CoOOH nanosheet electrodes: Simple fabrication for sensitive electrochemical sensing of hydrogen peroxide and hydrazine

Cobalt oxyhydroxide, CoOOH, nanosheets were prepared via a surface alkaline treatment of cobalt foil at room temperature without using templates and catalysts. The morphology, chemical composition and structures of the nanosheets were characterized by XRD, FTIR and Raman spectroscopy, FESEM and TEM. These oriented and nanostructured arrays can be used directly as electrodes, thus simplifying the electrode fabrication process, as well as offering advantages such as enhanced electrode-electrolyte contact area, minimum diffusion resistance and direct active material-current collector connection for fast electron transport. The electrode was used as an electrochemical sensor towards non-enzymatic detection of hydrogen peroxide and hydrazine in alkaline solution. The amperometric detection of H(2)O(2) and N(2)H(4) was carried out at low potential (0V and 0.1V). At 0.1V, the amperometric signals are linearly proportional to H(2)O(2) concentration up to 1.6mM (R(2)=0.995), showing a detection limit (S/N=3) of 40μM and a high sensitivity of 99μAmM(-1)cm(-2). For N(2)H(4), the amperometric signals are linearly proportional to concentration up to 1.2mM (R(2)=0.99), showing a detection limit (S/N=3) of 20μM and a high sensitivity of 155μAmM(-1)cm(-2) at 0.1V.     

Simultaneous detection of NADH and H₂O₂ using flow injection analysis based on a bifunctional poly(thionine)-modified electrode

We report here a novel detection scheme for simultaneous detection of NADH and H(2)O(2) based on a bifunctional poly(thionine)-modified electrode. Electropolymerization of thionine on a "preanodized" screen-printed carbon electrode effectively lowers the oxidation potential of NADH to 0.15 V (vs. Ag/AgCl). Since poly(thionine) is also a well known electrochemical mediator for H(2)O(2) reduction, we further developed a poly(thionine)-modified ring disk electrode for simultaneous measurement of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H(2)O(2)) by flow injection analysis. By applying the optimized detection potentials of 0.2V and -0.2V at disk and ring electrodes, respectively, this system allows the simultaneous measurement of both analytes with good sensitivity (0.13 μA/mM for H(2)O(2) and 0.34 μA/mM for NADH) and limit of detection (1.74 μM and 26.0 μM for NADH and H(2)O(2)). This opens the possibility of a whole series of biosensor applications.     

Pt based enzyme electrode probes assembled with Prussian Blue and conducting polymer nanostructures

Conductive polymer nanotubules of 1,2-diaminobenzene (1,2-DAB) were prepared using a porous polycarbonate membrane template, placed on a Pt foil and used to support the polymer, then, the electropolymerisation was performed by chronocoulometry. The obtained conductive polymer nanostructures were then placed on Pt electrode and used to support highly dispersed prussian blue (PB), which acts as the active component for H2O2 detection. The observed good stability of PB as catalyst of H2O2 was related to the presence of organic non-conventional conducting polymers in a composite nanostructured film. These nanostructured polymer/PB composite films were also characterised by scanning electron microscopy (SEM) and Raman spectroscopy. The non-conventional conducting polymer nanotubules/PB modified Pt electrodes were tested by cyclic voltammeter for stability at different pH values, then, by amperometry, for hydrogen peroxide, ascorbic acid, acetaminophen, uric acid and acetylcholine. Glucose oxidase (GOD), lactate oxidase (LOD), L-amino acid oxidase (L-AAOD), alcohol oxidase (AOD), glycerol-3-phosphate oxidase (GPO), lysine oxidase (LyOx), and choline oxidase (ChOx) were immobilised on PB layer supported on 1,2-diaminobenzene (1,2-DAB) nanotubules onto the Pt electrodes. Different strategies for enzyme immobilisation were performed and used. Analytical parameters such as reproducibility, interference rejection, response time, storage and operational stability of the sensors have been studied and optimised. Results provide a guide to design high sensitive, stable and interference-free biosensors. The glucose biosensors assembled with nanostructured poly(1,2-DAB) showed a detection limit of 5 x 10(-5) mol l(-1), a wide linearity range (5 x 10(-5) to 5 x 10(-3) mol l(-1)), a high selectivity, a stability of 3 months at 4 degrees C, and at least 4 weeks at room temperature. Similar analytical parameters and stability were also studied for L-(+)-lactic acid, L-leucine, ethanol, glycerol-3-phosphate, lysine, and choline biosensors.     

Highly Stable Supercapacitors with Conducting Polymer Core‐Shell Electrodes for Energy Storage Applications

Conducting polymers such as polyaniline (PAni) show a great potential as pseudocapacitor materials for electrochemical energy storage applications. Yet, the cycling instability of PAni resulting from structural alteration is a major hurdle to its commercial application. Here, the development of nanostructured PAni–RuO₂ core–shell arrays as electrodes for highly stable pseudocapacitors with excellent energy storage performance is reported. A thin layer of RuO₂ grown by atomic layer deposition (ALD) on PAni nanofibers plays a crucial role in stabilizing the PAni pseudocapacitors and improving their energy density. The pseudocapacitors, which are based on optimized PAni–RuO₂ core–shell nanostructured electrodes, exhibit very high specific capacitance (710 F g^?1 at 5 mV s^?1) and power density (42.2 kW kg^?1) at an energy density of 10 Wh kg^?1. Furthermore, they exhibit remarkable capacitance retention of ≈88% after 10 000 cycles at very high current density of 20 A g^?1, superior to that of pristine PAni‐based pseudocapacitors. This prominently enhanced electrochemical stability successfully demonstrates the buffering effect of ALD coating on PAni, which provides a new approach for the preparation of metal‐oxide/conducting polymer hybrid electrodes with excellent electrochemical performance.     

Template synthesis of highly ordered Prussian blue array and its application to the glucose biosensing

In this paper, we propose a strategy to form nanoelectrode arrays by electrochemical deposition of the Prussian blue (PB) through highly ordered porous anodic alumina (PAA) membrane. The structure and morphology of the nanoarrays were characterized by scanning electron microscopy (SEM). As the highly ordered PB arrays can behave as an ensemble of closely spaced but isolated nanoelectrodes, the nanostructured PB arrays are successfully applied to improve the analytical performances of glucose by electrocatalytic reduction enzymatically liberated H₂O₂. The resulting PB based nanoelectrode arrays show a wide linear calibration range over three orders of magnitude of glucose concentrations (5.0 × 10⁻⁶ to 8.0 × 10⁻³ M) and a low detection limit of 1 μM. Moreover, the biosensor exhibits other good characteristics, such as short response time, high selectivity, excellent operation stability. In addition, effects of the glucose oxidase (GOx) loading, applied potential and pH on the biosensor performance were also discussed.     

Optical detection of choline and acetylcholine based on H₂O₂-sensitive quantum dots

In this paper, we have constructed a simple, rapid and sensitive biosensor for detection of choline and acetylcholine (ACh) based on the hydrogen peroxide (H(2)O(2))-sensitive quantum dots (QDs). The detection limit for choline was 0.1 μM and the linear range was 0.1-0.9 μM and 5-150 μM, respectively. The detection limit for ACh was found to be 10 μM and the linear range was 10-5000 μM. The wide linear ranges were shown to be suitable for routine analyses of choline and ACh. Possible mechanism of the fluorescence of QDs quenched by H(2)O(2) was an electron transfer (ET) process. The experimental conditions of biosensors were optimized, and anti-interference ability was also presented. We also detected the choline in milk samples and the linear range was 5-150 μM. The detection linear range of ACh in serum was 10-140 μM. Most importantly, the recovery of choline in milk and ACh in serum samples were both close to 99%. The excellent performance of this biosensor showed that the method can be used in practice detection of choline and ACh.     

A comparison of redox polymer and enzyme co-immobilization on carbon electrodes to provide membrane-less glucose/O2 enzymatic fuel cells with improved power output and stability

Glassy carbon and graphite electrodes modified with films of enzyme and osmium redox polymer, cross linked with poly (ethylene glycol) diglycidyl ether, were used for elaboration of a glucose/O(2) enzymatic fuel cell. The redox polymers [Os(4,4'-dimethoxy-2,2'-bipyridine)(2)(polyvinylimidazole)(10)Cl](+) and [Os(4,4'-dichloro-2,2'-bipyridine)(2)(polyvinylimidazole)(10)Cl](+) were selected to facilitate transfer of electrons from the glucose oxidase (GOx) active site to the T1 Cu site of multicopper oxygenases of Trametes hirsuta laccase (ThLacc) and Myrothecium verrucaria bilirubin oxidase (MvBOD). Maximum power density at pH 5.5 of 3.5 μW cm(-2) at a cell voltage of 0.35 V was obtained for an assembled membrane-less fuel cell based on ThLacc on glassy carbon as cathode, in the presence of 0.1 M glucose, 37 °C, with lower power observed at pH 7.4 and 4.5. Replacement of the ThLacc cathode with that of MvBOD produced 10 μW cm(-2) at 0.25 V under pseudo-physiological conditions. Replacement of glassy carbon with graphite as base electrode material resulted in increased redox polymer loading, leading to an increase in power output to 43 μW cm(-2) at 0.25 V under similar conditions. Improved stabilization of biofilms was achieved through covalent anchoring of enzyme and redox polymer on graphite electrodes, derivatized via electrochemical reduction of the diazonium cation generated in situ from p-phenylenediamine. Enzymatic fuel cells using this approach retained 70% power at 24 h, whereas fuel cells prepared without chemical anchoring to graphite retained only 10% of power over the same interval.     

Recent progress and continuing challenges in bio-fuel cells. Part I: enzymatic cells

Recent developments in bio-fuel cell technology are reviewed. A general introduction to bio-fuel cells, including their operating principles and applications, is provided. New materials and methods for the immobilisation of enzymes and mediators on electrodes, including the use of nanostructured electrodes are considered. Fuel, mediator and enzyme materials (anode and cathode), as well as cell configurations are discussed. A detailed summary of recently developed enzymatic fuel cell systems, including performance measurements, is conveniently provided in tabular form. The current scientific and engineering challenges involved in developing practical bio-fuel cell systems are described, with particular emphasis on a fundamental understanding of the reaction environment, the performance and stability requirements, modularity and scalability. In a companion review (Part II), new developments in microbial fuel cell technologies are reviewed in the context of fuel sources, electron transfer mechanisms, anode materials and enhanced O(2) reduction.     

Bimetallic PtM (M=Pd, Ir) nanoparticle decorated multi-walled carbon nanotube enzyme-free, mediator-less amperometric sensor for H₂O₂

A new highly catalytic and intensely sensitive amperometric sensor based on PtM (where M=Pd, Ir) bimetallic nanoparticles (NPs) for the rapid and accurate estimation of hydrogen peroxide (H(2)O(2)) by electrooxidation in physiological conditions is reported. PtPd and PtIr NPs-decorated multiwalled carbon nanotube nanocatalysts (PtM/MWCNTs) were prepared by a modified Watanabe method, and were characterized by XRD, TEM, ICP, and XAS. The sensors were constructed by immobilizing PtM/MWCNTs nanocatalysts in a Nafion film on a glassy carbon electrode. Both PtPd/MWCNTs and PtIr/MWCNTs assemblies catalyzed the electrochemical oxidation of H(2)O(2). Cyclic voltammetry characterization measurements revealed that both the PtM (M=Pd, Ir)/MWCNTs/GCE possessed similar electrochemical surface areas (～0.55 cm(2)), and electron transfer rate constants (～1.23 × 10(-3)cms(-1)); however, the PtPd sensor showed a better performance in H(2)O(2) sensing than did the PtIr counterpart. Explanations were sought from XAS measurements to explain the reasons for differences in sensor activity. When applied to the electrochemical detection of H(2)O(2), the PtPd/MWCNTs/GC electrode exhibited a low detection limit of 1.2 μM with a wide linear range of 2.5-125 μM (R(2)=0.9996). A low working potential (0V (SCE)), fast amperometric response (<5s), and high sensitivity (414.8 μA mM(-1)cm(-2)) were achieved at the PtPd/MWCNTs/GC electrode. In addition, the PtPd/MWCNTs nanocatalyst sensor electrode also exhibited excellent reproducibility and stability. Along with these attractive features, the sensor electrode also displayed very high specificity to H(2)O(2) with complete elimination of interference from UA, AA, AAP and glucose.     

Kinetic and thermodynamic features reveal that Escherichia coli BCP is an unusually versatile peroxiredoxin

In Escherichia coli, bacterioferritin comigratory protein (BCP) is a peroxiredoxin (Prx) that catalyzes the reduction of H(2)O(2) and organic hydroperoxides. This protein, along with plant PrxQ, is a founding member of one of the least studied subfamilies of Prxs. Recent structural data have suggested that proteins in the BCP/PrxQ group can exist as monomers or dimers; we report here that, by analytical ultracentrifugation, both oxidized and reduced E. coli BCP behave as monomers in solution at concentrations as high as 200 μM. Unexpectedly, thioredoxin (Trx1)-dependent peroxidase assays conducted by stopped-flow spectroscopy demonstrated that V(max,app) increases with increasing Trx1 concentrations, indicating a nonsaturable interaction (K(m) > 100 μM). At a physiologically reasonable Trx1 concentration of 10 μM, the apparent K(m) value for H(2)O(2) is ~80 μM, and overall, the V(max)/K(m) for H(2)O(2), which remains constant at the various Trx1 concentrations (consistent with a ping-pong mechanism), is ~1.3 × 10(4) M(-1) s(-1). Our kinetic analyses demonstrated that BCP can utilize a variety of reducing substrates, including Trx1, Trx2, Grx1, and Grx3. BCP exhibited a high redox potential of -145.9 ± 3.2 mV, the highest to date observed for a Prx. Moreover, BCP exhibited a broad peroxide specificity, with comparable rates for H(2)O(2) and cumene hydroperoxide. We determined a pK(a) of ~5.8 for the peroxidatic cysteine (Cys45) using both spectroscopic and activity titration data. These findings support an important role for BCP in interacting with multiple substrates and remaining active under highly oxidizing cellular conditions, potentially serving as a defense enzyme of last resort.     

Quercetin both partially attenuates hydrogen peroxide-induced toxicity and decreases viability of rat glial cells

Quercetin is one of the most ubiquitous flavonoids in foods of plant origin. Although quercetin is generally considered to provide protection against oxidative injury, recent studies have shown to be cytotoxic to many cell types. We intended here to determine whether quercetin protects against H2O2-induced toxicity and/or affects viability of rat mixed glial cells. The cells were obtained from 1-3 day olds rat brains and incubated in a humidified atmosphere of 5% CO2, at 37 °C in flasks. In the quercetin groups, different quercetin concentrations (1, 10, 50, 75 or 100 μM) were applied alone for 24 h. For H2O2 cytotoxicity group, the glial cells were treated for 3 h with 100 μM H2O2 which induced 75% cell death. In another group, the cells were treated with 100 μM H2O2 plus respective quercetin concentrations simultaneously for 3 h, the medium was removed and refed for 24 h. MTT test was then applied and statistical significance was ascertained by one way analysis of variance, followed by Tukey's multiple comparison test. Quercetin starting from 50 μM decreased the glia survival significantly. In H2O2 plus quercetin co-treated groups, both 75 and 100 μM quercetin attenuated toxic effect of H2O2 by 15%. In conclusion, quercetin both partially protects H2O2-induced gliotoxicity and decreases rat glial cell viability in primary culture.     

Direct electrochemistry of hemoglobin on carbonized titania nanotubes and its application in a sensitive reagentless hydrogen peroxide biosensor

Carbonized TiO(2) nanotubes (TNT/C) prepared by carbonization with organic polymers possess advantages combined from high conductivity of carbon and nanostructure of TiO(2) nanotubes. The material was used as a supporting matrix to immobilize a redox protein, hemoglobin (Hb), to explore its direct electron transfer ability. The apparent heterogeneous electron transfer rate constant (k(ET)) of Hb on TNT/C is 108s(-1), which is much higher than that in the reported works, demonstrating excellent direct electrochemistry behavior. The TNT/C-Hb modified glassy carbon electrode (GCE) demonstrates significant electrocatalytic activity for reduction of hydrogen peroxide with a small apparent Michaelis-Menten constant (87.5 microM). The TNT/C-Hb based H(2)O(2) sensor has a low detection limit (0.92 microM), fast response time (3s) and high dynamic response range (10(-6) to 10(-4)M), a much better performance than the reported works. These results demonstrate that a direct electrochemistry behavior can be significantly enhanced through simple carbon coating on a nanostructured material for higher reaction surface area and better conductivity. This work suggests that Hb-immobilized TNT/C has potential applications in a sensitive H(2)O(2) sensor.     

A glucose fuel cell for implantable brain-machine interfaces

We have developed an implantable fuel cell that generates power through glucose oxidation, producing 3.4 μW cm(-2) steady-state power and up to 180 μW cm(-2) peak power. The fuel cell is manufactured using a novel approach, employing semiconductor fabrication techniques, and is therefore well suited for manufacture together with integrated circuits on a single silicon wafer. Thus, it can help enable implantable microelectronic systems with long-lifetime power sources that harvest energy from their surrounds. The fuel reactions are mediated by robust, solid state catalysts. Glucose is oxidized at the nanostructured surface of an activated platinum anode. Oxygen is reduced to water at the surface of a self-assembled network of single-walled carbon nanotubes, embedded in a Nafion film that forms the cathode and is exposed to the biological environment. The catalytic electrodes are separated by a Nafion membrane. The availability of fuel cell reactants, oxygen and glucose, only as a mixture in the physiologic environment, has traditionally posed a design challenge: Net current production requires oxidation and reduction to occur separately and selectively at the anode and cathode, respectively, to prevent electrochemical short circuits. Our fuel cell is configured in a half-open geometry that shields the anode while exposing the cathode, resulting in an oxygen gradient that strongly favors oxygen reduction at the cathode. Glucose reaches the shielded anode by diffusing through the nanotube mesh, which does not catalyze glucose oxidation, and the Nafion layers, which are permeable to small neutral and cationic species. We demonstrate computationally that the natural recirculation of cerebrospinal fluid around the human brain theoretically permits glucose energy harvesting at a rate on the order of at least 1 mW with no adverse physiologic effects. Low-power brain-machine interfaces can thus potentially benefit from having their implanted units powered or recharged by glucose fuel cells.     

Immobilization of lutetium bisphthalocyanine in nanostructured biomimetic sensors using the LbL technique for phenol detection

This study describes the development of amperometric sensors based on poly(allylamine hydrochloride) (PAH) and lutetium bisphthalocyanine (LuPc(2)) films assembled using the Layer-by-Layer (LbL) technique. The films have been used as modified electrodes for catechol quantification. Electrochemical measurements have been employed to investigate the catalytic properties of the LuPc(2) immobilized in the LbL films. By chronoamperometry, the sensors present excellent sensitivity (20 nA μM(-1)) in a wide linear range (R(2)=0.994) up to 900 μM and limit of detection (s/n=3) of 37.5 × 10(-8)M for catechol. The sensors have good reproducibility and can be used at least for ten times. The work potential is +0.3 V vs. saturated calomel electrode (SCE). In voltammetry measurements, the calibration curve shows a good linearity (R(2)=0.992) in the range of catechol up to 500 μM with a sensitivity of 90 nA μM(-1) and LD of 8 μM.     

Exceptionally Enhanced Electrode Activity of (Pr,Ce)O2−δ‐Based Cathodes for Thin‐Film Solid Oxide Fuel Cells

It is shown that an electrochemically‐driven oxide overcoating substantially improves the performance of metal electrodes in high‐temperature electrochemical applications. As a case study, Pt thin films are overcoated with (Pr,Ce)O_2?δ (PCO) by means of a cathodic electrochemical deposition process that produces nanostructured oxide layers with a high specific surface area and uniform metal coverage and then the coated films are examined as an O₂‐electrode for thin‐film‐based solid oxide fuel cells. The combination of excellent conductivity, reactivity, and durability of PCO dramatically improves the oxygen reduction reaction rate while maintaining the nanoscale architecture of PCO layers and thus the performance of the PCO‐coated Pt thin‐film electrodes at high temperatures. As a result, with an oxide coating step lasting only 5 min, the electrode resistance is successfully reduced by more than 1000 times at 500 °C in air. These observations provide a new direction for the design of high‐performance electrodes for high‐temperature electrochemical cells.     

N-acetyl-L-cysteine counteracts oxidative stress and prevents H2O2 induced germ cell apoptosis through down-regulation of caspase-9 and JNK/c-Jun

The mechanism of H(2)O(2) induced oxidative stress leading to male germ cell apoptosis was earlier reported from our laboratory. In the present study, we investigated the mechanisms by which N-acetyl-L-cysteine (NAC, which is highly cell specific with strong antioxidant and anti-genotoxic properties), stimulated cell survival under such conditions. Co-incubation with 5 mM NAC significantly (P<0.001) reduced the germ cell apoptosis induced by 10 μM H(2)O(2). Lipid peroxidation was brought down with significant restoration of activities of antioxidant enzymes, SOD, GST, and catalase. Expression of pro-apoptotic marker, Bax up-regulated following H(2)O(2) exposure, was reversed back to control levels. In contrast, expression of anti-apoptotic Bcl-2 and phospho-Akt revealed a completely opposite trend. While caspase-8 activity remained unaffected, NAC successfully attenuated the increased activities of caspase-3 and -9 in the H(2) O(2) treated cells. Simultaneously, the increased expression of caspase-9, phospho-JNK, and phospho-c-Jun after H(2)O(2) treatment was down-regulated by NAC. The above findings indicate that the mechanism of inhibition of H(2)O(2) induced male germ cell apoptosis by NAC is mediated through regulation of caspase-9 and JNK.     

A highly efficient buckypaper-based electrode material for mediatorless laccase-catalyzed dioxygen reduction

The redox enzyme laccase from Trametes versicolor efficiently catalyzes the oxygen reduction reaction (ORR) in mediatorless biofuel cell cathodes when adsorbed onto multi-walled carbon nanotubes (MWCNTs). In this work we demonstrate that the fabrication of MWCNTs in form of buckypaper (BP) results in an excellent electrode material for laccase-catalyzed cathodes. BPs are mechanically stable, self-entangling mats with high dispersion of MWCNTs resulting in easy to handle homogeneous layers with highly mesoporous structures and excellent electrical conductivities. All biocathodes have been electrochemically investigated in oxygen-saturated buffer at pH 5 by galvanostatic polarization and potentiodynamic linear sweep voltammetry. Both methods confirm an efficient direct interaction of laccase with BP with a high open circuit potential of 0.882 V vs. normal hydrogen electrode (NHE). The high oxygen reduction performance leads to high current densities of 422±71 μA cm(-2) at a typical cathode potential of 0.744 V vs. NHE. When the current density is normalized to the mass of the electrode material (mass activity), the BP-based film electrodes exhibit a 68-fold higher current density at 0.744 V vs. NHE than electrodes fabricated from the same MWCNTs in a non-dispersed agglomerated form as packed electrodes. This clearly shows that MWCNTs can act more efficiently as cathode when prepared in form of BP. This can be attributed to reduced diffusional mass transfer limitations and enhanced electrical conductivity. BP is thus a very promising material for the construction of mediatorless laccase cathodes for ORR in biofuel cells. In addition we demonstrated that these electrodes exhibit a high tolerance towards glucose, the most common bioanode fuel.     

Gold-coated silica-fiber hybrid materials for application in a novel hydrogen peroxide biosensor

We describe the preparation and characterization of a novel type of core-shell hybrid material for application in a novel hydrogen peroxide biosensor, where the structure consists of a continuous gold shell that encapsulates the silica fiber. The SiO(2)@Au nanofibers had been synthesized by electrospinning silica sol, and then golden seeds were in situ grown on the fiber, lastly the gold-seeded silica fibers were further coated by continuous gold shells. The above nanocomposites had satisfactory chemical stability, excellent biocompatibility and efficient electron transfer property, which may have potential application for the highly sensitive chemical or biological sensors. Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the SiO(2)@Au nanocomposites at indium tin oxide (ITO). The biosensor showed high sensitivity and fast response upon the addition of H(2)O(2) and the linear range to H(2)O(2) was from 5×10(-6) to 1.0×10(-3)M with a detection limit of 2 μM (S/N=3). The apparent Michaelis-Menten constant of the biosensor was 1.11 mmol L(-1). These results indicated that SiO(2)@Au nanocomposites have potential for constructing of a variety of electrochemical biosensors.     

A novel hydrogen peroxide biosensor based on the immobilization of horseradish peroxidase onto Au-modified titanium dioxide nanotube arrays

In this study, we report on a promising H(2)O(2) biosensor based on the co-immobilization of horseradish peroxidase (HRP) and chitosan onto Au-modified TiO(2) nanotube arrays. The titania nanotube arrays were directly grown on a Ti substrate using anodic oxidation first; a gold thin film was then uniformly coated onto the TiO(2) nanotube arrays by an argon plasma technique. The morphology and composition of the fabricated Au-modified TiO(2) nanotube arrays were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Cyclic voltammetry and chronoamperometry were used to study and to optimize the performance of the resulting electrochemical biosensor. The effect of pH, applied electrode potential, the presence of the electron-mediator methylene blue, and the anodic oxidation time of the Ti substrate on the electrochemical biosensor has been systemically studied. Our electrochemical measurements show that the Au-modified TiO(2) nanotube arrays provide excellent matrices for the immobilization of HRP and that the optimized electrochemical biosensor exhibits long linearity, a low detection limit, high stability and very good reproducibility for the detection of H(2)O(2). Under the optimized conditions the linearity of the developed biosensor for the detection of H(2)O(2) is observed from 5 x 10(-6) to 4 x 10(-4) moll(-1) with a detection limit of 2 x 10(-6) moll(-1) (based on the S/N=3).     

Intrinsically Stretchable Fuel Cell Based on Enokitake‐Like Standing Gold Nanowires

Conventional fuel cells are based on rigid electrodes, limiting their applications in wearable and implantable electronics. Here, it is demonstrated that enokitake‐like vertically‐aligned standing gold nanowires (v‐AuNWs) can also serve as powerful platform for stretchable fuel cells by using ethanol as model system. Unlike traditional fuel cell electrodes, the v‐AuNWs have “Janus Morphology” on both sides of the film and also are highly stretchable. The comparative studies demonstrate that tail side exposed v‐AuNWs based stretchable electrodes outperform the head‐side exposed v‐AuNWs toward the electro‐oxidation of ethanol due to the direct exposure of high‐surface‐area nanowires to the fuels. Therefore, a stretchable fuel cell is fabricated utilizing tail side based interdigitated electrodes, where v‐AuNWs and Pt black modified v‐AuNWs serve as the anode and cathode, respectively. The as‐prepared stretchable fuel cell exhibits good overall performance, including high power density, current density, open‐circuit voltage, stretchability, and durability. Most importantly, a wearable fuel cell is also achieved by integrating tattoo‐like interdigitated electrodes with a thin layer of sponge as a fuel container, exhibiting good performance under various deformations (compression, stretching, and twisting). Such attractive performance in conjunction with skin‐like in‐plane design indicates its great potential to power the next‐generation of wearable and implantable devices.