Abstract  A novel melamine electrochemiluminescence (ECL) sensor was developed based on mesoporous SiO(2) nanospheres/Ru(bpy)(3)(2+)/Nafion modified electrodes. The homogeneous mesoporous silica nanospheres, synthesized using modified Stöber sol-gel process, were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM) and Brunauer-Emmett-Teller (BET). The ECL and electrochemistry of the modified electrodes were investigated with tri-n-propylamine (TPA) as the coreactant. Furthermore, the mesporous SiO(2) nanospheres/Ru(bpy)(3)(2+)-based modified electrodes were used for ECL determination of melamine. The analytical performances of this ECL sensor for melamine based on its enhancement ECL emission of Ru(bpy)(3)(2+) were investigated. The results indicated that the sensor exhibited excellent performance during melamine determination with a wide linear range (7.81×10(-9)-5×10(-6) M), low detection limit (2.6×10(-9) M). The high sensitivity and stability mainly resulted from the high surface area and special structure of the mesoporous silica nanospheres. The proposed ECL approach was used to analyze the melamine content in powdered milk with satisfactory results.

Abstract  We study the energy relaxation and structural relaxation dynamics of hydrated protons in Nafion membranes at different hydration levels using femtosecond infrared transient absorption spectroscopy. At low hydration levels we observe that the excitation of the proton vibration of an Eigen-like proton hydration structure leads to a structural relaxation process in which the Eigen-like structure evolves to a Zundel-like proton hydration structure. This reorganization leads to a transfer of the proton charge and closely follows the mechanism of infrared-induced adiabatic proton transfer that has been proposed by S. Hammes-Schiffer, J. T. Hynes, and others. At high hydration levels, the spectral dynamics are dominated by vibrational energy relaxation and subsequent cooling of the proton hydration structures and the surrounding water molecules. Using a kinetic analysis of the transient spectral data, we determine the rates of proton transfer, vibrational energy relaxation, and cooling as a function of hydration level. We find that infrared-induced proton transfer occurs at all hydration levels but becomes less observable at high hydration levels due to the increasingly dominant influence of the vibrational energy relaxation.

Abstract  Direct electrochemistry of Trametes versicolor Laccase (LAC) was found at a Sonogel-Carbon electrode. The bioamplification, performed by dual immobilization of this enzyme and Mushroom Tyrosinase (TYR), of the bio-electrocatalytic reduction of O(2) was investigated. The calculated alpha transfer coefficients were 0.64 and 0.67, and the heterogeneous electron-transfer rate constants were 6.19 and 8.52 s(-1), respectively, for the individual LAC and dual LAC-TYR-based Nafion/Sonogel-Carbon bio-electrodes. The responses of the dual enzymes electrode to polyphenols were stronger than those of the individual LAC or TYR biosensors. Hypotheses are offered about the mechanism of bioamplification. The surfaces of the biosensors were also characterized by AFM.

Abstract  Nitric oxide (•NO) is a ubiquitous signaling molecule that participates in neuromolecular phenomena associated with memory formation as well as in excitotoxicity. In the hippocampus, neuronal •NO production is coupled to the activation of the NMDA-type of glutamate receptor. More recently, Cytochrome c oxidase has emerged as a novel target for •NO, which competes with O 2 for binding to this mitochondrial complex. This reaction establishes •NO not only as a regulator of cellular metabolism but possibly also as a regulator of mitochondrial production of reactive oxygen species which participate in cellular signaling. A major gap in the understanding of •NO bioactivity, namely, in the hippocampus, has been the lack of knowledge of its concentration dynamics. Here, we present a detailed description of the simultaneous recording of •NO and O2 concentration dynamics in rat hippocampal slices. Carbon fi ber microelectrodes are fabricated and applied for real-time measurements of both gases in a system close to in vivo models. This approach allows for a better understanding of the current paradigm by which an intricate interplay between •NO and O 2 regulates cellular respiration.

Abstract  To improve proton conduction at elevated temperatures, in situ impregnation of Nafion membranes has been carried out by infusing Noria ''waterwheel'' supramolecules, containing numerous hydroxyl terminal groups, into the ionic domains of Nafion via swelling in mixed methanol and dimethylacetamide solutions. Fourier transform infrared (FTIR) spectroscopy study reveals that interspecies hydrogen bonding occurs between hydroxyl groups of Noria and sulphonate groups of Nafion, which has facilitated retaining the modifier molecules within the membrane. Water uptake experiments exhibit that the impregnation of Noria into Nafion ionic domains suppresses the membrane swelling. The ion exchange capacity also increases upon this impregnation. The proton conductivity is reduced at low operating temperatures relative to neat Nafion due to the loss of hydronium ion transport. However, the proton conductivity of the Noria-impregnated membrane shows 60 % improvement over that of neat Nafion at elevated temperatures of 115 degree C. Of particular importance is that the Noria-impregnated membrane exhibits improved thermal, mechanical, and electrochemical stabilities with proton conductivity enhancement at elevated temperatures. Moreover, there is no noticeable difference in FTIR spectra before and after the proton fuel cell tests, indicating the improvement in the chemical stability of the Noria-impregnated membranes under the present proton fuel environment. It appears that these waterwheel supramolecules may have potential utility as high temperature electrolytes (or solid proton carriers) in proton fuel cells. 30 Refs.

Abstract  In this paper, we focus on improvement of the monovalent cation perm-selectivity of a perfluorinated cation-exchange membrane, Nafion 117, by depositing an anion-exchange layer using a plasma surface modification process. The anion-exchange layer was deposited from 4-vinylpyridine monomer vapor followed by quaternization with 1-bromopropane. The transference number of divalent cation (Fe2+) through the membrane, t(Fe), decreased with increasing thickness of the plasma polymer layer at the expense of enhanced membrane resistance. A large interfacial resistance was observed between Nafion and the plasma polymer layer which was ascribed to the implantation of cationic species containing nitrogen. To avoid the formation of an interfacial layer, a novel method of plasma-induced surface modification was devised. After a Nafion 117 sheet was placed on an RF (radio-frequency) electrode and sputtered with an oxygen or argon plasma in order to produce active sites on the Nafion, 4-vinylpyridine or 3-(2-aminoethyl)aminopropyltrimethoxysilane vapor was introduced into the reactor to react with radical sites. t(Fe) decreased with increasing RF power. t(Fe) through Nafion modified with 3-(2-aminoethyl)aminopropyltrimethoxysilane was lower than that for Nafion modified with 4-vinylpyridine, probably due to its weak Si-C bond. Nafion treated by the plasma surface modification method exhibited a very high monovalent cation perm-selectivity compared with Nafion treated by the plasma polymerization method.

Abstract  The effects of multiwalled carbon nanotubes (MWNTs) and carbon black (CB) as conducting additives on the Fate capability of natural graphite negative electrodes in lithium-ion (Li-ion) batteries is investigated within concentration ranges where no degradation of anode capacity is observed. MWNT or CB solutions prepared with Nafion in an 80:20 volume mixture of water: 1-propanol are incorporated into graphite precursor suspensions consisting of graphite particulates, carboxymethyl cellulose, and styrene butadiene rubber prepared in an aqueous medium. While negative electrodes with MWNTs demonstrate much better rate behaviour than those without MWNTs at a high C-rate, the rate capability of negative electrodes with MWNTs is not much different from that with CB. The reason for this similar behaviour is investigated with respect to the structural changes and aspect ratio of MWNTs, as well as the density difference between MWNTs and carbon black. Scanning electron microscopy images and Raman spectra for the dispersed MWNTs indicate that MWNTs are significantly damaged and shortened during dispersion, which reduces their electrical conductivity and increases their percolation threshold. This damage negatively affects the rate capability of graphite-nanotube composite electrodes. (C) 2008 Elsevier B.V. All rights reserved.

Abstract  In polymer electrolyte fuel cell operation, a decrease in the proton conductivity of the membrane at reduced humidity is a main cause for poor cell performance at high temperature. To alleviate the dehydration of the membrane at high temperature, sulfonated mesoporous benzene-silica (sMBS) particles are embedded in sulfonated poly(ether ether ketone) (sPEEK) membranes. As the sMBS itself is highly sulfonated on both organic and inorganic moieties, the proton conductivity of composite membranes is much higher than that of the pristine sPEEK membrane, and it reaches that of Nafion 117 at a high relative humidity (RH) of 90%. The dehydration rate of the membrane is reduced significantly by the capillary condensation effect of sMBS particles with the nanometer-scale 2-D hexagonal cylindrical pores, and the proton conductivity of the composite membranes, 0.234 x 10(-1-) S cm(-1), is much higher than that of pristine sPEEK membrane, 0.59 x 10(-3) S cm(-1), at a relatively low humidity of 40% RH. This maintenance of high conductivity at low humidity is attributed to the high water-holding capacity of the sMBS proton conductors. The sMBS-embedded sPEEK composite membranes show a much lower methanol permeability of 2 -5 x 10(-7) cm(2) s(-1) compared to that of Nafion 117, which is 1.6 x 10(-6) cm(2) s(-1) at room temperature. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Abstract  The influence of Cr3C2 and VC addition on the microstructure and mechanical properties of WC-Mg composites hot-pressed at 1650 degrees C for 90 min was comprehensively investigated. The grain growth of WC was significantly retarded and the homogeneity of MgO particulate dispersion was effectively improved with the addition of 0.5 wt.% Cr3C2 or 0.5 wt.% VC. The indentation size effect (ISE) on hardness was restrained and the load-independent hardness was increased by doping grain growth inhibitors. Improvements on fracture toughness of hot-pressed samples were also observed due to the refined WC grains and uniformly dispersed MgO particulates. In addition, experimental results demonstrated that Niihara's equation was preferable for estimating the indentation fracture toughness, by comparing the fracture toughness evaluated using the single-edge V-notch beam (SEVNB) method with the values estimated through the Vickers indentation technique. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract  Platinum-niobium catalysts were prepared as candidates for CO tolerant anode catalysts for low and high temperature PEM fuel cells (PEMFCs). Three different compositions were prepared by the formic acid method, from platinum (hexachloroplatinic acid) and niobium (niobium chloride) precursors on Vulcan XC-72R carbon black. Deposition of the niobium was found to be quite difficult, and only a fraction of the desired composition was achieved. Mean particle sizes were all in the nanometric range, between 2 and 3 nm. Diffraction patterns display neither insertion of niobium within the crystalline structure of platinum, nor any crystalline phase associated to that material. Nevertheless, the presence of Nb displays a noticeable effect on the CO tolerance of the catalyst firstly revealed by a reduction of the CO stripping onset potential. Fuel cell results, operating with Nafion(A (R)) at low temperature (80 A degrees C) and H-2 + 100 ppm of CO as fuel, and with H3PO4-doped ABPBI, at high temperature (150 A degrees C) and H-2 + 20,000 ppm of CO, display an enhancement in the performance compared to pure platinum, so niobium may be an interesting material for increasing the tolerance to carbon monoxide in PEMFC. Finally, CO/O-2 polarisation curves display a decrease in the current density in the presence of Nb, confirming that the enhanced CO tolerance can be attributed to a strong electronic effect that weakens the Pt-CO adsorption strength.

Abstract  A quantitative method for measuring polyvinylsulfonic acid (PVS) concentrations in 2-(N-morpholino)ethanesulfonic acid (MES) is described here. Utilizing a TSK-GEL G2500PW(xl) SEC column, PVS elutes in the void volume as a sharp peak, yielding group separation between PVS and MES. 20 mM formic acid is used as the mobile phase, as its volatility is compatible with a charged aerosol detector. The low pH mobile phase also suppresses residual negative charges on the stationary phase, reducing the ion exclusion effect commonly observed in aqueous SEC. This method was qualified to measure PVS concentration in MES per International Conference on Harmonization guidelines, using multiple MES lots and other Good's buffers such as N-(2-acetamido)-2-aminoethanesulfonic acid and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid.

Abstract  The hydration structure of the 'strongly bound water' around the sulfonic acid (SA) groups in Nafion, which has recently been revealed by (1)H NMR spectroscopy (Anal. Chem., 2013, 85, 7581), is studied using infrared spectroscopy with the aid of quantum chemical (QC) calculations. During a heated drying process, bulky water is firstly dehydrated, which is followed by the disappearance of the hydronium ion and the appearance of bands that have been assigned to the fully dehydrated species at 140 °C. However, a spectral simulation based on QC reveals that the spectrum at 140 °C comes from the SA group associated with a single-water molecule via two H-bonds. This implies that a thoroughly dried membrane is unavailable even at 140 °C, and the involved water corresponds to the 'strongly bound water.' The QC-analytical results are experimentally confirmed by evolved gas analysis mass spectrometry (EGA-MS). At ca. 300 °C, which is the temperature where the SA group is selectively decomposed, the molecular fragment of SO2 is observed accompanying water molecules as expected. This confirms that the last single-water molecule can remain on the SA group until the thermal decomposition.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. Eleven priority phenols were separated by capillary zone electrophoresis (CZE) and detected on-line with electrospray ionization mass spectrometry (ESI-MS) in the negative-ion mode. Parameters critical to the coupling of CZE and MS were studied. The best result was obtained with 2-(N-cyclohexylamino)ethanesulfonic acid (CHES) as the running buffer and a solution of water-2-propanol (20:90) containing 0.5% ammonia as the sheath liquid. With the use of field amplification as the preconcentration technique and the mass spectrometer operated in the selected ion monitoring mode, the detection limit of most phenols was found to be in the range of 50 ppb. This method has been successfully applied to the determination of pentachlorophenol in a paper clay sample.

Abstract  Because Ru(bpy)32+-modified electrodes are often used in aqueous condition, the development of a hydrophilic modified electrode is of critical importance. Herein a hydrophilic, thin film Ru(bpy)32+-modified electrode is successfully developed using polyacrylamide gel to embed halloysite nanotubes on the electrode surface which is used to adsorb Ru(bpy)32+ by cation-exchange. X-ray photoelectron spectroscopy demonstrates the formation of the film on an electrode and the high adsorbing capacity of the halloysite nanotubes toward Ru(bpy)32+. The different electrochemiluminescence (ECL) behaviors of the electrode using nitrilotriacetic acid and tripropylamine, as co-reactants, illustrate the hydrophilic character of the modified electrode. Contrary to the previous works, the addition of carbon nanotubes into the modified electrode film leads to a decreased ECL emission, due to the reduction in the porosity of the film, which hinders the diffusion of the analyte.

Abstract  Herein we report the covalent functionalization of multiwall carbon nanotubes by grafting sulfanilic acid and their dispersion into sulfonated poly(ether ether ketone). The nanocomposites were explored as an option for tuning the proton and electron conductivity, swelling, water and alcohol permeability aiming at nanostructured membranes and electrodes for application in alcohol or hydrogen fuel cells and other electrochemical devices. The nanocomposites were extensively characterized, by studying their physicochemical and electrochemical properties. They were processed as self-supporting films with high mechanical stability, proton conductivity of 4.47 x 10 super(-2) S cm super(-1) at 30 C and 16.8 x 10 super(-2) S cm super(-1) at 80 C and 100% humidity level, electron conductivity much higher than for the plain polymer. The methanol permeability could be reduced to 1/20, keeping water permeability at reasonable values. The ratio of bound water also increases with increasing content of sulfonated filler, helping in keeping water in the polymer in conditions of low external humidity level.

Abstract  A prototype amperometric immunosensor was evaluated based on the adsorption of antibodies onto perpendicularly oriented assemblies of single wall carbon nanotubes called SWNT forests. The forests were self-assembled from oxidatively shortened SWNTs onto Nafion/iron oxide coated pyrolytic graphite electrodes. The nanotube forests were characterized using atomic force microscopy and resonance Raman spectroscopy. Anti-biotin antibody strongly adsorbed to the SWNT forests. In the presence of a soluble mediator, the detection limit for horseradish peroxidase (HRP) labeled biotin was 2.5 pmol ml(-1) (2.5 nM). Unlabelled biotin was detected in a competitive approach with a detection limit of 16 nmol ml(-1) (16 microM) and a relative standard deviation of 12%. The immunosensor showed low non-specific adsorption of biotin-HRP (approx. 0.1%) when blocked with bovine serum albumin. This immunosensing approach using high surface area, patternable, conductive SWNT assemblies may eventually prove useful for nano-biosensing arrays.

Abstract  A novel amperometric sensor and chromatographic detector for determination of parathion has been fabricated from a multi-wall carbon nano-tube (MWCNT)/Nafion film-modified glassy-carbon electrode (GCE). The electrochemical response to parathion at the MWCNT/Nafion film electrode was investigated by cyclic voltammetry and linear sweep voltammetry. The redox current of parathion at the MWCNT/Nafion film electrode was significantly higher than that at the bare GCE, the MWCNT-modified GCE, and the Nafion-modified GCE. The results indicated that the MWCNT/Nafion film had an efficient electrocatalytic effect on the electrochemical response to parathion. The peak current was proportional to the concentration of parathion in the range 5.0x10(-9)-2.0x10(-5) mol L(-1). The detection limit was 1.0x10(-9) mol L(-1) (after 120 s accumulation). In high-performance liquid chromatography with electrochemical detection (HPLC-ED) a stable and sensitive current response was obtained for parathion at the MWCNT/Nafion film electrode. The linear range for parathion was over four orders of magnitude and the detection limit was 6.0x10(-9) mol L(-1). Application of the method for determination of parathion in rice was satisfactory.

Abstract  In this paper, a simple one-step electrodeposition method is described to fabricate chitosan-Prussian blue-multiwall carbon nanotubes-hollow PtCo nanochains (CS-PB-MWNTs-H-PtCo) film onto the gold electrode surface, then glucose oxidase (GOD) and Nafion were modified onto the film subsequently to fabricate a glucose biosensor. The morphologies and electrochemistry of the composite were investigated by using Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and electrochemical techniques including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. The performances of the biosensor have been investigated by chronoamperometry method under the optimized conditions. This biosensor showed a linear response to glucose range from 1.5 μM to 1.12 mM with a detection limit of 0.47 μM (S/N=3), a high sensitivity of 23.4 μA mM(-1) cm(-2), and a fast response time. The apparent Michaelis-Menten constant (K(M)(app)) was 1.89 mM. In addition, the biosensor also exhibited strong anti-interference ability, excellent stability and good reproducibility.

Abstract  A highly ordered mesoporous Nafion membrane with a remarkable water retention ability was synthesized via a micelle templating method with self-assembled Pluronic F108 surfactants and its capability to operate under completely dry gas streams is demonstrated.

Abstract  Electrochemically active composite film that contains multiwalled carbon nanotubes (MWCNTs), Nafion (NF), and poly(malachite green) (PMG) has been synthesized on glassy carbon electrode (GCE), gold, and indium tin oxide (ITO) electrodes by potentiodynamic method. The presence of MWCNTs in the composite film (MWCNT-NF-PMG) enhances the surface coverage concentration (Γ) of PMG by fivefold. Similarly, an electrochemical quartz crystal microbalance study revealed enhancement in the deposition of PMG at MWCNT-NF film when compared with bare and only NF modified electrodes. The surface morphology of the composite film was studied using atomic force microscopy, which revealed that the PMG incorporated on MWCNT-NF film. The composite film exhibited enhanced electrocatalytic activity toward the mixture of biochemical compounds catechol and quinol. The electrocatalytic responses of analytes at MWCNT-NF-PMG composite film were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electrocatalysis studies, well-separated voltammetric peaks were obtained at the composite film for catechol and quinol with a peak separation of 147mV. The sensitivity values of the composite film toward catechol and quinol by the DPV technique were 0.4 and 3.2mAmM(-1)cm(-2), respectively, which are higher than the values obtained by the CV technique. Similarly, the above-mentioned values are better than the previously reported electroanalytical values for the same analytes.

Abstract  A novel disposable amperometric biosensor strip for determination of blood alcohol concentration (BAC) with small volume of sample has been constructed using screen-printed electrodes (SPE), nanocomposite film and alcohol dehydrogenase (ADH). Firstly, the GNPs-MWCNT-Nafion nanocomposite film modified on a working electrode was made of Nafion-117, multi-wall carbon nanotubes (MWCNT) and gold nanoparticles (GNPs). After that Meldola's blue (MB) acted as an electron transfer mediator and the mixed solution of ADH, nicotinamide adenine dinucleotide (NAD(+)) were modified in order on the nanocomposite film. At last, a hydrophilic membrane which had an eyehole in center was placed at the outermost of the working area to make a reaction tank of 5 μL, then the hydrophilic membrane/ADH-NAD(+)/GNPs-MWCNT-MB-Nafion/SPE was prepared. The detection of BAC can be accomplished with 5 μL of blood sample obtained precisely by siphonage. Optimum conditions of the biosensor were experimentally determined by varying several important parameters: working potential, solution pH value, environmental temperature and interferences. Experimental results indicated that the biosensor possessed a good accuracy and stability, the linear response range was 2.0 × 10(-4) to 25 × 10(-3)mol/L and the detection limit of the biosensor was 5.0 × 10(-5)mol/L (S/N=3). In the measurement of blood samples, the proposed biosensor had excellent detection performance for measuring BAC and showed a good correlation with gas chromatography. The prepared biosensor strip can be valid for the analysis of BAC.