Cyclic Voltammetric Peak Currents Research Articles

Switchable Bioelectrocatalysis of Glucose Oxidase Immobilized into Multilayers with Lamellar Nanoparticles of Amino-Functionalized Magnesium Phyllosilicate Clay

Lamellar organic clay consisting of amino-functionalized magnesium phyllosilicate (AMPC) with controllable positive charges was successfully prepared by simple one-pot synthesis. Then, the positively charged AMPC was assembled layer by layer with negatively charged glucose oxidase (GOx) enzyme into {AMPC/GOx} n multilayer films on pyrolytic graphite (PG) electrode surface, where n is the number of the bilayers. The {AMPC/GOx} n film electrodes demonstrated sensitive and reversible pH-responsive switchable behavior toward the cyclic voltammetric (CV) responses of the ferrocenedicarboxylic acid (Fc(COOH)2) probe in solution. The CV peak currents were strongly enhanced at pH 5.0 and were significantly reduced at pH 9.0. The pH-sensitive behavior of the system originated from the electrostatic interactions between the nanolayered films and Fc(COOH)2 in solution. This property was applied to realize pH-triggered electrocatalytically oxidation of glucose by GOx enzyme in the {AMPC/GOx} n films. This model system demonstrates the great potential perspective of the fabrication of novel multiple factor-switchable biosensors with immobilized enzymes.

Electrochemical performance of nanofibrous highly flexible electrodes enhanced by different structural configurations

Due to their unique physicomechanical properties, one dimensional (1D) nanostructured conductive materials offer remarkable potential as a flexible electroactive medium for developing miniaturized electronic devices such as supercapacitors, sensors and actuators. In this work, thin films composed of nanocomposite nanofibers with two different architectures, i.e. whiskered nanofibers (WNFs) and hierarchical-structured nanofibers (H-SNFs), were fabricated and their capability to serve as flexible and bendable electrodes were evaluated. The main difference of these two architectures is how the distributions of the nano-fillers (carboxylated multiwalled carbon nanotubes, CMWCNTs) through the nanofibers, i.e. the isotropic and anisotropic arrangements, lead to WNFs and H-SNFs, respectively. The percolation threshold of conduction for the H-SNFs (composed of 0.5 wt% CMWCNTs) and the WNFs (composed of 5 wt% CMWCNTs) were 0.13 S cm−1 and 0.07 S cm−1, respectively. Moreover, according to the electrochemical characterizations, although the WNFs had ten orders of magnitude higher nanotube content, the electroactivity and electron transfer rate of H-SNFs was considerably higher than those of WNFs, so that the cyclic voltammetric peak currents of H-SNFs was approximately 1.6 times higher than that of WNFs. As a proof-of-concept, our results indicate that the structural configuration is a major determinative factor, which can largely dictate the final electrical and electrochemical properties of the nanocomposite nanofibers. The bending durability results showed good electrochemical performance even upon 100 bending cycles with ±120° bending angles (retained 93.4% and 83.3% of the initial peak currents for H-SNFs and WNFs, respectively). These two flexible nanocomposite nanofibrous structures could be promising materials for the development of flexible electrodes for biosensing to energy storage applications.

Multiple-stimuli responsive bioelectrocatalysis based on reduced graphene oxide/poly(N-isopropylacrylamide) composite films and its application in the fabrication of logic gates.

In the present work, reduced graphene oxide (rGO)/poly(N-isopropylacrylamide) (PNIPAA) composite films were electrodeposited onto the surface of Au electrodes in a fast and one-step manner from an aqueous mixture of a graphene oxide (GO) dispersion and N-isopropylacrylamide (NIPAA) monomer solutions. Reflection-absorption infrared (IR) and Raman spectroscopies were employed to characterize the successful construction of the rGO/PNIPAA composite films. The rGO/PNIPAA composite films exhibited reversible potential-, pH-, temperature-, and sulfate-sensitive cyclic voltammetric (CV) on-off behavior to the electroactive probe ferrocenedicarboxylic acid (Fc(COOH)2). For instance, after the composite films were treated at -0.7 V for 7 min, the CV responses of Fc(COOH)2 at the rGO/PNIPAA electrodes were quite large at pH 8.0, exhibiting the on state. However, after the films were treated at 0 V for 30 min, the CV peak currents became much smaller, demonstrating the off state. The mechanism of the multiple-stimuli switchable behaviors for the system was investigated not only by electrochemical methods but also by scanning electron microscopy and X-ray photoelectron spectroscopy. The potential-responsive behavior for this system was mainly attributed to the transformation between rGO and GO in the films at different potentials. The film system was further used to realize multiple-stimuli responsive bioelectrocatalysis of glucose catalyzed by the enzyme of glucose oxidase and mediated by the electroactive probe of Fc(COOH)2 in solution. On the basis of this, a four-input enabled OR (EnOR) logic gate network was established.

Fabrication of molecular imprinted polymer sensor for chlortetracycline based on controlled electrochemical reduction of graphene oxide

A molecular imprinted polymer (MIP) sensor was fabricated by directly eletropolymerizing monomer o-phenylenediamine in the presence of template chlortetracycline (CTC), based on controlled electrochemical reduction of graphene oxide (GO) at cathodic potentials. In comparison with GO, the reduced GO (RGO) increased the cyclic voltammetric peak currents of [Fe(CN)6]3−/[Fe(CN)6]4− redox pair by a factor of about 300%, which was influenced by the amount of used GO and the reduction time. Integrating the excellent response amplification of RGO and the special recognition of MIP, the new MIP sensor was used to detect CTC indirectly by using [Fe(CN)6]3−/[Fe(CN)6]4− redox pair as an electrochemical probe. The electrochemical performances of the sensor were evaluated with cyclic voltammetry and differential pulse voltammetry (DPV). The MIP sensor exhibited a wide-range linear correlation between the peak current variation (ΔI) of the DPV cathodic peak and the concentration of CTC in the range of 10.0–500.0μM. The use of the RGO-based MIP sensor gave satisfactory results in the analysis of tap water and laboratory wastewater samples.

Triply switchable bioelectrocatalysis based on poly(N-isopropylacrylamide) hydrogel films with immobilized glucose oxidase

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel films containing glucose oxidase (GOD), designated as PNIPAM-GOD, were synthesized on the surface of pyrolytic graphite (PG) electrodes through radical cross-linking polymerization method. Cyclic voltammetric (CV) response of ferrocenecarboxylic acid (Fc(COOH)) at PNIPAM-GOD film electrodes was very sensitive to the environmental temperature, sulfate concentration, and addition of methanol solvent. For example, at 25°C, Fc(COOH) exhibited a quasi-reversible CV peak pair with large peak currents in pH 7.0 aqueous solutions containing no sulfate for the films; while at 37°C, the CV response was greatly suppressed. By switching the film electrodes in solutions between 25 and 37°C, the CV peak currents of Fc(COOH) cycled between a quite large value and a very small one, showing the reversible thermo-sensitive switching property between the on and off states. Similarly, the reversible SO42−- and methanol-sensitive on–off behavior of the films toward the probe was also observed. This triply responsive property could be used to realize the thermo-, SO42−-, and methanol-controlled electrochemical oxidation of glucose catalyzed by GOD immobilized in the films and mediated by Fc(COOH) in solution. This “smart” interface may establish a foundation for fabricating a novel type of multi-controllable biosensors based on bioelectrocatalysis.

PH-switchable bioelectrocatalysis based on layer-by-layer films assembled with glucose oxidase and branched poly(ethyleneimine)

Branched poly(ethyleneimine) (BPEI) and glucose oxidase (GOD) were assembled into {BPEI/GOD} n layer-by-layer films on the surface of electrodes mainly by electrostatic interaction between them. The cyclic voltammetric (CV) response of ferrocenedicarboxylic acid (Fc(COOH) 2) at {BPEI/GOD} n film electrodes was very sensitive to the environmental pH. The CV peak currents of Fc(COOH) 2 were quite large at pH 4.0 but greatly suppressed at pH 7.0, demonstrating reversible pH-sensitive on–off behavior. The factors influencing the pH-dependent switching behavior of the system were investigated. A series of comparative experiments supports the conclusion that the electrostatic interaction between the films and the probe plays a key role in deciding the pH-sensitive on–off behavior of the system. This smart interface could be used to realize pH-switchable electrocatalytic oxidation of glucose by GOD in the films and mediated by Fc(COOH) 2 in solution, which may establish a foundation for fabricating novel pH-controllable electrochemical biosensors based on bioelectrocatalysis with immobilized enzymes.

PH-Controllable Bioelectrocatalysis Based on “On−Off” Switching Redox Property of Electroactive Probes for Spin-Assembled Layer-by-Layer Films Containing Branched Poly(ethyleneimine)

Weak polybase branched poly(ethyleneimine) (BPEI) and strong polyacid poly(styrenesulfonate) (PSS) were assembled into BPEI/{PSS/BPEI}(n) layer-by-layer (LBL) films on electrodes by electrostatic interaction between them with spin-coating approach. The cyclic voltammetric (CV) response of ferrocenedicarboxylic acid (Fc(COOH)(2)) at BPEI/{PSS/BPEI}(n) film electrodes was very sensitive to the pH of the testing solutions. At pH 4.0, the probe showed a well-defined CV peak pair with relatively large peak currents for the films, while, at pH 7.0, the CV response was significantly depressed. By switching the film electrodes in buffers between pH 4.0 and 7.0, the CV peak currents changed periodically between a relatively high value at the "on" state and a very low value at the "off" state, indicating that the pH-sensitive "on-off" switching function of the films toward the probe is reversible. A series of comparative experiments indicates that the electrostatic interaction between the films and the probe plays a predominant role in deciding the pH-sensitive behavior of the films. This pH-dependent property of the films could be used to control or modulate the bioelectrocatalysis of glucose by glucose oxidase (GOD) with Fc(COOH)(2) as the mediator by changing the surrounding pH. This "smart" bioelectrocatalytic film system may establish a foundation for fabricating novel pH-controllable electrochemical biosensors.

Cyclic voltammetric detection of chemical DNA damage induced by styrene oxide in natural dsDNA layer-by-layer films using methylene blue as electroactive probe

In this work, an electrochemical sensor for detecting damage of natural double-stranded DNA (dsDNA) was constructed based on PSS/{PDDA/dsDNA} 3 layer-by-layer films, where PSS was poly(styrene sulfonate) and PDDA was poly(diallyldimethyl ammonium). When the PSS/{PDDA/dsDNA} 3 films assembled on pyrolytic graphite (PG) electrodes were immersed into methylene blue (MB) solution and loaded MB into the films, the formed PSS/{PDDA/dsDNA} 3-MB films in blank buffers at pH 7.0 showed a reversible cyclic voltammetric (CV) peak pair at −0.23 V vs. SCE for MB redox couple. In blank solutions, the MB loaded into the films was released gradually from the films, but the complete reloading of MB into the films could be realized by immersing the films into MB solution again, indicating the good reversibility of MB incorporation. However, after incubation in the solution of known genotoxic agent styrene oxide (SO), the damaged PSS/{PDDA/dsDNA} 3-MB films could not return to their original and fully-loaded state with reloading of MB, and showed smaller CV peak currents than those of intact PSS/{PDDA/dsDNA} 3-MB films. The relative peak current ratio, I p,I/ I p,III, where I p,I was the anodic peak current of intact DNA films in blank buffers after fully loading with MB and I p,III was that of SO-damaged DNA films after reloading with MB, increased linearly with the incubation time with SO in the range of 5–40 min with a damage rate of 0.0099 min −1. While the formation of SO adducts with dsDNA had no substantial effect on the dsDNA conformation, the steric hindrance of SO adducts with guanine or adenine blocked the intercalation of MB into the base pairs of dsDNA, resulting in the decrease of CV peak currents of loaded MB. The specific intercalation of MB into dsDNA base pairs and the sensitive electrochemical response of MB, combined with the unique feature of loading reversibility of MB in the DNA layer-by-layer films, make the difference in CV response between the intact and damaged dsDNA films become pronounced in the “loading/release/reloading” procedure. This may provide a new and general approach for constructing a biosensor for screening genetoxic chemicals in vitro.

Electrooxidation of methanol on polyaniline without dispersed catalyst particles

Electrooxidation of methanol in H 2SO 4 is studied on platinum and polyaniline (PANI) deposited platinum electrodes by cyclic voltammetry. In contrast to reports in the literature, which suggest the need of fine particles of a catalyst dispersed in PANI matrix for occurrence of electrooxidation of CH 3OH, in the present study, the reaction is shown to take place on PANI without additional catalyst particles at CH 3OH concentrations higher than 1 M. At lower concentrations, adsorption of CH 3OH occurs on PANI resulting in a reduction in intrinsic voltammetric peak currents of PANI in H 2SO 4. The kinetics of adsorption follows Langmuir isotherm. By a comparison of cyclic voltammetric peak currents of methanol on platinum and PANI deposited platinum electrodes, the catalytic efficiency of PANI towards oxidation of CH 3OH is evaluated.

Graphite Electrodes Coated with Poly(dimethyldiallylammonium)chloride Network Films Cross-Linked by Gamma-Irradiation

Properties of graphite electrodes coated with poly(dimethyldiallylammonium) chloride (PDMDAAC) are described. Gamma-irradiation was used to immobilize the polymer on the graphite surface by cross-linking the water-soluble polymer into an insoluble network. Immobilization of the network is aided by the high porosity of the graphite electrodes. Potassium ferricyanide was used as a model analyte to demonstrate electrochemical properties of the polymer modified electrode. Cyclic voltammograms of Fe(CN)63– at the PDMDAAC modified electrodes exhibit partitioning of the analyte into the polymer film. Chronocoulometry was used to determine the quantities of Fe(CN)63– trapped in the polymer network. The results of ion-exchange reactions of Fe(CN)63– with the PDMDAAC film were used to determine distribution coefficients (Kd) between the polymer film and the bulk solution of the analyte. Kd is 4000 for 0.01 M Fe(CN)63– in 0.2 M KCl. Analytical calibration plots of cyclic voltammetric peak currents for Fe(CN)63– at gamma-irradiated PDMDAAC/graphite electrodes were linear from 0.01 mM to 0.4 mM. Substantial enhancement of current signal was observed at the PDMDAAC modified graphite vs. bare electrodes. Variation in radiation dosage from 0.48 to 5.5 Mrad does not change the cross-link density of PDMDAAC on the graphite surface as evidenced by almost identical cyclic voltammograms of Fe(CN)63– at electrodes exposed to dosages over this range.

Electrochemical and spectroscopic studies on nickel(II/III) complexes with novel 14-membered hexaaza macrocycle functionalized with propenyl groups

A nickel(II) macrocyclic complex functionalized with propenyl groups, [Ni(1,8-di( n-propenyl)-1,3,6,8,10,13-hexaazacyclotetradecane)] 2+ {abbreviated as [Ni(A)] 2+}, has been synthesized by a simple template condensation reaction of the Ni 2+ ion, ethylenediamine, allylamine and formaldehyde in methanol. Spectral and electrochemical properties of the [Ni(A)] 2+ complex in various media have been investigated and compared with those of [Ni(1,8-dialkyl-1,3,6,8,10,13-hexaazacyclotetradecane)] 2+ complexes. The interaction of olefinic groups appended to the macrocycle with the nickel metal center is recognized by the spectral and electrochemical studies; in acetonitrile solution, the molar extinction coefficient of [Ni(A)] 2+ at λ max=458 nm grows up gradually and attains a maximum, and at the same time the cyclic voltammetric peak currents for the [Ni(A)] 2+/3+ redox couple decrease slowly with a concomitant growth of a new redox wave at more positive potentials. The first-order kinetic rate constants for the time dependent decrease of the peak currents of [Ni(A)] 2+/3+ redox couple are determined.

Host−Guest Interaction at a Self-Assembled Monolayer/Solution Interface: An Electrochemical Analysis of the Inclusion of 11-(Ferrocenylcarbonyloxy)undecanethiol by Cyclodextrins

A host−guest equilibrium involving the redox guest 11-(ferrocenylcarbonyloxy)undecanethiol (FcSH) in a self-assembled monolayer on gold electrode surfaces and a β-cyclodextrin (β-CD) host in solution is investigated. The effect of varying the ratio of FcSH to a diluent (n-decanethiol) in the self-assembly solution on the electrochemical characteristics of the ferrocene/ferricenium redox process and the inclusion properties of FcSH self-assembled monolayers (FcSH-SAMs) is examined using cyclic voltammetry and chronoamperometry. α- and γ-cyclodextrin have a negligible effect on both the thermodynamics and kinetics of the redox reaction. The electrochemical and ion-pairing behavior of FcSH-SAMs in solutions containing β-CD suggests that an inclusion complex is formed and that the included form of the ferrocenyl group is electroinactive in the potential window investigated. Inclusion results in a decrease in cyclic voltammetric peak currents (surface coverage of electroactive FcSH) and a slight increase in the standard electron transfer rate constant for the ferrocene/ferricenium redox process. The decrease in surface coverage of electroactive FcSH upon addition of β-CD exhibits a response similar to that expected for a Langmuir adsorption isotherm. Stability constants for the inclusion complexes of β-CD and the ferrocenyl or ferricenium forms of an FcSH-SAMs, containing a FcSH surface coverage of 5.2 × 10-11 mol cm-2, have been evaluated as 3.6 (0.4) × 104 and 3.2 (0.4) × 104, respectively. The stability constants thus evaluated were shown to be dependent on the surface coverage of FcSH in the FcSH-SAMs.

Covalent modification of carbon electrodes for voltammetric differentiation of dopamine and ascorbic acid

Conventional-size glassy carbon electrodes and glassy carbon fibre microelectrodes have been covalently modified with P-phenylacetate groups via a diazonium salt coupling procedure. Using catecholates of different charge, changes in electrode processes and accumulation or exclusion of analyte at the electrode surface are shown to be controlled by electrostatic interactions with surface groups. The modified electrodes have been assessed for the voltammetric differentiation of dopamine (DA) and ascorbic acid (AA). At the macroelectrode, the differential pulse peak current for oxidation of DA is significantly enhanced after modification of the electrode and that for AA is drastically decreased. The detection limit for DA at the modified electrode (measured as 3σ for 0.2 μM DA) is 90 nM, and the linear working range is 0.45–32.0 μM. Under optimized chronoamperometric conditions, the relative sensitivity for equimolar AA: DA is 0.43%. Modification of glassy carbon fibre microelectrodes leads to larger cyclic voltammetric peak currents for DA at fast scan rates and gives excellent resolution between the DA and AA signals in the differential pulse mode.

Determination of ultramicroelectrode array dimensions at graphite and one-dimensional organic conductor electrodes using simulations, chronocoulometry and chronoamperometry

The dimensions of ultramicroelectrode arrays at graphite and tetrathiafulvalene-tetracyanoquinodi-methane (TTF-TCNQ) electrodes were determined using a combination of chronoamperometry and a least squares optimization method which was used to fit simulated chronoamperometric responses to experimental data. The ultramicroelectrode array dimensions obtained from the fit were verified with chronocoulometry. The ultramicroelectrode array dimensions obtained for electrochemically treated TTF-TCNQ/poly(vinyl chloride) polymer paste electrodes are consistent with a transition from semi-infinite linear diffusion at slow scan rates to radial diffusion characteristic of ultramicroelectrode arrays at fast scan rates in plots of cyclic voltammetric peak currents vs. scan rate. Scanning electron micrographs of copper electrodeposited on these surfaces support the results obtained by chonoamperometry revealing the random structure of the ultramicroelectrode array. Chronoamperometric and chronocoulometric responses at polished TTF-TCNQ/poly(vinyl chloride), untreated glassy carbon and rough pyrolytic graphite electrodes do not reveal the presence of ultramicroelectrode array behavior. Scanning electron micrographs of electrodeposited copper on polished TTF-TCNQ/poly(vinyl chloride) electrodes demonstrate that the dimensions of the ultramicroelectrode array are too small to be resolved by the methods used. Chronocoulometric responses at electrochemically treated glassy carbon electrodes suggest the presence of a microhole array.

Electrocatalysis of oxygen reduction by water-soluble iron porphyrins: Thermodynamic and kinetic advantage studies

Several structurally modified water-soluble iron porphyrins have been synthesized and investigated for their catalytic behaviour toward oxygen reduction. The redox potentials for the iron(III/II) couple of the metallated species were in the order Fe(2-TMPyP) > Fe(4-TMPyP) > Fe(3-TMPyP) ( n-TMPyP = tetrakis( N-methyl- n-pyridyl)porphyrin), and paralleled those of the non-metallated forms in nitrogen-purged 0.05 M H 2SO 4, solution. The normalized cyclic voltammetric peak currents for the catalyzed reduction of oxygen as a function of catalyst concentration were approximately equivalent for Fe(4-TMPyP) and Fe(3-TMPyP), whereas the peaks were considerably lower for Fe(2-TMPyP). Iron tetrakis (2-aminophenyl)porphyrin, Fe(2-TAPP), appeared to absorb strongly on a glassy carbon surface to catalyze an overall four-electron reduction of oxygen at a rate constant of 8(±2) × 10 5 M −1 s −1. The adsorption shifted the E °' and p K a compared with those of the bulk Fe(2-TAPP). Results from CV, chronoamperometry and RRDE experiments were in agreement with the proposed EC mechanism. Effects of adsorption on the thermodynamic potential as well as the kinetic rate have been discussed.

Electrochemistry of various substituted aminophenyl iron porphyrins

Abstract The redox properties of dissolved, adsorbed and electropolymerized films of iron(III) tetrakis( o -aminophenyl)porphyrin (Fe(III) ( o -NH 2 )TPP), iron(III) tetrakis( p -aminophenyl)porphyrin (Fe(III) ( p -NH 2 )TPP) and iron(III) tetrakis( p - N, N ' -dimethylaminophenyl)porphyrin (Fe(III) ( p -NMe 2 TPP) have been studied in aqueous solutions. Cyclic voltammetry at glassy carbon electrodes for the complexes dissolved in 1 M HCl showed two Fe(III)/Fe(II) waves with cathodic peak potentials of −0.14 and −0.38 V for Fe( o -NH 2 )TPP, −0.15 and −0.36 V for Fe( p -NH 2 )TPP, and −0.17 and −0.45 V for Fe( p -NMe 2 )TPP. Differential pulse voltammetry also revealed two reduction waves for Fe( o -NH 2 )TPP adsorbed on a glassy carbon electrode (−0.16 and +0.08 V) and only one reduction process for Fe( p -NH 2 )TPP (−0.24 V) and Fe(NMe 2 )TPP (−0.25 V). The reduction peak potentials for the polymeric films at pH 3.2 ±0.2 are −0.22 and +0.12 V for poly[Fe( o -NH 2 )TPP], −0.22 and -0.07 V for poly[Fe( p -NH 2 )TPP and −0.18 and −0.02 V for poly[Fe( p -NMe 2 )TPP]. Thin-layer spectroelectrochemical techniques for the dissolved iron porphyrins and cyclic voltammetry for the polymeric films in strong acidic solutions indicated irreversible changes resulting from a demetallation process occurring upon reduction. The demetallation rate for the Fe(II) ( p -NMe 2 TPP compound (8×10 −4 s −1 ) was about 20-fold smaller than that of the Fe(II) ( p -NH 2 )TPP complex. In contrast, the polymeric films showed high stability at pH > 3: the cyclic voltammetric peak currents decreased by only 2% after 100 subsequent cycles in the potential range +0.4 to −0.8 V.