Multiscale-tailored bioelectrode surfaces for optimized catalytic conversion efficiency

We describe the elaboration of a multiscale-tailored bioelectrocatalytic system. The combination of two enzymes, D-sorbitol dehydrogenase and diaphorase, is studied with respect to the oxidation of D-sorbitol as a model system. The biomolecules are immobilized in an electrodeposited paint (EDP) layer. Reproducible and efficient catalysis of D-sorbitol oxidation is recorded when this system is immobilized on a gold electrode modified by a self-assembled monolayer of 4-carboxy-(2,5,7-trinitro-9-fluorenylidene)malonitrile used as a mediator. The insertion of mediator-modified gold nanoparticles into the EDP film increases significantly the active surface area for the catalytic reaction, which can be further enhanced when the whole system is immobilized in macroporous gold electrodes. This multiscale architecture finally leads to a catalytic device with optimized efficiency for potential use in biosensors, bioelectrosynthesis, and biofuel cells.     

Effect of Partial Pressure of Oxygen on Its Bioelectrocatalytic Reduction at a Laccase–Nafion Composite

Dependences of the rate of bioelectrocatalytic reduction of oxygen at an electrode with a laccase–Nafion composite on the partial oxygen pressure are obtained in a wide potential range. The saturation concentration by oxygen for this enzyme electrode is 0.98 mM and the solution stirring tells only at low partial oxygen pressures. The Michaelis constants and catalytic constants are compared in conditions bioelectrocatalysis and enzymic catalysis.     

Bioelectrocatalytic and Enzymic Activity of Laccase in Water–Ethanol Solutions

The effect the composition of a water–ethanol mixture has on the enzymic (in the pyrocatechol oxidation reaction) and bioelectrocatalytic in a broad potential range (in the oxygen reduction reaction) activity of laccase (L) is studied. On the basis of obtained results conclusions are made about the influence exerted by ethanol in the composition of the water–ethanol mixture on the activity of laccase solubilized and immobilized in the composition of a composite (laccase–Nafion). The decrease in the activity in both the enzymic and the bioelectrocatalytic reactions is probably caused by the denaturation of laccase, which is due to the replacement of the hydration shell of a protein globule by a solvation shell. Besides, there take place a retardation of the kinetic stage of the formation of a laccase–substrate complex (LHO₂OH) because of the slowness of the diffusion of water into an active center and an inhibiting effect of ethanol, which is capable of binding itself to an enzyme globule in the vicinity of the active center of laccase.     

Mediator‐Free Bioelectrocatalytic Oxidation of Ethanol on an Electrode from Thermally Expanded Graphite Modified by Gluconobacter oxydans Membrane Fractions

We studied bioelectrocatalytic oxidation of ethanol with membrane fractions of Gluconobacter oxydans VKM B‐1280 bacterial cells participating as an electrocatalyst. Material of the electrode was graphene‐like thermally expanded graphite of a high surface area and low resistivity. Membrane fractions were immobilized on the electrode surface by application in chitosan gel to prevent desorption of the biocatalyst. The bioelectrode characteristics were studied by the voltammetric and chronopotentiometric methods. It was shown that electrooxidation of ethanol on the bioanode could proceed both in the mode of direct mediator‐free electrocatalysis and by the mediator mechanism.     

Bioelectrocatalytic Reduction of Peroxide Compounds on the Peroxidase–Nafion Composite

Electrochemical reactions of peroxide compounds (hydrogen peroxide and peracetic and perbenzoic acids) on an electrode of pyrocarbon with immobilized horseradish peroxidase (HRP) are studied. The immobilization of HRP is performed in the composition of a composite with Nafion whose structure is studied by a method of scanning tunneling microscopy. The proposed composite material provides for a high catalytic activity and stability of enzyme in the reaction of reduction of peroxide compounds. It is shown that the electrocatalytic reduction of the studied compounds on the electrode with the peroxidase–Nafion composite proceeds in conditions of direct bioelectrocatalysis. The effect of the solution pH and the concentration of substrates on the electrocatalytic activity of HRP in the composition of the composite is studied. On the basis of the obtained results a possible mechanism of the electrocatalytic reduction of peroxide compounds in the presence of HRP is suggested. The rate of a bioelectrocatalytic process is defined by the nature and concentration of the substrate as well as by the electrode potential and the solution pH.     

Electrochemical study of methylene blue incorporated into mordenite type zeolite and its application for amperometric determination of ascorbic acid in real samples

Methylene blue (MB) was incorporated into mordenite zeolite by ion exchange reaction in aqueous phase. The dye is strongly retained and not easily leached from the zeolite matrix. The solid was characterized by XRD prior to using it for the electrode preparation. This compound was incorporated into a carbon paste electrode for cyclic voltammetric and amperometric measurements. Methylene blue immobilized on the support underwent a quasi-reversible electrochemical redox reaction. In various electrolyte solutions and changing the pH between 2.0 and 7.0, the midpoint potential remained practically constant, i.e. 153.7±0.8 mV. This is not the usual behavior of MB, because in solution phase its midpoint potential changes considerably as the pH changes. The electrode made with this material was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry was linearly dependent on the ascorbic acid concentration. At a fixed potential under static conditions, the calibration plot was linear over the ascorbic acid concentration range 2.0×10⁻⁵ to 8.0×10⁻⁴ M. The detection limit of the method is 1.21×10⁻⁵ M, low enough for trace ascorbic acid determination in various real samples.     

Bioamperometric Assay of Phenol Derivatives Using a Laccase–Nafion Composite

Results of using a laccase–Nafion composite for bioamperometric assay of phenol derivatives are presented. Of the compounds studied, only pyrocatechol, dopamine, and 2-amino-4-chlorophenol can be assayed bioamperometrically. The concentration of phenol substrates is determined from the reduction current of enzymic oxidation products at 0.1 V (Ag/AgCl) on a pyrocarbon electrode with the composite and by the oxygen consumption for enzymic oxidation on a Clark electrode with the composite membrane at –0.7 V. The sensitivity of both methods that use composite of the same composition is compared. Kinetic parameters of either electrode are determined. Ways for improving sensitivity of methods intended for assaying phenol derivatives by using laccase-based electrodes are suggested.     

Amperometric Urea Biosensor Using Aminated Glassy Carbon Electrode Covered with Urease Immobilized Carbon Sheet,Based on the Electrode Oxidation of Carbamic Acid

A large oxidation current can be observed when ammonium carbamate aqueous solution is electrolyzed using a glassy carbon electrode (GCE) at a potential exceeding 1.0 V vs. Ag/AgCl and amino groups are introduced at the surface of the GCE. Aminated GCE exhibits the electrocatalytic activity of the oxidation of ammonium carbamate that is produced from urea as an intermediate product of urease reaction, and a distinct oxidation current is observed when the aminated GCE is used to oxidize the urea in the urease solution. A novel amperometric determination method to detect urea has been developed. This method is based on the electrooxidation of carbamic acid produced during urease reactions. Urease is immobilized to polymaleimidostyrene (PMS) coated on the insulated amorphous carbon sheet set on the aminated GCE surface. A good linear relationship is observed between urea concentration and the electrolytic current of the urease‐immobilized electrode in the concentration range from 0.5 mM to 21.0 mM. The proposed urea biosensor has an effective merit in that the interference resulting from ammonia and pH change caused by the urease reaction can be eliminated, differing from conventional urea biosensors.     

Mediated amperometric biosensor for hypoxanthine based on a hydroxymethylferrocene-modified carbon paste electrode

An amperometric enzyme electrode for the determination of hypoxanthine in fish meat is described. The hypoxanthine sensor was prepared from xanthine oxidase immobilized by covalent binding to cellulose triacetate and a carbon paste electrode containing hydroxymethylferrocene. The xanthine oxidase membrane was retained behind a dialysis membrane at a carbon paste electrode. The sensor showed a current response to hypoxanthine due to the bioelectrocatalytic oxidation of hypoxanthine, in which hydroxymethyiferrocene served as an electron-transfer mediator. The limit of detection is 6 × 10^?7 M, the relative standard deviation is 2.8% (n=28) and the response is linear up to 7 × 10^?4 M. The sensor responded rapidly to a low hypoxanthine concentration (7 × 10^?4 M), the steady-state current response being achieved in less than 1 min, and was stable for more than 30 days at 5 ° C. Results for tuna samples showed good agreement with the value determined by the conventional method.     

Polymer-based bilayer interfaces for electrochemical rectification

In this paper, the electrochemical current rectification phenomenon exhibited at an electrochemical interface constituted by a glassy carbon electrode covered with a bilayer of polymer films is discussed. The authors have shown that Methylene Blue (MB) redox species can be confined to a very thin insulating polymer film formed from orthophenylene diamine. The poly(opd) film exhibited excellent blocking properties to redox molecules in solution. On the other hand, the insulating poly(opd) film trapped with MB could mediate electron transfer between the redox molecules in solution and the electrode. Further, a second polymeric layer (Nafion film) trapped with ferrocene redox species was formed as the outer layer over the inner poly (opd) film containing MB. This bilayer-modified electrode, due to the significant difference in the redox potentials of the MB and ferrocene species immobilized in the inner and outer layers, respectively, exhibits unidirectional current flow and the results of the voltammetric investigations on the modified electrodes are described in this communication.