Direct Electron Transfer Process Research Articles

Direct electron transfer of glucose oxidase and biosensing of glucose on hollow sphere-nanostructured conducting polymer/metal oxide composite

A hollow sphere-nanostructured conductive polymer/metal oxide composite was synthesized and used to investigate the electrochemical behavior of glucose oxidase, demonstrating a significantly enhanced direct electron transfer ability of glucose oxidase. In particular, the long-standing puzzle of whether enzymatic glucose sensing involves an enzyme direct electron transfer process was studied. The results indicate the mechanism is indeed a glucose oxidase direct electron transfer process with competitive glucose oxidation and oxygen reduction to detect glucose. A glucose biosensor with the glucose oxidase-immobilized nanomaterial was further constructed, demonstrating superior sensitivity and reliability, and providing great potential in clinical applications.

Conjugated polymers and an iron complex as electrocatalytic materials for an enzyme-based biofuel cell

Poly-5,2′:5′,2″-terthiophen-3′-carboxylic acid (polyTTCA) and poly-Fe(III)-[N,N′-bis[4-(5,2′:5′,2″-terthien-3′-yl)salicyliden]-1,2-ethanediamine] (polyFeTSED) were synthesized and electrochemically polymerized on an Au surface for use as mediators and catalysts for a biofuel cell. The atomic force microscopy (AFM) images of (a) the TTCA homopolymer (polyTTCA) and (b) the TTCA–FeTSED copolymer (poly(TTCA–FeTSED)) layers show a nanoparticle structure. The enzymes (glucose oxidase (GOx) or horseradish peroxidase (HRP)) were immobilized onto the conducting polymer layer through covalent bond formation, which allowed for direct electron transfer processes of the enzymes. A quartz crystal microbalance (QCM) revealed that the surface coverages of GOx and HRP were 4.21×10−12M and 9.65×10−12M, respectively. The anode with immobilized GOx and the cathode with immobilized HRP were used as model enzyme systems in biofuel cells for glucose and H2O2 detection, respectively. The biofuel cell composed of the GOx/polyTTCA/Au and the HRP/poly(TTCA–FeTSED)/Au electrodes was assembled and examined for cell performance. The copolymer of polyFeTSED complex with polyTTCA revealed a catalytic activity for the electrochemical reduction of H2O2 and resulted in approximately a sevenfold increase in the power density of the biofuel cell over that of polyTTCA itself. Moreover, the conjugated polymers extend the biofuel cell lifetime to 4 months through the stabilization of immobilized enzymes. The biofuel cell operated in a solution containing glucose and anode-produced H2O2 generated an open-circuit voltage of approximately 366.0mV, while the maximum electrical power density extracted from the cell was 5.12μWcm−2 at an external optimal load of 25.0kΩ.

Direct electrochemistry of glucose oxidase and biosensing for glucose based on carbon nanotubes@SnO2-Au composite

Multiwalled carbon nanotubes@SnO2-Au (MWCNTs@SnO2-Au) composite was synthesized by a chemical route. The structure and composition of the MWCNTs@SnO2-Au composite were confirmed by means of transmission electron microscopy, X-ray photoelectron and Raman spectroscopy. Due to the good electrocatalytic property of MWCNTs@SnO2-Au composite, a glucose biosensor was constructed by absorbing glucose oxidase (GOD) on the hybrid material. A direct electron transfer process is observed at the MWCNTs@SnO2-Au/GOD-modified glassy carbon electrode. The glucose biosensor has a linear range from 4.0 to 24.0mM, which is suitable for glucose determination by real samples. It should be worthwhile noting that, from 4.0 to 12.0mM, the cathodic peak currents of the biosensor decrease linearly with increasing the glucose concentrations in human blood. Meanwhile, the resulting biosensor can also prevent the effects of interfering species. Moreover, the biosensor exhibits satisfying reproducibility, good operational stability and storage stability. Therefore, the MWCNTs@SnO2-Au/GOD biocomposite could be promisingly applied to determine blood sugar concentration in the practical clinical analysis.

Direct electrochemistry and electrocatalysis of hemoglobin on nanostructured gold colloid-silk fibroin modified glassy carbon electrode

In this paper, the electrochemical behavior of Hb assembled on glassy carbon (GC) electrode modified with nanostructured gold colloid-silk fibroin (NGC-SF) was investigated. Electrochemical results show that direct electron transfer of the immobilized Hb occurs as indicated by a couple of quasi-reversible redox peaks with a formal potential of −0.38 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer. This direct electron transfer process is accompanied by proton exchange and thus the formal potential of Hb changes linearly with solution pH in the range from pH 6.0 to 8.0 with a slope value of −45.2 mV/pH. In addition, the immobilized Hb retains its native catalytic activity to H 2O 2 without the aid of any electron mediator. This indicates that the presence of NGC-SF can provide a suitable microenvironment for Hb and enhance the direct electron transfer between the hemoglobin (Hb) and electrodes.

Degradation of RDX using granular iron and nickel-plated granular iron

Using granular iron (Fe) and nickel-plated iron (Ni/Fe), this paper examines the effectiveness of these two types of reactive materials for the treatment of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a common groundwater and soil contaminant at military facilities. RDX degraded very rapidly in the presence of both Fe and Ni/Fe in column and batch experiments. Enhancement by Ni/Fe did not prove to be effective as the half-lives of RDX ranged from 3 to 24 seconds and 3 to 11 seconds in the Fe and Ni/Fe columns, respectively. Reaction vessel experiments and estimation of the mass transfer coefficient in the column indicated that reaction kinetics was mass transfer limited. Detailed analyses of reaction intermediates and products suggest that RDX degradation proceeds through direct electron transfer processes and following to the same pathways in the presence of Fe and Ni/Fe. The formation of carbon-containing products, including formaldehyde (up to 60%), CO2 (up to 45%) and formic acid (1%) and the nitrogen containing products of ammonium (up to 48%) and N2O (up to 13%), provides convincing evidence that RDX was completely decomposed to non-toxic end products. CO2, previously reported to form only in biological or Fe-microbial combined systems, was detected as one of the main C-bearing end product. Therefore, this study shows that Fe is an effective material for remediating groundwater and industrial effluents containing RDX; and the use of additional enhancement, either biological or with Ni catalyst, does not provide additional advantages.

A third-generation hydrogen peroxide biosensor based on Horseradish Peroxidase (HRP) enzyme immobilized in a Nafion–Sonogel–Carbon composite

A third-generation biosensor based on HRP and a Sonogel–Carbon electrode has been fabricated with the aim of monitoring hydrogen peroxide in aqueous media via a direct electron transfer process. The redox activity of native HRP, typical of thin-layer electrochemistry, was observed. The charge coefficient transfer, α, and the heterogeneous electron transfer rate constant, k s, were calculated to be 0.51 ± 0.04 and 1.29 ± 0.04 s −1, respectively. Topographic study by atomic force microscopy (AFM) shows that the enzyme may have been introduced inside the ionic cluster of the Nafion. The immobilized HRP exhibited excellent electrocatalytical response to the reduction of H 2O 2 and preserved its native state after the immobilization stage. Several important experimental variables were optimized. The resulting biosensor showed a linear response to H 2O 2 over a concentration range from 4 to 100 μM, with a sensitivity of 12.8 nA/μM cm −2 and a detection limit of 1.6 μM, calculated as (3 S.D./sensitivity). The apparent Michaelis–Menten constant K m app was calculated to be 0.295 ± 0.020 mM. The biosensor showed high sensitivity as well as good stability and reproducibility. The performance of the biosensor was evaluated with respect to four possible interferences.

Fabrication of Electroactive Layer-by-layer Films with Myoglobin and Zirconium Phosphate Nanosheets

Abstract Electroactive multilayer films composed of exfoliated nanosheets of α-zirconium phosphate and myoglobin (Mb) have been fabricated on the surface of glassy carbon electrodes through electrostatic layer-by-layer self-assembly technique. Direct electron-transfer process of Mb immobilized in the film was investigated.

Characterization of Protein-Attached Conducting Polymer Monolayer

Cytochrome c (cyt c)-immobilized monolayers and multiple monolayers of a conducting polymer [poly(terthiophene-3-carboxylic acid) polymer (poly-TTCA)] were prepared, where the monolayer of monomer precursor was fabricated with the Langmuir-Blogett technique. Covalent immobilization of cyt c was achieved by the formation of an amide bond between the carboxylic groups of the conducting polymer and amines groups of lysine in cyt c. The monolayer of poly-TTCA and poly-TTCA/cyt c was characterized by cyclic voltammetry, XPS, EQCM, Auger electron spectra (AES), and atomic force microscopy (AFM). The immobilization of cyt c on the polymer layer reveals the direct electron-transfer processes of cyt c. Cyclic voltammetry of the poly-TTCA/cyt c-modified electrode showed a pair of reversible peaks at approximately +212/+201 mV (Epa/Epc) versus Ag/AgCl in a 0.2 M phosphate buffer solution (pH 7.0). The peak separation and the redox peak current of the poly-TTCA/cyt c-modified electrodes were gradually increased by increasing the number of poly-TTCA/cyt c layers on the electrode. The heterogeneous electron-transfer rate constant (ks) of cyt c at the poly-TTCA/cyt c-monolayer-modified electrode was estimated to be 0.874 s(-1). The method provides a novel route for the fabrication of protein (cyt c)-immobilized and/or lipid (palmitoyloleoylphosphatidic acid)-immobilized monolayers and multiple monolayers of a conducting polymer. Cyt c bonded on the conductive polymer layers was applied for bioelectronic devices with unique functionality.

Hemoglobin protein hollow shells fabricated through covalent layer-by-layer technique

Hemoglobin (Hb) protein microcapsules held together by cross-linker, glutaraldehyde (GA), were successfully fabricated by covalent layer-by-layer (LbL) technique. The Schiff base reaction occurred on the colloid templates between the aldehyde groups of GA and free amino sites of Hb results in the formation of GA/Hb microcapsules after the removal of the templates. The structure of obtained monodisperse protein microcapsule was characterized by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). The UV–Vis spectra measurements demonstrate the existence of Hb in the assembled capsules. Cyclic voltammetry (CV) and potential-controlled amperometric measurements (I–t curve) confirm that hemoglobin microcapsules after fabrication remain their heme electroactivity. Moreover, direct electron transfer process from protein to electrode surface was performed to detect the heme electrochemistry without using any mediator or promoter. The experiments of fluorescence recovery after photobleaching (FRAP) by CLSM demonstrate that the hemoglobin protein microcapsules have an improved permeability comparing to the conventional polyelectrolyte microcapsules.

Direct electron transfer in nanostructured sol–gel electrodes containing bilirubin oxidase

Bilirubin oxidase encapsulated within a silica sol-gel/carbon nanotube composite electrode effectively catalyzed the reduction of molecular oxygen into water through direct electron transfer at the carbon nanotube electrode surface. In this nanocomposite approach, the silica matrix is designed to be sufficiently porous for substrate molecules to have access to the enzyme and yet provides a protective cage for immobilization without affecting biological activity. The incorporation of carbon nanotubes adds electrical connectivity and increases active electrode surface area. The standard surface electron transfer rate constant was calculated to be 59 s(-1) which indicates that the carbon nanotube side walls are primarily responsible for electron transfer. The use of direct electron transfer processes simplifies biofuel cell fabrication by eliminating the need for redox mediator and ion-conducting separators.

Direct Electron TransferA Favorite Electron Route for Cellobiose Dehydrogenase (CDH) from Trametes villosa. Comparison with CDH from Phanerochaete chrysosporium

This paper presents some functional differences as well as similarities observed when comparing the newly discovered cellobiose dehydrogenase (CDH) from Trametes villosa (T.v.) with the well-characterized one from Phanerochaete chrysosporium (P.c.). The enzymes were physically adsorbed on spectrographic graphite electrodes placed in an amperometric flow through cell connected to a flow system. In the case of T.v.-CDH-modified graphite electrodes, a high direct electron transfer (DET) current was registered at the polarized electrode in the presence of the enzyme substrate reflecting a very efficient internal electron transfer (IET) process between the reduced FAD-cofactor and the oxidized heme-cofactor. In the case of P.c.-CDH-modified graphite electrodes, the DET process is not as efficient, and the current will greatly increase in the presence of a mediator (mediated electron transfer, MET). As a consequence, when comparing the two types of enzyme-modified electrodes an inverted DET/MET ratio for T.v.-CDH is shown, in comparison with P.c.-CDH. The rates of the catalytic reaction were estimated to be comparable for both enzymes, by measuring the combined DET + MET currents. The inverted DET/MET ratio for T.v.-CDH-modified electrodes might suggest that probably there is a better docking between the two domains of this enzyme and that the linker region of P.c.-CDH might have an active role in modulating the rate of the IET (by changing the interdomain distance), with respect to pH. Based on the new properties of T.v.-CDH emphasized in the present study, an analytical application of a third-generation biosensor for lactose was recently published.

Direct electrochemistry of horseradish peroxidase immobilized on gold colloid/cysteine/nafion-modified platinum disk electrode

Direct electron transfer process of immobilized horseradish peroxidase (HRP) on a gold colloid-cysteine-nafion membrane, and its application as a biosensor were investigated by using electrochemical methods. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The modified process was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The sensor displayed an excellent electrocatalytic response to the reduction of H2O2 without the aid of an electron transfer mediator. Analytical parameters such as pH and temperature were also studied. Linear calibration for H2O2 was obtained in the range 3.50×10−7 to 5.87×10−3M under the optimized conditions. The sensor was highly sensitive to H2O2 with a detection limit of 1.05×10−7M (S/N=3), and the sensor achieved 95% of the steady-state current within 10s. The sensor exhibited high sensitivity, selectivity and stability.

Tobacco Peroxidase as a New Reagent for Amperometric Biosensors

The results of testing a new enzyme, anionic tobacco peroxidase (TOP), in various amperometric biosensors are summarized. The biochemical and electrochemical properties of the enzyme are briefly charac- terized. As compared to the commonly used cationic peroxidase from horseradish roots, TOP exhibits a wider optimum stability pH range, higher stability to inactivation with hydrogen peroxide, and higher efficiency in direct electron-transfer processes. The enzyme immobilized by adsorption on graphite is effective in determin- ing aminophenols and aromatic diamines under flow conditions with a detection limit of 10 nM. Upon immo- bilization on graphite by incorporation into a gel of a redox-active polymer (crosslinked polyvinylimidazole with osmium 4,4'-dimethylbipyridinium chloride), TOP exhibited sensitivity and stability comparable to those of horseradish peroxidase and a wider linearity range. Upon immobilization on a self-assembled thiol mono- layer at a gold electrode, TOP was much superior to horseradish peroxidase in the sensitivity of determining hydrogen peroxide, regardless of the charge of the monolayer. Prospects for the further use of the native enzyme and its genetically engineered unglycosylated form are considered.

Self-assembly of Horseradish Peroxidase on Biocompatible Gold Nanoparticles–Vaterite Core–Shell Composite and its Direct Electrochemistry

Abstract Biocompatible AuNPs–vaterite core–shell composite, which combines the advantages of mineral compound and nanoparticles, was firstly used in the construction of biosensor. Direct electron transfer process of HRP on it was investigated.

A reagentless biosensor of nitric oxide based on direct electron transfer process of cytochrome C on multi-walled carbon nanotube

Direct electron transfer between Cytochrome c (Cyt.c) and electrode can be achieved through immobilizing Cyt.c on the surface of multi-walled carbon nanotubes (MWNTs). Under the condition of cyclic potential scans, Cyt.c can be adsorbed on the surface of MWNTs that were modified on a glassy carbon (GC) electrode to form an approximate monolayer. The redox characteristic and bioactivity of Cyt.c could be remained after it was adsorbed on MWNTs' surface. This provides a way to construct a new biosenser based on the activity of Cyt.c. Further investigation displayed that Cyt.c adsorbed on MWNTs showed an enzyme-like activity to catalyze the reduction of nitric oxide (NO). Due to catalyzing by Cyt.c, the reduction of NO in aqueous solution was achieved, which reductive potential appeared at -0.747V (vs. SCE). The peak currents were linearly proportional to concentration of NO in the range from 2 to 48 micromol/l with a limit of detection of 1.3 microM. The biosensor showed a good stability and excellent repeatability.

Direct electrochemistry of horseradish peroxidase bonded on a conducting polymer modified glassy carbon electrode

Direct electron transfer process of immobilized horseradish peroxidase (HRP) on a conducting polymer film, and its application as a biosensor for H 2O 2, were investigated by using electrochemical methods. The HRP was immobilized by covalent bonding between amino group of the HRP and carboxylic acid group of 5,2′:5′,2″-terthiophene-3′-carboxylic acid polymer (TCAP) which is present on a glassy carbon (GC). A pair of redox peaks attributed to the direct redox process of HRP immobilized on the biosensor electrode were observed at the HRP ∣ TCAP ∣ GC electrode in a 10 mM phosphate buffer solution (pH 7.4). The surface coverage of the HRP immobilized on TCAP ∣ GC was about 1.2×10 −12 mol cm −2 and the electron transfer rate ( ks) was determined to be 1.03 s −1. The HRP ∣ TCAP ∣ GC electrode acted as a sensor and displayed an excellent specific electrocatalytic response to the reduction of H 2O 2 without the aid of an electron transfer mediator. The calibration range of H 2O 2 was determined from 0.3–1.5 mM with a good linear relation.

Electrochemical Studies of Cytochrome c on Electrodes Modified by Single‐Wall Carbon Nanotubes

AbstractSingle‐wall carbon nanotubes (SWNTs) modified gold electrodes were prepared by using two different methods. The electrochemical behavior of cytochrome c on the modified gold electrodes was investigated. The first kind of SWNT‐modified electrode (noted as SWNT/Au electrode) was prepared by the adsorption of carboxylterminated SWNTs from DMF dispersion on the gold electrode. The oxidatively processed SWNT tips were covalently modified by coupling with amines (AET) to form amide linkage. Via Au—S chemical bonding, the self‐assembled monolayer of thiol‐unctionalized nanotubes on gold surface was fabricated so as to prepare the others SWNT‐modified electrode (noted as SWNT/AET/Au electrode). It was shown from cyclic voltammetry experiments that cytochrome c exhibited direct electrochemical responses on the both electrodes, but only the current of controlled diffusion existed on the SWNT/Au electrode while both the currents of controlled diffusion and adsorption of cytochrome c occurred on the SWNT/AET/Au electrode. Photoelastic Modulation Infared Reflection Absorption Spectroscopy (PEM‐IRRAS) and Quartz Crystal Microbalance (QCM) were employed to verify the adsorption of SWNTs on the gold electrodes. The results proved that SWNTs could enhance the direct electron transfer process between the electrodes and redox proteins.

Theoretical Study on Electron Transfer Matrix Element in Oxidation of α ‐ Amino Carbon‐Centered Radical by O2

AbstractAs a successive work of our previous paper,1 the electron transfer matrix element (Vrp) in the oxidation of the simplified model molecule of α‐amino carbon‐centered radical by O2 has been investigated with ab initio calculation at the level of UHF/6‐31 + + G*. Based on the optimized geometries of the reactant and the ion‐pair complex obtained previously, the reaction heat and the inner reorganization energy have been obtained by constructing the potential energy curves of reactant and product states considering the solvent effect with the conductor‐like screening model (COSMO). The solvent reorganization energy has been estimated using Lippert‐Mataga relationship. The calculated results show that the value of Vrp, is several times larger than that of RT, which means that the model reaction is an adiabatic one. Theoretical investigation indicates that the solvent effect on the direct electron transfer (ET) process of oxidation of α‐amino carbon‐centered radical by oxygen is remarkable.

A theoretical study of electron transfer in nanoparticle-catalysed redox reactions

Nanoparticle-catalysed electron transfer reactions have been investigated by using an extended version of the theory of electron transfer reactions for the bridge-mediated three-centre process and approximate expressions for various free energy quantities as well as the matrix elements. It is observed that the calculated rates for nanoparticle-catalysed reactions for the reduction of various dyes by standard reducing agents are considerably higher than the rates of direct electron transfer processes and are also found to agree quite well with recently reported experimental results.

Electrooxidation mechanism of biogenic amines at amine oxidase modified graphite electrode.

Amine oxidase (AO, EC. 1.4.3.6) was previously shown to be a very efficient biological recognition element of amperometric biosensors for monitoring biogenic amines. The enzyme was effectively working in both mono- and bienzyme electrode designs, based on either a direct or a mediated electron-transfer pathway. This work focuses on the elucidation of the electron-transfer mechanism of the monoenzymatic unmediated AO-modified biosensor. The observed unmediated catalytic currents were assumed to be caused by (i) a direct electron-transfer process, (ii) the electrooxidation of the formed product, or (iii) their combination. Experiments supporting these assumptions are discussed in detail.