. coli and maintain its biological activity. • Trans-membrane and trans -wall direct electron transfer of E. coli was successfully realized. • Two electrons and two protons participated in the direct electron transfer of E. coli . We developed a novel method of microwave irradiation to deal with Escherichia coli ( E. coli ), realized the trans -membrane and trans -wall direct electron transfer of Guanine in viable E. coli . Typical surface controlled irreversible electrode process of E. coli was achieved by cyclic voltammetry with the participating of two electrons and two protons. The method of bacterium culture and colony count showed that the direct electrochemistry of E. coli could be realized with its biological activity maintained. In addition, the electrochemical parameters of E. coli were further achieved, which provided a paradigm for direct electrochemical study of other bacteria.

Electrochemical detection of hydrocortisone using green-synthesized cobalt oxide nanoparticles with nafion-modified glassy carbon electrode

Developing highly sensitive and selective sensors is important for the detection of steroid hormones. Electrochemical sensors are of great interest in this regard. Also utilization of bio-derived substances as an electrode material is environment friendly. In this study, we used green-synthesized cobalt oxide nanoparticles (CoO NPs) along with nafion (Naf) on a glassy carbon electrode to detect hydrocortisone (HC) by voltammetry. Electron microscopy, X-ray diffraction, Raman spectroscopy, ultraviolet–visible spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy were used to characterize the CoO NPs prepared using Nigella sativa seeds extract. Cyclic voltammetry and differential pulse voltammetry was utilized for the detection of HC. Only one reduction peak at −0.5 V was observed in the presence of HC in 0.1 M sodium hydroxide, indicating an irreversible electrode process. The Naf-CoO NPs enhanced the active surface area of the glassy carbon electrode (GCE) that resulted in a good response for detecting HC with two linear ranges: 0.001–1 μM and 1–9 μM. In comparison to other published electrochemical sensors, the current sensor displayed a low limit of detection of 0.49 nM, as well as remarkable stability and reproducibility. The sensor exhibited credibility for the sensing of HC in pharmaceutical injections and blood serum samples with recovery percentages ranging from 97.7% to 102.5%. The electrochemical sensor has proved to be valuable for HC detection.

Development of a Cytosensor for the Detection of Fusarium Oxysporum - A Functional Approach Towards Bioanalytical Applications

The development of bio-analytical methods for monitoring microorganisms have created opportunities for applications in biosensors, bioprocess monitoring, assessment of cell signalling, analysis of drug responses, among several others. The voltammetric sensing system employed for studying the electrode behavior of the fungus Fusarium oxysporum comprised working (gold) electrode (0.2 cm2 ) platinum as counter electrode (0.2 cm2 ) and a saturated calomel as the reference, where the electrochemical response corresponded to the growth phases (lag, log, stationary and decline) of the fungus. The electrochemical method based on voltammetric response matched well with the response obtained through conventional methodology, where the dry weight of the fungus is estimated against time. The peak potential is a function of scan rate, which is one of the characteristic features of a totally irreversible electrode process. It is important to mention here that this dependence is true regardless of reversibility for any diffusing redoxactive species. The proposed electrochemical method is less cumbersome and more accurate. Furthermore, the proposed electrochemical method captures the decline phase of fungal growth, which is generally difficult using the conventional method of assessment of the growth curve. Further experiments confirm that the anodic peaks were not due to the biomass or the fungal spores and only due to the extracellular metabolites. However, at this stage it is difficult to exactly determine the metabolite or the group of metabolites that are responsible for the anodic peak. In conclusion this cytosensor is capable of accurately and rapidly quantifying fungi with Fusarium oxysporum as a model organism.

Electrochemical Kinetics of Diffusion Problems with a Moving Phase Boundary

The growth and dissolution of nuclei and a deposit film on a solid electrode are considered. The diffusion problems of the growth and dissolution of hemispherical nuclei and a thin deposit film are solved. Equations are derived to describe the I–V characteristics and chronoamperograms of reversible, irreversible, and quasi-reversible electrode processes, and the dependences of the peak current, the amount of deposit on an electrode, the potential of the peak current, and the full width at half-maximum of an I–V characteristic on the preelectrolysis parameters are determined. The formation of a new phase at the solid–solution interface and the mass-exchange processes at the weakly soluble film–solution interface are discussed. Anodic films are experimentally studied. In the case of nuclei or a thin anodic film, the amount of compound formed on the electrode surface linearly depends on the ionic concentration and the preelectrolysis time.

Choline chloride based ionic liquids containing nickel chloride: Physicochemical properties and kinetics of Ni(II) electroreduction

The effect of Ni(II) salt content in ethaline (a deep eutectic solvent containing a mixture of ethylene glycol and choline chloride) on density, surface tension, viscosity and conductivity of ionic liquids has been investigated in the temperature range of 25 to 80°C. The introduction of NiCl2·6H2O into ethaline (ca. 0.1–1moldm−3 Ni(II)) causes an increase in the density, surface tension and viscosity of solutions and a decrease in their conductivity. The obtained results are explained in terms of hole theory. Both the electrical conductivity and the viscosity of ionic solutions under consideration are controlled by the availability of suitably sized holes in the liquid. The cyclic voltammetry study performed on nickel electrode shows an irreversible electrochemical behavior of the system Ni(II)/Ni, although the experimental results cannot be interpreted by means of common equations, derived for linear sweep voltammetric responses involving uncomplicated irreversible electrode processes. This may be due to the fact that the solutions do not contain an excess of supporting electrolyte and there is an appreciable migration contribution. In addition, our findings confirm previously developed concept according to that diffusion in ionic liquids disobeys the Stokes–Einstein equation and the transport behavior in ionic liquids cannot be described in terms of “classical” model of diffusion. The activation energy of the charge transfer for the reaction Ni(II) + 2e− → Ni in ethaline has been determined at constant values of electrode potential (the so-called formal activation energy).

Voltammetric behaviors of an emerging pollutant benzotriazole on multiwall carbon nanotubes (MWNTs)—Nafion modified electrode in various pH mediums

The electrochemical behaviors of an emerging pollutant, benzotriazole (BTA), at multiwall carbon nanotubes and Nafion modified glassy carbon electrode (MWNTs-Nafion/GCE) were investigated systematically. The electrochemical reduction of BTA was significantly improved by MWNTs-Nafion compared to bare GCE, ascribed to the excellent adsorption capacity and electrocatalytic activity of MWNTs. BTA presented well-defined reduction peaks only at pH <3.0, suggesting the involvement of lots of protons in the reduction process. Peak potential shifted negatively and peak current decreased significantly with pH increase. BTA showed various UV–Vis absorption spectra in acidic and alkaline mediums. Cathodic peak current increased linearly with square root of sweep rate as well as with the concentration of BTA from 3.0 × 10−6 to 1.6 × 10−4 mol L−1. This suggests a diffusion-controlled and irreversible electrode process. Diffusion coefficient of BTA on MWNTs-Nafion/GCE was obtained as 2.67 × 10−2 cm2 s−1 with four orders of magnitude larger than that on GCE. MWNTs-Nafion/GCE showed a good selectivity between BTA and O2 but poor selectivity between BTA and tolyltriazole.

Sensitive Hydrazine Electrochemical Biosensor Based on a Porous Chitosan–Carbon Nanofiber Nanocomposite Modified Electrode

A novel electrochemically-based biosensor was developed for the determination of hydrazine by modifying a glassy carbon electrode with an aqueous dispersion of carboxylic group-functionalized carbon nanofiber/chitosan solution, and then absorbing hemoglobin on the surface of chitosan-carbon nanofibers. Nafion was used to coat the hemoglobin membrane. The interactions of hemoglobin and the nafion/chitosan-carbon nanofibers were investigated by ultraviolet-visible absorption, infrared, and circular dichroism spectroscopies. The results indicated that the native structure of hemoglobin was retained post-immobilization. The circular dichroism results showed that the α-helical structure of hemoglobin was preserved though a small change was observed in the presence of the nafion/chitosan-carbon nanofibers. The modified nanofibers were further characterized by scanning electron microscopy, electron impendence spectroscopy, and cyclic voltammetry. The electrocatalytic mechanism of hemoglobin to the oxidation of hydrazine was investigated and an irreversible diffusion-controlled electrode process was obtained. The electron transfer rate constant (ks), transfer coefficient (α), and Michaelis–Menten constant (Km) were also evaluated. The peak current of the catalytic oxidation was linear with hydrazine concentration from 3.722 × 10−5 to 1.601 × 10−3 molar with a correlation coefficient of 0.995. The detection limit was estimated to be 2.7 micromoles per liter. The sensitivity, stability, and reproducibility of the nafion/hemoglobin/chitosan-carbon nanofiber/glassy carbon electrode for the oxidation of hydrazine were also investigated.

Surface modification imparts selectivity, facilitating redox catalytic studies: quinone mediated oxygen reduction

Modifying a gold electrode surface with hydroxy-alkyl-thiols significantly reduces the observed rate of electron transfer. This designed and controlled decrease in electron transfer rate readily allows reversible and irreversible electrode processes to be more clearly delineated. Separation of such voltammetric responses can facilitate the direct study of redox catalytic processes, which would, under other experimental conditions be obscured. The reduction of oxygen by anthraquinone hydroxy derivatives are used as a paradigmatic example, demonstrating the importance of the hydroxyl groups in the reduction process. Specifically, the reduced form of 1,8-dihydroxy-anthraquinone is shown to be significantly more reactive towards oxygen reduction than the 1,4-dihydroxyl analogue.

Electrodeposition of Sb(III) in alkaline solutions containing xylitol

The electrodeposition of antimony in alkaline solutions containing xylitol was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The antimony electrodeposition and the chemical stability of xylitol in alkaline solutions were studied by cyclic voltammetric technique. Apparent activation energy, apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetric technique. Initial stages of antimony electrocrystallization were determined by chronoamperometry. Xylitol in alkaline solutions exhibits high chemical stability and there is no redox in solutions when the potential ranges from −1.20 V to +0.60 V (vs Hg/HgO). There is no other redox reaction but hydrolysis occurring on stainless steel in the potential range of −1.75 V to 1.25 V (vs Hg/HgO) while the xylitol decomposition maybe take place on antimony electrode when potential is more negative than −1.70 V (vs Hg/HgO). Cyclic voltammograms with different scan rates indicate that the antimony electrodeposition process is an electrocrystallization which is a completely irreversible electrode process. The apparent activation energy, apparent transfer coefficient and exchange current density were calculated to be 46.33 kJ/mol, 0.64 and 4.40×10−6 A/m2, respectively. The analyses of the chronoamperometric responses support the view of a three-dimensional growth under progressive nucleation. The average diffusion coefficient of antimony was calculated to be 1.53×10−6 cm2/s.

Diffusive problem of Stephan and its solution for processes of electrodissolution of semispherical nuclei of the deposit

We modeled the processes of growth and dissolution of small amounts of deposit on the solid electrode. Quasi-stationary diffusion method solved the basic problem of growth and dissolution of the semi-spherical nuclei deposit. Equations are obtained for current–voltage curves and chronoamperogram for reversible and irreversible electrode processes of electrodissolution of deposit nuclei. We have derived relations for the peak current and peak potentials of the current–voltage curve.

Voltammetric Study of Adenine Complex with Copper on Mercury Electrode

AbstractThe determination of adenine (Ade), adenosine (Ado) and hydrolyzed adenosine (h‐Ado) in the presence of copper(II) ions is described by cyclic (CV) and elimination voltammetry with linear scan (EVLS) in connection with adsorptive stripping technique. Signals of adenine and copper‐adenine complex were measured on a hanging mercury drop electrode (HMDE) in buffered solutions with different pH. The differences in electrochemical behavior of Ade and Ado were found not only in dependence on the presence of copper ions, scan rate, Ade concentration and pH, but also on the accumulation time and potential where a copper‐Ade complex is formed. A deeper evaluation of voltammetric responses was carried out by EVLS. The EVLS function E4 eliminating charging and kinetic current components and conserving the diffusion current component was capable of enhancing the current sensitivity of CV peaks and of detecting electron transfer in adsorbed state. The irreversible electrode process of a totally adsorbed electroactive species is indicated by means of a peak‐counterpeak signal. Our results show that EVLS in connection with the adsorptive stripping procedure is not only a useful tool for both qualitative and quantitative microanalysis of Ade but also for revealing certain details in electrode processes.

Determination of the Diffusion Coefficient of Monosaccharides with Scanning Electrochemical Microscopy (SECM)

AbstractThe principle of a simple time of flight (TOF) diffusion coefficient measuring method is presented. It is based on the special capability of Scanning Electrochemical Microscopy (SECM). Its applicability has been investigated experimentally in comparison with conventional electrochemical methods. Complex irreversible electrode processes usually bring in uncertainty into electrochemical diffusion coefficient measurements. One of these, the electrochemical oxidation of saccharides in basic media at a copper electrode, was selected for the studies. Microsize copper electrodes used also as SECM tip, and conventional size copper electrodes were used. Diffusion coefficients of D‐glucose, D‐arabinose, D‐ribose, and D‐galactose were measured. The results prove the advantages of the SECM‐TOF method in the case investigated.

Synthesis, crystal structure, spectroscopic and electrochemical properties of nickel(II) dipicolinate complex with ethylisonicotinate

The diaqua(ethylisonicotinate)(pyridine-2,6-dicarboxylato)nickel(II) monohydrate complex was synthesized and characterized by spectroscopic (IR, UV/vis), X-ray diffraction and electrochemical methods. The Ni(II) ion is bonded to dipicolinate (dpc) through pyridine N atom and one O atom of each carboxylate group, two aqua ligands and N pyridine atom of ethylisonicotinate (ein), form the distorted octahedral geometry. The molecules are connected via O–H ··· O hydrogen bonds, forming motifs in three dimensional networks. IR and UV-Vis spectroscopies agree with the observed crystal structure. The voltammetric behaviour of the complex was investigated in aqueous solution by square-wave and cyclic voltammetry using a NH3/NH4Cl buffer. The square-wave voltammogram of the complex yields three reduction peaks at −0.88, −1.20 and −1.28 V. The irreversible reduction as a shoulder at −1.20 V is due to Ni-dpc-ein complex. The peak at −0.88 V corresponds to irreversible electrode process of Ni(II)-ein complex while the peak at −1.28 V is attributed to the reduction of the coordinated dpc ligands.

A novel nitrite biosensor based on the direct electron transfer of hemoglobin immobilized on CdS hollow nanospheres

A novel nitrite biosensor based on the direct electron transfer of hemoglobin (Hb) immobilized on CdS hollow nanospheres (HS-CdS) modified glassy carbon electrode was constructed. The direct electron transfer of Hb showed a pair of redox peaks with a formal potential of −286 mV (vs. SCE) in 0.1 M pH 7.0 phosphate buffer solution. It was a surface-controlled electrode process involving a single proton transfer coupled with a reversible one-electron transfer for each heme group of Hb. HS-CdS had a large specific surface area and good biocompatibility and had a better electrochemical response than that of solid spherical CdS. The immobilized Hb on HS-CdS displayed an excellent response to NO 2 − with one irreversible electrode process for NO reduction. Under optimal conditions, the biosensor could be used for the determination of NO 2 − with a linear range from 0.3 to 182 μM and a detection limit of 0.08 μM at 3σ based on the irreversible reduction of NO. HS-CdS provided a good matrix for protein immobilization and had a promising application in constructing sensors.

Direct electrochemistry of lactate dehydrogenase immobilized on silica sol–gel modified gold electrode and its application

The direct electrochemistry of lactate dehydrogenase (LDH) immobilized in silica sol–gel film on gold electrode was investigated, and an obvious cathodic peak at about −200 mV (versus SCE) was found for the first time. The LDH-modified electrode showed a surface controlled irreversible electrode process involving a one electron transfer reaction with the charge-transfer coefficient ( α) of 0.79 and the apparent heterogeneous electron transfer rate constant ( K s) of 3.2 s −1. The activated voltammetric response and decreased charge-transfer resistance of Ru(NH 3) 6 2+/3+ on the LDH-modified electrode provided further evidence. The surface morphologies of silica sol–gel and the LDH embedded in silica sol–gel film were characterized by SEM. A potential application of the LDH-modified electrode as a biosensor for determination of lactic acid was also investigated. The calibration range of lactic acid was from 2.0 × 10 −6 to 3.0 × 10 −5 mol L −1 and the detection limit was 8.0 × 10 −7 mol L −1 at a signal-to-noise ratio of 3. Finally, the effect of environmental pollutant resorcinol on the direct electrochemical behavior of LDH was studied. The experimental results of voltammetry indicated that the conformation of LDH molecule was altered by the interaction between LDH and resorcinol. The modified electrode can be applied as a biomarker to study the pollution effect in the environment.

Theoretical investigation on cyclic reciprocal derivative chronopotentiometry: Kinetic study of totally irreversible electrode processes

Theoretical expressions and mathematical analysis in cyclic reciprocal derivative chronopotentiometry (CRDCP) are presented for totally irreversible electrode processes corresponding to the application of symmetrical and unsymmetrical programmed currents. For two successive unsymmetrical programmed currents, the effect of the currents ratio b ( b = | I 2( t)/ I 1( t)|) on the (d t/d E)– E curves is discussed. The electrochemical behavior of totally irreversible electrode processes has been studied corresponding to the application of the unique unsymmetrical programmed Φ m ( I 0) proposed recently. CRDCP characteristic parameters obtained for totally irreversible electrode processes are different from those of reversible electrode processes. Therefore, a comparison of CRDCP between both mechanisms is presented. Based on the mathematical derivation, alternative methods for kinetic measuring are described. It is prospected that CRDCP is convenient and applicable for studying the reversibility of the electrode processes in form of CRDCP characteristic parameters.

Voltammetric Behavior of Antileukemia Drug Glivec. Part I – Electrochemical Study of Glivec

AbstractThe electrochemical behavior of the antileukemia drug glivec was investigated at a glassy carbon electrode (GCE). The oxidation is a complex, pH‐dependent, irreversible electrode process involving the transfer of 2 electrons and 2 protons and the formation of an electroactive product, Pglivec, which strongly adsorbs on the GCE surface and undergoes reversible oxidation. The adsorption of Pglivec at the GCE surface yields a compact monolayer that inhibits further oxidation of glivec. The electrochemical reduction is a simple pH dependent irreversible process involving the transfer of 2 electrons and 2 protons and occurs with the formation of a nonelectroactive product. The diffusion coefficient of glivec was calculated to be DO=7.35×10−6 cm2 s−1 in pH 4.5 0.1 M acetate buffer.

Electroanalytical Determination of Carbaryl in Natural Waters on Boron Doped Diamond Electrode

AbstractThe anodic voltammetric behavior of carbaryl on a boron‐doped diamond electrode in aqueous solution is reported. The results, obtained by square‐wave voltammetry at 0.1 mol L−1 Na2SO4 and pH 6.0, allow the development of a method to determine carbaryl, without any previous step of extraction, clean‐up, preconcentration or derivatization, in the range 2.5–30.0×10−6 mol L−1, with a detection limit of 8.2±0.2 μg L−1 in pure water. The analytical sensitivity of this electrochemical method diminished slightly, from 3.07 mA mmol−1 L to 2.90 mA mmol−1L, when the electrolyte was prepared with water samples collected from two polluted points in an urban creek. In these conditions, the recovery efficiencies obtained were around 104%. The effect of other pesticides (fenthion and 4‐nitrophenol) was evaluated and found to exert a negligible influence on carbaryl determination. The square‐wave voltammetric data obtained for carbaryl were typical of an irreversible electrode process with mass transport control. The combination of square‐wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.