ELECTROANALYSIS, Issue 2 2010
Christopher
Abstract Gold electrodes modified by underpotential deposition to expose a layer of silver atoms on their surfaces were used to measure thiocyanate concentrations in aqueous solutions. When exposed to thiocyanate, the ion adsorbs onto the modified electrode and causes changes in the electrochemical properties of the silver adlayer. Coulometric measurement of the fraction of the silver adlayer that remains in its original state provides a means for determining thiocyanate concentrations. The adsorption of thiocyanate onto the electrode follows a first-order process with a rate constant of ca. 440,L/mol s that defines its concentration/time response. [source]

Electrochemical Properties of Ordered Mesoporous Carbon Film Adsorbed onto a Self-Assembled Alkanethiol Monolayer on Gold Electrode

ELECTROANALYSIS, Issue 2 2009
Dan Zheng
Abstract A stable ordered mesoporous carbon (OMC) film electrode was successfully constructed by adsorbing OMC onto a self-assembled monolayer (SAM) of C18H37SH chemisorbed on the Au electrode. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and electrochemical methods were used to characterize the properties of the OMC film electrode. The adsorbed OMC can restore the heterogeneous electron transfer almost totally blocked by the alkanethiol monolayer. Nyquist plots show a sharply decrease of the charge transfer resistance (Rct) of the Fe(CN) couple at the OMC film electrode. Furthermore, the OMC film electrode is found to possess a significantly reduced interfacial capacitance and largely enhanced current response of hydrogen peroxide. This novel approach to the fabrication of stable OMC film electrode with excellent electrochemical properties is believed to be very attractive for electrochemical studies and electroanalytical applications. [source]

4-Aminothiophenol Self-Assembled Monolayer for the Development of a DNA Biosensor Aiming the Detection of Cylindrospermopsin Producing Cyanobacteria

ELECTROANALYSIS, Issue 22 2008
Elisabete Valério
Abstract The development of a DNA biosensor for the detection of cylindrospermopsin, based on self-assembled monolayers (SAMs) of 4-aminothiophenol, is investigated. SAMs were characterized by electrochemical reductive desorption. Detection of probe immobilization and hybridization has been achieved by cyclic and square-wave voltammetry (SWV), using methylene blue (MB) as electroactive indicator. The SWV data obtained in phosphate buffer, with and without NaCl, after MB accumulation, revealed an increase of the redox indicator current peaks after the hybridization step. This behavior is consistent with MB intercalation into DNA, for high ionic strength media and attributed to electrostatic interactions in the absence of salt. Evidence for surface modification is also provided by atomic force microscopy and ellipsometry. [source]

Electrochemical Characterization of In Situ Functionalized Gold Cysteamine Self-Assembled Monolayer with 4-Formylphenylboronic Acid for Detection of Dopamine

ELECTROANALYSIS, Issue 5 2008
Karimi 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]

FIA Determination of Paracetamol in Pharmaceutical Drugs by Using Gold Electrodes Modified with a 3-Mercaptopropionic Acid Monolayer

ELECTROANALYSIS, Issue 9 2006
Valber
Abstract A flow injection analysis (FIA) method for the determination of paracetamol in pharmaceutical drugs using a gold electrode modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid is described. At optimized experimental conditions the dynamic concentration range was 0.15 to 15.0,mg L,1 with a detection limit of 0.2,,g mL,1 (S/N=3). The repeatability of current responses for injections of 10,,mol L,1 paracetamol was evaluated to be 3.2% (n=30) and the analytical frequency was 180,h,1. The lifetime of the modified electrode was found to be 15 days. The results obtained by using the proposed amperometric method for paracetamol determination in four different drug samples compared well with those found by spectrophotometry. [source]

Cell Adhesion and Cellular Patterning on a Self-Assembled Monolayer of Zeolite L Crystals

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
Nermin Seda Kehr
Abstract Chemically functionalized self-assembled monolayers made by disk-shaped zeolite L nanocrystals are used as models for biocompatible surfaces to study cell-adhesion behavior. Different chemical groups lead to different cellular behavior and fluorescent-molecule-loaded zeolites allow the position of the cells to be determined. Furthermore, a patterned monolayer of asymmetrically functionalized zeolite L obtained by microcontact chemistry is used to grow cells. A spatial recognition of the cells, which proliferate only on the bioactive-molecule-functionalized stripes, is possible. [source]

A preliminary in vitro study into the use of IL-1Ra gene therapy for the inhibition of intervertebral disc degeneration

INTERNATIONAL JOURNAL OF EXPERIMENTAL PATHOLOGY, Issue 1 2006
Christine L. Le Maitre
Summary Conventional therapies for low back pain (LBP) are purely symptomatic and do not target the cause of LBP, which in approximately 40% of cases is caused by degeneration of the intervertebral disc (DIVD). Targeting therapies to inhibit the process of degeneration would be a potentially valuable treatment for LBP. There is increasing evidence for a role for IL-1 in DIVD. A natural inhibitor of IL-1 exists, IL-1Ra, which would be an ideal molecular target for inhibiting IL-1-mediated effects involved in DIVD and LBP. In this study, the feasibility of ex vivo gene transfer of IL-1Ra to the IVD was investigated. Monolayer and alginate cultures of normal and degenerate human intervertebral disc (IVD) cells were infected with an adenoviral vector carrying the IL-1Ra gene (Ad-IL-1Ra) and protein production measured using an enzyme-linked immunosorbent assay. The ability of these infected cells to inhibit the effects of IL-1 was also investigated. In addition, normal and degenerate IVD cells infected with Ad-IL-1Ra were injected into degenerate disc tissue explants and IL-1Ra production in these discs was assessed. This demonstrated that both nucleus pulposus and annulus fibrosus cells infected with Ad-IL-1Ra produced elevated levels of IL-1Ra for prolonged time periods, and these infected cells were resistant to IL-1. When the infected cells were injected into disc explants, IL-1Ra protein expression was increased which was maintained for 2 weeks of investigation. This in vitro study has shown that the use of ex vivo gene transfer to degenerate disc tissue is a feasible therapy for the inhibition of IL-1-mediated events during disc degeneration. [source]

Immunophenotypic analysis of human articular chondrocytes: Changes in surface markers associated with cell expansion in monolayer culture

JOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2005
Jose Diaz-Romero
Cartilage tissue engineering relies on in vitro expansion of primary chondrocytes. Monolayer is the chosen culture model for chondrocyte expansion because in this system the proliferative capacity of chondrocytes is substantially higher compared to non-adherent systems. However, human articular chondrocytes (HACs) cultured as monolayers undergo changes in phenotype and gene expression known as "dedifferentiation." To gain a better understanding of the cellular mechanisms involved in the dedifferentiation process, our research focused on the characterization of the surface molecule phenotype of HACs in monolayer culture. Adult HACs were isolated by enzymatic digestion of cartilage samples obtained post-mortem. HACs cultured in monolayer for different time periods were analyzed by flow cytometry for the expression of cell surface markers with a panel of 52 antibodies. Our results show that HACs express surface molecules belonging to different categories: integrins and other adhesion molecules (CD49a, CD49b, CD49c, CD49e, CD49f, CD51/61, CD54, CD106, CD166, CD58, CD44), tetraspanins (CD9, CD63, CD81, CD82, CD151), receptors (CD105, CD119, CD130, CD140a, CD221, CD95, CD120a, CD71, CD14), ectoenzymes (CD10, CD26), and other surface molecules (CD90, CD99). Moreover, differential expression of certain markers in monolayer culture was identified. Up-regulation of markers on HACs regarded as distinctive for mesenchymal stem cells (CD10, CD90, CD105, CD166) during monolayer culture suggested that dedifferentiation leads to reversion to a primitive phenotype. This study contributes to the definition of HAC phenotype, and provides new potential markers to characterize chondrocyte differentiation stage in the context of tissue engineering applications. © 2004 Wiley-Liss, Inc. [source]

Role of interfaces on the direct tunneling and the inelastic tunneling behaviors through metal/alkylsilane/silicon junctions

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006
D. K. Aswal
Abstract We studied the influence of the end group of the alkylsilane molecule used in Self Assembled Monolayer (SAM) in Silicon/SAM/Metal junctions. By Inelastic Electron Tunneling spectroscopy (IETS), we showed the formation of a covalent bond between the molecules and the gold electrode in the case of a thiol terminated alkylsilane. By electrical characterizations, we demonstrated that the thiol group at the interface avoids diffusion of gold into the molecule even for a 3 carbons chain. For this short molecule, we observed pure tunnel conduction with barrier height at the monolayer/Si and monolayer/Au interfaces found to be respectively 2.14 and 2.56 eV. These values were obtained using Simmons equation with an effective mass parameter m * = 0.16me (me = mass of the electron). This extends the demonstration of the excellent tunnel dielectric behavior of these organic monolayers down to 3 carbon atoms with a thiol/Au bond at the interface. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Regulating Copper-Binding Affinity with Photoisomerizable Azobenzene Ligand by Construction of a Self-Assembled Monolayer,

ANGEWANDTE CHEMIE, Issue 33 2009
Isao Takahashi Dr.
Einer bleibt, einer geht: Selbstorganisierte Monoschichten (SAMs) aus trans - oder cis -Azobenzolliganden können CuII -Ionen komplexieren. Die an die trans -SAM gebundenen Ionen werden in cyclovoltammetrischen Redoxzyklen (CV) freigesetzt, während die cis -Komplexe stabil bleiben (siehe Bild). Bestrahlung der cis -SAM mit sichtbarem Licht führt zu einer cis-trans -Photoisomerisierung, wodurch ebenfalls eine Freisetzung der Cu-Ionen resultiert. [source]

Directional Surface Plasmon-Coupled Emission from a 3 nm Green Fluorescent Protein Monolayer

BIOTECHNOLOGY PROGRESS, Issue 6 2005
Yordan Kostov
High-sensitivity detection schemes are of great interest for a number of applications. Unfortunately, such schemes are usually high-cost. We demonstrate a low-cost approach to a high-sensitivity detection scheme based on surface plasmon-coupled emission (SPCE). The SPCE of a monomolecular layer of green fluorescent protein (GFP) is reported here. The protein was electrostatically attached to a thin, SiO2 -protected silver film deposited on a quartz substrate. The visible, directional emission of GFP was observed at a sharp, well-defined angle of 47.5° from the normal to the coupling prism, and the spectrum corresponded to that of GFP. The SPCE resulting from the reverse Kretschmann configuration showed a 12-fold enhancement over the free space fluorescence. The directional emission was 97% p-polarized. The directionality and high polarization can be coupled with the intrinsic spectral resolution of SPCE to be used in the design miniaturized spectrofluorometers. The observation of SPCE in the visible region of the spectrum from a monolayer of protein opens up new possibilities in protein-based sensing. [source]

Oligothiophenes Nano-organized on a Cyclotetrasiloxane Scaffold as a Model of a Silica-Bound Monolayer: Evidence for Intramolecular Excimer Formation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 46 2009
Wojciech Mróz
Abstract Excimer formation in a new class of terthiophene-based fluorophores covalently bonded to a cyclotetrasiloxane scaffold has been demonstrated and the photophysical process ruling it has been investigated in detail and modeled theoretically. In contrast to the conventional systems in which long-living fluorophores such as pyrene are linked in the same molecule, an excimer is formed only when two terthiophene-based branches nano-organized on the same cyclotetrasiloxane scaffold are close enough together when excitation takes place. In such a case, excimer formation is extremely efficient, and the new bound excited states are quite stable. [source]

Covalent Attachment of Bacteriorhodopsin Monolayer to Bromo-terminated Solid Supports: Preparation, Characterization, and Protein Stability

CHEMISTRY - AN ASIAN JOURNAL, Issue 7 2008
Yongdong Jin Dr.
Abstract The interfacing of functional proteins with solid supports and the study of related protein-adsorption behavior are promising and important for potential device applications. In this study, we describe the preparation of bacteriorhodopsin (bR) monolayers on Br-terminated solid supports through covalent attachment. The bonding, by chemical reaction of the exposed free amine groups of bR with the pendant Br group of the chemically modified solid surface, was confirmed both by negative AFM results obtained when acetylated bR (instead of native bR) was used as a control and by weak bands observed at around 1610,cm,1 in the FTIR spectrum. The coverage of the resultant bR monolayer was significantly increased by changing the pH of the purple-membrane suspension from 9.2 to 6.8. Although bR, which is an exceptionally stable protein, showed a pronounced loss of its photoactivity in these bR monolayers, it retained full photoactivity after covalent binding to Br-terminated alkyls in solution. Several characterization methods, including atomic force microscopy (AFM), contact potential difference (CPD) measurements, and UV/Vis and Fourier transform infrared (FTIR) spectroscopy, verified that these bR monolayers behaved significantly different from native bR. Current,voltage (I,V) measurements (and optical absorption spectroscopy) suggest that the retinal chromophore is probably still present in the protein, whereas the UV/Vis spectrum suggests that it lacks the characteristic covalent protonated Schiff base linkage. This finding sheds light on the unique interactions of biomolecules with solid surfaces and may be significant for the design of protein-containing device structures. [source]

Microscopic Evidence of the Metalation of a Free-Base Porphyrin Monolayer with Iron

CHEMPHYSCHEM, Issue 2 2007
Florian Buchner
Microscopic evidence of the in situ complexation of Fe-porphyrins is presented. The figure shows the sub-molecular resolved scanning tunneling microscopy images which document the metalation of 2H-TPP (central cavity; TPP: tetraphenylporphyrin) with evaporated iron (protrusions are identified as Fe-TPP). This promising technique enables future surface science investigations of clean iron porphyrin films under ultrahigh vacuum conditions. [source]

Molecular Self-Assembly of Jointed Molecules on a Metallic Substrate: From Single Molecule to Monolayer

CHEMPHYSCHEM, Issue 9 2006
Tomaso Zambelli Dr.
Organic hinges: The "flexure hinges" in V -Landers (VL) molecules (C108H104) play an essential role in the adaptability of the molecule to the substrate (see figure). The molecules cannot simply be considered as rigid objects and it is mandatory to take into account their internal molecular degrees of freedom in order to understand the observed structures. [source]

Overcoming surfactant inhibition with polymers

ACTA PAEDIATRICA, Issue 12 2000
PA Dargaville
Inhibition of the function of pulmonary surfactant in the alveolar space is an important element of the pathophysiology of many lung diseases, including meconium aspiration syndrome, pneumonia and acute respiratory distress syndrome. The known mechanisms by which surfactant dysfunction occurs are (a) competitive inhibition of phospholipid entry into the surface monolayer (e.g. by plasma proteins), and (b) infiltration and destabilization of the surface film by extraneous lipids (e.g. meconium-derived free fatty acids). Recent data suggest that addition of non-ionic polymers such as dextrano and polyethylene glycol to surfactant mixtures may significantly improve resistance to inhibition. Polymers have been found to neutralize the effects of several different inhibitors, and can produce near-complete restoration of surfactant function. The anti-inhibitory properties of polymers, and their possible role as an adjunct to surfactant therapy, deserve further exploration. [source]

The impact of SiC substrate treatment on the heteroepitaxial growth of GaN by plasma assisted MBE

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005
A. S. Brown
Abstract We report on the impact of the preparation of the Si-face 4H-SiC(0001)Si substrate using a Ga flash-off process on the epitaxial growth of GaN by plasma-assisted molecular beam epitaxy. The nucleation, as well as the resultant structural and morphological properties of GaN grown directly on 4H-SiC(0001)Si are strongly influenced by the chemical and morphological modifications of the SiC surface induced by the Ga flash-off process. Herein we describe the impact of the specific concentration of Ga incident on the surface (quantified in terms of monolayer (ML) coverage): of 0.5 ML, 1ML and 2ML. The residual oxygen at the SiC surface, unintentional SiC nitridation and the formation of cubic GaN grains during the initial nucleation stage, are all reduced when a 2 ML Ga flash is used. All of the above factors result in structural improvement of the GaN epitaxial layers. The correlation between the SiC surface modification, the initial nucleation stage, and the GaN epitaxial layer structural quality has been articulated using x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy and spectroscopic ellipsometry data. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Sensitivity of alveolar macrophages to substrate mechanical and adhesive properties

CYTOSKELETON, Issue 6 2006
Sophie Féréol
Abstract In order to understand the sensitivity of alveolar macrophages (AMs) to substrate properties, we have developed a new model of macrophages cultured on substrates of increasing Young's modulus: (i) a monolayer of alveolar epithelial cells representing the supple (,0.1 kPa) physiological substrate, (ii) polyacrylamide gels with two concentrations of bis-acrylamide representing low and high intermediate stiffness (respectively 40 kPa and 160 kPa) and, (iii) a highly rigid surface of plastic or glass (respectively 3 MPa and 70 MPa), the two latter being or not functionalized with type I-collagen. The macrophage response was studied through their shape (characterized by 3D-reconstructions of F-actin structure) and their cytoskeletal stiffness (estimated by transient twisting of magnetic RGD-coated beads and corrected for actual bead immersion). Macrophage shape dramatically changed from rounded to flattened as substrate stiffness increased from soft ((i) and (ii)) to rigid (iii) substrates, indicating a net sensitivity of alveolar macrophages to substrate stiffness but without generating F-actin stress fibers. Macrophage stiffness was also increased by large substrate stiffness increase but this increase was not due to an increase in internal tension assessed by the negligible effect of a F-actin depolymerizing drug (cytochalasine D) on bead twisting. The mechanical sensitivity of AMs could be partly explained by an idealized numerical model describing how low cell height enhances the substrate-stiffness-dependence of the apparent (measured) AM stiffness. Altogether, these results suggest that macrophages are able to probe their physical environment but the mechanosensitive mechanism behind appears quite different from tissue cells, since it occurs at no significant cell-scale prestress, shape changes through minimal actin remodeling and finally an AMs stiffness not affected by the loss in F-actin integrity. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source]

Signaling in the third dimension: The peripodial epithelium in eye disc development

DEVELOPMENTAL DYNAMICS, Issue 9 2009
Mardelle Atkins
Abstract The eye-antennal imaginal disc of Drosophila melanogaster has often been described as an epithelial monolayer with complex signaling events playing out in two dimensions. However, the imaginal disc actually comprises two opposing epithelia (the peripodial epithelium, or PE, and the disc proper, or DP) separated by a lumen to form a sac-like structure. Recent studies expose complex molecular interactions between the PE and the DP, and reveal dynamic communication between the two tissues. Further findings suggest the PE makes important contributions to DP development by acting as a source of signaling molecules as well as cells. Here we summarize those findings and highlight implications for further research. Developmental Dynamics 238:2139,2148, 2009. © 2009 Wiley-Liss, Inc. [source]

Complete reconstruction of the retinal laminar structure from a cultured retinal pigment epithelium is triggered by altered tissue interaction and promoted by overlaid extracellular matrices

DEVELOPMENTAL NEUROBIOLOGY, Issue 14 2009
Fusako Kuriyama
Abstract The retina regenerates from retinal pigment epithelial (RPE) cells by transdifferentiation in the adult newt and Xenopus laevis when it is surgically removed. This was studied under a novel culture condition, and we succeeded, for the first time, in developing a complete retinal laminar structure from a single epithelial sheet of RPE. We cultured a Xenopus RPE monolayer sheet isolated from the choroid on a filter cup with gels overlaid and found that the retinal tissue structure differentiated with all retinal layers present. In the culture, RPE cells isolated themselves from the culture substratum (filter membrane), migrated, and reattached to the overlaid gel, on which they initiated transdifferentiation. This was exactly the same as observed during in vivo retina regeneration of X. laevis. In contrast, when RPE monolayers were cultured similarly without isolation from the choroid, RPE cells proliferated, but remained pigmented instead of transdifferentiating, indicating that alteration in tissue interaction triggers transdifferentiation. We then examined under the conventional tissue culture condition whether altered RPE-choroid interaction induces Pax6 expression. Pax6 was upregulated in RPE cells soon after they were removed from the choroid, and this expression was not dependent of FGF2. FGF2 administration was needed for RPE cells to maintain Pax6 expression. From the present results, in addition to our previous ones, we propose a two-step mechanism of transdifferentiation: the first step is a reversible process and is initiated by the alteration of the cell-extracellular matrix and/or cell,cell interaction followed by Pax6 upregulation. FGF2 plays a key role in driving RPE cells into the second step, during which they differentiate into retinal stem cells. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source]

Enameloid microstructure in the oldest known chondrichthyan teeth

ACTA ZOOLOGICA, Issue 2009
H. Botella
Abstract Previous studies on tooth enameloid microstructure in several chondrichthyan taxa spanning the phylogeny of the group provided support for the homology of chondrichthyan tooth enameloid. This hypothesis requires that a single crystallite enameloid (SCE) monolayer must be present in the teeth of the most primitive chondrichthyan. However, the dental microstructure of the earliest sharks has yet to be investigated. We have studied the tooth enameloid microstructure of the two oldest tooth-bearing shark species currently known, Leonodus carlsi Mader (1986) and Celtiberina maderi Wang (1993), from the lowermost Lochkovian (Lower Devonian) of Spain. Our study demonstrates the presence of a SCE monolayer in the teeth of both species. These results show that a superficial cap of SCE is present in the oldest shark teeth known, which suggest its presence in the most basal chondrichthyans. [source]

Design of an Ultrasound Contrast Agent for Myocardial Perfusion

ECHOCARDIOGRAPHY, Issue 2000
Michel Schneider Ph.D.
Myocardial contrast echography (MCE) has been a major research objective in cardiovascular ultrasound for almost two decades. The design of a contrast agent fulfilling the needs of MCE requires taking into consideration a number of points: a basic decision has to be made whether a deposit agent or a free-flowing agent would be more appropriate and whether an agent active at low/medium mechanical index (MI) is preferable to an agent active only at high MI; only a small percentage of the cardiac output enters the coronary microcirculation, which means that highly sensitive bubble detection methods, such as harmonic imaging or pulse inversion, are needed; the low velocity of blood in the microcirculation that leads to extensive bubble destruction during imaging means that intermittent imaging and/or an agent active at low MI is (are) required; the duration of the contrast effect must be sufficient to allow a complete examination and is affected by the rate of contrast administration; the performance of the contrast agent should not be equipment-dependent. The ultimate goal in MCE is to be able to quantify blood flow in the various segments to determine if adequate oxygenation is achieved. Ultrasound-mediated bubble destruction followed by the measurement of bubble replenishment kinetics opens new perspectives for quantification. SonoVue is a free-flowing ultrasound contrast agent made of sulphur hexafluoride microbubbles stabilized by a highly elastic phospholipid monolayer. SonoVue is able to produce myocardial opacification at a wide range of acoustic pressures and in particular at Mis as low as 0.1. Its performance is not equipment-dependent. Good results for myocardial opacification have been observed in all animal species tested (dogs, minipigs, rabbits), using continuous as well as intermittent imaging. Trials are in progress to demonstrate the clinical utility of SonoVue for rest and stress perfusion studies, in particular for the diagnosis of CAD, the detection of myocardial infarction, the assessment of the success of interventions and myocardial viability, and the detection of hibernating myocardium. [source]

Mediated Electron Transfer Across Supported Bilayer Lipid Membrane with TCNQ-Based Organometallic Compounds

ELECTROANALYSIS, Issue 4 2010
Meili 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]

Electrochemical Properties of Ordered Mesoporous Carbon Film Adsorbed onto a Self-Assembled Alkanethiol Monolayer on Gold Electrode

Some Properties of Sodium Dodecyl Sulfate Functionalized Multiwalled Carbon Nanotubes Electrode and Its Application on Detection of Dopamine in the Presence of Ascorbic Acid

ELECTROANALYSIS, Issue 16 2008
Dan 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]

Electrochemical Characterization of In Situ Functionalized Gold Cysteamine Self-Assembled Monolayer with 4-Formylphenylboronic Acid for Detection of Dopamine

Study of Factors Affecting the Performance of Voltammetric Copper Sensors Based on Gly-Gly-His Modified Glassy Carbon and Gold Electrodes

ELECTROANALYSIS, Issue 12 2006
Guozhen Liu
Abstract This paper reports a study of the factors affecting the analytical performance of gold and glassy carbon electrodes modified with the tripeptide Gly-Gly-His for the detection of copper ions. Gly-Gly-His is attached to a glassy carbon (GC) surface modified with 4-carboxyphenyl moieties or a gold surface modified with 3-mercaptopropionic acid by the reaction of the N-terminal amine group of the peptide with the carboxylic acid groups of the monolayer via carbodiimide activation. X-ray photoelectron spectroscopy was used to characterize the steps in the biosensor fabrication. It was found that the analytical performance of a sensor prepared with Gly-Gly-His on a GC electrode was similar to that on a gold electrode under the same conditions. The performance was greatly enhanced at higher temperature, no added salt during copper accumulation and longer accumulation time within a pH range of 7,9. Interference studies and investigations of stability of the Gly-Gly-His sensor are reported. Analysis of natural water samples show that the sensors measure only copper ions that can complex at the sensor surface. Strongly complexed copper in natural water is not measured. Despite greater stability of diazonium salt derived monolayers on carbon surfaces compared with alkanethiols self-assembled monolayers on gold, the stability of the sensors was essentially the same regardless of the modification procedure. [source]

FIA Determination of Paracetamol in Pharmaceutical Drugs by Using Gold Electrodes Modified with a 3-Mercaptopropionic Acid Monolayer

Gold Nanoparticle-Based Mediatorless Biosensor Prepared on Microporous Electrode

ELECTROANALYSIS, Issue 3 2006
Fenghua Zhang
Abstract A mediatorless biosensor was fabricated with a double-sided microporous gold electrode by successively immobilizing a mixed self-assembled monolayer (SAM) comprising carboxylic-acid- and thiol-terminated thiolate (dl -thiorphan and 1,8-octanedithiol), glucose oxidase (GOx) and finally gold nanoparticle (Au NP) on one working side. The double-sided microporous gold electrodes were formed by plasma sputtering of gold on a porous nylon substrate, yielding a face-to-face type two-electrode electrochemical cell. While the straight chain molecule 1,8-octanedithiol forms a dense insulating monolayer, the side armed dl -thiorphan forms a low density layer for the diffusion of redox couples to the electrode surface. The mixed SAM not only provided the linking functional groups for both enzyme and Au NP but also resulted in the appropriately spaced monolayer for direct electron tansfer (ET) process from the center of the redox enzyme to the electrode surface. After covalently immobilizing GOx onto the carboxylic-acid-terminated monolayer, Au NP was easily immobilized to both enzyme and nearby thiols by simple dispensing of the colloidal gold solution. It was observed that the resulting amperometric biosensor exhibited quantitatively the same response to glucose in the presence and in the absence of dissolved oxygen, which evidence that the Au NPs immobilized on and around the GOx promote direct ET from the enzymes to the electrode, assuming the role of a common redox mediator. [source]

Impedance Spectroscopy: A Powerful Tool for Rapid Biomolecular Screening and Cell Culture Monitoring

ELECTROANALYSIS, Issue 23 2005
Isaac
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]