Cyclic Voltammetry Response Research Articles

Application of Polarization Modulated Infrared Reflection Absorption Spectroscopy for electrocatalytic activity studies of laccase adsorbed on modified gold electrodes

Orientation of the enzyme macromolecule on the electrode surface is crucially important for the efficiency of the electron transport between the active site and electrode surface. The orientation can be controlled by affecting the surface charge and the pH of the buffer solution. In this contribution we study laccase physically adsorbed on gold surface modified by mercapto-ethanol, lipid and variously charged diazonium salts.Polarization Modulated Infrared Reflection Absorption Spectroscopy (PMIRRAS) enables the molecular orientation study of the protein molecule by comparison of the amide I to amide II band intensity ratios assuming that the protein secondary structure does not change. We observe significant differences in the intensity ratios depending on the kind of support and the enzyme deposition. The comparison of infrared spectra and cyclic voltammetry responses of variously prepared laccase layers reveals that the parallel orientation of beta-sheet moieties results in high enzyme activity.

Voltammetric behaviour of free DNA bases, methylcytosine and oligonucleotides at disposable screen printed graphite electrode platforms

Improvements in analytical methods for the determination and quantification of methylcytosine in DNA are vital since it has the potential to be used as a biomarker to detect different diseases in the first stage such as in the case of carcinomas and sterility. In this work we utilized screen printed graphite electrodes (SPGE) for studying the electrochemical response of all free DNA bases, methylcytosine and short oligonucleotides by cyclic voltammetry (CV) and square wave voltammetry (SWV). CV and SWV responses of free DNA bases and methylcytosine have been investigated by using SPGE platforms and the feasibility of detecting and quantifying cytosine and methylcytosine as free DNA moieties has been evaluated as a function of pH, concentration and the presence of the other free DNA bases in solution simultaneously. Repeatability of using SWV has been performed for the electrochemical behavior of both 250 μM cytosine and 250 μM methylcytosine in the presence of 25 μM guanine, with coefficient of variations of 6.9% and 2.6% respectively based upon peak current (N = 5). Six-mer oligonucleotides with a sequence 5'-XXXCGC-3', where the XXX motif corresponds to TTT, TTA, TAA and AAA have been performed using SWV in 0.1 M acetate buffer pH 5.0 to explore how the DNA base position effects the electrooxidation of guanine and cytosine into the oligonucleotide. Furthermore SWV comparisons of the electrooxidation of the oligonucleotides 5'-CGCGCG-3' and its methylated 5'-mCGmCGmCG-3' have been performed with concentrations in acetate buffer solutions, and the interaction of both oligonucleotides with the graphitic surface of the SPGE has been demonstrated by fitting well-known adsorption models such as Freundlich and Langmuir kinetics according to the SWV current response of guanine, cytosine and methylcytosine into the oligonucleotide.

The Morphologies of Pt Decorated on PANI Membrane and Effects on Glucose Biosensor

This paper mainly studies on the morphologies of Platinum(Pt) nanoparticles decorated on polyanilene(PANI)and their influence on the sensitivity of glucose biosensor. Seldom researches were carried on the morphologies of Pt nanoparticles and the optimization of parameters. Compared by scanning electron microscopy(SEM), cyclic voltammetry(CV) and glucose current response, Pt completely wrapped PANI nanofibers shows better electrochemical stability, sensitivity and larger catalytic area than different kinds of Pt decorated PANI membranes. Pt completely wrapped PANI nanofibers are provided by electrochemical deposition Pt nanoparticles on PANI nanofibers under a special voltage. The average diameter of nanofibers which form porous Pt/PANI membrane is 100 nm. CVs of this membrane become stable in seven circles and provide a higher current peak which indicates larger catalytic area. The sensitivity indicated by current-time glucose response is several times of the other membranes.

Controllable synthesis of silver nanodendrites on copper rod and its application to hydrogen peroxide and glucose detection

Silver nanodendrites were synthesized on Cu rods by a simple and facile displacement reaction without using any surfactants. The morphologies were investigated by scanning electron microscopy (SEM). The phase analysis of the dendritic nanostructure was revealed by X-ray diffraction (XRD). The element analysis was characterized by energy dispersive X-ray spectroscopy (EDS). Then a novel Ag nanodendrites/Cu rod electrode (named Ag NDS/CRE) based non-enzymatic hydrogen peroxide (H2O2) and glucose (GO) sensor was fabricated and evaluated by cyclic voltammetry (CV) and typical amperometric response (I–t) method. Exhilaratingly, the electrode shows significant electrocatalytic activity toward the reduction of H2O2 and oxidation of GO. Its advantage lies in its wide linear range from 0.2 mM to 19.2 mM for the detection of H2O2 with a low detection limit of 0.1 μM (S/N = 3) and also has a good response for GO with a linear range from 0.02 mM to 7.4 mM with the optimized detection limit of 0.1 μM (S/N = 3). The response time of the proposed electrode is less than 3 s. What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability.

In situ detection of dopamine using nitrogen incorporated diamond nanowire electrode

Significant difference was observed for the simultaneous detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA) mixture using nitrogen incorporated diamond nanowire (DNW) film electrodes grown by microwave plasma enhanced chemical vapor deposition. For the simultaneous sensing of ternary mixtures of DA, AA, and UA, well-separated voltammetric peaks are obtained using DNW film electrodes in differential pulse voltammetry (DPV) measurements. Remarkable signals in cyclic voltammetry responses to DA, AA and UA (three well defined voltammetric peaks at potentials around 235, 30, 367 mV for DA, AA and UA respectively) and prominent enhancement of the voltammetric sensitivity are observed at the DNW electrodes. In comparison to the DPV results of graphite, glassy carbon and boron doped diamond electrodes, the high electrochemical potential difference is achieved via the use of the DNW film electrodes which is essential for distinguishing the aforementioned analytes. The enhancement in EC properties is accounted for by increase in sp(2) content, new C-N bonds at the diamond grains, and increase in the electrical conductivity at the grain boundary, as revealed by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure measurements. Consequently, the DNW film electrodes provide a clear and efficient way for the selective detection of DA in the presence of AA and UA.

Direct electrochemistry and electrocatalysis of hemoglobin incorporated in composite film based on diblock weak polyelectrolyte PHAEMA-b-PDMAEMA and multi-walled carbon nanotubes

Abstract The new composite films composed of diblock weak polyelectrolyte poly(2-hydroxyethyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (PHEMA-b-PDMAEMA, noted as PHD in the later content) and multi-walled carbon nanotubes (MWCNTs) were applied to immobilize hemoglobin (Hb) for biosensor fabrication. The characterization of Hb/PHD/MWCNTs films were demonstrated by ultraviolet–visible (UV–vis) spectra, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and typical amperometric response ( i – t ) measurements. The immobilized Hb maintains its bioactivities and displays an excellent electrochemical behavior. The modified electrode exhibited good electrocatalytic activity to the reduction of hydrogen peroxide (H 2 O 2 ). The linear response range of the H 2 O 2 biosensor was from 1.0 × 10 −6 to 1.5 × 10 −3 M with a detection limit of 3.5 × 10 −7 M. The apparent Michaelis–Menten constant of Hb on the PHD/MWCNTs film was estimated to be 0.51 mM. These results indicated that the composite films have potential applicability of new types third-generation biosensors or bioreactors based on direct electrochemistry of the proteins.

Electropolymerization and properties of 3,4‐ethylenedioxythiophene backbone polymer with tetrathiafulvalene as pendant

AbstractThree 3,4‐ethylenedioxythiophene (EDOT) derivatives, including an EDOT‐tetrathiafulvalene (TTF) derivative, were synthesized by Steglich esterification of carboxylic acids with hydroxymethyl EDOT (3,4‐ethylenedioxythiophene methanol). The UV spectra showed that there was no distinctive intramolecular interaction for the EDOT–TTF monomer between the EDOT and the TTF moieties in the ground state; however, the cyclic voltammetry responses implied that such intramolecular interaction occurred. Electropolymerization in excessive potential could bring in strong overoxidation effects and degradation in the polymer film. The polymers were simulated using density functional theory with Gaussian03 package and the optimized HOMO and LUMO state were figured out. The conductivity of TTF‐polymer was 6 S·cm−1 obtained by galvano station and 4.8 × 10−3 S·cm−1 obtained by potentiostatic electropolymerization after doping with 7,7,8,8‐tetracyanoquinodimethane. The results indicated that this polymer was a reasonable candidate for conducting materials and it was meaningful to increase the conductive dimensions of TTF polymers by chemical doping. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Influence of oxidation state on the pH dependence of hydrous iridium oxide films

Many electrochemical reactions taking place in aqueous solution consume or produce protons. The pH in the diffusion layer can therefore be significantly altered during the reaction and there is a need for in situ pH measurements tracing this near surface pH. In the present paper the rotating ring disc technique was used to measure near surface pH changes during oxygen reduction, utilising hydrous iridium oxide as the pH sensing probe. Before such experiments a good understanding of the pH sensing properties of these films is required and the impact of the oxidation state of the film on the pH sensing properties was investigated as well as the influence of solution redox species. The pH sensitivity (depicted by dE/dpH) was found to depend on the average oxidation state of the film in a manner resembling the cyclic voltammetry response. In all cases the pH response is “supernernstian” with more than one proton per electron. The origin of this behaviour is discussed in the context of acid-base properties of the film and the existence of both hydrous and anhydrous oxide phases. The pH response depends also on the redox properties of the solution but can be optimised for various purposes by conditioning the film at different potentials. This was clearly illustrated by adding hydrogen peroxide, an intermediate in the oxygen reduction reaction, to the solution. It was shown that hydrous iridium oxide can be used as a reliable in situ pH sensor provided that care is taken to optimise the oxidation state of the film.

Layers of Polyaniline Nanotubes Deposited by Langmuir–Blodgett Method

The Langmuir–Blodgett (LB) method has long been used for the preparation of ultrathin films, offering the unique control over the film thickness and the molecular orientation. Here, we report on the deposition and the characterization of LB layers of polyaniline (PANI) nanotubes on solid supports. Stable suspension of the nanotubes in chloroform was obtained by adding sodium dodecyl sulfate (SDS). The nanotubes to SDS ratio is important for the stability of the suspension. Langmuir films were spread at the water/air interface and transferred on gold or ITO glass substrate. The electroactivity of obtained films was investigated using cyclic voltammetry. The degree of assembly of the PANI nanotubes in thin films was characterized by optical microscopy and scanning electron microscopy (SEM). To evaluate the molecular structure and the PANI oxidation state, UV–vis and Raman mapping were used. The PANI nanotube films on the gold support are electroactive with cyclic voltammetry responses closely resembling typ...

Voltammetric studies of hexachromic anion transfer reactions across micro-water/polyvinylchloride-2-nitrophenyloctylether gel interfaces for sensing applications

The transfer reactions of various anionic hexavalent chromium species across a polarized water/polyvinylchloride-2-nitrophenyloctylether (PVC-NPOE) interface featuring a 66 microhole array are described for the development of selective and sensitive Cr(VI) sensors. The transfer of hydrophilic hexachromic anions across a liquid/liquid interface typically involves setting the potential window in a negative region. Therefore, a highly hydrophobic tetraoctylammonium tetrakis(pentafluorophenyl)borate (TOATB) salt was synthesized and incorporated into the PVC-NPOE gel phase as an organic supporting electrolyte to provide a larger potential window at the negative end. The transfer of different hexachromic anions across the microhole array interface between the aqueous and PVC-NPOE gel phase containing TOATB was first characterized by voltammetric measurements. Since Cr(VI) ion species can hold different anionic forms such as Cr2O72−, HCrO4−, and CrO42− depending upon the pH and the Cr(VI) concentration, the effect of these two parameters on the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) responses was also investigated. In order to utilize the ion transfer reaction across the microhole array interface for the selective and sensitive detection of Cr(VI) ions, the assisted transfer of HCrO4− anion by an Aliquat 336 ionophore incorporated into the PVC-NPOE gel phase was investigated using CV and differential pulse stripping voltammetry (DPSV). An excellent detection limit of 0.5μM (26ppb) with a wide linear dynamic range extending from 0.5μM to 10μM was achieved.

Structural variations in polynuclear copper(II) complexes based on salicylaldimine type ligands along with dicyanamido co-ligand

Two new polynuclear complexes of Cu(II), [(CuL1)Cu(N3C2)2]n (1) and [(CuL2)2Cu(N3C2)2]·H2O (2), have been synthesized by reacting the “ligand complexes”, [CuL1] and [CuL2] respectively with copper perchlorate and sodium dicyanamide (NaN3C2) in ethanol–water, where the di-Schiff base ligands H2L1=N,N′-bis(salicylidene)-1,3-propanediamine and H2L2=N,N′-bis(α-methylsalicylidene)-1,3-propanediamine. Structural analysis shows that complex 1 is a 2D polymer formed by linking the dinuclear units through a μ1,5-dicyanamido bridge. It contains alternating helical chains of P and M types. Complex 2 is a discrete bent trinuclear species where phenoxido groups of two terminal “ligand complexes” coordinate to a central Cu(II) along with terminally coordinated dicyanamido anions. Both complexes exhibit irreversible reductive Cu(II)/Cu(I) and quasi-reversible oxidative Cu(II)/Cu(III) responses in cyclic voltammetry. The electrochemically generated Cu(I) species for both complexes are unstable and undergo disproportionation to Cu0 and Cu2+.

Cyclic voltammetry response of an undoped CVD diamond electrodes

Abstract The polycrystalline undoped diamond layers were deposited on tungsten wire substrates by using hot filament chemical vapor deposition (HFCVD) technique. As a working gas the mixture of methanol in excess of hydrogen was used. The morphologies and quality of as-deposited films were monitored by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy respectively. The electrochemical activity of the obtained diamond layers was monitored by using cyclic voltammetry measurements. Analysis of the ferrocyanide–ferricyanide couple at undoped diamond electrode suggests that electrochemical reaction at diamond electrode has a quasireversibile character. The ratio of the anodic and cathodic peak currents was always close to unity. In this work we showed that the amorphous carbon admixture in the CVD diamond layer has a crucial influence on its electrochemical performance.

Fabrication of a novel hydrogen peroxide biosensor based on Au-(PEO106PPO70PEO106) hairy nanospheres

Abstract In this case, the Au-F127 (triblock copolymer PEO 106 PPO 70 PEO 106 , PEO is short for polyethylene oxide and PPO is the abbreviation of polypropene oxide) hybrid hairy nanospheres were obtained by the redox reaction using pluronic F127 and HAuCl 4 as precursor. A novel hemoglobin (Hb) biosensor was fabricated by immobilizing the Hb onto the Au-F127 film on the surface of glassy carbon electrode (GCE). The Au-F127 nanocomposites and Hb were characterized by transmission electron microscopy (TEM), polycrystalline electron diffraction ring pattern and ultra-violet visible spectra (UV–vis). UV–vis spectra suggested that Hb in the film could keep its native secondary structure. The performances of Hb/(Au-F127) on GCE were characterized with cyclic voltammetry (CV) and typical amperometric response ( i – t ) measurements. The immobilized Hb maintained its bioactivity and displayed an excellent electrochemical behavior with a formal potential of −339 mV. The resulting electrode showed an electrocatalytic activity to hydrogen peroxide (H 2 O 2 ). The linear response range of the H 2 O 2 biosensor was from 3.0 × 10 −7 to 5.7 × 10 −4 M with a low detection limit of 4.0 × 10 −8 M.

Chiral Interactions of the Drug Propranolol and α1-Acid-Glycoprotein at a Micro Liquid–Liquid Interface

The investigation of chiral interactions of drugs with plasma proteins is of fundamental importance for drug efficacy and toxicity studies. In this paper, we demonstrate a simple liquid-liquid interface procedure for investigating chiral interactions. Chiral discrimination of the enantiomers of a basic drug, propranolol, was achieved at a micro liquid-liquid interface, using α(1)-acid-glycoprotein (AGP) as a chiral acute phase plasma protein. When the protein is added to an aqueous phase containing the enantiomers of propranalol hydrochloride, the binding of (S)- and (R)-propranolol hydrochloride to the protein results in a decrease in the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) current responses corresponding to the decrease in transfer of propranolol at an aqueous-1,2-dichloroethane interface. This decrease is a consequence of the complexation of the drug and the protein. The complex drug-protein does not transfer across the interface nor changes the transfer potential of the uncomplexed form of propranolol enantiomers. The bound concentration of propranolol enantiomers in the presence of AGP was found to be greater for (S)-propranolol than (R)-propranolol for solutions containing constant concentrations of AGP (50 μM). Scatchard analysis yielded association constants of 2.7 and 1.3 × 10(5) M(-1) for (S)- and (R)-propranolol, respectively.

Electrochemistry and Electrocatalysis of Myoglobin Loaded into Multilayer Films Assembled with Phytic Acid and Chitosan

Natural polymer polysaccharides chitosan (CS) was successfully assembled with phytic acid (PA) into {PA/CS}n layer-by-layer films. Myoglobin (Mb) could be gradually “absorbed” or loaded into {PA/CS}n films when the films were immersed into Mb solutions, forming {PA/CS}n-Mb films. The {PA/CS}n-Mb films demonstrated well-defined and quasi-reversible cyclic voltammetry (CV) responses for Mb FeIII/FeII redox couple and were used to catalyze electrochemical reduction of oxygen and hydrogen peroxide. The interaction between Mb and {PA/CS}n films was explored and discussed, which suggested that the electrostatic attraction might play a major role in loading Mb into the films. This new kind of film incorporated with redox proteins could be used to fabricate the new type of biosensors or bioreactors without using mediators.

Au NPs–Ni(OH)2–Cu nanocomposites enhanced electrochemical properties for detection of H2O2

Ni(OH)2 nanoplates grown on Cu substrate were synthesized by a simple hydrothermal method. Au nanoparticles were dropped onto Ni(OH)2 nanoplates according to optimal ratio to get Au NPs–Ni(OH)2–Cu nanocomposites. These were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray energy dispersive spectrometer (EDS). The electrode (Au NPs–Ni(OH)2–Cu/glassy carbon electrode) constructed by the composites was evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and typical amperometric response (i-t). Its wide linear range covered 2.5 μM to 1229.5 μM for the detection of peroxide hydrogen (H2O2), the optimized detection limit 0.3 μM (S/N = 3) and the response time was less than 3 s. Besides, the proposed electrode showed satisfactory selectivity, and good stability.

Immobilization of double functionalized carbon nanotubes on glassy carbon electrodes for the electrochemical sensing of the biotin–avidin affinity

Multi-walled carbon nanotubes (MWCNTs) double functionalized with redox-active ferrocene and biotin ( Fc–Biot-MWCNTs) were synthesized and used for the electrochemical detection of avidin. After dispersion in perfluorosulfonated polymer Nafion and immobilization on the electrode surfaces, the cyclic voltammetry response of the modified electrodes showed in aqueous medium a quasi-reversible one-electron system at 0.46 V vs. SCE, assigned to the bound ferrocene/ferrocenium redox couple. Upon the addition of avidin in the range 0.9–20 nM, a stepwise decrease of both anodic and cathodic peak currents ascribed to the ferrocene was observed. These electrochemical changes are specifically due to the formation of biotin–avidin complex and are explained by complexation-induced modifications in the environment of covalently bound ferrocene.

Polymer-based technology platform for robust electrochemical sensing using gold microelectrodes

Rapid and inexpensive development of electrochemical sensors with good exploitation potential may be produced using a polymer as a substrate material. However, fabrication of polymer-based sensors is challenging. Using photolithography and etching of gold-coated poly(ethylene-2,6-naphthalate) (PEN), we have succeeded in fabricating disk-shaped and interdigitated microelectrodes (μEs). The electrodes have an excellent adhesion to the polymer and are encapsulated using a novel room-temperature process, applicable for low-cost, high-throughput fabrication. The PEN surface has been characterized in respect of wettability, surface energy and surface roughness. Finally, the electrodes give stable and reproducible electrochemical impedance spectroscopy and cyclic voltammetry responses, using the redox couple ferrocyanide and ruthenium hexamine. The results demonstrate the robustness and functionality of the polymer-based sensor platform with minimum feature sizes of 6 μm.

Electrooxidation of chloro, nitro, and amino substituted phenols in aqueous medium and their heterogeneous kinetics

The present study deals with the electrochemical investigation of seven different phenols through cyclic voltammetry (CV). Phenols can be partly eliminated from aqueous solutions by electrochemically initiated polymerization. Thus, the basic CV behavior was studied under the optimized conditions such as; pH of the medium, concentration of the analyte, the supporting electrolyte, potential window, and scan rate. The CV curves of all of the phenols showed that the electro-polymerization phenomenon on the electrode surface causes surface fouling for further electrooxidation of these compounds. The influence of substituents in the ring was especially noted in terms of their tendency to foul the electrode surface. The formation of new intermediates during the electrooxidation was observed whose nature was found to be highly dependent on the type and position of the substituent. As far as the influence of pH is concerned, phenols in basic medium were electrooxidized earlier but with low current. Difference in CV response because of the substituent attached under varied pH was also noted. From the diffusion coefficient (D) and heterogeneous rate constant (ksh) mixed nature of electron transfer process was proposed.

Synthesis, Spectroscopic Studies, Crystal Structure and Electrochemical Properties of New Cobalt(III) Complex Derived from 2-Aminophenol and 4-(Dimethylamino)Cinnamaldehyde: Nano-Sized Complex Thin Film Formation via Surface Layer-by-Layer Chemical Deposition Method

New Schiff base (HL) ligand is prepared via condensation of 2-aminophenol and 4-(dimethylamino) cinnamaldehyde. The cobalt complex with the formula of [Co(L)2(MePy)2]PF6 is prepared in good yield from the reaction of the ligand with cobalt(II) acetate. The compounds were characterized by the analytical and spectroscopic methods. The ligand (HL) behaves as a bidentate ligand and coordinates to the cobalt ions via the nitrogen and oxygen atoms with mononuclear structure. The ligand (HL) has been structurally characterized by X-ray crystallography. There is O–H···N–H bond linking the molecules together. FT-IR spectra show that HL is coordinated to the cobalt ion in a mono-negative bidentate manner with ON donor sites of the azomethene N and deprotonated phenolic-OH. There are two methylpyridine molecules apically coordinated to Co(III) ion in octahedral environment. Electrochemical properties were investigated as metal centres in the dimethylformamide solvents. The Co(III) complex exhibit both irreversible reductive (CoIII/CoII; Epc, −1.24 V) and oxidative (CoII/CoIII; Epa, +0.79 V, respectively) responses in cyclic voltammetry. Thin film of nano-sized [M(L)2(MePy)2]PF6 complex was formed by surface layer-by-layer chemical deposition method. The formation of uniform thin films of nano-crystalline metal complex is dependent on metal and ligand concentrations.