Home  About us  Contact
 

Da

Distribution by Scientific Domains
Chemistry45%
Life Sciences22%
Medical Sciences16%
Polymers and Materials Science3%
Engineering3%
Humanities and Social Sciences2%
Earth and Environmental Science2%
5 Other Domains7%
Distribution within Chemistry
Crystallography40%
General & Introductory Chemistry22%
Mass Spectrometry11%
General & Introductory Food Science & Technology4%
18 Other Subdomains23%

Kinds of Da

  • auf da
  • dialysate da
    		•
  • durch da
  • extracellular da
    		•
  • für da

    • Terms modified by Da

  • da cell
  • da concentration
  • da grün fluoreszierende protein
  • da level
    		•
  • da neuron
  • da receptor
  • da release
  • da score
    		•
  • da system
  • da transporter
  • da vinci surgical system
  • da ziel
    		•
  • da ziel dieser studie war e

    • Selected Abstracts

    Treatment of Anemia With Darbepoetin Alfa in Heart Failure

    CONGESTIVE HEART FAILURE, Issue 3 2010
    William T. Abraham MD
    Anemia is common in heart failure (HF) patients. A prespecified pooled analysis of 2 randomized, double-blind, placebo-controlled studies evaluated darbepoetin alfa (DA) in 475 anemic patients with HF (hemoglobin [Hb], 9.0,12.5 g/dL). DA was administered subcutaneously every 2 weeks and titrated to achieve and maintain a target Hb level of 14.0±1.0 g/dL. By week 27, mean (SD) Hb concentrations did not increase with placebo but increased with DA from 11.5 (0.7) to 13.3 (1.3) g/dL. Hazard ratios (HRs) for DA compared with placebo for all-cause death or first HF hospitalization (composite end point), all-cause death, and HF hospitalization by month 12 were 0.67 (95% confidence interval [CI], 0.44,1.03; P=.067), 0.76 (95% CI, 0.39,1.48; P=.419), and 0.66 (95% CI, 0.40,1.07; P=.093), respectively. Incidence of adverse events was similar in both groups. In post hoc analyses, improvement in the composite end point was significantly associated with the mean Hb change from baseline (adjusted HR, 0.40; P=.017) with DA treatment. There was no increased risk of all-cause mortality or first HF hospitalization with DA in patients with reduced renal function or elevated baseline B-type natriuretic peptide, a biomarker of worse HF. These results suggest that DA is well tolerated, corrects HF-associated anemia, and may have favorable effects on clinical outcomes., Congest Heart Fail. 2010;16:87,95. © 2010 Wiley Periodicals, Inc. [source]

    Using Population Count Data to Assess the Effects of Changing River Flow on an Endangered Riparian Plant

    CONSERVATION BIOLOGY, Issue 4 2006
    DIANE M. THOMSON
    análisis de viabilidad poblacional; gestión ribereña; método de difusión; presas; riesgo de extinción Abstract:,Methods for using simple population count data to project extinction risk have been the focus of much recent theoretical work, but few researchers have used these approaches to address management questions. We analyzed 15 years of census data on the federally endangered endemic riparian plant Pityopsis ruthii (Small) with the diffusion approximation (DA). Our goals were to evaluate relative extinction risk among populations in two different watersheds (in Tennessee, U.S.A.) and potential effects of variation in managed river flow on population dynamics. Populations in both watersheds had high projected risks of extinction within 50 years, but the causes of this risk differed. Populations of P. ruthii on the Hiwassee River had higher initial population sizes but significantly lower average growth rates than those on the Ocoee River. The only populations with low predicted short-term extinction risk were on the Ocoee. Growth rates for populations on both rivers were significantly reduced during periods of lower river flow. We found only marginal evidence of a quadratic relationship between population performance and flow. These patterns are consistent with the idea that low flows affect P. ruthii due to growth of competing vegetation, but the degree to which very high flows may reduce population growth is still unclear. Simulations indicated that populations were most sensitive to growth rates in low-flow years, but small changes in the frequency of these periods did not strongly increase risk for most populations. Consistent with results of other studies, DA estimates of extinction risk had wide confidence limits. Still, our results yielded several valuable insights, including the need for greater monitoring of populations on the Hiwassee and the importance of low-flow years to population growth. Our work illustrates the potential value of simple methods for analyzing count data despite the challenges posed by uncertainty in estimates of extinction risk. Resumen:,Los métodos que utilizan datos de conteos simples de la población para proyectar el riesgo de extinción han sido el foco reciente de mucho trabajo teórico, pero pocos investigadores han utilizado estos métodos para responder preguntas de gestión. Analizamos 15 años de datos de censos de la planta ribereña, endémica y federalmente en peligro Pityopsis ruthii (Small) mediante el método de difusión. Nuestras metas fueron evaluar el riesgo de extinción de poblaciones en dos cuencas hidrológicas distintas y con dos efectos potenciales de la variación del flujo de agua sobre la dinámica de la población. Las poblaciones en ambas cuencas tenían alto riesgo de extinción proyectado a 50 años, pero las causas de este riesgo difirieron. Las poblaciones de P. ruthii en el Río Hiwassee tuvieron poblaciones iniciales más grandes, pero tasas de crecimiento significativamente menores, que las poblaciones en el Río Ocoee. Las únicas poblaciones con bajo riesgo de extinción pronosticado estaban en el Ocoee. Las tasas de crecimiento de las poblaciones en ambos ríos se redujeron significativamente durante períodos de bajo flujo en el río. Sólo encontramos evidencia marginal de la relación cuadrática entre el funcionamiento de la población y el flujo. Estos patrones son consistentes con la idea de que los bajos flujos afectan a P. ruthii debido al crecimiento de vegetación competitiva, pero aun no es claro el grado en que flujos muy grandes pueden reducir el crecimiento poblacional. Las simulaciones indicaron que las poblaciones son más sensibles a las tasas de crecimiento en años con bajo flujo en los ríos, pero pequeños cambios en la frecuencia de esos períodos no aumentaron el riesgo en la mayoría de las poblaciones. Consistentemente con los resultados de otros estudios, las estimaciones del riesgo de extinción mediante el método de difusión tienen amplios límites de confianza. Aun así, nuestros resultados aportaron varios conocimientos valiosos, incluyendo la necesidad de mayor monitoreo de las poblaciones en el Hiwassee y la importancia para el crecimiento poblacional de los años con bajo flujo. Nuestro trabajo ilustra el valor potencial de métodos sencillos de análisis de datos de conteo a pesar de los retos impuestos por la incertidumbre en las estimaciones del riesgo de extinción. [source]

    Circulatory effects of apnoea in elite breath-hold divers

    ACTA PHYSIOLOGICA, Issue 1 2009
    F. Joulia
    Abstract Aim:, Voluntary apnoea induces several physiological adaptations, including bradycardia, arterial hypertension and redistribution of regional blood flows. Elite breath-hold divers (BHDs) are able to maintain very long apnoea, inducing severe hypoxaemia without brain injury or black-out. It has thus been hypothesized that they develop protection mechanisms against hypoxia, as well as a decrease in overall oxygen uptake. Methods:, To test this hypothesis, the apnoea response was studied in BHDs and non-divers (NDs) during static and dynamic apnoeas (SA, DA). Heart rate, arterial oxygen saturation (SaO2), and popliteal artery blood flow were recorded to investigate the oxygen-conserving effect of apnoea response, and the internal carotid artery blood flow was used to examine the mechanisms of cerebral protection. Results:, The bradycardia and peripheral vasoconstriction were accentuated in BHDs compared with NDs (P < 0.01), in association with a smaller SaO2 decrease (,2.7% vs. ,4.9% during SA, P < 0.01 and ,6% vs. ,11.3% during DA, P < 0.01). Greater increase in carotid artery blood flow was also measured during apnoea in BHDs than in controls. Conclusion:, These results confirm that elite divers present a potentiation of the well-known apnoea response in both SA and DA conditions. This response is associated with higher brain perfusion which may partly explain the high levels of world apnoea records. [source]

    Changes in perfectionism following cognitive-behavioral treatment for social phobia,

    DEPRESSION AND ANXIETY, Issue 3 2007
    Andrea Ashbaugh M.A.
    Abstract Previous studies have found that social phobia (social anxiety disorder) is associated with elevated levels of perfectionism, particularly concerns over making mistakes (CM) and doubts about actions (DA). This study investigated the extent to which various dimensions of perfectionism change as a result of participating in a 12-session cognitive-behavioral group treatment for social phobia. One hundred seven individuals completed the Frost Multidimensional Perfectionism Scale before and after treatment. Participants improved on several measures of social anxiety, generalized anxiety, and depression. With respect to perfectionism, significant reductions were seen on total perfectionism scores and scores on particular dimensions (CM, DA, organization), but not on other dimensions (personal standards, parental expectations, parental criticism). Furthermore, changes in DA and to some extent CM predicted posttreatment levels of social anxiety after controlling for pretreatment levels of social anxiety and changes in anxiety and depression. Implications of these findings are discussed. Depression and Anxiety 24:169,177, 2007. © 2006 Wiley-Liss, Inc. [source]

    Neural protein Olig2 acts upstream of the transcriptional regulator sim1 to specify diencephalic dopaminergic neurons

    DEVELOPMENTAL DYNAMICS, Issue 4 2009
    Nataliya Borodovsky
    Abstract Neural factors are expressed in neural progenitors and regulate neurogenesis and gliogenesis. Recent studies suggested that these factors are also involved in determining specific neuronal fates by regulating the expression of their target genes, thereby creating transcriptional codes for neuronal subtype specification. In the present study, we show that in the zebrafish the neural gene Olig2 and the transcriptional regulator Sim1 are co-expressed in a subset of diencephalic progenitors destined towards the dopaminergic (DA) neuronal fate. While sim1 mRNA is also detected in mature DA neurons, the expression of olig2 is extinguished prior to terminal DA differentiation. Loss of function of either Olig2 or Sim1 leads to impaired DA development. Finally, Olig2 regulates the expression of Sim1 and gain of function of Sim1 rescues the deficits in DA differentiation caused by targeted knockdown of Olig2. Our findings demonstrate for the first time that commitment of basal diencephalic DA neurons is regulated by the combined action of the neural protein Olig2 and its downstream neuronal specific effector Sim1. Developmental Dynamics 238:826,834, 2009. © 2009 Wiley-Liss, Inc. [source]

    Dopamine modulation of the In vivo acetylcholine response in the Drosophila mushroom body

    DEVELOPMENTAL NEUROBIOLOGY, Issue 11 2009
    Vitold Tsydzik
    Abstract Olfactory sensory information in Drosophila is transmitted through antennal lobe projections to Mushroom Body neurons (Kenyon cells) by means of cholinergic synapses. Application of acetylcholine (ACh) and odors produce significant increases in intracellular calcium ([Ca2+]i) in these neurons. Behavioral studies show that Kenyon cell activity is modulated by dopaminergic inputs and this modulation is thought to be the basis for an olfactory conditioned response. However, quantitative assessment of the synaptic inputs to Kenyon cells is currently lacking. To assess neuronal activity under in vivo conditions, we have used the endogenously-expressed camgaroo reporter to measure [Ca2+]i in these neurons. We report here the dose-response relationship of Kenyon cells for ACh and dopamine (DA). Importantly, we also show that simultaneous application of ACh and DA results in a significant decrease in the response to ACh alone. In addition, we show inhibition of the ACh response by cyclic adenosine monophosphate. This is the first quantitative assessment of the effects of these two important transmitters in this system, and it provides an important basis for future analysis of the cellular mechanisms of this well established model for associative olfactory learning. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source]

    Cell-type-specific limitation on in vivo serotonin storage following ectopic expression of the Drosophila serotonin transporter, dSERT

    DEVELOPMENTAL NEUROBIOLOGY, Issue 5 2006
    Sang Ki Park
    Abstract The synaptic machinery for neurotransmitter storage is cell-type specific. Although most elements of biosynthesis and transport have been identified, it remains unclear whether additional factors may be required to maintain this specificity. The Drosophila serotonin transporter (dSERT) is normally expressed exclusively in serotonin (5-HT) neurons in the CNS. Here we examine the effects of ectopic transcriptional expression of dSERT in the Drosophila larval CNS. We find a surprising limitation on 5-HT storage following ectopic expression of dSERT and green fluorescence protein-tagged dSERT (GFP-dSERT). When dSERT transcription is driven ectopically in the CNS, 5-HT is detectable only in 5-HT, dopamine (DA), and a very limited number of additional neurons. Addition of exogenous 5-HT does not dramatically broaden neuronal storage sites, so this limitation is only partly due to restricted intercellular diffusion of 5-HT. Furthermore, this limitation is not due to gross mislocalization of dSERT, because cells lacking or containing 5-HT show similar levels and subcellular distribution of GFP-dSERT protein, nor is it due to lack of the vesicular transporter, dVMAT. These data suggest that a small number of neurons selectively express factor(s) required for 5-HT storage, and potentially for function of dSERT. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006 [source]

    Dopamine's role in social modulation of infant isolation-induced vocalization: I. Reunion responses to the dam, but not littermates, are dopamine dependent

    DEVELOPMENTAL PSYCHOBIOLOGY, Issue 2 2009
    Harry N. Shair
    Abstract Rat pups' vocalization during social separation and the cessation of vocalization upon social reunion (contact quieting) model early life affiliative relationships. The present study examined the roles of dopamine (DA) receptors in regulating contact quieting. Contact quieting to the dam, but not to littermates, was disrupted by either blockade or exogenous stimulation of DA D1-like receptors. The D2 antagonist raclopride also prevented the quieting effect of reunion with the dam and had a lesser effect on the quieting properties of littermates. In contrast, the D2 agonist quinpirole permitted or enhanced contact quieting. Combined systemic and local striatal administration of D2 ligands showed that stimulation of striatal D2 receptors can enhance, but is not necessary for, contact quieting to the dam. These results are consistent with the literature linking the neural mechanisms of affiliation and reinforcement. This is also the first demonstration that the neurochemical substrates of an infant comfort response to dams differ from a behaviorally similar response to siblings. © 2008 Wiley Periodicals, Inc. Dev Psychobiol 51: 131,146, 2009 [source]

    Motivational systems and the neural circuitry of maternal behavior in the rat

    DEVELOPMENTAL PSYCHOBIOLOGY, Issue 1 2007
    Michael Numan
    Abstract Jay Rosenblatt's approach-avoidance model of maternal behavior proposes that maternal behavior occurs when the tendency to approach infant stimuli is greater than the tendency to avoid such stimuli. Our research program has uncovered neural circuits which conform to such a model. We present evidence that the medial preoptic area (MPOA: located in the rostral hypothalamus) may regulate maternal responsiveness by depressing antagonistic neural systems which promote withdrawal responses while also activating appetitive neural systems which increase the attractiveness of infant-related stimuli. These MPOA circuits are activated by the hormonal events of late pregnancy. Preoptic efferents may suppress a central aversion system which includes an amygdala to anterior hypothalamic circuit. Preoptic efferents are also shown to interact with components of the mesolimbic dopamine (DA) system to regulate proactive voluntary maternal responses. We make a distinction between specific (MPOA neurons) and nonspecific motivational systems (mesolimbic DA system) in the regulation of maternal responsiveness. © 2006 Wiley Periodicals, Inc. Dev Psychobiol 49: 12,21, 2007. [source]

    Application of DA-preconditioned FINN for electric power system fault detection

    ELECTRICAL ENGINEERING IN JAPAN, Issue 2 2009
    Tadahiro Itagaki
    Abstract This paper proposes a hybrid method of deterministic annealing (DA) and fuzzy inference neural network (FINN) for electric power system fault detection. It extracts features of input data with two-staged precondition of fast Fourier transform (FFT) and DA. FFT is useful for extracting the features of fault currents while DA plays a key role in classifying input data into clusters in a sense of global classification. FINN is a more accurate estimation model than the conventional artificial neural networks (ANNs). The proposed method is successfully applied to data obtained by the Tokyo Electric Power Company (TEPCO) power simulator. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 39, 46, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20497 [source]

    The Influence of the Cathodic Pretreatment on the Electrochemical Detection of Dopamine by Poly(1-aminoanthracene) Modified Electrode

    ELECTROANALYSIS, Issue 19 2010
    Estela de Pieri Troiani
    Abstract In this study we demonstrated the influence of the cathodic pretreatment of poly(1-aminoanthracene) (PAA) electropolymerized on a platinum electrode for determination of dopamine (DA). The DA electrochemical response was obtained after a cathodic pretreatment of the PAA electrode which consisted of applying a potential of ,0.7,V (vs. Ag/AgCl) for 3,s before each measurement. The pretreatment of the electrode changed the PAA electrocatalytic properties so that the electrode began to present electrochemical response to DA without interference of ascorbic acid (AA). The anodic peak currents determined by differential pulse voltammetry using pretreated PAA showed a linear dependence on the DA concentration from 0.56 to 100,µM with a detection limit of 0.13,µM and a correlation coefficient of 0.9986. The electrode exhibits a relative standard deviation of 1.2,% for ten successive measurements of a 0.5,mM DA solution. The analysis by scanning electron microscopy and atomic force microscopy show a homogeneous and nanostructured film with globular structures with diameter of about 20,nm. The analytical results obtained for DA determination at a pretreated PAA electrode in pharmaceutical formulation sample were in good agreement with those obtained by a comparative procedure at a 95,% confidence level. PAA electrode after the pretreatment showed electrochemical responses to DA with excellent selectivity, sensitivity, and high stability without interference of AA. [source]

    Simultaneous Determination of Ascorbic Acid, Dopamine and Uric Acid at Pt Nanoparticles Decorated Multiwall Carbon Nanotubes Modified GCE

    ELECTROANALYSIS, Issue 10 2010
    Zekerya 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]

    Silver Doped Poly(L -valine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Uric Acid, Ascorbic Acid and Dopamine

    ELECTROANALYSIS, Issue 5 2010
    Wenna Hu
    Abstract In this paper, a silver doped poly(L -valine) (Ag-PLV) modified glassy carbon electrode (GCE) was fabricated through electrochemical immobilization and was used to electrochemically detect uric acid (UA), dopamine (DA) and ascorbic acid (AA) by linear sweep voltammetry. In pH,4.0 PBS, at a scan rate of 100,mV/s, the modified electrode gave three separated oxidation peaks at 591,mV, 399,mV and 161,mV for UA, DA and AA, respectively. The peak potential differences were 238,mV and 192,mV. The electrochemical behaviors of them at the modified electrode were explored in detail with cyclic voltammetry. Under the optimum conditions, the linear ranges were 3.0×10,7 to 1.0×10,5,M for UA, 5.0×10,7 to 1.0×10,5,M for DA and 1.0×10,5 to 1.0×10,3,M for AA, respectively. The method was successfully applied for simultaneous determination of UA, DA and AA in human urine samples. [source]

    Simultaneous Determination of Dopamine and Ascorbic Acid Using the Nano-Gold Self-Assembled Glassy Carbon Electrode

    ELECTROANALYSIS, Issue 10 2009
    Guangzhi Hu
    Abstract Electrochemical behavior of dopamine (DA) was investigated at the gold nanoparticles self-assembled glassy carbon electrode (GNP/LC/GCE), which was fabricated by self-assembling gold nanoparticles on the surface of L -cysteine (LC) modified glassy carbon electrode (GCE) via successive cyclic voltammetry (CV). A pair of well-defined redox peaks of DA on the GNP/LC/GCE was obtained at Epa=0.197,V and Epc=0.146,V, respectively. And the peak separation between DA and AA is about 0.2,V, which is enough for simultaneous determination of DA and AA. The peak currents of DA and AA were proportional with their concentrations in the range of 6.0×10,8,8.5×10,5 mol L,1 and 1.0×10,6,2.5×10,3 mol L,1, with the detection limit of 2.0×10,8 mol L,1 and 3.0×10,7 mol L,1 (S/N=3), respectively. The modified electrode exhibits an excellent reproducibility, sensibility and stability for simultaneous determination of DA and AA in human serum with satisfactory result. [source]

    Fabrication, Characterization, and Application of ,Sandwich-Type' Electrode Based on Single-Walled Carbon Nanotubes and Room Temperature Ionic Liquid

    ELECTROANALYSIS, Issue 17 2008
    Xuzhi 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]

    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]

    Paste Electrode Based on Short Single-Walled Carbon Nanotubes and Room Temperature Ionic Liquid: Preparation, Characterization and Application in DNA Detection

    ELECTROANALYSIS, Issue 12 2008
    Xuzhi 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]

    Selective Determination of Dopamine in the Presence of Ascorbic Acid at Porous-Carbon-Modified Glassy Carbon Electrodes

    ELECTROANALYSIS, Issue 11 2008
    Shuqing Song
    Abstract Selective dopamine (DA) determinations using porous-carbon-modified glassy carbon electrodes (GCE) in the presence of ascorbic acid (AA) were studied. The effects of structure textures and surface functional groups of the porous carbons on the electrochemical behavior of DA was analyzed based on both cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements. The differential pulse voltammetry of DA on the modified GCE was determined in the presence of 400-fold excess of AA, and the linear determination ranges of 0.05,0.99, 0.20,1.96, and 0.6,12.60,,M with the lowest detected concentrations of 4.5×10,3, 4.4×10,2, and 0.33,,M were obtained on the mesoporous carbon, mesoporous carbon with carboxylic and amino groups modified electrodes, respectively. [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]

    Chitosan Incorporating Cetyltrimethylammonium Bromide Modified Glassy Carbon Electrode for Simultaneous Determination of Ascorbic Acid and Dopamine

    ELECTROANALYSIS, Issue 17 2007
    Xuelian Zou
    Abstract Simultaneous determination of a neurotransmitter, dopamine (DA), and ascorbic acid (AA) is achieved at neutral pH on a chitosan incorporating cetyltrimethylammonium bromide (CTAB) modified glassy carbon (GC) electrode. Differential pulse voltammetry (DPV) technique was used to investigate the electrochemical response of DA and AA at a glassy carbon electrode modified with chitosan incorporating CTAB. An optimum 6.0,mmol L,1 of CTAB together with 0.5 wt% of chitosan was used to improve the resolution and the determination sensitivity. In 0.1,mol L,1 aqueous phosphate buffer solution of pH,6.8, the chitosan-CTAB modified electrode showed a good electrocatalytic response towards DA and AA. The anodic peak potential of DA shifted positively, while that of AA shifted negatively. Thus, the difference of the anodic peaks of DA and AA reached 0.23,V, which was enough to separate the two anodic peaks very well. The presented method herein could be applied to the direct simultaneous determination of DA and AA without prior treatment. The anodic peak currents (Ipa) of DPV are proportional to DA in the concentration range of 8,,M to 1000,,M, to that of AA 10,,M to 2000,,M, with correlation coefficients of 0.9930 and 0.9945, respectively. The linear range is much wider than previously reported. [source]

    Sensitive Biomimetic Sensor Based on Molecular Imprinting at Functionalized Indium Tin Oxide Electrodes

    ELECTROANALYSIS, Issue 16 2007
    Na Gao
    Abstract We initially report an electrochemical sensing platform based on molecularly imprinted polymers (MIPs) at functionalized Indium Tin Oxide Electrodes (ITO). In this research, aminopropyl-derivatized organosilane aminopropyltriethoxysilane (APTES), which plays the role of functional monomers for template recognition, was firstly self-assembled on an ITO electrode and then dopamine-imprinted sol was spin-coated on the modified surface. APTES which can interact with template dopamine (DA) through hydrogen bonds brought more binding sites located closely to the surface of the ITO electrode, thus made the prepared sensor more sensitive for DA detection. Potential scanning is presented to extract DA from the modified film, thus DA can rapidly and completely leach out. The affinity and selectivity of the resulting biomimetic sensor were characterized using cyclic voltammetry (CV). It exhibited an increased affinity for DA over that of structurally related molecules, the anodic current for DA oxidation depended on the concentration of DA in the linear range from 2×10,6 M to 0.8×10,3 M with a correlation coefficient of 0.9927. In contrast, DA-templated film prepared under identical conditions on a bare ITO showed obviously lower response toward dopamine in solution. It should be noted that potential scanning is a very effective approach for DA extraction, and surface modification of the electrochemical transducer with functional monomers is responsible for the development of MIPs-based highly sensitive biomimetic sensor. [source]

    Electrocatalysis and Voltammetric Determination of Dopamine at a Calix[4]arene Crown-4 Ether Modified Glassy Carbon Electrode

    ELECTROANALYSIS, Issue 4 2007
    Guo-Song Lai
    Abstract A sensitive and selective electrochemical method for the determination of dopamine (DA) was developed using a calix[4]arene crown-4 ether (CACE) film modified glassy carbon electrode (GCE). The modified electrode exhibited good electrocatalytic activity for electrochemical oxidation of DA in the pH,6.00 Britton,Robinson buffer solution, and ascorbic acid (AA) did not interfere with it. The diffusion coefficient (D=2.7×10,5,cm2 s,1), and the kinetic parameter such as the electron transfer coefficient (,=0.54) of DA at the surface of CACE were determined using electrochemical approaches. The catalytic oxidation peak currents showed a linear dependence on the DA concentration and a linear analytical curve was obtained in the range of 2.0×10,5,1.0×10,3,M of DA with a correlation coefficient of 0.9990. The detection limit (S/N=3) was estimated to be 3.4×10,6,M. This method was also examined for the determination of DA in an injection sample. In addition, effects of possible interferences were investigated. The present work shows the potential of the proposed method for the fabrication of a modified electrode, as it can be effectively used for voltammetric detection of DA. [source]

    Preparation, Characterization and Analytical Applications of a New and Novel Electrically Conducting Polymer

    ELECTROANALYSIS, Issue 15 2006
    F. D'Eramo
    Abstract In this study, a glassy carbon electrode (GC) was modified with an electropolymerized film of 1-naphthylamine (1-NAP) with a subsequent overoxidation treatment in 0.2,M sodium hydroxide solution. This polymer p-1-NAPox film coated GC electrode was used for the selective determination of dopamine (DA) in the presence of a triple concentration of ascorbic acid (AA). These studies were performed using cyclic voltammetry and square-wave voltammetry at physiological pH. p-1-NAPox shows an attractive permselectivity, a marked enhancement of the current response and antifouling properties when compared to a bare GC electrode activated in basic media. With a preconcentration time of 3,minutes at open circuit, linear calibration plots were obtained for DA in buffer solution (pH,7.4) over the concentration range from 1×10,6,1×10,4 M with a detection limit of 1.59×10,7 M. [source]

    The Electrochemical Properties of Co(TPP), Tetraphenylborate Modified Glassy Carbon Electrode: Application to Dopamine and Uric Acid Analysis

    ELECTROANALYSIS, Issue 5 2006
    Yunlong Zeng
    Abstract We report the combination of the charge repelling property of tetraphenyl-borate (TPB) anion and the electrooxidation catalytic effect of cobalt(II) tetrakisphenylporphyrin (CoTPP) embedded in a sol gel ceramic film to develop a modified glassy carbon electrode (CoTPP-TPB-SGGCE) for the simultaneous determination of dopamine (DA) and uric acid (UA). The optimized CoTPP-TPB-SGGCE shows excellent sensitivity and selectivity for the DA and UA analysis. As high as 2000 fold acceptable tolerance of ascorbic acid (AA) for the determination of trace DA and UA is reached. In the presence of 0.10,mM AA, the linear concentration range for DA is from 6.0×10,8 to 2.5×10,5,M, and the detection limit is 2.0×10,8,M. For UA, the linear concentration range is from 1.0×10,7 to 3.5×10,5,M, and the detection limit is 7.0×10,8,M. Our study has also demonstrated that the novel CoTPP-TPB-SGGCE shows high stability and reliability. For 6.00,,M DA and UA, a total of 12,measurements were taken in one week, and the relative standard deviation is 2.05% and 2.68% respectively. No obvious shift of peak current and peak potential is observed over a three-month lifetime test. The response of the sensor is very quick and response time is approximately 1,s. Satisfactory results are also achieved when the CoTPP-TPB-SGGCEs being used to detect the DA and UA in human urine samples. [source]

    Electrochemical Behavior and Detection of Dopamine and Ascorbic Acid at an Iron(II)tetrasulfophthalocyanine Modified Carbon Paste Microelectrode

    ELECTROANALYSIS, Issue 10 2003
    Joshua Oni
    Abstract In this article the electrocatalytic behavior of an iron(II)tetrasulfophthalocyanine modified carbon paste microelectrode for the oxidation of dopamine (DA) and ascorbic acid (AA) is described. Although the oxidation potential of ascorbic acid is shifted by over 100,mV to more positive potentials, no peak separation could be obtained. This can be explained by the immediate homogeneous reduction of the oxidation product of dopamine by ascorbic acid in solution. However, this reaction induces a shift of the half-wave potential as a function of ratio of concentration of dopamine to ascorbic acid (cDA/cAA). Therefore it was possible to determine the cAA and cDA from this potential shift and the experimental peak current. Detection limits of 4.5±0.2×10,7 and 7.5±0.5×10,7,mol,L,1 were obtained respectively for dopamine and ascorbic acid for cDA/cAA>0.01. [source]

    Amperometric detection in microchip electrophoresis devices: Effect of electrode material and alignment on analytical performance

    ELECTROPHORESIS, Issue 19 2009
    David J. Fischer
    Abstract The fabrication and evaluation of different electrode materials and electrode alignments for microchip electrophoresis with electrochemical detection is described. The influences of electrode material, both metal and carbon-based, on sensitivity and LOD were examined. In addition, the effects of working electrode alignment on analytical performance (in terms of peak shape, resolution, sensitivity, and LOD) were directly compared. Using dopamine (DA), norepinephrine, and catechol (CAT) as test analytes, it was found that pyrolyzed photoresist electrodes with end-channel alignment yielded the lowest LOD (35,nM for DA). In addition to being easier to implement, end-channel alignment also offered better analytical performance than off-channel alignment for the detection of all three analytes. In-channel electrode alignment resulted in a 3.6-fold reduction in peak skew and reduced peak tailing by a factor of 2.1 for CAT in comparison to end-channel alignment. [source]

    Capillary electrophoresis-time of flight-mass spectrometry using noncovalently bilayer-coated capillaries for the analysis of amino acids in human urine

    ELECTROPHORESIS, Issue 12 2008
    Rawi Ramautar
    Abstract A capillary electrophoresis-time of flight-mass spectrometry (CE-TOF-MS) method for the analysis of amino acids in human urine was developed. Capillaries noncovalently coated with a bilayer of Polybrene (PB) and poly(vinyl sulfonate) (PVS) provided a considerable EOF at low pH, thus facilitating the fast separation of amino acids using a BGE of 1,M formic acid (pH,1.8). The PB,PVS coating proved to be very consistent yielding stable CE-MS patterns of amino acids in urine with favorable migration time repeatability (RSDs <2%). The relatively low sample loading capacity of CE was circumvented by an in-capillary preconcentration step based on pH-mediated stacking allowing 100-nL sample injection (i.e. ca. 4% of capillary volume). As a result, LODs for amino acids were down to 20,nM while achieving satisfactory separation efficiencies. Preliminary validation of the method with urine samples showed good linear responses for the amino acids (R2 >0.99), and RSDs for peak areas were <10%. Special attention was paid to the influence of matrix effects on the quantification of amino acids. The magnitude of ion suppression by the matrix was similar for different urine samples. The CE-TOF-MS method was used for the analysis of urine samples of patients with urinary tract infection (UTI). Concentrations of a subset of amino acids were determined and compared with concentrations in urine of healthy controls. Furthermore, partial least squares,discriminant analysis (PLS,DA) of the CE-TOF-MS dataset in the 50,450,m/z region showed a distinctive grouping of the UTI samples and the control samples. Examination of score and loadings plot revealed a number of compounds, including phenylalanine, to be responsible for grouping of the samples. Thus, the CE-TOF-MS method shows good potential for the screening of body fluids based on the analysis of endogenous low-molecular weight metabolites such as amino acids and related compounds. [source]

    Microchip capillary electrophoresis with a cellulose-DNA-modified screen-printed electrode for the analysis of neurotransmitters

    ELECTROPHORESIS, Issue 15 2005
    Muhammad Johirul
    Abstract A microfluidic chip based on capillary electrophoresis coupled with a cellulose-single-stranded DNA (cellulose-ssDNA) modified electrode was used for the simultaneous analysis of dopamine (DA), norepinephrine (NE), 3,4-dihydroxy- L -phenylalanine (L -DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic acid (AA). The modification of the electrode improved the electrophoretic analysis performance by lowering the detection potential and enhancing the signal-to-noise characteristic without surface poisoning of the electrode. The sensitivity of the modified electrode was about 12 times higher than those of the bare ones. The test compounds were separated using a 62,mm long separation channel at the separation field strength of +200,V/cm within 220,s in a 10,mM phosphate buffer (pH,7.4). The most favorable potential for the amperometric detection was 0.7,V (vs. Ag/AgCl). A reproducible response (relative standard deviation of 1.3, 1.3, 2.1, 3.1, 3.4% for DA, NE, L -DOPA, DOPAC, and AA, respectively, for n,=,9) for repetitive sample injections reflected the negligible electrode fouling at the cellulose-ssDNA modified electrode. Square-wave voltammetric analyses reflected the sensitivities of the modified electrode for DA, NE, L -DOPA, DOPAC, and AA which were 1.78, 0.82, 0.69, 2.45, and 1.23,nC/µM with detection limits of 0.032, 0.93, 1.13, 0.31, and 0.62,µM, respectively. The applicability of this microsystem to real sample analysis was demonstrated. [source]

    Occurrence of toxic cyanobacterial blooms in San Roque Reservoir (Córdoba, Argentina): A field and chemometric study

    ENVIRONMENTAL TOXICOLOGY, Issue 3 2003
    María Valeria Amé
    Abstract We evaluated the presence of cyanobacterial blooms in San Roque Reservoir (Córdoba, Argentina). Cyanobacterial blooms and water samples were collected over 4 years (1998,2002). We confirmed the presence of microcystin-LR and microcystin-RR in 97% of these blooms. The total amount of microcystin (MC) ranged between 5.8 and 2400.0 ,g g,1 of freeze-dried bloom material. These values suggest that guidelines for safe water consumption and recreational use should be established for this reservoir. Twenty-eight physical and chemical parameters were measured in water samples and evaluated by discriminant analysis (DA). A first DA was used to evaluate the factors promoting cyanobacteria occurrence, identifying nine parameters following three patterns associated with cyanobacterial growth. Inorganic phosphorous was found to promote the presence of blooms, whereas the highest proliferation of cyanobacteria was observed in the presence of smaller amounts of carbonate, bicarbonate, sulfate, and fecal coliform bacteria. The results observed during our fieldwork, analyzed using DA, agreed with the results of other laboratory studies, thus confirming the usefulness of DA to help with the evaluation of a complicated environmental data matrix. A second DA, using only water samples collected during the presence of cyanobacteria blooms, identified another nine parameters. The analysis of these parameters allowed us to identify certain environmental factors that could lead to the dominance of toxic strains, thus increasing the amount of MC. The results showed that, in our case, an increase in the water temperature was associated with higher amounts of MC per dry weight unit, whereas an increase in the concentrations of ammonia,nitrogen and iron were associated with lower amounts of MC, thus disfavoring the dominance of toxic strains. © 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 192,201, 2003. [source]

    Monoamine variability in the chronic model of atypical absence seizures

    EPILEPSIA, Issue 4 2009
    Eduard Bercovici
    Summary Purpose:, We studied the variability of the slow-spike-and-wave discharges (SSWDs) derived from AY-9944 (AY) treatment during brain development of Long-Evans hooded (LEh) rats. Methods:, Although all LEh rats received the standard dose of AY (7.5 mg/kg), we have observed an intersubject variability of the total SSWD duration at postnatal day (P) 55. Therefore, we set out to investigate the underlying brain levels of norepinephrine (NE), dopamine (DA), and serotonin (5-HT) and its metabolite (5-HIAA), as determined by high-performance liquid chromatography (HPLC) analyses from four different brain regions: thalamus (Th), frontoparietal cortex (Cx), hippocampus (Hp), and brainstem (Bs). Results:, All brains were obtained after two baseline electrocorticographic (ECoG) recordings with characteristic chronic, recurrent, bilaterally synchronous 4,6 Hz SSWD, at P 55 (336.25 ± 97.23 s/h) and P60 (494.50 ± 150.36 s) (r = 0.951, r2 = 0.904, p < 0.005, Pearson product). The thalamic NE levels and the brainstem NE, DA, and 5HT levels were all significantly correlated with baseline SSWD duration at P55 and P60 (p < 0.01, Pearson product). Conclusion:, Our data indicate that brain monoamine levels may determine the intersubject variability of SSWD duration in AY rats with chronic atypical absence seizures. [source]