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Impedance Spectroscopy (impedance + spectroscopy)
Kinds of Impedance Spectroscopy Terms modified by Impedance Spectroscopy Selected AbstractsLabel-Free and Ultra-Low Level Detection of Salmonella enterica Serovar Typhimurium Using Electrochemical Impedance SpectroscopyELECTROANALYSIS, Issue 20 2009Jeffrey Abstract An immunosensor for rapid and low level detection of the bacterial pathogen Salmonella enterica Serovar Typhimurium was designed and developed based upon label-free electrochemical impedance spectroscopy and correlated to viable cell counts. The immunosensor was fabricated by electroplating gold onto a disposable printed circuit board (PCB) electrode by immobilizing monoclonal antibody (MAb) specific against Salmonella typhimurium cell surface lipopolysaccharide (LPS) onto the surface of the electrode. Use of mass-fabricated and electroplated PCB electrodes allowed for disposable, highly sensitive, and rapid detection of Salmonella in an aqueous environment. Results demonstrate that in purified solution, Salmonella can be detected as low as 10 CFU in a 100,,L volume and label-free and rapid manner in fewer than 90,s. The cost effective approach described here can be used for detection of pathogens with relevance for healthcare, food, and environmental applications. [source] Detecting Biorecognition Events at Blocked Interface Polymeric Membrane Ion-Selective Electrodes Using Electrochemical Impedance Spectroscopy and Atomic Force MicroscopyELECTROANALYSIS, Issue 3 2008Marco, Roland De Abstract Immobilization of a biorecognition element onto a polymeric membrane ion-selective electrode (ISE) using a self-assembly approach may provide scope for a novel biosensor technology platform based on the altered potentiometric response at the blocked ISE interface. In this paper, the authors have investigated the influence of solution adsorption of the model biorecognition element, avidin-biotin, on the electrode kinetics of a conventional polymeric membrane Ca2+ ISE using atomic force microscopy (AFM) coupled with electrochemical impedance spectroscopy (EIS). It is demonstrated that solution adsorption of avidin followed by biotin incorporation leads to a demonstrable biorecognition event characterized by an impediment in the Ca2+ ion transfer kinetics of the modified ISE surface. This kinetic principle is amenable to biosensing using pulsed chronopotentiometric polymeric ISEs, which is an established dynamic electrode technique for use with polymeric membrane ISEs. [source] Disposable Gold Electrode Array for Simultaneous Electrochemical StudiesELECTROANALYSIS, Issue 1 2008Graciela Priano Abstract An efficient and inexpensive eight gold electrode array has been manufactured by a combination of screen printing and gold electrodeposition techniques. Gold electrodeposition was performed in potentiostatic and galvanostatic conditions. Different treatments, involving temperature and polishing control, led to electrodes with different roughness. The electrochemical behavior of the generated gold surface was studied by cyclic voltammetry showing the characteristic response of polycrystalline gold, in contrast with disposable gold electrodes fabricated by screen printing from gold inks. The electrodes were chemically modified through the adsorption of alkanethiols self-assembled monolayers and the coupling of a model protein. Both reactions were followed by cyclic voltammetry and Electrochemical Impedance Spectroscopy (EIS). The electrodes have shown high reproducibility in their electrochemical behavior as well as in their modifications. [source] Impedance Spectroscopy: A Powerful Tool for Rapid Biomolecular Screening and Cell Culture MonitoringELECTROANALYSIS, Issue 23 2005Isaac Abstract Dielectric spectroscopy or Electrochemical impedance spectroscopy (EIS) is traditionally used in corrosion monitoring, coatings evaluation, batteries, and electrodeposition and semiconductor characterization. However, in recent years, it is gaining widespread application in biotechnology, tissue engineering, and characterization of biological cells, disease diagnosis and cell culture monitoring. This article discusses the principles and implementation of dielectric spectroscopy in these bioanalytical applications. It provides examples of EIS as label-free, mediator-free strategies for rapid screening of biocompatible surfaces, monitoring pathogenic bacteria, as well as the analysis of heterogeneous systems, especially biological cells and tissues. Descriptions are given of the application of nanoparticles to improve the analytical sensitivities in EIS. Specific examples are given of the detection of base pair mismatches in the DNA sequence of Hepatitis B disease, TaySach's disease and Microcystis spp. Others include the EIS detection of viable pathogenic bacteria and the influence of nanomaterials in enhancing biosensor performance. Expanding applications in tissue engineering such as adsorption of proteins onto thiolated hexa(ethylene glycol)-terminated (EG6) self-assembled monolayer (SAM) are discussed. [source] Fourier Transformed Large Amplitude Square-Wave Voltammetry as an Alternative to Impedance Spectroscopy: Evaluation of Resistance, Capacitance and Electrode Kinetic Effects via an Heuristic ApproachELECTROANALYSIS, Issue 15-16 2005Abstract A detailed simulation of Fourier transformed large amplitude square-wave voltammetry is presented in the frequency domain for the process Red,Ox+e,. The simulation takes into account the influence of the electrode kinetics (Butler,Volmer model), uncompensated resistance (Ru) and double layer capacitance (Cdl). Of particular significance is the prediction that the even harmonic responses are only detected in the presence of quasi-reversibility or uncompensated resistance, and also are essentially devoid of charging current. In contrast, the DC and odd harmonic AC components exhibit much larger faradaic currents and also contain charging current. Conveniently, detailed analysis of the simulated DC and AC harmonic components reveals the presence of readily recognised patterns of behaviour with unique levels of sensitivity to electrode kinetics, Ru and Cdl, that facilitate quantitative analysis of these terms. These electrochemical parameters are generally calculated by small amplitude impedance spectroscopy and utilisation of linear analysis of equivalent circuits. Experimental studies on the one electron oxidation of ferrocene in dichloromethane (0.1,M Bu4NPF6) and the one electron reduction of [Fe(CN)6]3, in aqueous 0.5,M KCl electrolyte analysed via heuristic forms of data analysis based on recognition of patterns of behaviour, are presented as examples of a reversible process with significant uncompensated resistance and a quasi-reversible process with minimal ohmic drop, respectively. Results demonstrate the advantages of a more intuitively implemented form of data analysis than presently available with conventional forms of impedance spectroscopy. [source] Probing Biomolecular Interactions at Conductive and Semiconductive Surfaces by Impedance Spectroscopy: Routes to Impedimetric Immunosensors, DNA-Sensors, and Enzyme BiosensorsELECTROANALYSIS, Issue 11 2003Eugenii Katz Abstract Impedance spectroscopy is a rapidly developing electrochemical technique for the characterization of biomaterial-functionalized electrodes and biocatalytic transformations at electrode surfaces, and specifically for the transduction of biosensing events at electrodes or field-effect transistor devices. The immobilization of biomaterials, e.g., enzymes, antigens/antibodies or DNA on electrodes or semiconductor surfaces alters the capacitance and interfacial electron transfer resistance of the conductive or semiconductive electrodes. Impedance spectroscopy allows analysis of interfacial changes originating from biorecognition events at electrode surfaces. Kinetics and mechanisms of electron transfer processes corresponding to biocatalytic reactions occurring at modified electrodes can be also derived from Faradaic impedance spectroscopy. Different immunosensors that use impedance measurements for the transduction of antigen-antibody complex formation on electronic transducers were developed. Similarly, DNA biosensors using impedance measurements as readout signals were developed. Amplified detection of the analyte DNA using Faradaic impedance spectroscopy was accomplished by the coupling of functionalized liposomes or by the association of biocatalytic conjugates to the sensing interface providing biocatalyzed precipitation of an insoluble product on the electrodes. The amplified detections of viral DNA and single-base mismatches in DNA were accomplished by similar methods. The changes of interfacial features of gate surfaces of field-effect transistors (FET) upon the formation of antigen-antibody complexes or assembly of protein arrays were probed by impedance measurements and specifically by transconductance measurements. Impedance spectroscopy was also applied to characterize enzyme-based biosensors. The reconstitution of apo-enzymes on cofactor-functionalized electrodes and the formation of cofactor-enzyme affinity complexes on electrodes were probed by Faradaic impedance spectroscopy. Also biocatalyzed reactions occurring on electrode surfaces were analyzed by impedance spectroscopy. The theoretical background of the different methods and their practical applications in analytical procedures were outlined in this article. [source] Application of Electrochemical Impedance Spectroscopy for Fuel Cell Characterization: PEFC and Oxygen Reduction Reaction in Alkaline Solution,FUEL CELLS, Issue 3 2009N. Wagner Abstract The most common method used to characterise the electrochemical performance of fuel cells is the recording of current/voltage U(i) curves. Separation of electrochemical and ohmic contributions to the U(i) characteristics requires additional experimental techniques like electrochemical impedance spectroscopy (EIS). The application of EIS is an approach to determine parameters which have proved to be indispensable for the characterisation and development of all types of fuel cell electrodes and electrolyte electrode assemblies [1]. In addition to EIS semi-empirical approaches based on simplified mathematical models can be used to fit experimental U(i) curves [2]. By varying the operating conditions of the fuel cell and by the simulation of the measured EIS with an appropriate equivalent circuit, it is possible to split the cell impedance into electrode impedances and electrolyte resistance. Integration in the current density domain of the individual impedance elements enables the calculation of the individual overpotentials in the fuel cell (PEFC) and the assignment of voltage loss to the different processes. In case of using a three electrode cell configuration with a reference electrode, one can directly determine the corresponding overvoltage. For the evaluation of the measured impedance spectra the porous electrode model of Göhr [3] was used. This porous electrode model includes different impedance contributions like impedance of the interface porous layer/pore, interface porous layer/electrolyte, interface porous layer/bulk, impedance of the porous layer and impedance of the pores filled by electrolyte. [source] Insight into Proton Conduction of Immobilised Imidazole Systems Via Simulations and Impedance Spectroscopy,FUEL CELLS, Issue 3-4 2008W. L. Cavalcanti Abstract The proton conduction in immobilised imidazole systems has been investigated in order to support the design of new membrane materials for polymer electrolyte membrane fuel cells (PEMFC). In the experimental part of this work, proton conductivities are measured via impedance spectroscopy. The simulation and modelling are performed combining molecular dynamics simulations and energy barrier calculations; the analysis is done via the proton jump energy barrier, collision ratio and radial distribution function. The dependence of the proton mobility on the temperature, spacer length and the density of conducting groups per area is presented. Donors and acceptors groups approach to each other within a distance from 2.8 to 3,Å where the energy barrier for a proton transfer is very low, which favours the proton jump under the studied conditions. The proton conductivity increases with increase in the spacer length. The simulation results are in good agreement with the proton conductivities presented. [source] Electrochemical Reduction of Oxygen on Carbon Supported Pt and Pt/Ru Fuel Cell Electrodes in Alkaline SolutionsFUEL CELLS, Issue 4 2003E.H. Yu Abstract A study of O2 reduction in 1 M NaOH solution at gas diffusion electrodes made from carbon supported Pt and Pt/Ru catalysts is reported. Two Tafel regions were observed for both the Pt and Pt/Ru electrodes. Although the same mechanism was suggested for oxygen reduction on both Pt and Pt/Ru catalysts, the O2 reduction activity was lower on Ru. Electrochemical Impedance Spectroscopy (EIS) analysis was carried out at different potentials and showed the significant contribution of diffusion on the reaction process and kinetics. The effect of methanol on O2 reduction was investigated in solutions containing various concentrations of methanol. The electrode performance deteriorated with increasing methanol concentration because of a mixed cathode potential. The methanol tolerance, i. e., the methanol concentration which polarises the O2 reduction reaction for O2 reduction, at the Pt/C electrode with a Pt loading of 1.2 mg cm,2 is 0.2 M methanol in 1 M NaOH. [source] Impedance Spectroscopy: Theory, Experiment, and Applications Second Edition.JOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2007Evgenij Barsoukov, J. Ross Macdonald (eds). No abstract is available for this article. [source] Physical Modeling and Electrodynamic Characterization of Dielectric Slurries by Impedance Spectroscopy (Part II)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Vladimir Petrovsky Electrical characterization of dielectric slurries, as 0,3 composite systems, can provide valuable information on the dielectric properties of suspended particles. A new approach developed in our laboratory is based on impedance spectroscopy measurements of the slurries containing dispersed dielectric powders. Dielectric constants of the particles are determined through analysis of the low-frequency section of the impedance spectra. It was shown previously that this approach allows accurate and reliable measurement of dielectric constant of particles (,: ,100,2000) using host liquids (,: ,10,65). This study addresses the validation of this new method with physical model experiments using millimeter-sized sintered BaTiO3 model samples suspended in the liquid. Impedance spectra of barium titanate powder slurries were compared with the spectra of the model samples containing macroscopic cubes prepared by sintering of the same starting powder. This comparison shows a good agreement between the impedance spectra of powder and bulk BaTiO3 and validates the reliability of the new method to determine the dielectric constant of particulate materials. [source] Proton Conductivity Measurements in Yttrium Barium Cerate by Impedance SpectroscopyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2002W. Grover Coors Proton-conducting solid-electrolyte perovskite ceramics based on acceptor-doped barium and strontium cerates have become the focus of extensive investigations as candidate materials for fuel cells that operate at moderate temperatures. To assess the suitability of a material for this application, it is necessary that bulk electrolyte conductivity be measured at the operating temperature. However, very little reliable published conductivity data exist above 600°C. Protonic conductivity in yttrium-doped barium cerate has been observed to be less at high temperatures than would be expected, based on the activation energy and preexponential for hydrogen transport at temperatures <300°C. Conductivity data obtained from impedance spectroscopy on BaCe0.9Y0.1O3,, over the extended temperature range of 100°,900°C are presented. An Arrhenius plot of the data shows two distinct linear regions, suggesting that two different rate-limiting processes occur in series with a break-over transition at ,250°C. The decrease in conductivity is apparently not due to dehydration. An activation energy for protonic transport of 0.26 eV, about one-half of the low-temperature value, is proposed, based on curve fitting of the high-temperature data. [source] Characterization of Electrical Properties of Li(FexAl1,x)5O8 Solid Solutions by Impedance SpectroscopyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Shuichi Arakawa To examine polaronic transport properties in Li(FexAl1,x)5O8 spinel solid solutions, a scaling analysis for their conductivity spectra and modulus spectra was performed. As in the case of ionic conductors, two significant parameters of a crossover frequency and a power-law exponent were extracted from the conductivity spectra which displayed the universal dynamic response behavior. Both the mobility and the concentration of carriers were successfully determined from the crossover frequency. The power-law exponent and the stretching parameter obtained from the modulus spectra varied with composition, implying that the increase in Fe concentration would enhance the Coulomb interactions between small polarons. [source] Impedance measurements on oxide films on aluminium obtained by pulsed tensionsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2003K. Belmokre Anodisation; Elektrochemische Impedanzspektroskopie (EIS); pulsierende Spannung; Alterung von Oxidfilmen Abstract We have performed this study on oxide films sealed or not in boiling water. The films are first obtained on type 1050 A aluminium substrat by pulsed tensions anodizing technique, in a sulfuric acid solution. Afterwards the, Electrochemical Impedance Spectroscopy (EIS) is employed to appreciate the films behaviour in a neutral solution of 3.5% K2SO4, in which the interface processes interest only the ageing phenomenon of the oxide films and not their corrosion. We have also attempted a correlation between pulse parameters of anodization and the electrical parameters characterizing these films. The sealing influence on ageing has been studied as well. For all films, ageing is appreciated using impedance diagrams evolution versus time. The results show: , the existence of two capacitive loops confirming the presence of two oxide layers characteristic of oxide films obtained in a sulfuric acid medium. The first loop, at high frequencies, is related to the external porous layer and the second one, at lower freqencies, is related to the internal barrier layer. , the thickness of the barrier layer varies between 25 and 40 nm in relation with the electrical pulse parameters. , the sealing acts favorably against anodic oxide films ageing. Impedanzmessungen an durch pulsierende Spannung erzeugten Oxidfilmen auf Aluminium Die vorliegenden Untersuchungen wurden an versiegelten und nicht versiegelten Oxidfilmen in kochendem Wasser durchgeführt. Die Filme wurden zuerst auf Aluminiumsubstrat des Typs 1050A durch anodische Technik mit pulsierender Spannung in einer Schwefelsäurelösung erzeugt. Anschließend wurde die elektrochemische Impedanzspektroskopie eingesetzt, um das Filmverhalten in einer neutralen 3,5% K2SO4 -Lösung zu beurteilen, wobei bezüglich der Grenzflächenprozesse nur das Alterungsphänomen der Oxidfilme und nicht ihr Korrosionsverhalten interessierte. Es wurde versucht, eine Korrelation zwischen den Pulsparametern der Anodisierung und den elektrischen Parametern, die diese Filme charakterisieren, zu finden. Ebenfalls wurde der Versiegelungseinfluss auf die Alterung untersucht. Für alle Filme wurde die Alterung mit Hilfe der Entwicklung von Impedanzdiagrammen über die Zeit beurteilt. Die Ergebnisse zeigen: , die Existenz von zwei kapazitiven Schleifen, die die Anwesenheit von zwei Oxidschichten bestätigen, was charakteristisch ist für Oxidfilme, die in einer Schwefelsäurelösung erzeugt wurden. Die erste Schleife, bei hohen Frequenzen, bezieht sich auf die äußere poröse Schicht und die zweite, bei niedrigeren Frequenzen, bezieht sich auf die innere Barriereschicht , die Dicke der Barriereschicht variiert zwischen 25 und 40 nm, abhängig von den elektrischen Pulsparametern , die Versiegelung wirkt günstig gegenüber der Alterung des anodischen Oxidfilms. [source] Fluid Volumes Determination by Impedance Spectroscopy and Hematocrit Monitoring: Application to Pediatric HemodialysisARTIFICIAL ORGANS, Issue 2 2001Marianne Fenech Abstract: A method for extracting fluid volumes from multifrequency bioimpedance, which takes into account the body geometry and the presence of nonconducting elements, was tested on 12 young dialyzed patients against correlations for total body water volumes (TBW) from Watson et al. and Humes et al. Our calculations of TBW from impedance were found to overestimate Humes' values by 0.25 L (0.8%) postdialysis and by 2.08 L (6.5%) predialysis. Extracellular water (ECW) was found to contribute an average of 93% of ultrafiltered volume. Intracellular water volume (ICW) determination from impedance was found to be too imprecise to predict its variation during dialysis; therefore, ICW variations were calculated as the difference between ultrafiltration and ECW changes. The continuous recording of hematocrit by an optical device monitored changes in plasma and interstitial volumes. In most cases, ultrafiltration was compensated mainly by a contribution from interstitial fluid, and the drop in plasma volume was generally moderate. [source] Probing Biomolecular Interactions at Conductive and Semiconductive Surfaces by Impedance Spectroscopy: Routes to Impedimetric Immunosensors, DNA-Sensors, and Enzyme BiosensorsELECTROANALYSIS, Issue 11 2003Eugenii Katz Abstract Impedance spectroscopy is a rapidly developing electrochemical technique for the characterization of biomaterial-functionalized electrodes and biocatalytic transformations at electrode surfaces, and specifically for the transduction of biosensing events at electrodes or field-effect transistor devices. The immobilization of biomaterials, e.g., enzymes, antigens/antibodies or DNA on electrodes or semiconductor surfaces alters the capacitance and interfacial electron transfer resistance of the conductive or semiconductive electrodes. Impedance spectroscopy allows analysis of interfacial changes originating from biorecognition events at electrode surfaces. Kinetics and mechanisms of electron transfer processes corresponding to biocatalytic reactions occurring at modified electrodes can be also derived from Faradaic impedance spectroscopy. Different immunosensors that use impedance measurements for the transduction of antigen-antibody complex formation on electronic transducers were developed. Similarly, DNA biosensors using impedance measurements as readout signals were developed. Amplified detection of the analyte DNA using Faradaic impedance spectroscopy was accomplished by the coupling of functionalized liposomes or by the association of biocatalytic conjugates to the sensing interface providing biocatalyzed precipitation of an insoluble product on the electrodes. The amplified detections of viral DNA and single-base mismatches in DNA were accomplished by similar methods. The changes of interfacial features of gate surfaces of field-effect transistors (FET) upon the formation of antigen-antibody complexes or assembly of protein arrays were probed by impedance measurements and specifically by transconductance measurements. Impedance spectroscopy was also applied to characterize enzyme-based biosensors. The reconstitution of apo-enzymes on cofactor-functionalized electrodes and the formation of cofactor-enzyme affinity complexes on electrodes were probed by Faradaic impedance spectroscopy. Also biocatalyzed reactions occurring on electrode surfaces were analyzed by impedance spectroscopy. The theoretical background of the different methods and their practical applications in analytical procedures were outlined in this article. [source] Silicon-Doped LiFePO4 Single Crystals: Growth, Conductivity Behavior, and DiffusivityADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Ruhul Amin Abstract Single crystals of silicon doped LiFePO4 with a silicon content of 1% are grown successfully by the floating zone technique and characterized by single-crystal and powder X-ray diffraction, secondary ion mass spectroscopy, and chemical analysis. Electron paramagnetic resonance demonstrates the presence of only Fe2+; no traces of Fe3+ are found. Impedance spectroscopy as well as step-function polarization/depolarization (DC) measurements are carried out using the cells Ti/LiFe(Si)PO4/Ti and LiAl/LiI/LiFe(Si)PO4/LiI/LiAl. The electronic and ionic conductivities as well as the Li-diffusivity of the sample in the major crystallographic directions ([h00], [0k0], and [00l]) are determined. Within experimental error the transport properties along the b- and c-axes are found to be the same but differ significantly from the a-axis, which exhibits lower values. Compared to undoped LiFePO4, Si-doping leads to an increase of the ionic conductivity while the electronic conductivity decreases, which is in agreement with a donor effect. The activation energies of conductivities and diffusivities are interpreted in terms of defect chemistry and relevant Brouwer diagrams are given. [source] Synthetic diamond films as a platform material for label-free protein sensorsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2009Nathalie Bijnens Abstract In the framework of developing a fast and label-free immunosensor for C-reactive protein (CRP) detection, H-terminated nanocrystalline diamond (NCD) was functionalised with anti-CRP antibodies that were physically adsorbed to the surface. Impedance spectroscopy was used to electronically detect real-time CRP recognition. Different impedance behaviours were observed after CRP addition as compared to after FITC-labelled ssDNA addition at low (100 Hz) as well as at high frequencies (1 MHz). Physical interpretations of the observed impedance changes were obtained by fitting the data to an equivalent electrical circuit. Concentrations of 1 ,M CRP were recognised with a reaction time of 30 minutes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Impedance spectroscopy as a tool for non-intrusive detection of extracellular mediators in microbial fuel cellsBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Ramaraja P. Ramasamy Abstract Endogenously produced, diffusible redox mediators can act as electron shuttles for bacterial respiration. Accordingly, the mediators also serve a critical role in microbial fuel cells (MFCs), as they assist extracellular electron transfer from the bacteria to the anode serving as the intermediate electron sink. Electrochemical impedance spectroscopy (EIS) may be a valuable tool for evaluating the role of mediators in an operating MFC. EIS offers distinct advantages over some conventional analytical methods for the investigation of MFC systems because EIS can elucidate the electrochemical properties of various charge transfer processes in the bio-energetic pathway. Preliminary investigations of Shewanella oneidensis DSP10-based MFCs revealved that even low quantities of extracellular mediators significantly influence the impedance behavior of MFCs. EIS results also suggested that for the model MFC studied, electron transfer from the mediator to the anode may be up to 15 times faster than the electron transfer from bacteria to the mediator. When a simple carbonate membrane separated the anode and cathode chambers, the extracellular mediators were also detected at the cathode, indicating diffusion from the anode under open circuit conditions. The findings demonstrated that EIS can be used as a tool to indicate presence of extracellular redox mediators produced by microorganisms and their participation in extracellular electron shuttling. Biotechnol. Bioeng. 2009; 104: 882,891. © 2009 Wiley Periodicals, Inc. [source] Synthesis, characterization and impedance spectroscopy of the new material [(CH3) (C6H5) 3P] 2CoBr4: a member of the A2BX4 familyCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2008M. F. Mostafa Abstract The crystal structure of bis-(methyltriphenylphosphonium) tetrabromocobaltate (II), [(C19H18P)2 CoBr4] is determined: Mr = 933.203, monoclinic, P21, a = 9. 6977 (3) Å, b = 12.5547 (4)Å, c = 16.4503 (6)Å, , = 105.603 (2)°, V = 1929.04 (11)Å3, Z = 2, Dx = 1.607 Mg m -3, T = 298 K. Differential thermal analysis at high temperatures shows three endothermic peaks characterizing four phases, with onset temperatures at T1= 313±2 K, T2 = 320±4 K and T3= 360±1 K. The structural instability detected via the temperature dependence of permittivity at T1 is ascribed to order-disorder transition associated with cation dipole reorientation. Permittivity and ac conductivity studies as a function of temperature (295 K-375 K) and frequency (0.11 kHz < f <100 kHz) are presented. The results indicate the importance of the cation size and shape on the phase transitions in the system. Bulk conductivity behavior is thermally activated. The associated activation energies are in the range 2.9 to 1.0 eV depending on the temperature regime. Two contributions to the ac conductivity, one dominating at low temperatures and high frequencies which are characterized by superlinear frequency exponent and the second dominates at high temperatures characterized by a sublinear frequency exponent. The behavior is interpreted in terms of the jump relaxation model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Simultaneous Determination of Ascorbic Acid, Dopamine and Uric Acid at Pt Nanoparticles Decorated Multiwall Carbon Nanotubes Modified GCEELECTROANALYSIS, Issue 10 2010Zekerya Dursun Abstract A modified electrode was fabricated by electrochemically deposition of Pt nanoparticles on the multiwall carbon nanotube covered glassy carbon electrode (Pt nanoparticles decorated MWCNT/GCE). A higher catalytic activity was obtained to electrocatalytic oxidation of ascorbic acid, dopamine, and uric acid due to the enhanced peak current and well-defined peak separations compared with both, bare and MWCNT/GCE. The electrode surfaces were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS). Individual and simultaneous determination of AA, DA, and UA were studied by differential pulse voltammetry. The detection limits were individually calculated for ascorbic acid, dopamine, and uric acid as being 1.9×10,5,M, 2.78×10,8,M, and 3.2×10,8,M, respectively. In simultaneous determination, LODs were calculated for AA, DA, and UA, as of 2×10,5,M, 4.83×10,8,M, and 3.5×10,7,M, respectively. [source] Mediated Electron Transfer Across Supported Bilayer Lipid Membrane with TCNQ-Based Organometallic CompoundsELECTROANALYSIS, Issue 4 2010Meili Qu Abstract Supported bilayer lipid membrane (s-BLM) containing one-dimensional compound 1, TCNQ-based (TCNQ=7,7,8,8-tetracyanoquinodimethane) organometallic compound {(Cu2(,-Cl)(,-dppm)2)(,2 -TCNQ)},, was prepared and characterized on the self-assembled monolayer (SAM) of 1-octadecylmercaptan (C18H37SH) deposited onto Au electrode. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results showed that the compound 1, dotted inside s-BLM, can act as mediator for electron transfer across the membrane. Two redox peaks and the charge-transfer resistance of 400,k, were observed for compound 1 inside s-BLM. The mechanism of the electron transfer across s-BLM by TCNQ is by electron hopping while TCNQ-based organometallic compound is by conducting. Further conclusion drawn from this finding is that the TCNQ-based organometallic compound embedded inside s-BLM exhibits excellent electron transfer ability than that of free TCNQ. This opens a new path for the development of s-BLM sensor and/or biosensor by incorporation with TCNQ-based organometallic compounds. [source] Label-Free and Ultra-Low Level Detection of Salmonella enterica Serovar Typhimurium Using Electrochemical Impedance SpectroscopyELECTROANALYSIS, Issue 20 2009Jeffrey Abstract An immunosensor for rapid and low level detection of the bacterial pathogen Salmonella enterica Serovar Typhimurium was designed and developed based upon label-free electrochemical impedance spectroscopy and correlated to viable cell counts. The immunosensor was fabricated by electroplating gold onto a disposable printed circuit board (PCB) electrode by immobilizing monoclonal antibody (MAb) specific against Salmonella typhimurium cell surface lipopolysaccharide (LPS) onto the surface of the electrode. Use of mass-fabricated and electroplated PCB electrodes allowed for disposable, highly sensitive, and rapid detection of Salmonella in an aqueous environment. Results demonstrate that in purified solution, Salmonella can be detected as low as 10 CFU in a 100,,L volume and label-free and rapid manner in fewer than 90,s. The cost effective approach described here can be used for detection of pathogens with relevance for healthcare, food, and environmental applications. [source] Direct Electrochemistry and Electrocatalysis of Hemoglobin in Lipid Film Incorporated with Room-Temperature Ionic LiquidELECTROANALYSIS, Issue 20 2008Gaiping Li Abstract A facile phospholipid/room-temperature ionic liquid (RTIL) composite material based on dimyristoylphosphatidylcholine (DMPC) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) was exploited as a new matrix for immobilizing protein. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were adopted to characterize this composite film. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. UV-vis absorbance spectra showed that Hb still maintained its heme crevice integrity in this composite film. By virtue of the Hb/DMPC/[bmim]PF6 composite film-modified glassy carbon electrode (GCE), a pair of well-defined redox peaks of Hb was obtained through the direct electron transfer between protein and underlying GCE. Moreover, the reduction of O2 and H2O2 at the Hb/DMPC/[bmim]PF6 composite film-modified GCE was dramatically enhanced. [source] Some Properties of Sodium Dodecyl Sulfate Functionalized Multiwalled Carbon Nanotubes Electrode and Its Application on Detection of Dopamine in the Presence of Ascorbic AcidELECTROANALYSIS, Issue 16 2008Dan Zheng Abstract A sodium dodecyl sulfate (SDS) functionalized multiwalled carbon nanotubes (MWNTs) electrode (SDS/MWNTs) was successfully constructed in this study. The electrochemical property of the SDS/MWNTs electrode has been characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Nyquist plots suggest that the immersion time of SDS affects the resistances of the MWNTs electrodes. The thickness of adsorbed SDS on MWNTs surface is estimated to be 1.23,nm, which is close to the value of SDS monolayer. CV results demonstrate a 5-fold enhanced response for dopamine (DA) at the SDS/MWNTs electrode compared to the bare MWNTs one. DPV results illustrate that DA can be selectively determined in the presence of high concentration ascorbic acid (AA) with a linear range from 20,,M to 0.20,mM and a sensitivity of 0.024,,A ,M,1 at the SDS/MWNTs electrode. [source] Paste Electrode Based on Short Single-Walled Carbon Nanotubes and Room Temperature Ionic Liquid: Preparation, Characterization and Application in DNA DetectionELECTROANALYSIS, Issue 12 2008Xuzhi Zhang Abstract A paste electrode (SWNT&RTIL PE) has been prepared using carboxylic group-functionalized short single-walled carbon nanotubes (SWNTs) mixed with 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6, one kind of room temperature ionic liquid, RTIL). Its electrochemical behavior was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in comparison with the paste electrode using mineral oil as a binder. Results highlighted the advantages of the paste electrode: not only higher conductivity, but also lower potential separation (,Ep), higher peak current (ip) and better reversibility towards dopamine (DA), methylene blue (MB) and K3[Fe(CN)6]. The SWNT&RTIL PE could be used to detect the number of guanine bases and adenine bases contents in per mol oligonucleotides according to the current response in the range of 0.05,2.0,nM. Based on the current response of guanine bases, oligonucleotides could be detected sensitively in the B,R buffer solution with a detection limit of 9.9,pM. The heterogeneous electron transfer rate constant (ks) of guanine bases contents in the oligonucleotides was investigated and its value was 0.90,s,1. In essence the SWNT&RTIL PE showed high sensitivity, reliability, stability and reproducibility for the detection of DNA. [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] Electrochemical Characterization of In Situ Functionalized Gold Cysteamine Self-Assembled Monolayer with 4-Formylphenylboronic Acid for Detection of DopamineELECTROANALYSIS, Issue 5 2008Karimi Shervedani Abstract Functionalization of gold cysteamine (AuCA) self-assembled monolayer with 4-formylphenylboronic acid (BA) via Schiff's base formation, through in situ method to fabricate Au-CA-BA electrode is presented and described. The fabricated electrode was used as a novel sensor for accumulation and determination of dopamine (DA). The accumulation of DA as a diol on the topside of Au-CA-BA as a Lewis acid, was performed via esterification (AuCABADA), and followed for determination of DA. Functionalization, characterization, and determination steps were probed by electrochemical methods like cyclic voltammetry and electrochemical impedance spectroscopy. The data will be presented and discussed from which a new sensor for DA is introduced. [source] Detecting Biorecognition Events at Blocked Interface Polymeric Membrane Ion-Selective Electrodes Using Electrochemical Impedance Spectroscopy and Atomic Force MicroscopyELECTROANALYSIS, Issue 3 2008Marco, Roland De Abstract Immobilization of a biorecognition element onto a polymeric membrane ion-selective electrode (ISE) using a self-assembly approach may provide scope for a novel biosensor technology platform based on the altered potentiometric response at the blocked ISE interface. In this paper, the authors have investigated the influence of solution adsorption of the model biorecognition element, avidin-biotin, on the electrode kinetics of a conventional polymeric membrane Ca2+ ISE using atomic force microscopy (AFM) coupled with electrochemical impedance spectroscopy (EIS). It is demonstrated that solution adsorption of avidin followed by biotin incorporation leads to a demonstrable biorecognition event characterized by an impediment in the Ca2+ ion transfer kinetics of the modified ISE surface. This kinetic principle is amenable to biosensing using pulsed chronopotentiometric polymeric ISEs, which is an established dynamic electrode technique for use with polymeric membrane ISEs. [source] Gold Nanoparticles in Nonenzymatic Electrochemical Detection of SugarsELECTROANALYSIS, Issue 19-20 2006Fredy Kurniawan Abstract A nonenzymatic electrochemical sensor for detection of sugars was prepared by layer-by-layer deposition of gold nanoparticles on thin gold electrodes. The deposition was optimized by using of surface plasmon resonance. Voltammetric investigation and impedance spectroscopy of the sensor was performed. Electrical currents caused by glucose on bare gold electrodes and on gold electrodes coated by immobilized gold nanoparticles were compared. The electrodes with nanoparticles display much higher current of glucose oxidation. The oxidation becomes blocked when the swept electrode potential exceeded +0.25,V, during the back scan an oxidation peak is observed again but at less positive potential. The magnitudes of these current peaks are linearly dependent on the glucose concentration; this dependence can be used as calibration for analytical applications. The limit of detection for glucose is below 0.5,mM, the sensitivity (normalized to the macroscopic electrode surface) is about 160,,A,cm,2,mM,1. The sensor response is linear till at least 8,mM of glucose concentration. [source] | |||||||||||||||||||