Redox Peak Currents Research Articles

Anion-Exchange-Based Amperometric Assay for Heparin Using Polyimidazolium as Synthetic Receptor

This study demonstrates a facile yet effective strategy for amperometric assay of electrochemically inactive heparin based on an anion-exchange mechanism with polyimidazolium (Pim) as the synthetic receptor. The rationale for the amperometric heparin assay is essentially based on the different binding affinity of the synthetic Pim receptor toward electrochemically active ferricyanide (Fe(CN)6(3-)) and electrochemically inactive heparin. To accomplish the amperometric assay, Pim is first synthesized and used as the artificial receptor to recognize the anions (i.e., Fe(CN)6(3-) and heparin). The stronger binding affinity of the synthetic Pim receptor toward heparin than toward Fe(CN)6(3-) essentially validates the amperometric heparin assay through an anion-exchange mechanism with the decrease in the redox peak current of Fe(CN)6(3-) adsorbed onto the Pim film as the signal readout. The anion exchange between Fe(CN)6(3-) and heparin on the Pim receptor is verified by cyclic voltammetry and Fourier transform IR and UV-visible spectroscopies. The ratio of the current decrease shows a linear relationship with heparin concentration with a concentration range from 0.5 to 10 μM. With animal experiments by dosing intraperitoneally and collecting the serum sample, the method is demonstrated to be potentially useful for investigating heparin metabolism in the biological system. This study not only provides a simple yet effective route to a heparin assay but also opens a new way to developing amperometric methods for electrochemically inert species by fully utilizing the supramolecular principles.

Electrochemical characterization of the redox couple of Fe(III)/Fe(II) mediated by grafted polymer reference electrode (GPRE)

A grafted polymer reference electrode (GPRE) (polystyrene grafted with acrylonitrile as a monomer using gamma irradiation) was fabricated as a reference electrode using cyclic voltammetry (CV). The redox process of K3Fe(CN)6 during CV was studied. It was found that the redox current peaks of Fe(II)/Fe(III) in 0.1 M of KCl as supporting electrolyte is given the same oxidation–reduction current as in the Ag/AgCl reference electrode, indicating a good result of GPRE and, hence, it can be used for voltammetric analysis technique. The physical properties of GPRE include good hardness, insoluble in non-aqueous electrolytes (except dimethyl formamide and chloroform), and good stability at different solvents. In addition, the sensitivity under conditions of CV is significantly dependent on the scan rate (SR) and variation in concentration. At different SRs, redox peaks of K3Fe(CN)6 were observed in a reversible process: Fe(II)/Fe(III). Interestingly, the redox reaction of Fe(II)/Fe(III) solution using GCE versus GPRE remains constant even after 15 cyclings. It is therefore evident that the GPRE possesses some degree of stability. Also, the new reference electrode GPRE has improved the properties of electroanalysis of CV on the working electrode GCE in reliability with the relative standard deviation.

Graphene-MnO2 nanocomposite modified carbon ionic liquid electrode for the sensitive electrochemical detection of rutin

In this paper a carbon ionic liquid electrode (CILE) was fabricated with ionic liquid N-hexylpyridinium hexafluorophosphate, which was further modified by a graphene (GR)-MnO2 nanocomposite to get an electrode denoted as GR-MnO2/CILE. Due to the presence of GR-MnO2 nanocomposite on the electrode surface the electrochemical performances of the modified electrode were greatly enhanced. The fabricated electrode showed strong electrocatalytic ability to the electrochemical reaction of rutin with a pair of well-defined redox peaks appeared. Compared with other modified electrodes, the increase of redox peak currents and the decrease of peak-to-peak separation appeared, which could be attributed to the synergistic effects of the materials used. Electrochemical parameters of rutin on GR-MnO2/CILE were calculated with the electron transfer coefficient as 0.5, the electron transfer number as 1.81, the apparent heterogeneous electron transfer rate constant as 1.61s−1 and the diffusion coefficient as 1.57×10−4cm2/s. Under the selected conditions the reduction peak current was in linear with rutin concentration from 0.01 to 500.0μmol/L with the detection limit as 2.73nmol/L (3σ) by differential pulse voltammetry. The proposed method was further applied to the rutin tablet samples determination with satisfactory results.

Glassy carbon electrodes modified with gold nanoparticles for the simultaneous determination of three food antioxidants

Electrochemical behavior of three antioxidants: butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and butylated hydroquinone (TBHQ), was investigated at a glassy carbon electrode modified with gold nanoparticles (AuNPs/GCE). This electrode was characterized by scanning electron microscopy (SEM). The experimental results indicated that the modified electrode was strongly electroactive during the redox reactions of BHA, BHT and TBHQ, and this was confirmed by the observed increased redox peak currents and shifted potentials; in addition, the oxidation products of BHA and TBHQ were found to be the same. The experimental conditions were optimized and the oxidation peaks of BHA and BHT were clearly separated. Based on this, an electrochemical method was researched and developed for the simultaneous determination of BHA, BHT and TBHQ in mixtures with the use of first derivative voltammetry; the linear concentration ranges were 0.10–1.50μgmL−1, 0.20–2.20μgmL−1 and 0.20–2.80μgmL−1, and detection limits were 0.039, 0.080 and 0.079μgmL−1, for BHA, BHT and TBHQ, respectively. The proposed method was successfully applied for the analysis of the three analytes in edible oil samples.

Carbon Encapsulated FeCu4 Alloy Nanoparticles Modified Glass Carbon Electrode to Promote the Degradation for P–Nitrophenol

The electrochemical redox of p–nitrophenol was carried out with bare glassy carbon electrode modified by carbon encapsulated FeCu4 alloy nanoparticles by cyclic voltammetry. The reductive peak potential was positively moved and the value of redox peak currents were increased compared to the based on bare GCE. The conditions of the scan rate and the stability were also discussed. Through the cyclic voltammograms, we can know that the catalytic activity of the FeCu4/C nanoparticles increased with increasing the scanning rate in the range from 50 to 100 mVs–1. The results indicated that the bare GCE modified with FeCu4/C demonstrated perfect catalytic activity and stability for the degradation of p–NP.

Investigation into the crystal structure of bis(pyridine)-bis(trichloroacetato) copper(II) and its electrophotochemical properties

A novel chained Cu(II) complex was synthesized from trichloroacetato copper(II) and pyridine in ethanol solvent, and characterized by elemental analysis and infrared (IR) spectroscopy. The special crystal structure of the Cu(II) complex was determined by X-ray single-crystal diffraction. The results indicate that a chained structure of the Cu(II) complex formed through intermolecular hydrogen bonds. Cu(CCl3COO)2(C5H5N)2(H2O) was monoclinic, with unit cell P21/c and cell parameters as follows: a = 14.389(3) A, b = 7.1911(14) A, c = 23.107(8) A, V = 2,257.5(10) A3, Z = 4, M r = 564.51, D c = 1.661 mg/m3, T = 293(2) K, F(000) = 1,124, μ(Mo Kα) = 1.704 mm−1, R = 0.0984, and ωR = 0.2791. The electrochemical behavior of the Cu(II) complex on a glassy carbon working electrode determined by cyclic voltammetry showed the electrochemical activity of the title compound at 0.2 to −0.3 V (versus SCE) in NH3–NH4Cl buffer solution (pH 9.2), and the redox peak current of the complex had a good linear relationship with the square root of the scan rate in the range 0.02–0.2 V/s.

Charge–transfer interaction between melamine and quinones: Towards voltammetric determination of melamine

This communication describes a new voltammetric method for the determination of melamine based on the charge–transfer interaction between quinones and melamine. Three types of quinones, i.e., tetrachloro-p-benzoquinone (TCBQ), benzoquinone (BQ), and vitamin K1 (VK1) were employed in this study. The charge–transfer interaction activity of quinones with melamine was found to depend on the structure of quinones, of which TCBQ with four electron-withdrawing chloro groups exhibits the highest interaction activity with melamine. Such a property was further employed for the voltammetric determination of melamine based on the decrease in the redox peak currents of TCBQ/TCBQ− caused by the pre-consumption of TCBQ with melamine. Under the conditions employed in this study, the decrease in the peak current of TCBQ was linear with the concentration of melamine within a concentration range from 10μM to 1.0mM.

Application of graphene–SnO2 nanocomposite modified electrode for the sensitive electrochemical detection of dopamine

In this paper a nanocomposite prepared by graphene (GR) and SnO2 nanosheets was used to modify a N-hexylpyridinium hexafluorophosphate based carbon ionic liquid electrode. The presence of GR–SnO2 nanocomposite on the electrode surface exhibited synergistic effects to improve the electrochemical performance of the modified electrode. Electrochemical behaviors of dopamine (DA) on the electrode were evaluated by cyclic voltammetry and differential pulse voltammetry. The results indicated that the GR–SnO2 nanocomposite modified electrode displayed high electrocatalytic activity to the oxidation of DA with the increase of the redox peak currents and the decrease of the peak-to-peak separation. Under the selected conditions the oxidation peak current was proportional to the DA concentration in the range from 0.5 to 500.0μmol/L with a detection limit of 0.13μmol/L (S/N=3). The modified electrode showed excellent selectivity and sensitivity even in the presence of high concentration of uric acid. The proposed method was applied to determine DA content in real samples with satisfactory results.

Multiwall carbon nanotube–CdS/hemoglobin multilayer films for electrochemical and electrochemiluminescent biosensing

This paper presents both electrochemical and electrochemiluminescence (ECL) detections based on the layer-by-layer (LBL) films fabricated with hemoglobin (Hb) and the optimal nanocomposite containing multiwall carbon nanotubes (MWCNTs) and CdS quantum dots (QDs). Hb and the MWCNT–CdS nanocomposite were electrostatically assembled on the chitosan (CS) modified glassy carbon electrode (GCE) forming with up to six bilayer films. Our results on cyclic voltammograms (CVs) revealed that the redox peak currents of Hb at the six-bilayer film ({MWCNT–CdS/Hb}6) modified GCE were the largest. Hydrogen peroxide (H2O2) could be stably detected using the six bilayer films modified GCE with a wide linear range from 0.125 μM to 1.20 mM. Nitrite (NO2−) could also be determined through CdS QDs of the multilayer films based on stable ECL intensities with a linear range from 0.60 μM to 0.80 mM.

Synthesis of cyclodextrin-reduced graphene oxide hybrid nanosheets for sensitivity enhanced electrochemical determination of diethylstilbestrol

β-Cyclodextrin functionalized reduced graphene oxide hybrid nanosheets (β-CD-RGO) were successfully prepared by using l-ascorbic acid (l-AA) as the reducing agent under a mild condition and used as enhanced material for sensitivity determination of diethylstilbestrol (DES). In 0.1M PBS (pH 7.0), the redox peak currents of DES increased significantly on β-CD-RGO modified glassy carbon electrode (β-CD-RGO/GCE), suggesting that the composite film not only shows excellent electronic properties of RGO sheets but also exhibits high supramolecular recognition capability of β-CD. The experimental conditions were optimized and the kinetic parameters were investigated. Under the optimal conditions, the reduction peak current of DES increased linearly with increasing the concentration in the range from 0.01 to 13μM with the detection limit of 4nM (S/N=3). The developed electrochemical sensor exhibited high selectivity, good stability and reproducibility, and also successfully determined DES in milk samples with satisfactory results.

An amperometric sensor for the determination of benzophenone in food packaging materials based on the electropolymerized molecularly imprinted poly-o-phenylenediamine film

Benzophenone is one of the most commonly used photoinitiators of UV-cured inks on food packaging materials and can migrate into foodstuffs. In this study, an amperometric benzophenone sensor based on molecularly imprinted polymer (MIP) was successfully constructed for the first time. The sensor was prepared by electropolymerizing o-phenylenediamine (o-PD) on a glassy carbon electrode (GCE) in the presence of template benzophenone, and then removing the template by immersing the poly-o-phenylenediamine film-modified GCE in ethanol. The molecularly imprinted sensor was tested in the presence or absence of benzophenone by cyclic voltammetry and linear sweep voltammetry to verify the changes in the redox peak currents of potassium ferricyanide. The sensor responded sensitively to benzophenone over a linear range of 0.05–5μM with a detection limit of 10nM. The imprinted sensor showed high recognition ability for benzophenone and was successfully applied to the determination of benzophenone in food packaging material samples.

Direct electrochemistry of glucose oxidase immobilized on TiO2–graphene/nickel oxide nanocomposite film and its application

A novel electrochemical platform based on nickel oxide (NiO) nanoparticles and TiO2–graphene (TiO2–Gr) was developed for the direct electrochemistry of glucose oxidase (GOD). The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The experimental results demonstrated that the nanocomposite well retained the activity of GOD and the modified electrode GOD/NiO/TiO2–Gr/GCE exhibited excellent electrocatalytic activity toward the redox of GOD as evidenced by the significant enhancement of redox peak currents in comparison with bare GCE. The biosensor responded linearly to glucose in the range of 1.0–12.0 mM, with a sensitivity of 4.129 μA mM−1 and a detection limit of 1.2 × 10−6 M under optimized conditions. The response time of the biosensor was 3 s. In addition, the developed biosensor possessed good reproducibility and stability, and there was negligible interference from other electroactive components.

Electrochemical behavior and DNA-binding properties of binuclear copper(II) complex containing mixed ligands of N-hydroxyethylaminoethyl oxamido and 2,2′-bipyridine

The electrochemical property of dinuclear copper(II) complex containing mixed ligands of N-hydroxyethylaminoethyl oxamido and 2,2′-bipyridine [Cu2(bpy)2(HAO) 2 2+ ] was studied with cyclic voltammetry. Cu2(bpy)2(HAO) 2 2+ had irreversible oxidation peaks in 0.1 mol/L NaCl solution at the stearic acid-modified carbon paste electrode. Cyclic voltammetry and absorption spectra measurements were used to study the interaction between Cu2(bpy)2(HAO) 2 2+ and herring fish sperm DNA. All the experimental results showed that Cu2(bpy)2(HAO) 2 2+ interacted with DNA mainly through electrostatic affinity to make tiny difference between Cu2(bpy)2(HAO) 2 2+ –ssDNA and Cu2(bpy)2(HAO) 2 2+ –dsDNA. The binding ratio and the binding constant of DNA–Cu2(bpy)2(HAO) 2 2+ were calculated as 1:1 and 6.41 × 104, respectively. The redox peak current of Cu2(bpy)2(HAO) 2 2+ decreased markedly after its interaction with DNA. This was used to detect the concentration of DNA quantitatively.

Synthesis and Ag-content-depended electrochemical properties of Ag/ZnO heterostructured nanomaterials

Ag/ZnO core/shell heterostructured nanomaterials were for the first time synthesized by Ag nanoparticle-mediated method, using which a novel hydrogen peroxide biosensor could be constructed. TEM and XRD measurements revealed that the Ag/ZnO heterojunctions were successfully acquired. Moreover, their sizes and shapes depended on Ag nanoparticles concentrations (i.e., Ag/ZnO-1, Ag/ZnO-2, and Ag/ZnO-3 heterojunctions were prepared using one-, two-, and three-fold Ag nanoparticles, respectively). Electrochemical measurements indicated that electrochemical properties of the Ag/ZnO-x-based biosensors also associated with the Ag nanoparticle content and the Hb–Nafion–Ag/ZnO-2 biosensor had the best electrochemical property, strongest redox peak currents and smallest ΔEp of about 40mV. Moreover, the Ag/ZnO-2-based biosensor displayed excellent electrocatalytic properties such as wide linear range (2–540μM), high sensitivity (83mAcm−2mol−1), low detection limit (0.18μM), and good stability and reproducibility.

Preparation of electrochemically reduced graphene oxide-modified electrode and its application for determination of p-aminophenol

A simple and eco-friendly electrochemical method to reduce graphene oxide precursor was employed for fabrication of graphene sheets modified glassy carbon electrode, and then, the resulting electrode [electrochemically reduced graphene oxide (ERGO)/glassy carbon electrode (GCE)] was used to determine p-aminophenol. The experimental results demonstrated that the modified electrode exhibited excellent electrocatalytic activity toward the redox of p-aminophenol as evidenced by the significant enhancement of redox peak currents and the decreased peak-to-peak separation in comparison with a bare GCE. A highly sensitive and selective voltammetry determination of p-aminophenol is developed using the ERGO/GCE. This method has been applied for the direct determination of p-aminophenol in artificial wastewater.

Inlaid Nd-substituted bismuth titanate nanoplates for protein immobilization and Nd-controlled electrochemical properties

Neodymium (Nd) substituted bismuth titanate (Bi4−xNdxTi3O12, BNTO-x) nanoplates inlaid one another were prepared by sol–gel hydrothermal method, which was explored for protein immobilization and biosensor fabrication. Comparative experiments witnessed that Bi3+ ions in bismuth titanate (Bi4Ti3O12, BTO) were successfully substituted with Nd3+ ions, and the electrochemical properties of the Hb–Chi–BNTO biosensors closely depended on the Nd3+ ion content. With increasing the Nd3+ doping content, the electrochemical performance of the Hb–Chi–BNTO-x biosensors showed regularly variable. Moreover, compared with the Hb–Chi–BTO and other Hb–Chi–BNTO-x biosensors, the Hb–Chi–BNTO-0.85 biosensor had more excellent electrochemical and electrocatalytic properties such as stronger redox peak currents (approximately three-fold), smaller peak-to-peak separation (50mV), larger heterogeneous electron transfer rate (14.1±3.8s−1), higher surface concentration of electroactive redox protein (about 8.16×10−11mol/cm2), and better reproducibility and stability. The Nd-depended electrochemical properties of the Hb–Chi–BNTO biosensors may open up a new idea for designing third-generation electrochemical biosensors, and the BNTO-0.85-based biosensor is also expected to find potential applications in many areas such as biomedical, food, and environmental detection.

Electrochemical Determination of Melamine with a Glassy Carbon Electrode Coated with a Multi-Wall Carbon Nanotube/Chitosan Composite

A simple and rapid electrochemical determination method of melamine with a glassy carbon electrode coated with a multi-wall carbon nanotube/chitosan composite was developed using differential pulse voltammetry. Herein the diameter of multi-wall carbon nanotubes enwrapped with chitosan is about 28 nm and it is larger than that of as-prepared multi-wall carbon nanotubes (a diameter of 20 nm). The results indicated that the redox peak currents of [Fe(CN)6]3−/4− were linear while the melamine concentration range from 9.9 × 10−9 to 1.9 × 10−7 M. The linear coefficient of the redox peak current was 0.998 and the detection limit was 3.0 × 10−9 M. The proposed method was applied to analyze the content of melamine in Yili milk of China. The calculated concentration of melamine in this experiment was 4.2 × 10−6 M and the recovery rate was up to 104.8%.

A label-free electrochemical immunosensor for carbofuran detection based on a sol-gel entrapped antibody.

In this study, an anti-carbofuran monoclonal antibody (Ab) was immobilized on the surface of a glassy carbon electrode (GCE) using silica sol-gel (SiSG) technology. Thus, a sensitive, label-free electrochemical immunosensor for the direct determination of carbofuran was developed. The electrochemical performance of immunoreaction of antigen with the anti-carbofuran monoclonal antibody was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), in which phosphate buffer solution containing [Fe(CN)6]3−/4− was used as the base solution for test. Because the complex formed by the immunoreaction hindered the diffusion of [Fe(CN)6]3−/4− on the electrode surface, the redox peak current of the immunosensor in the CV obviously decreased with the increase of the carbofuran concentration. The pH of working solution, the concentration of Ab and the incubation time of carbofuran were studied to ensure the sensitivity and conductivity of the immunosensor. Under the optimal conditions, the linear range of the proposed immunosensor for the determination of carbofuran was from 1 ng/mL to 100 μg/mL and from 50 μg/mL to 200 μg/mL with a detection limit of 0.33 ng/mL (S/N = 3). The proposed immunosensor exhibited good high sensitivity and stability, and it was thus suitable for trace detection of carbofuran pesticide residues.

Magnetic-Field-Assisted Assembly of Layered Double Hydroxide/Metal Porphyrin Ultrathin Films and Their Application for Glucose Sensors

The ordered ultrathin films (UTFs) based on CoFe-LDH (layered double hydroxide) nanoplatelets and manganese porphyrin (Mn-TPPS) have been fabricated on ITO substrates via a magnetic-field-assisted (MFA) layer-by-layer (LBL) method and were demonstrated as an electrochemical sensor for glucose. The XRD pattern for the film indicates a long-range stacking order in the normal direction of the substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the MFA LDH/Mn-TPPS UTFs reveal a continuous and uniform surface morphology. Cyclic voltammetry, impedance spectroscopy, and chronoamperometry were used to evaluate the electrochemical performance of the film, and the results show that the MFA-0.5 (0.5 T magnetic field) CoFe-LDH/Mn-TPPS-modified electrode displays the strongest redox current peaks and fastest electron transfer process compared with those of MFA-0 (without magnetic-field) and MFA-0.15 (0.15 T magnetic field). Furthermore, the MFA-0.5 CoFe-LDH/Mn-TPPS exhibits remarkable electrocatalytic activity toward the oxidation of glucose with a linear response range (0.1-15 mM; R(2) = 0.999), low detection limit (0.79 μM) and high sensitivity (66.3 μA mM(-1) cm(-2)). In addition, the glucose sensor prepared by the MFA LBL method also shows good selectivity and reproducibility as well as resistance to poisoning in a chloride ion solution. Therefore, the novel strategy in this work creates new opportunities for the fabrication of nonenzyme sensors with prospective applications in practical detection.

Voltammetric response of ferroceneboronic acid to diol and phenolic compounds as possible pollutants

A voltammetric determination of possible organic pollutants such as diol and phenolic compounds in water was studied using ferroceneboronic acid (FBA) as a redox-active marker. A cyclic voltammogram of FBA exhibited a pair of oxidation and reduction peaks at 230 and 170 mV at pH 7.0, respectively, while another pair of redox peaks was observed in the presence of diol or phenolic compounds tested. The results were rationalized based on the formation of boronate esters of FBA with the added compounds. The changes in the redox peak currents were dependent on the concentration of the additives, suggesting a usefulness of FBA in the electrochemical determination of these compounds in water.