Electrochemical Oxidation Of Hydrogen Peroxide Research Articles

Nanoscale materials in the composition of biosensors for the determination of amitriptyline

Biosensor devices including hybrid nanostructures as modifiers of transducer surfaces meet current requirements for the methods of research and determination of drugs, including antidepressants. The fea­tures of amperometric monoamine oxidase biosensors based on printed carbon electrodes modified with nanocomposite compositions C60 / cobalt nanoparticles/amino derivative of polyether polyol of the second generation/chitosan nanocomposite structures used for the detection of tricyclic antidepressant amitriptyline are considered. The choice of the best modifier was made proceeding from the data of transmission electron microscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. When developing the biosensor, conditions for depositing the composite composition of cobalt nanoparticles/amino derivative of polyether polyol on the electrode surface were varied: electrochemical deposition, sequential layer-by-layer deposition, and deposition of the mixture. The peak of electrochemical oxidation of hydrogen peroxide, which is formed during the enzymatic reaction of serotonin oxidation under the action of monoamine oxidase was used as an analytical signal of the biosensor. The principle of the biosensor action is based on the inhibitory effect of amitriptyline on the catalytic activity of immobilized monoamine oxidase. The proper choice of a modifier and optimal working conditions provided the range of detectable concentrations of amitriptyline: 1 x 10-4 - 1 x 10-8 M, the lower limit of the determined content at a level of 5 x 10-9 M for monoamine oxidase biosensor. Comparison of the results on the amitriptyline content determination in the pharmaceutical preparation and urine obtained using the monoamine oxidase biosensor and polarization fluorescence immunoassay (dilution of the tracer 1:32, dilution of antibodies 1:128, the range of working concentrations 5 x 10 -8 — 5 x 10-9 M), well-proven in the quantitative determination of medicinal substance, confirmed the correctness of the results obtained.

The recovery of sulfuric acid from spent piranha solution over a dimensionally stable anode (DSA) Ti-RuO2 electrode

Piranha solution is a highly acidic mixture of sulfuric acid and hydrogen peroxide. The present study aimed at developing a dimensionally stable anode (DSA), made of titanium metal foil coated with Ruthenium Dioxide (RuO2), for the electrochemical oxidation of hydrogen peroxide in the presence of strong sulfuric acid under ambient conditions. Results showed that hydrogen peroxide in the piranha solution was fully degraded in 5 h under a constant current of 2 A (or current density of 0.32 A-cm-2). The oxidation kinetics of hydrogen peroxide followed the Langmuir-Hinshelwood model. The observed rate constant was a function of applied current. The initial current efficiency was 17.5% at 0.5 A (or 0.08 A-cm-2) and slightly decreased to about 13.5% at applied current between 1.3 and 1.5 A (or current density of 0.208 and 0.24 A-cm-2). Results showed the capability and feasibility of the electrochemical oxidation process for the recovery of sulfuric acid from the spent piranha solution in semiconductor industrial installations or general laboratories.

Enzyme-modified microelectrodes for electrochemical detection of sphingomyelin in the plasma membranes of single cells

In this communication, sphingomyelin (SM) in the plasma membrane of single cells is detected electrochemically using an enzyme-modified Pt microelectrode for the first time. The enzymes immobilized at the electrode surface, which include sphingomyelinase (SMase), alkaline phosphatase (ALP), and choline oxidase, react with SM in a series of reactions to generate hydrogen peroxide. The electrochemical oxidation of hydrogen peroxide induces an elevation in the current, which offers a quantitative determination of SM in a range from 140 to 560 µM. Further contact of the microelectrode with one oocyte cell results in the reaction of SM in the plasma membrane with the enzymes at the electrode. The resulting current increase is correlated with the content of SM in the plasma membrane, confirming the electrochemical detection of membrane SM in single cells. This success in single cell electrochemical analysis of membrane SM expands the application of microelectrodes in single cell studies, which will help in the elucidation of cellular heterogeneity in lipid trafficking.

Electrochemical Studies of Hydrogen Peroxide Oxidation on a Nanoporous Gold Surface: Fundamental and Analytical Applications

A nanoporous gold (NPG) surface with high electroactive surface area and roughness factor was prepared via anodization-electrochemical reduction method and was used as a new platform to study the electrochemical oxidation of hydrogen peroxide (H2O2). Field-emission scanning electron microscopy (FE-SEM) analysis, cyclic voltammetry, and amperometry techniques were employed for structural morphology and electrochemical studies. The H2O2 oxidation peak potential was significantly shifted (∼0.23 V) towards a less positive direction with increased current response at the NPG surface compared to that of a bare gold electrode. The mechanism for the H2O2 anodic oxidation at the NPG surface was proposed based on the calculated transfer coefficient (α = 0.32) and the total number of electrons involved (n = 2.0) in the electrochemical process. Besides, the diffusion coefficient (D) of H2O2 in PBS solution was also calculated using the Randles-Sevcik equation (2.18 × 10−5 cm2 s−1). In addition, the analytical application of the NPG electrode was demonstrated by amperometric detection of H2O2 at a relatively less positive potential (0.57 V). The current increased proportionally to H2O2 concentration in the linear range of 0.01 to 1.8 mM and the detection limit was found to be 0.6 μM (S/N = 3).

Single-atom electrocatalysis: a new approach to in vivo electrochemical biosensing

Modulation of interfacial electron transfer has been proven to pave a new approach to in vivo electrochemical monitoring of brain chemistry; however, designing and establishing highly efficient electrocatalytic scheme towards neurochemicals remain a long-standing challenge. Here, we find that recently established single-atom catalyst (SAC) can be used for catalyzing the electrochemical process of physiologically relevant chemicals and thus offers a new avenue to in vivo electrochemical biosensing. To prove this new concept, we used Co single-atom catalyst (Co-SAC), in which the atomic active sites are dispersed in ordered porous N-doping carbon matrix at atomic level, as an example of SACs for analyzing glucose as the physiologically relevant model chemicals. We found that Co-SAC catalyzes the electrochemical oxidation of hydrogen peroxide (H2O2) at a low potential of ca. +0.05 V (vs. Ag/AgCl). This property was further used for developing an oxidase-based glucose biosensor that was used subsequently as a selective detector of an online electrochemical system (OECS) for continuous monitoring of microdialysate glucose in rat brain. The OECS with Co-SAC-based glucose biosensor as the online detector was well responsive to glucose without interference from other electroactive species in brain microdialysate. This study essentially offers a new approach to in vivo electrochemical analysis with SACs as electrocatalysts to modulate interfacial electron transfer.

Behind Modeling Electrochemical Impedance Response of a Continuous Glucose Monitor

The continuous glucose monitor is used to measure the glucose concentration in interstitial fluids by means of a glucose oxidase enzyme that converts glucose into hydrogen peroxide, which can be detected electrochemically. The development of a model for the electrochemical impedance response of the sensor may be envisioned as a sequential series of steps. The electrochemical oxidation of hydrogen peroxide, in the absence of the enzyme, can be treated as a charge-transfer resistance coupled with a diffusion impedance. In the present case, however, the enzyme provides a homogeneous production of the hydrogen peroxide. The coupling of a homogeneous reaction with a heterogeneous electrochemical reaction was addressed, in the 1950s, by Gerischer, who assumed that homogeneous kinetics can be described by a linear equation, that all diffusion coefficients were equal, and that diffusion took place within a film. The resulting diffusion impedance had two loops, the high-frequency loop corresponding to the homogeneous reaction and the low-frequency loop corresponding to diffusion. While the simplified model represented by the electrochemical oxidation of hydrogen peroxide coupled with a Gerischer impedance yields insight into the impedance response of a glucose sensor, the chemistry of the sensor is much more complex. Three electrochemical reactions may take place in the potential range of interest. The enzymatic production of hydrogen peroxide involves more than one homogeneous reaction, and these reactions may not be modeled by linear equations. In addition, the diffusion coefficients of species associated with the coupled heterogeneous and homogeneous reactions are not equal. The present work describes the development of a mathematical model for the impedance response of glucose-oxidase based electrochemical biosensors [3]. The homogeneous reactions included anomerization between -D-glucose and -D-glucose, four reversible enzymatic catalytic reactions transforming -D-glucose and oxygen into gluconic acid and hydrogen peroxide, weak acid dissociation equilibrium, two reactions accounting of the pH-dependence of enzymatic activity, and a series of reactions associated with the buffer system. The electroactive hydrogen peroxide was considered to be oxidized or reduced at the electrode. In addition, reduction of oxygen was considered as a potential cathodic reaction. The heterogeneous reactions were coupled by the concentration of hydrogen ions, which appear as reactants for the cathodic reactions and as a product of the anodic reaction. Thus, the faradaic impedances associated with the three heterogeneous reactions could not be considered independent. The mathematical model was solved numerically by using the finite-difference method and Newman’s BAND algorithm [4]. The model demonstrates how the coupled non-linear homogeneous reactions affect the diffusion impedance, which has broadened the scope of the Gerischer impedance. The model can be used to explore the influence of various system parameters on limiting current, reaction profiles, and diffusion impedance. The system parameters, including interstitial glucose concentration, oxygen concentration, active enzyme concentration, diffusion coefficients, reaction rate constants and layer thickness, are related to various sensor working conditions such as body sugar level, inflammation, sensor degradation and sensor design. References H. Gerischer, “Wechselstrompolarisation Von Elektroden Mit Einem Potentialbes- timmenden Schritt Beim Gleichgewichtspotential,” Zeitschrift fur Physikalische Chemie, 198 (1951) 286-313.M. E. Orazem and B. Tribollet, Electrochemical Impedance Spectroscopy (John Wiley & Sons, Hoboken, NJ, 2017), 2nd edition, p. 279-293.M. Gao, M. S. Hazelbaker, R. Kong, and M. E. Orazem, “Mathematical Model for the Electrochemical Impedance Response of a Continuous Glucose Monitor,” Electrochimica Acta, 275 (2018), 119-132J. S. Newman and K. E. Thomas-Alyea, Electrochemical Systems (John Wiley & Sons, Hoboken, NJ, 2004), 3rd edition. Acknowledgement The support of Medtronic Diabetes (Northridge, CA) and Andrea Varsavsky, program monitor, is gratefully acknowledged.

Facile electrochemical synthesis of three dimensional flowerlike gold microstructure for electrochemical oxidation of hydrogen peroxide

In the present work, we report a simple and facile templateless electrodeposition of hierarchical flowerlike gold microstructure which was synthesized by using a chronoamperometric (CA) i–t curve technique at a constant applied potential of E = 0.5 V with respect to sat Ag/AgCl (KCl) on indium tin oxide electrode (ITO) substrate. The surface morphology, elemental composition and the preferred orientation of gold microflowers (AuMFs) were characterized using scanning electron microscopy (SEM) and X–ray photoelectron spectroscopy (XPS) analyses. The SEM images of the as-prepared AuMFs resembled nanoflakes which are building block for the formation of a three dimensional hierarchical flower–like morphology. Surface elemental composition and valence state of AuMFs is further examined by X–ray photoelectron spectroscopy (XPS). The electrochemical oxidation behavior of AuMFs was investigated by using Cyclic Voltammetry (CV) and chronoamperometric CA techniques with the H2O2 analyst in 0.1 M phosphate buffer solution (pH 7.4). The AuMFs deposited ITO electrodes exhibited excellent electrocatalytic reactivity towards H2O2 oxidation due to the increase of in adsorption of H2O2 on gold–oxide surfaces and it was enhancing the amperometric sensing of H2O2 in neutral solutions.

Development of a Glucose Sensor Using Palladium Electrode

An amperometric glucose sensor was introduced where glucose oxidase was immobilized on palladium electrode. This sensor based on the glucose oxidase catalyzed oxidation of glucose and electrochemical oxidation of hydrogen peroxide which was produced by enzyme reaction. Basic concept of the glucose sensor is composed of inner and outer membrane systems, immobilized glucose oxidase layer, and palladium electrode. Inner membrane prevents the access of electrochemical interfering substrates. Outer membrane works as a diffusion barrier of glucose. The glucose sensor can achieve a wide dynamic range with this outer membrane. In this research, to verify this concept especially the role of outer membrane, the glucose sensor which was made with palladium electrode, glucose oxidase layer, and outer membrane was tested on different glucose concentrations. The sensor showed a good correlation between sensor responses and glucose concentrations. In addition, the dynamic range of this sensor was enough for glucose monitoring of diabetic patients. This sensor also demonstrated stable sensor responses during several days. These results show that this sensor has a strong potential for application to continuous glucose monitoring, or CGM. Disclosure T. Han: Employee; Self; Panasonic Healthcare Co., Ltd. S. Noda: Employee; Self; Panasonic Healthcare Co., Ltd. K. Haneda: Employee; Self; Panasonic Healthcare Co., Ltd. N. Shigetou: Employee; Self; Panasonic Healthcare Co., Ltd.

Highly Sensitive Glucose Sensor Based on Organic Electrochemical Transistor with Modified Gate Electrode.

An organic electrochemical transistor (OECT) with a glucose oxidase (GOx) and poly(n-vinyl-2-pyrrolidone)-capped platinum nanoparticles (Pt NPs) gate electrode was successfully integrated with a microfluidic channel to act as a highly sensitive chip-based glucose sensor. The sensing mechanism relies on the enzymatic reaction between glucose and GOx followed by electrochemical oxidation of hydrogen peroxide (H2O2) produced in the enzymatic reaction. This process largely increases the electrolyte potential that applies on PEDOT:PSS channel and causes more cations penetrate into PEDOT:PSS film to reduce it to semi-conducting state resulting in lower electric current between the source and the drain. The extremely high sensitivity and low detection limit (0.1μM) of the sensor was achievable due to highly efficient Pt NPs catalysis in oxidation of H2O2. Pt NPs were deposited by a bias-free two-step dip coating method followed by a UV-Ozone post-treatment to enhance catalytic ability. A polydimethylsiloxane (PDMS) microfluidic channel was directly attached to the OECT active layer, providing a short detection time (~1min) and extremely low analyte consumption (30μL). Our sensor has great potential for real-time, noninvasive, and portable glucose sensing applications due to its compact size and high sensitivity.

A Highly Sensitive Non-Enzymatic Sensor Based on a Cu/MnO2/g-C3N4-Modified Glassy Carbon Electrode for the Analysis of Hydrogen Peroxide Residues in Food Samples

A simple and highly sensitive method for the determination of hydrogen peroxide was developed by electrodepositing Cu and MnO2 onto a g-C3N4 coated glassy carbon electrode in a one-step procedure. The morphology of the fabricated electrode material was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The electrochemical properties were measured using cyclic voltammetry (CV) and chronoamperometry. The modified sensor exhibits high catalytic activity towards electrochemical oxidation of hydrogen peroxide in a neutral phosphate buffer solution. Within the concentration ranges of 0.01–20 mM and 20–400 mM, the fabricated sensor shows a good linear relationship with the oxidation peak current, the detection limit is 0.85 × 10−6 M. Furthermore, the sensor exhibits high selectivity, good stability, and reproducibility. We successfully applied the sensor to detect hydrogen peroxide residues in food samples with satisfactory results, providing a new approach for food security evaluation.

Enhanced Electrochemical Oxidation of Hydrogen Peroxide at Hydroxyl Ion-Modified Gold Electrode in Alkaline Media

Chemisorption of hydroxyl ion (OH-) from aqueous solution of KOH at the polycrystalline gold (Au (poly)) electrode under stirring condition was studied. A pre-wave at ca. 0.19 V was observed due to partial discharging of the chemisorbed OH-. The linear plot of the pre-wave current vs. scan rate passed through the origin suggesting that it was associated with a surface confined process. An extraordinary enhanced electrocatalytic oxidation of hydrogen peroxide (HO - 2 ) at the in situ fabricated OH--modified Au (poly) (OH-ôAu (poly)) electrode was achieved. A mechanism of the observed catalytic activity was proposed on the basis of electrostatic attraction between the chemisorbed OH- and partial positively charged hydrogen (Hd+) of HO - 2 molecules.Journal of Bangladesh Academy of Sciences, Vol. 40, No. 2, 125-135, 2016

Origin of the different behavior of some platinum decorated nanocarbons towards the electrochemical oxidation of hydrogen peroxide

The electrochemical behavior of different platinum-decorated nanocarbons (Pt@C) towards the oxidation of hydrogen peroxide (H2O2) was investigated. Three different types of nanocarbons were considered: i) carbon black, ii) dahlia-like carbon nanohorns and iii) carbon nanotubes, which included both commercial (single-wall and multi-wall) and laboratory prepared (multi-wall) samples. Shape and size distribution of the platinum nanoparticles and morphology of the nanocarbons were analyzed by transmission electron microscopy. Their nanostructure was investigated by micro-Raman spectroscopy, while elemental composition of the samples and chemical bonding states were studied by X-ray photoelectron spectroscopy. Electrochemical behavior towards H2O2 oxidation was evaluated by means of cyclic voltammetry modifying the working screen-printed carbon electrode surface with the prepared Pt@C nanocomposites. Data obtained suggest that the size and dispersion of the Pt nanoparticles play a key role in increasing the sensitivity towards H2O2 detection. Thanks to the presence of smaller and more dispersed platinum particles and of a greater amount of platinum hydroxide, acting as intermediary in the H2O2 oxidation process, Pt@dahlia-like carbon nanohorns result to be the most promising platform for the development of H2O2 electrochemical sensors.

TEMPO as a Promising Electrocatalyst for the Electrochemical Oxidation of Hydrogen Peroxide in Bioelectronic Applications

A number of bioelectronic applications work with oxidase enzymes and many of them can operate with small molecule or polymer redox mediators. However, for some oxidases, there are no known redox mediators able to mediate electron transfer. Therefore, electron transfer must occur through peroxide production and oxidation at the electrode surface. Organic redox catalysts such as oxoammonium cations, are able to oxidize H2O2 to form nitroxyl radicals, which can be electro-oxidized and regenerate the oxoammonium cation form. In this study, we investigate the ability to use TEMPO as a platform for the electrocatalytic oxidation of H2O2 at different pHs. The results have shown that TEMPO can be used to monitor H2O2 in broad pH range (≥4) at 530 mV (vs SCE). Combining TEMPO with cholesterol oxidase, we have shown the possibility to monitor the cholesterol oxidation with a linear range between 20 μM and 2.5 mM with a sensitivity of 54.86 mA cm−2 M−1. Furthermore, we have studied the electrocatalytic oxidation of oxalate by oxalate oxidase for biofuel cell applications. These combined results demonstrate TEMPO as a promising electrocatalyst applied for the development of electrochemical biosensors or enzymatic biofuel cells.

A simple route for electrochemical preparation of Cu/Pt nanoparticles supported on glassy carbon electrode based on p-isopropyl calix[6]arene matrix and its activity for electrochemical oxidation of H2O2

In this article, the Cu nanoparticles were prepared on the p-isopropyl calix[6]arene-modified glassy carbon electrode by preconcentration of copper ions in open circuit potential and consecutive electrochemical reduction of them. P-isopropyl calix[6]arene was used as a template for synthesis of the Cu nanoparticles due to the ability of its cavities to trap the copper ions. Bimetallic Cu/Pt nanoparticles were also obtained by galvanic replacement of metallic Cu with Pt by simply immersing the electrode surface in a PtCl4 aqueous solution. The surface morphology of the Cu and Cu/Pt fabricated nanoparticles was investigated using scanning electron microscopy (SEM). Then, the electrochemical characteristics were analyzed through the cyclic voltammetry and electrochemical impedance spectroscopy techniques. The morphology analysis of the deposits using SEM reveals that the sizes and distribution of the nanoparticles were tuned using calix[6]arene matrix. Cu/Pt-coated glassy carbon electrode exhibited a promising activity for electrochemical oxidation of hydrogen peroxide (H2O2). The proposed modified electrode showed two linear ranges for H2O2 detection, 0.05–1.00 mM and 1.00–13.00 mM, and a detection limit equal to 0.01 mM (S/N = 3).

An Efficient Amperometric Sensor for Hydrogen Peroxide by Using a Carbon Paste Electrode Modified with Cobalt Impregnated Zeolite

Cobalt impregnated zeolite-modified electrode was prepared by mixing cobalt–zeolite (Co–Z) and graphite powder with different percentages. Using the cyclic voltammetric technique, the electrochemical oxidation of hydrogen peroxide at such electrodes was investigated. Experiments on zeolite show that it is not electrochemically active towards hydrogen peroxide oxidation in NaOH solution. The presence of cobalt ions in the zeolite matrix, by soaking the electrode in an aqueous Co(NO 3)2 solution, markedly enhances the electrocatalytic activity which was found to depend on the cobalt content. On the other hand, the presence of zeolite and/or Co metals in the catalyst is essential; however, the electro-catalytic activity depends on different percentages of Co–Z. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of the hydrogen peroxide in the range 0.03–9 and 0.006-0.1 mM with CV and amperometric methods, respectively. The detection limits (S/N=3) were also estimated to be 17 and 2.5 µM.

Амперометрические моноаминоксидазные биосенсоры на основе графитовых электродов и оксида графена как модификатора поверхности для определения некоторых антидепрессантов

Амперометрические моноаминоксидазные биосенсоры на основе графитовых электродов и оксида графена как модификатора поверхности для определения некоторых антидепрессантов

Nanodiamond pretreatment for the modification of diamond electrodes by platinum nanoparticles

The preparation of Pt-modified diamond electrodes by electrodeposition is known to be hampered by poor particle adhesion and a lack of uniformity in the spatial distribution of the deposit over the electrode surface. Here we demonstrate the results can be improved significantly if the electrode is given a simple ultrasonic treatment in the presence of diamond powders prior to electrodeposition. An improvement in spatial distribution and a higher Pt dispersion are seen and, especially, a greater Pt particle stability is observed. Application of these Pt modified diamond electrodes in the electrochemical oxidation of hydrogen peroxide is demonstrated.

Metallic impurity free carbon nanotube paste electrodes

Electrodes modified with carbon nanomaterials find wide ranging applications in electrochemistry such as in energy generation and storage through to applications in electroanalysis. A substantial limitation is the presence of metallic impurities which vary between batches and can produce erroneous results. Consequently we have explored the electrochemical properties of metallic impurity free carbon nanotube paste electrodes using potassium ferrocyanide and hydrogen peroxide as model compounds. In terms of the latter utilising cyclic voltammetry, a linear range from 0.75 to 3 mM with a limit of detection of 0.19 mM is possible using the electrochemical oxidation of hydrogen peroxide while using the electrochemical reduction of the target analyte, a linear range from 0.5 to 249 mM is possible with a detection limit of 0.43 mM. The ultra-small size of the carbon nanotubes and fabrication methodology result in a tightly bound carbon nanotube electrode surface which does not exhibit thin-layer behaviour resulting in highly reproducible electrodes with the %RSD found to be 5.5%. These analytical ranges, detection limits and reproducibility are technologically useful. The carbon nanotubes utilised are completely free from metallic impurities and do not require lengthy processing to remove impurities and consequently have no variation in the purity of the nanomaterial between batches as is commonly the case for other available carbon nanotube material. The impurity free nature of this nanomaterial allows for highly reproducible and intelligent sensors based on carbon nanotubes to be understood and realised for the first time.

Cobalt Phthalocyanine-Modified Boron-Doped Diamond Electrode for Highly Sensitive Detection of Hydrogen Peroxide

A cobalt phthalocyanine-modified boron-doped diamond (CoPc-BDD) electrode was fabricated for a sensitive detection of hydrogen peroxide. The hydrogen-terminated BDD electrode surface was terminated with pyridine moieties via photochemical modification with 4-vinylpyridine followed by immobilization of CoPc on the surface by immersion in a CoPc solution. X-ray photoelectron spectroscopy studies suggested that the coordination of the surface pyridine and the Co atom in CoPc contributes to surface modification. Electrochemical detection of hydrogen peroxide at the modified electrode was also investigated. Cyclic voltammetry confirmed that the CoPc-BDD electrode exhibited a catalytic activity for the electrochemical oxidation of hydrogen peroxide. Using a flow-injection analysis–electrochemical detection system, we demonstrated that the CoPc-BDD electrode is well suited for the detection of hydrogen peroxide, with a limit of detection of 4.9 nM.

Multistep filling of porous silicon with conductive polymer by electropolymerization

The filling of porous silicon with polypyrrole by electropolymerization was investigated. The filling with polypyrrole proceeded preferentially along the porous silicon wall, leading to the formation of tubular structures. By repeating the porosification, the pore filling and the additional porosification, through-tubes of polypyrrole were formed in macropores. The technique to form through-tube was also applied to medium-sized pores. A double layer with polypyrrole was produced by the repetition of porosification and pore filling twice. The immobilization of glucose oxidase was performed by electropolymerization in an aqueous solution containing glucose oxidase and pyrrole. Glucose oxidase was immobilized physically in the polypyrrole film. In the double layer, the sensitivity of glucose oxidase was measured by electrochemical oxidation of hydrogen peroxide, which was produced by the enzymatic reaction of glucose oxidase to gluconolactone. When glucose oxidase was immobilized in the upper layer, glucose was detected sensitively. On the other hand, when glucose oxidase was immobilized in the lower layer, the sensing current showed a slow and a low response. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)