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Good Stability (good + stability)
Selected AbstractsFabrication of Diverse Microcapsule Arrays of High Density and Good StabilityMACROMOLECULAR RAPID COMMUNICATIONS, Issue 12 2010Jie Yang Abstract Microcapsule arrays attract a lot of interest due to their potential applications in sensing technology. A strategy for fabricating diverse microcapsule arrays through covalent linking is reported here. The self-assembly of microcapsules was directed by using a poly(allylamine hydrochloride) (PAH)-patterned template, which was created via microcontact printing. The microcapsules with PAH as the outermost layer were treated with glutaraldehyde and then covalently immobilized on the PAH regions, resulting in ordered microcapsule arrays. The arrays had a high density of capsules and the aggregate number in a pattern could be well controlled by adjusting the area of the PAH pattern. A single microcapsule array could be obtained if the diameter of the PAH region was smaller than that of the microcapsules. These covalently assembled arrays could survive through successive incubation in solutions of high ionic strength and extreme pHs. Such good stability ensures further treatments, such as chemical reactions and loading of functional substances. [source] Multimode fiber ring-down pressure sensorMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2007Huiye Qiu Abstract A fiber-loop ring-down spectroscopy based on multimode fiber is proposed for pressure measurement. It has been found that the multimode fiber-loop ring-down pressure sensor has higher sensitivity and larger dynamic range up to 6.2 × 107 Pa compared to the single mode counterpart. Good stability and repeatability of the sensor are also demonstrated. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1698,1700, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22553 [source] Original Fuel-Cell Membranes from Crosslinked Terpolymers via a "Sol,gel" StrategyADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Ozlem Sel Abstract Hybrid organic/inorganic membranes that include a functionalized (-SO3H), interconnected silica network, a non-porogenic organic matrix, and a -SO3H-functionalized terpolymer are synthesized through a sol,gel-based strategy. The use of a novel crosslinkable poly(vinylidene fluoride- ter -perfluoro(4-methyl-3,6-dioxaoct-7-ene sulfonyl fluoride)- ter -vinyltriethoxysilane) (poly(VDF- ter -PFSVE- ter -VTEOS)) terpolymer allows a multiple tuning of the different interfaces to produce original hybrid membranes with improved properties. The synthesized terpolymer and the composite membranes are characterized, and the proton conductivity of a hybrid membrane in the absence of the terpolymer is promising, since 8,mS cm,1 is reached at room temperature, immersed in water, with an experimental ion-exchange-capacity (IECexp) value of 0.4,meq g,1. Furthermore, when the composite membranes contain the interfaced terpolymer, they exhibit both a higher proton conductivity (43,mS cm,1 at 65 °C under 100% relative humidity) and better stability than the standard hybrid membrane, arising from the occurrence of a better interface between the inorganic silica and the poly[(vinylidene fluoride)- co -hexafluoropropylene] (poly(VDF- co -HFP)) copolymer network. Accordingly, the hybrid SiO2 -SO3H/terpolymer/poly(VDF- co -HFP) copolymer membrane has potential use as an electrolyte in a polymer-electrolyte-membrane fuel cell operating at intermediate temperatures. [source] Thermoelectric Performance of Epitaxial Thin Films of Layered Cobalt Oxides Grown by Reactive Solid-Phase Epitaxy with Topotactic Ion-Exchange MethodsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2007Kenji Sugiura This article reviews high-quality epitaxial film growth of layered cobalt oxides by reactive solid-phase epitaxy (R-SPE) with topotactic ion-exchange methods. Epitaxial film of Na0.8CoO2 was grown on a (0001)-oriented ,-Al2O3 substrate by R-SPE using CoO film as the starting material. The Na0.8CoO2 epitaxial films were converted into high-quality epitaxial films of Sr0.32Na0.21CoO2 and [Ca2CoO3]xCoO2 by topotactic ion-exchange methods. The Sr0.32Na0.21CoO2 film exhibited better stability against moisture than that of the Na0.8CoO2 film, while it retained the good thermoelectric properties of Na0.8CoO2. The [Ca2CoO3]xCoO2 film exhibited a high electrical conductivity of 2.95 × 102 S/cm and a large Seebeck coefficient of +125 ,V/K at 300 K. [source] Chitosan(chitin)/cellulose composite biosorbents prepared using ionic liquid for heavy metal ions adsorptionAICHE JOURNAL, Issue 8 2009Xiaoqi Sun Abstract Chitosan(chitin)/cellulose composites as biodegradable biosorbents were prepared under an environment-friendly preparation processes using ionic liquids. Infrared and X-ray photoelectron spectra indicated the stronger intermolecular hydrogen bond between chitosan and cellulose, and the hydroxyl and amine groups were believed to be the metal ion binding sites. Among the prepared biosorbents, freeze-dried composite had higher adsorption capacity and better stability. The capacity of adsorption was found to be Cu(II) (0.417 mmol/g) > Zn(II) (0.303 mmol/g) > Cr(VI) (0.251 mmol/g) > Ni(II) (0.225 mmol/g) > Pb(II) (0.127 mmol/g) at the same initial concentration 5 mmol L,1. In contrast to some other chitosan-type biosorbenrts, preparation and component of the biosorbent were obviously more environment friendly. Moreover, adsorption capacity of chitosan in the blending biosorbent could be fully shown. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Tooth loss and the condition of the prosthodontic appliances in a group of elderly home residentsJOURNAL OF ORAL REHABILITATION, Issue 3 2000atovi The study assessed the number of missing teeth, the state of the existing prosthodontic appliances and the need for their replacement. Dental status and anamnesis were taken on a group of 120 elderly home residents by trained examiners. Prosthodontic appliances were evaluated according to the Karlsson's index for the crowns and bridges, and according to the modified Nevalainen et al. index for the evaluation of the complete dentures, as well as the need for prosthetic treatment. The most persistent teeth in both jaws were lower canines, while the most commonly missing teeth were lower first molars. On average, the crowns were older and in poorer condition than the bridges. Lower complete dentures had better stability but were also less retentive in comparison with the upper complete dentures. More than 82% of the subjects were in need of either fixed, removable or combined prosthodontic treatment. The high prevalence of needs for prosthodontic treatment pointed to the requirement for frequent dental check ups within elderly home residents in order to better identify and meet their dental needs. [source] Carbazolevinylene-based polymers and model compounds with oxadiazole and triphenylamine segments: Synthesis, photophysics, and electroluminescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2008Panagiotis D. Vellis Abstract Two new soluble alternating carbazolevinylene-based polymers POXD and PTPA as well as the corresponding model compounds MOXD and MTPA were synthesized by Heck coupling. POXD and MOXD contained 2,5-diphenyloxadiazole segments, while PTPA and MTPA contained triphenylamine segments. All samples displayed high thermal stability. The polymers had higher glass transition temperature (Tg) than their corresponding model compounds. The samples showed absorption maximum at 364,403 nm with optical band gap of 2.62,2.82 eV. They emitted blue-green light with photoluminescence (PL) emission maximum at 450,501 nm and PL quantum yields in THF solution of 0.15,0.36. The absorption and the PL emission maxima of PTPA and MTPA were blue-shifted as compared to those of POXD and MOXD. The electroluminescence (EL) spectra of multilayered devices made using four materials exhibited bluish green emissions, which is well consistent with PL spectra. The EL devices made using poly(vinyl carbazole) doped with MOXD and MTPA as emitting materials showed luminances of 12.1 and 4.8 cd m,2. POXD and PTPA exhibited 25.4, and 96.3 cd m,2, respectively. The polymer containing the corresponding molecules in the repeating group showed much higher device performances. Additionally, POXD and MOXD exhibited better stability of external quantum efficiency (EQE) and luminous efficiency with current density resulting from enhancing the electron transporting properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5592,5603, 2008 [source] An improved sample preparation for an LC method used in the age estimation based on aspartic acid racemization from human dentinJOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2007Raja Yekkala Abstract The determination of age on the basis of aspartic acid (Asp) racemization in teeth is one of the most reliable and accurate methods to date. In this paper, the usefulness of HPLC coupled with fluorescence detection for determination of Asp racemization was evaluated. A modified sample preparation is proposed for better stability of o -phthaldialdehyde- N -acetyl- L -cysteine derivatives of D/L -Asp (due to the instability below pH 7). To ensure the accuracy of the method, the validation parameters' specificity, precision, linearity, and LOD were determined. Three dentin samples of premolar teeth, extracted from living individuals (bucco-lingual longitudinal sections of 1 mm thickness), were analyzed and quantitative results are discussed. [source] Center of body mass and the evolution of female body shapeAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2003Bogus, aw Paw, owski Among primates, the genus Homo has a unique sexual dimorphism in general body shape. The stenotypic female "hourglass figure" has often been attributed to sexual selection. Sexual dimorphism both in shape and in position of the center of body mass (CoM) emerges during puberty and is related to hormonal influences. These are only the proximal and not the ultimate causes of this feature. This article explores the hypothesis that the evolutionary (i.e., ultimate) reason for female body shape and male preference for a lower waist-to-hip ratio (WHR) is due to the acquisition of bipedal locomotion and different biomechanical constraints on each sex. The demands of pregnancy and subsequently carrying infants may have more tightly constrained CoM in females than in males. A lower-position of CoM relative to height (RCoM=(CoM/height)*100%) would contribute to better stability during pregnancy and infant carrying. Using body measurements from 119 female students, we show that RCoM correlates negatively with only maximal thigh circumference and positively with only WHR and shoulder width. The relationship between RCoM and traits that best characterize female body shape seems to confirm a hypothesis of biomechanical selection pressure that may have acted on Homo female morphology, thus contributing to sexual dimorphism. Am. J. Hum. Biol. 15:144,150, 2003. © 2003 Wiley-Liss, Inc. [source] Pt/SiO2 as addition to multilayer SPSU/PTFE composite membrane for fuel cellsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2008L. Wang Abstract A multilayer composite membrane was prepared by reinforcing sulfonated polysulfone (SPSU) with porous polytetrafluoroethylene (PTFE), and adding Pt/SiO2,Nafion® membranes on both sides of the SPSU/PTFE membrane to self-humidify and protect the inside membrane. The ex situ Fenton test and open circuit voltage (OCV) accelerated test show that the composite membrane has better stability than the initial membrane because of the protection of the outside Pt/SiO2,Nafion layers. The composite membrane has similar performance to that of NRE-212 under the fully humidified condition and better performance than NRE-212 without humidifying. The self-humidifying membrane shows great potential for use in low humidifying conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Direct utilization of ethanol on ceria-based anodes for solid oxide fuel cellsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Massimiliano Cimenti Abstract The direct utilization of ethanol was investigated in CuCeO2, CuZr0.35Ce0.65O2 (ZDC) and Cu/RuZr0.35Ce0.65O2 anodes for solid oxide fuel cells (SOFC). The anodes were prepared by impregnation with nitrate precursors on a porous layer of yttria-stabilized zirconia (YSZ) obtained by tape casting, while (La0.8Sr0.2MnO3,,) LSM cathodes were screen-printed. The cells were tested in both hydrogen and ethanol. The outlet gas composition was monitored with a gas chromatograph, which showed that almost all the ethanol was decomposed, mainly to H2, CH4, CO, H2O and C2H4. The maximum power outputs obtained in ethanol were 0.075 and 0.400 W/cm2 on CuCeO2|YSZ|LSM and CuZDC|YSZ|LSM, respectively. All cells were more active in alcohol than in hydrogen with the peak performance occurring after approximately 4 h. That is, the power density initially increased, peaked and then decreased. This behavior was likely a consequence of carbon deposition that initially results in an improvement of the electronic conductivity in the anode but later results in the blocking of the active sites. Zirconia doping (in the ZDC anodes) resulted in better stability and, in addition, the initial activity of the ZDC anodes could be recovered after approximately 1 h of exposure to humidified hydrogen, whereas the initial activity of the ceria anodes could not be recovered. The addition of ruthenium (<0.5 wt%) further improved the stability by delaying the onset of carbon formation. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Selenium Derivatization of Nucleic Acids for X-Ray Crystal-Structure and Function StudiesCHEMISTRY & BIODIVERSITY, Issue 4 2010Jia Sheng Abstract It is estimated that over two thirds of all new crystal structures of proteins are determined via the protein selenium derivatization (selenomethionine (Se-Met) strategy). This selenium derivatization strategy via MAD (multi-wavelength anomalous dispersion) phasing has revolutionized protein X-ray crystallography. Through our pioneer research, similarly, Se has also been successfully incorporated into nucleic acids to facilitate the X-ray crystal-structure and function studies of nucleic acids. Currently, Se has been stably introduced into nucleic acids by replacing nucleotide O-atom at the positions 2,, 4,, 5,, and in nucleobases and non-bridging phosphates. The Se derivatization of nucleic acids can be achieved through solid-phase chemical synthesis and enzymatic methods, and the Se-derivatized nucleic acids (SeNA) can be easily purified by HPLC, FPLC, and gel electrophoresis to obtain high purity. It has also been demonstrated that the Se derivatization of nucleic acids facilitates the phase determination via MAD phasing without significant perturbation. A growing number of structures of DNAs, RNAs, and protein,nucleic acid complexes have been determined by the Se derivatization and MAD phasing. Furthermore, it was observed that the Se derivatization can facilitate crystallization, especially when it is introduced to the 2,-position. In addition, this novel derivatization strategy has many advantages over the conventional halogen derivatization, such as more choices of the modification sites via the atom-specific substitution of the nucleotide O-atom, better stability under X-ray radiation, and structure isomorphism. Therefore, our Se-derivatization strategy has great potentials to provide rational solutions for both phase determination and high-quality crystal growth in nucleic-acid crystallography. Moreover, the Se derivatization generates the nucleic acids with many new properties and creates a new paradigm of nucleic acids. This review summarizes the recent developments of the atomic site-specific Se derivatization of nucleic acids for structure determination and function study. Several applications of this Se-derivatization strategy in nucleic acid and protein research are also described in this review. [source] The Origin of the Improved Efficiency and Stability of Triphenylamine-Substituted Anthracene Derivatives for OLEDs: A Theoretical Investigation,CHEMPHYSCHEM, Issue 17 2008Bing Yang Dr. Abstract Herein, we describe the molecular electronic structure, optical, and charge-transport properties of anthracene derivatives computationally using density functional theory to understand the factors responsible for the improved efficiency and stability of organic light-emitting diodes (OLEDs) with triphenylamine (TPA)-substituted anthracene derivatives. The high performance of OLEDs with TPA-substituted anthracene is revealed to derive from three original features in comparison with aryl-substituted anthracene derivatives: 1) the HOMO and LUMO are localized separately on TPA and anthracene moieties, respectively, which leads to better stability of the OLEDs due to the more stable cation of TPA under a hole majority-carrier environment; 2) the more balanceable hole and electron transport together with the easier hole injection leads to a larger rate of hole,electron recombination, which corresponds to the higher electroluminescence efficiency; and 3) the increasing reorganization energy for both hole and electron transport and the higher HOMO energy level provide a stable potential well for hole trapping, and then trapped holes induce a built-in electric field to prompt the balance of charge-carrier injection. [source] Electrogenerated Chemiluminescence Sensor Based on Tris(2,2,-bipyridine)ruthenium(II)-Immobilized Natural Clay and Ionic LiquidELECTROANALYSIS, Issue 2 2010Ping Jiang Abstract A novel electrogenerated chemiluminescence (ECL) sensor based on natural clay and ionic liquid was fabricated. Tris(2,2,-bipyridine)ruthenium(II) (Ru(bpy)32+) was immobilized on natural clay surface through simple adsorption. An ECL sensor was prepared by mixing Ru(bpy)32+ -incorporated clay, graphite powder and an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) as the binder. The electrochemical behavior and ECL of the immobilized Ru(bpy)32+ was investigated. It was observed that the ECL of immobilized Ru(bpy)32+ was activated by the ionic liquid. The proposed ECL sensor showed high sensitivity to tri- n -propylamine (TPrA) and the detection limit was found to be 20,pM. In addition, the ECL sensor displayed good stability for TPrA detection and long-term storage stability. [source] Fabrication of a Sensitive Cholesterol Biosensor Based on Cobalt-oxide Nanostructures Electrodeposited onto Glassy Carbon ElectrodeELECTROANALYSIS, Issue 24 2009Abdollah Salimi Abstract Electrodeposited cobalt oxide (CoOx) nanomaterials are not only used for immobilization of cholesterol oxidase (ChOx) but also as electron transfer mediator for oxidation of H2O2 generated in the enzymatic reaction. Voltammetry and flow injection analysis (FIA) were used for determination of cholesterol. FIA determination of cholesterol with biosensors yielded a calibration curve with the following characteristics: linear range up to 50,,M, sensitivity of 43.5,nA ,M,1 cm,2 and detection limit of 4.2,,M. The apparent Michaelis-Menten constant and the response time of the biosensor are 0.49,mM and 15,s, respectively. This biosensor also exhibits good stability, reproducibility and long life time. [source] Direct Electrochemistry of Hemoglobin Immobilized on Colloidal Gold-Hydroxyapatite Nanocomposite for Electrocatalytic Detection of Hydrogen PeroxideELECTROANALYSIS, Issue 2 2009Juan You Abstract A novel nanocomposite of colloidal gold (GNPs) and hydroxyapatite nanotubes (Hap) was prepared for immobilization of a redox protein, hemoglobin (Hb), on glassy carbon electrode. The immobilized Hb showed fast direct electron transfer and excellent electrocatalytic behavior toward reduction of hydrogen peroxide. A synergic effect between GNPs and Hap for accelerating the surface electron transfer of Hb was observed, which led to a pair of redox peaks with a formal potential of (,340±2) mV at pH,7.0, and a new biosensor for hydrogen peroxide with a linear range from 0.5 to 25,,M and a limit of detection of 0.2,,M at 3,. Owing to the good biocompatibility of the nanocomposite, the biosensor exhibited good stability and acceptable reproducibility. The as-prepared nanocomposite film provided a good matrix for protein immobilization and biosensor preparation. [source] Comparison of Electrochemical and Surface Plasmon Resonance Immunosensor Responses on Single Thin FilmELECTROANALYSIS, Issue 20 2008Ryoji Kurita Abstract This paper reports results obtained when comparing an electrochemical enzyme immunosensor and a surface plasmon resonance (SPR) based immunosensor on the same gold surface installed in an electrochemical SPR flow cell. Simultaneous electrochemical and SPR measurements were performed on a gold surface modified with multilayers of poly- L -lysine and poly-styrenesulfonate assembled with the layer-by-layer method. First, we obtained the SPR response induced by the formation of an immunocomplex from the shift in the SPR angle by injecting an anti tumor necrosis factor-, antibody solution labeled with alkaline phosphatase into the flow cell containing the multilayer modified with tumor necrosis factor-,. Then we compared this SPR result with that obtained for the electrochemical oxidation current of p -aminophenol catalyzed by alkaline phosphatase from p -aminophenolphosphate on the same gold film. We compared the two immunosensor responses obtained using the different measurement principles and found that there was a high correlation efficient of 0.973 between them. This was because we were able to immobilize the immunoreagents with good stability and without losing the transport of the enzyme product in the multilayer whose thickness we easily controlled with nanometer scale accuracy. We also report that the detection limit of our electrochemical immunosensor after optimization was around 100,pg/mL (0.4,pM), which is one of the lowest values yet reported for an electrochemical immunosensor. [source] Dendritic Silver/Silicon Dioxide Nanocomposite Modified Electrodes for Electrochemical Sensing of Hydrogen PeroxideELECTROANALYSIS, Issue 17 2008Peixi Yuan Abstract A novel biosensor for hydrogen peroxide was prepared by immobilizing horseradish peroxidase (HPR) on newly synthesized dendritic silver/silicon dioxide nanocomposites, which were coated on a glassy carbon electrode. The modified electrode was characterized with XPS, SEM, and electrochemical methods. This biosensor showed a very fast amperometric response to hydrogen peroxide with a linear range from 0.7 to 120,,M, a limit of detection of 0.05,,M and a sensitivity of 1.02,mA mM,1 cm,2. The Michaelis-Menten constant of the immobilized HRP was estimated to be 0.21,mM, indicating a high affinity of the HRP to H2O2 without loss of enzymatic activity. The preparation of the proposed biosensor was convenient, and it showed high sensitivity and good stability. [source] Fabrication, Characterization, and Application of ,Sandwich-Type' Electrode Based on Single-Walled Carbon Nanotubes and Room Temperature Ionic LiquidELECTROANALYSIS, Issue 17 2008Xuzhi Zhang Abstract The much-enhanced electrochemical responses of potassium ferricyanide and methylene blue (MB) were firstly explored at the glassy carbon electrode modified with single-walled carbon nanotubes (SWNT/GCE), indicating the distinct electrochemical activity of SWNTs towards electroactive molecules. A hydrophobic room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), was used as electrode modification material, which presented wide electrochemical windows, proton permeation and selective extraction ability. In consideration with the advantages of SWNTs and RTIL in detecting target molecules (TMs), a novel strategy of ,sandwich,type' electrode was established with TMs confined by RTIL between the SWNT/GCE and the RTIL membrane. The strategy was used for electrochemical detection of ascorbic acid (AA) and dopamine (DA), and detection limits of 400 and 80 fmol could be obtained, respectively. The selective detection of DA in the presence of high amount of AA could also be realized. This protocol presented many attractive advantages towards voltammetric detection of TMs, such as low sample demand, low cost, high sensitivity, and good stability. [source] Synthesis and Characterization of MWNTs/Au NPs/HS(CH2)6Fc Nanocomposite: Application to Electrochemical Determination of Ascorbic AcidELECTROANALYSIS, Issue 16 2008Jian-Ding Qiu Abstract In this article, a detailed electrochemical study of a novel 6-ferrocenylhexanethiol (HS(CH2)6Fc) self-assembled multiwalled carbon nanotubes-Au nanoparticles (MWNTs/Au NPs) composite film was demonstrated. MWNTs/Au NPs were prepared by one-step in situ synthesis using linear polyethyleneimine (PEI) as bifunctionalizing agent. HS(CH2)6Fc, which acted as the redox mediator, was self-assembled to MWNTs/Au NPs via Au-S bond. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Fourier transformed infrared absorption spectroscopy (FT-IR), UV-visible absorption spectroscopy, and cyclic voltammetry were used to characterize the properties of the MWNTs/Au NPs/HS(CH2)6Fc nanocomposite. The preparation of the nanocomposite was very simple and effectively prevented the leakage of the HS(CH2)6Fc mediator during measurements. The electrooxidation of AA could be catalyzed by Fc/Fc+ couple as a mediator and had a higher electrochemical response due to the unique performance of MWNTs/Au NPs. The nanocomposite modified electrode exhibited excellent catalytic efficiency, high sensitivity, good stability, fast response (within 3,s) and low detection limit toward the oxidation of AA at a lower potential. [source] Fabrication and Application of a Novel Modified Electrode Based on Multiwalled Nanotubes/Cerium(III) 12-Tungstophosphoric Acid NanocompositeELECTROANALYSIS, Issue 11 2008Bin Fang Abstract A novel multiwalled nanotubes (MWNTs)/Cerium(III) 12 - tungstophosphoric acid (CePW) nanocomposite film glassy carbon electrode was prepared in this paper. Electrochemical behaviors of the CePW/MWNTs modified electrode were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). This modified electrode brought new capabilities for electrochemical devices by combining the advantages of carbon nanotubes, rare-earth, and heteropoly-acids. The results demonstrated that the CePW/MWNTs modified electrode exhibited enhanced electrocatalytic behavior and good stability for the detection of guanine and adenine in 0.1,M PBS (pH,7.0). The experimental parameters were optimized and a direct electrochemical method for the simultaneous determination of guanine and adenine was proposed. The detection limit (S/N=3) for guanine and adenine was 2.0×10,8,M and 3.0×10,8,M, respectively. Further, the acid-denatured calf thymus DNA was also detected and the result was satisfied. [source] Automatic Voltammetric System for Continuous Trace Metal Monitoring in Various Environmental SamplesELECTROANALYSIS, Issue 19-20 2007Øyvind Mikkelsen Abstract Some recent developments and results in the field of automatic monitoring of electrolabile concentration of zinc and iron in the low ,g/L range in river water, drainage water, and waste water by use of solid dental amalgam electrode (DAM) as a working electrode are reviewed for three different geographical sites representing the mentioned matrixes. At all sites, voltammetric measurements were carried out continuously every 30 or 60,minutes for periods up to 4,months, and compared with total amounts of the metals found by ICP-MS on manually collected samples. In total, the observed concentration ranges analyzed was in the ranges of sub-,g/L to approximately 30,,g/L for zinc, and from approximately 1,,g/L to 150,,g/L. for iron. Results shows good calibration curves for the metals in the different matrixes (r2avg=0.99) with standard deviation within 5%. The voltammetric system showed good stability and gave reliable results which were in a reasonable agreement with ICP-MS measurements for all analyses when comparing the concentration trends. The frequency of maintenance varied from once a week in waste water samples to once a month in river water. [source] Electrocatalytic Oxidation of Sulfur Containing Amino Acids at Renewable Ni-Powder Doped Carbon Ceramic Electrode: Application to Amperometric Detection L -Cystine, L -Cysteine and L -MethionineELECTROANALYSIS, Issue 21 2006Abdollah Salimi Abstract A sol-gel technique was used here to prepare a renewable carbon ceramic electrode modified with nickel powder. Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple due to Ni(II)/Ni(III) system with surface confined characteristics. The modified electrode shows excellent catalytic activity toward L -cystine, L -cysteine and L -methionine oxidation at reduced overpotential in alkaline solutions. In addition the antifouling properties at the modified electrode toward the above analytes and their oxidation products increases the reproducibility of results. L -cystine, L -cysteine and L -methionine were determined chronoamperometricaly at the surface of this modified electrode at pH range 9,13. Under the optimized conditions the calibration curves are linear in the concentration range 1,450,,M, 2,90,,M and 0.2,75,,M for L -cystine, L -methionine and L -cysteine determination, respectively. The detection limit and sensitivity were 0.64,,M, 3.8,nA/ ,M for L -cystine, 2,,M, 5.6,nA/ ,M for L -methionine and 0.2,,M and 8.1,nA/,M for L -cysteine. The advantageous of this modified electrode is high response, good stability and reproducibility, excellent catalytic activity for oxidation inert molecules at reduced overpotential and possibility of regeneration of the electrode surface by potential cycling for 5,minutes. Furthermore, the modified electrode has been prepared without using specific reagents. This sensor can be used as an amperometric detector for disulfides detection in chromatographic or flow systems. [source] Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube-Modified ElectrodesELECTROANALYSIS, Issue 11 2006Xiliang Luo Abstract The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)-modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH,7.4 phosphate buffer solutions (PBS) with the formal potential of about ,455,mV (vs. Ag/AgCl) and shows a surface-controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0,mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD. [source] Organically Modified Sol-Gel/Chitosan Composite Based Glucose BiosensorELECTROANALYSIS, Issue 7 2003Xu Chen Abstract A new type of organically modified sol-gel/chitosan composite material was developed and used for the construction of glucose biosensor. This material provided good biocompatibility and the stabilizing microenvironment around the enzyme. Ferrocene was immobilized on the surface of glassy carbon electrode as a mediator. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The effects of enzyme-loading, buffer pH, applied potential and several interferences on the response of the enzyme electrode were investigated. The simple and low-cost glucose biosensor exhibited high sensitivity and good stability. [source] Direct electrochemical detection of glucose in human plasma on capillary electrophoresis microchipsELECTROPHORESIS, Issue 21-22 2004Yan Du Abstract We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 ,M to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument. [source] Synthesis of para -Amino Benzoic Acid,TiO2 Hybrid Nanostructures of Controlled Functionality by an Aqueous One-Step ProcessEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2008Raed Rahal Abstract In situ amino acid surface-modified TiO2 nanoparticle syntheses were performed by a simple one-pot hydrolysis of heteroleptic titanium alkoxide [Ti(OiPr)3(O2CC6H4NH2)]m in water with NnBu4Br. This process allowed precise control of the surface grafting rate by varying the amount of precursors and provided highly functionalized nanomaterials. Their compositions and microstructures were determined by C, H and N elemental analyses, TGA-MS, 13C CP-MAS NMR, XRD, TEM, BET, Raleigh diffusion, FTIR, Raman, XPS and UV/Vis experiments. The results indicated that (i) the aggregation rate increased with an increase in the loading of the organic substrate and (ii) the amino acid is chemisorbed as a carboxylate group onto the TiO2 nanoparticles, which leads to a strong interaction between the amino acid and the TiO2 nanoparticle and good stability of these hybrids. Applications of low-aggregated nanomaterials were demonstrated as efficient protection additive against UVA + UVB radiations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] TAME-Hex A , A Novel Bifunctional Chelating Agent for RadioimmunoimagingEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2004Enver Arslantas Abstract Two novel (bifunctional) chelating agents, TAME-Hex A and B, which are polyaminopolycarboxylic acids based on the tripodal TAME [tris(aminomethyl)ethane] structure, have been designed and synthesized. The chelators show very good stability with gallium(III) ions and thus are highly effective candidates for use in radioimmunoimaging (RII), especially in positron emission tomography (PET). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Diamond Transistor Array for Extracellular Recording From Electrogenic CellsADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Markus Dankerl Abstract The transduction of electric signals from cells to electronic devices is mandatory for medical applications such as neuroprostheses and fundamental research on communication in neuronal networks. Here, the use of diamond with its advantages for biological applications as a new material for biohybrid devices for the detection of cell signals is investigated. Using the surface conductivity of hydrogen-terminated single-crystalline diamond substrates, arrays of solution-gate field-effect transistors were fabricated. The characterization of the transistors reveals a good stability in electrolyte solutions for at least 7 days. On these devices, cardiomyocyte-like HL-1 cells as well as human embryonic kidney cells (HEK293), which were stably transfected with potassium channels, are cultured. Both types of cells show healthy growth and good adhesion to the substrate. The diamond transistors are used to detect electrical signals from both types of cells by recording the extracellular potential. For the HL-1 cells, the shape of action potentials can be resolved and the propagation of the signal across the cell layer is visible. Potassium currents of HEK293 cells are activated with the patch-clamp technique in voltage-clamp mode and simultaneously measured with the field-effect transistors. The ion sensitivity of the diamond surface enables the detection of released potassium ions accumulated in the cleft between transistor and cell. [source] Field Emission and Cathodoluminescence of ZnS Hexagonal Pyramids of Zinc Blende Structured Single CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Zhi-Gang Chen Abstract Single-crystal hexagonal pyramids of zinc blende ZnS are fabricated by facile thermal evaporation in an ammonia atmosphere at 1150,°C. It is found that ZnS pyramids grow along the [111] crystal axis and possess a sharp tip with a diameter of ,10,nm and a micrometer-sized base. The structural model and growth mechanism are proposed based on crystallographic characteristics. This unique ZnS pyramid structure exhibits a low turn-on field (2.81,V µm,1), a high field-enhancement factor (over 3000), a large field-emission current density (20,mA cm,2), and good stability with very small fluctuation (0.9%). These superior field-emission properties are clearly attributed to the pyramid morphology, with micrometer-sized bases and nanotips, and high crystallinity. Moreover, a stable UV emission of 337,nm at room temperature is observed and can be ascribed to the band emission of the zinc blende phase. These results suggest that the ZnS hexagonal pyramids can be expected to find promising applications as field emitters and optoelectronic devices. [source] | |||||||||||||||||||||||||||||||||||||||||||