Pair Of Redox Peaks Research Articles

Redox-Functionalized Graphene Oxide Architecture for the Development of Amperometric Biosensing Platform

We describe the redox functionalization of graphene oxide (GO) and the development of versatile amperometric biosensing platforms for clinically important analytes such as cholesterol ester, uric acid and glucose. Ferrocene (Fc) redox units were covalently tethered onto the GO backbone using diamine sigma spacers of different chain lengths (C3-, C6-, and C9-diamines). The functionalized GO (Fc-GO) displays a pair of redox peak corresponding to Fc/Fc(+) redox couple at ~0.225 V. The surface coverage and heterogeneous electron transfer rate constant of Fc-GO depends on the length of sigma spacer. Amperometric biosensors for cholesterol (total), uric acid and glucose have been developed by integrating Fc-GO and the respective redox enzymes with screen printed electrode. Fc-GO efficiently mediates the bioelectrocatalytic oxidation of the substrates in the presence of the redox enzymes. The spacer length of Fc-GO controls the bioelectrocatalytic response of the biosensing platforms. The sensitivity of the biosensors based on C9 sigma spacer is significantly higher than the others. The detection limit (S/N = 3) of the biosensors for cholesterol and uric acid was 0.1 μM and for glucose it was 1 μM. Excellent stability, reproducibility, selectivity and fast response time were achieved. Biosensing of cholesterol, uric acid and glucose in human serum sample is successfully demonstrated with the biosensors, and the results are validated with the clinical laboratory measurement.

Direct electrochemistry of hemoglobin immobilized on the water-soluble phosphonate functionalized multi-walled carbon nanotubes and its application to nitric oxide biosensing

The direct electron transfer and electrocatalysis of hemoglobin (Hb) immobilized on the phosphonate functionalized multi-walled carbon nanotubes (MWCNTs) are investigated. Fourier transform infrared (FT-IR) spectra, UV–vis spectra and cyclic voltammetry (CV) analyses reveal that the phosphonate functionalized MWCNTs have good biocompatibility for Hb immobilization, and promote the electron communication between Hb and electrode. The immobilized Hb shows a pair of redox peak with a formal potential of −406±10mV (vs. SCE) and the electrochemical behavior of Hb was a surface-controlled process in a pH 7.0 phosphate buffer solution. And the immobilized Hb can act in an electrocatalytic manner in the electrochemical reduction of nitric oxide (NO). Accordingly, an unmediated NO electrochemical biosensor is constructed. Under optimized experimental conditions, the NO electrochemical biosensor shows the fast response (less than 3s), the wide linear range (1.5×10−7 to 2.7×10−4M) and the low detection limit (1.5×10−8M), which is attributed to the good mass transport, the large Hb loading per unit area and the fast electron transfer rate of Hb.

Modulated Intermolecular Interactions in Ferrocenylalkanethiolate Self-Assembled Monolayers on Gold

Redox-labeled self-assembled monolayers (SAMs) on gold are excellent model systems for the study of long-range electron transfer processes at electrolyte–electrode interfaces, particularly the distance and reorganization energy dependences. In this work, we have shown that the intermolecular interaction among redox centers is in fact a crucial factor in the overall, nonideal electrochemical response of ferrocenylalkanethiolate SAMs on gold. In both single-component and high-ratio binary monolayers of 11-ferrocenyl-1-undecanethiol (FcC11SH), the two distinct pairs of redox peaks are corresponding to rather moderate differences in the packing densities of the two structural domains. We have discovered that the redox peak at lower potential becomes narrower and higher when organic solvents (nitrobenzene or octanol) are added to the aqueous electrolyte, while the peak at the higher potentials is barely influenced. On the basis of the Frumkin isotherm, we have obtained the intermolecular interaction parameters in the different structural domains of the monolayers by fitting the experimental data. The results showed that the intermolecular interaction in the FcC11S–Au SAMs can change from repulsion to attraction upon adding organic solvent in the aqueous electrolyte. It is suggested that the solvent perturbation to the SAM structure at monolayer/electrolyte interface induces remarkable change in the intermolecular interactions and therefore modulates the observed electrochemical responses from nonideal to nearly ideal.

Anodization strategy to fabricate nanoporous gold for high-sensitivity detection of p-nitrophenol

The anodization of a gold electrode in oxalic acid aqueous solution of different concentration has been investigated at different applied potentials, which enables the formation of nanoporous gold (NPG). Electrochemical measurements show that the electrochemically active surface areas of the as-anodized Au samples show an obvious potential, electrolyte concentration and time dependence. The as-prepared NPG samples were used as the working electrode to investigate the redox behavior of p-nitrophenol (p-NP) by cyclic voltammetry (CV). The CV profiles of NPG display a pair of redox peaks, and the peak current densities increase linearly with increasing p-NP concentration. Besides, o-nitrophenol (o-NP) has little influence on the electrochemical detection of p-NP. Through the anodization strategy, NPG electrodes with a high sensitivity and good selectivity can be developed to detect trace p-NP in water.

Hydrogen Peroxide Biosensor Based on Direct Electrochemistry of Hemin in Egg-Phosphatidylcholine Films

The mixture of egg-phosphatidylcholine( PC) vesicles and hemin was casted onto indium-tin oxide glass( ITO) electrode. The hemin showed a direct electrochemical behavior on the modified electrode. A welldefined pair of redox peaks was obtained from the cyclic voltammograms at the mixture of hemin and egg-PC modified ITO electrode. The average value of the surface coverage of electroactive hemin,Γ,was equal to3. 25 × 10!12mol / cm2. The formal potential( Eo') of hemin in the lipid film was linearly varied with the pH of phosphate buffer solution in the range from 4. 0 to 9. 0 with a slope of 43. 7 mV / pH. The pH value of buffer solution for measuring hydrogen peroxide was decided to be 4. 0. The linear range of our biosensor was from10 μmol / L to 200 μmol / L with a detection limit of 5 μmol / L. The modified electrode exhibited a good catalytic activity towards hydrogen peroxide. Therefore a third generation biosensor was developed.

Amperometric detection of hydrogen peroxide utilizing synergistic action of cobalt hexacyanoferrate and carbon nanotubes chemically modified with platinum nanoparticles

In this study, a novel composite of cobalt hexacyanoferrate nanoparticles (CoNP) and platinum nanoparticles (Pt) on carbon nanotubes (CNTs) is obtained by ultrasonically mixing CoNP synthesized in a microemulsion with CNTs chemically modified with platinum nanoparticles (Pt/CNTs). Cyclic voltammetric and amperometric measurements on a glass carbon electrode showed that the composite (called CoNP–Pt/CNTs) exhibits a well-defined pair of redox peaks and a prominent electrocatalytic activity toward hydrogen peroxide (H2O2) reduction. Besides, the current response of CoNP–Pt/CNTs is 2 orders of magnitude higher than the response of CoNP alone and 1 order of magnitude higher than the response of Pt/CNTs or CoNP/CNTs alone. This higher efficiency can be attributed to a remarkable synergistic effect between CoNP, Pt and CNTs. This sensor shows a linear response to H2O2 concentrations ranging from 0.2 μM to 1.25 mM with a detection limit of 0.1 μM, a maximum sensitivity of 0.744 A·M−1 and a fast response time below 2 s.

Synthesis and electrochemical properties of PANI–TiC nanocomposite and its electrocatalytic behavior

A novel nanocomposite (PANI–TiC) prepared from polyaniline (PANI) and titanium carbide (TiC) was synthesized through an in situ chemical oxidative polymerization method. Detected by scanning electron microscopy and Fourier transform infrared spectra, morphologies and compositions of the nanocomposite were characterized. Experimental results of cyclic voltammetry (CV) indicated that PANI–TiC on PANI–TiC/GCE showed three pairs of redox peaks in acid medium and a pair of obvious redox peak in neutral medium. Electrocatalysis for ascorbic acid (AA) revealed good catalytic performance with the linear range from 50μM to 2.25mM and a sensitivity of 13.3μAmM−1cm−2 in neutral medium. This simple synthesis technique of preparing PANI–TiC nanocomposites showed great potential applications in sensor, catalysis, biomedical, environmental analysis, and so on.

Synthesis and Electrochemical Behavior of LiTi2(PO4)3 as Anode Materials for Aqueous Rechargeable Lithium Batteries

Electrochemical intercalation of lithium ions into LiTi2(PO4)3 prepared by sol-gel method in 1 M Li2SO4 aqueous electrolyte solution was studied with cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS). It was found that there was one step of intercalation for LiTi2(PO4)3 anode in the presence of aqueous electrolyte, corresponding to a pair of redox peak at ESCE = −0.67/−0.86 V. The initial discharge capacity of the LiTi2(PO4)3‖LiMn2O4 cell is 44.41 mAh g−1, the capacity retention of 67.3% after 60 cycles. The EIS for LiTi2(PO4)3 electrode consisted of two semicircles in the aqueous electrolyte, which were attributed to Schottky contact resistance and charge transfer process, respectively.

One-step synthesis of PANI/Mn3O4 nanocomposites and evaluation of their electrochemical properties

In this paper, we have developed a simple, facile, and efficient approach to synthesize polyaniline/Mn3O4 (PANI/Mn3O4) nanocomposites using aniline as a reducer in the presence of KMnO4 without any additives or templates. The morphology of the composites is characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results demonstrate that the tetrahedral Mn3O4 nanoparticles have uniform sizes and are finely dispersed in the PANI matrix. The crystallinity and chemical constituents of the composites are characterized by powder X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and UV-vis spectrophotometry. Moreover, cyclic voltammetry (CV) measurements are used to characterize the electrochemical properties of PANI/Mn3O4 nanocomposites. The developed materials give a pair of redox peaks and have better operation stability, which indicates that the composites show distinct electrochemical performance. So the PANI/Mn3O4 nanocomposites would have potential applications in bioanalysis, biodetection and so on.

A nanostructured hybrid synthesized by the intercalation of CoTMPyP into layered titanate: Direct electrochemistry and electrocatalysis

A novel intercalation compound of layered titanate (K2Ti4O9) with 5,10,15,20-tetrakis(N-methylpyridinium-4-yl) porphyrinato cobalt(III), CoTMPyP, has been successfully synthesized through a guest–guest ion exchange route. Its structural characterization was carried out by means of XRD, IR, elemental analysis and SEM. The CV results of CoTMPyP–Ti4O9 modified electrode showed a pair of redox peaks and an irreversible cathodic peak corresponding to the stepwise reduction of CoIIITMPyP ion. The intercalated cobalt porphyrin also displayed its good electrocatalytic activity for the reduction of oxygen in neutral medium. The reduction peak current had a linear relationship with the square root of scan rates, indicating the catalytic reaction was governed by oxygen diffusion.

Simultaneous Determination of Nitrophenol Isomers Based on β‐Cyclodextrin Functionalized Reduced Graphene Oxide

Abstractβ‐CD modified reduced graphene oxide (RGO) sheets have been prepared and characterized by TEM, AFM, IR, EIS and CVs. In comparison with bare glass carbon electrode (GCE) and RGO modified GCE, CD‐RGO/GCE showed much higher peak currents to the reduction of nitrophenol isomers (NPs), attributed to the larger specific surface area of RGO and high quantities of host–guest recognition sites. Three pairs of redox peaks are observed on the CVs of CD‐RGO for p‐NP (0.3 V), o‐NP (−0.2 V) and m‐NP (0.05 V), separating well with each other. Under the optimized condition, the anodic peak currents were linear over ranges around 1–10 mg dm−3 for p‐NP, 1–9 mg dm−3 for o‐NP and 1–6 mg dm−3 for m‐NP, with the detection limits of 0.05 mg dm−3, 0.02 mg dm−3 and 0.1 mg dm−3, respectively. Thus, the CD‐RGO is expected to be a promising sensor material for detecting trace NPs in waste water.

Glycerol-Assisted Synthesis and Electrochemical Properties of Co<sub>3</sub>O<sub>4</sub> Nanowires

Cobalt oxide (Co O ) nanowires were controllably synthesized using glycerol and Co(NO ) as reagents and adjustment of the experimental parameters. The morphology and structure of the asprepared products were characterized by a series of techniques such as X-ray podwer diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical performance of the nanowires was studied by cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. It was found that two pairs of redox peaks appeared in the CV curves of Co O nanowire electrodes at low scan rates. The specific capacitance of the Co O nanowire electrodes was 163 F·g at a current density of 1 A·g , according to the galvanostatic charge-discharge measurements. Cycle stability tests showed that the specific capacitance increased over the first tens of cycles and then reduced slowly. After 1000 cycles, the capacitance retention was over 98% at 1 A·g and 80% at 4 A·g ; it then decreased obviously with further increase in cycle number. In Li-ion battery measurements, Co O nanowire electrodes showed a discharge capacitance of 1124 mAh·g which decreased rapidly during the cycle test. The formation mechanism and the relationship between the structure and electrochemical properties of Co O nanowires were discussed based on the experimental results.

Layered double hydroxide supported Prussian blue nanocomposites for electrocatalytic reduction of H2O2

Layered double hydroxide supported Prussian blue nanocomposites (denoted as LDH-PB) were successfully prepared via chemical method and characterized by Fourier transform IR, X-ray diffraction, transmission electron microscope (TEM) and cyclic voltammetry. With polyaniline, polystyrene sulfonate and LDH-PB the composite film could be immobilized on a glassy carbon electrode for electrochemical detection of hydrogen peroxide (H2O2). The fabricated electrode exhibited a well-defined pair of redox peaks and excellent electrocatalytic activity. The sensor response to H2O2 shows a linear range of 6.00 × 10−6–1.86 × 10−4 mol L−1 with a low detection limit of 0.38 μmol L−1 at a signal-to-noise ratio of 3. For the advantages of easy update, low cost and good stability, this sensor can be expected to be widely use in pharmaceutics, clinical diagnostics, and for industrial detection of hydrogen peroxide.

Polyaniline/polysulfone composite film electrode for simultaneous determination of hydroquinone and catechol

Polyaniline (PAN)/polysulfone (PSF) composite film electrodes were successfully prepared by electropolymerization using cyclic votammetry technique. The composite film electrodes show a great enhancement in electron transfer kinetics, and the separation between oxidation and reduction peaks (Δ E p) decreases from 200 to 35 mV for hydroquinone (H 2Q) and from 275 to 42 mV for catechol (CC) at bare Pt and composite film electrodes respectively. In their mixed systems, the redox peak of H 2Q and two pairs of redox peaks of CC on this composite film electrode could be obviously distinguished which indicates the composite film electrodes have excellent electrocatalytic activity and reversibility towards the oxidation of two diphenols (hydroquinone and catechol). The linear relationships between the peak current and concentration are observed for single solute and mixed systems within the certain concentration range, implying that the composite film electrodes have potential application in the qualitative or quantitative analysis of diphenol.

Nitrogen-doped carbon nanotube/polyaniline composite: Synthesis, characterization, and its application to the detection of dopamine

Nitrogen-doped carbon nanotubes (N-CNTs)/polyaniline (PANI) composites are developed as an electrode material for biosensors. The morphology, composition, and optical properties of the resulting products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet-visible absorption spectra (UV-vis). Furthermore, N-CNTs/PANI composite was immobilized on the surface of a glassy carbon electrode (GCE) and applied to construct a sensor. The obtained N-CNTs/PANI-modified GCE showed one pair of redox peaks and high catalytic activity for the oxidation of dopamine (DA) in a neutral environment. Differential pulse voltammograms results illustrate that the fabricated DA biosensor has high anti-interference ability towards ascorbic acid (AA). In addition, the fabricated biosensor showed superior performances with two wide linear ranges from 1 to 80 μM and from 1.5 to 3.5 mM and a low detection limit of 0.01 μM.

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.

Versatile functionalization of polyester hydrogels with electroactive aniline oligomers

AbstractFunctionalizing aliphatic polyester hydrogels with an aniline oligomer is a means of achieving electrically conductive and degradable hydrogels. To lower the aniline oligomer content while maintaining a high conductivity and to overcome the acidic degradation product from polylactide reported in our previous work, a series of electroactive and degradable hydrogels based on polycaprolactone (PCL) hydrogels and carboxyl‐capped aniline pentamer (CCAP) were synthesized by a simple coupling reaction at room temperature. The reaction was carried out between the hydroxyl groups of hydroxyethylmethacrylate in a photopolymerized glycidyl methacrylate (GMA)‐functionalized PCL‐poly(ethylene glycol)‐PCL degradable network and carboxyl group of CCAP, using 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide as water‐condensing agent and 4‐dimethylaminopyridine as catalyst. The electroactivity of the hydrogels was verified by cyclic voltammetry, which showed three pairs of redox peaks. The electrical conductivities and swelling ratios of these hydrogels were controlled by the CCAP content, the poly(ethylene glycol) molecular weight in the macromer, and the crosslinking density of the hydrogels. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Electrochemistry of a C84-C2(IV)-Modified Electrode in Aqueous Solutions and Its Interaction with Guanine

The electrochemistry of C84 isomer-modified electrodes was investigated in aqueous solutions. It is found that the C84-C2(IV) (denoted as C2(IV) for short)-modified electrode shows one pair of redox peaks, and its electrochemical responses depend on the nature of cations of the supporting electrolyte. Scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet−visible-near-infrared (UV−vis-NIR) spectral characterizations reveal that the pair of redox peaks originate from one-electron-transfer reduction and reoxidation of C2(IV) in the aqueous solution. Furthermore, interaction between C2(IV) and guanine has been investigated by electrochemistry, XPS, and UV−vis-NIR, and the results illustrate that C2(IV) and guanine have formed a charge-transfer complex.

Synthesis of electroactive tetraaniline-b-PEG diblock copolymer

A novel rod-coil diblock copolymer, tetraaniline-b-PEEG in short, was prepared from electroactive tetraaniline and hydrophilic poly (ethylene glycol) and characterized using infrared and UV-vis spectra. Gel permeation chromatography (GPC) was used to measure its molecular weight and molecular weight distribution, and a narrow molecular weight distribution of 1.29 stated that the resulting tetraaniline-b-PEG copolymer possessed uniform and nearly monodispersed block structures. The electroactivity of tetraaniline-b-PEG in hydrochloric acid aqueous solution was confirmed using cyclic voltammetry, and one pair of redox peaks was detected which could be attributed to the transition between LB and ES state of tetraaniline block in copolymer.

Electropolymerization of brilliant cresyl blue on carbon ionic liquid electrode and electrocatalytic application for the voltammetric determination of ascorbic acid

Brilliant cresyl blue (BCB) was electropolymerized on the surface of a carbon ionic liquid electrode (CILE) by cyclic voltammetric sweep in the potential range from -0.5 to 1.0 V. CILE was prepared by using 1-ethyl-3-methyl- imidazolium tetrafluoroborate ([EMIM]BF4) as modifier. The stable polymer film of BCB was obtained on the CILE and a pair of redox peaks appeared. The characteristics of PBCB film was studied by different methods such as scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. This modified electrode showed excellent electrocatalytic response to ascorbic acid with the increase of the electrochemical responses. Under the optimal conditions a good linear voltammetric response could be obtained over the range of 2.0x10-5-3.0x10-3 mol L-1 and the detection limit was got as 6.5 µmol L-1 (3σ).