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    Fabrication of an electrochemical E. coli biosensor in biowells using bimetallic nanoparticle-labelled antibodies
    (Wiley-V C H Verlag Gmbh, 2015) Ekşi, Haslet; Güzel, Remziye; Güven, Burcu; Boyacı, İsmail Hakkı; Solak, Ali Osman; 0000-0003-1333-060X
    An electrochemical biosensor was developed for the determination of Escherichia coli (E. coli) in water. For this purpose, silver-gold core-shell (Ag@Au) bioconjugates and anti-E. coli modified PS-microwells were designed in a sandwich-type format in order to obtain higher sensitivity and selectivity. Ag@Au bimetallic nanoparticles were synthesized by co-reduction method. The core-shell formation was analyzed by using UV-Vis spectroscopy and transmission electron microscopy. Biotin labeled anti-E. coli antibodies were coupled with Ag@Au nanoparticles to form bioconjugates. The electrochemical immunosensor was prepared by immobilizing anti-E. coli on polystyrene (PS)-microwells via chemical bonding. These modified microwells were identified with X-ray photoelectron spectroscopy and surface enhanced Raman spectroscopy. E. coli was sandwiched between Ag@Au bioconjugates and anti-E. coli on PS-microwells at different concentrations. The relationship between the E. coli concentration and stripping current of gold ions (Au3+) were investigated by square wave anodic stripping voltammetry at pencil graphite electrode. The proposed method can provide some advantages such as lower detection limit and shorter detection time. The electrochemical response for the immunosensor was linear with the concentration of the E. coli in the range of 10(1) and 10(5) cfu/mL with a limit of detection 3 cfu/mL. The procedure maintains good sensitivity and repeatability and also offers utility in the fields of environmental monitoring and clinical diagnosis.
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    New voltammetric approach to the quantitative estimation of sildenafil citrate in tablets using disposable pencil graphite electrode
    (American Scientific Publishers, 2014) Güzel, Remziye; Ekşi, Haslet; Dinç, Erdal; Solak, Ali Osman
    The voltammetric behavior of sildenafil citrate (SC) was studied through differential pulse stripping voltammetry. The best sensitivity, optimal experimental conditions and settings for the voltammetric method development were obtained by applying experimental design and optimization methodology to the designed sample runs at different accumulation times, accumulation potentials and pHs. The linearity over the concentration range 1 × 10-7 M-8 × 10-6 M for SC was determined and the limit of detection (LOD) was 3.1 × 10-8 M. For the method ability and validity, mean recovery result and relative standard deviation were found to be 99.3% and 2.19%, respectively. The method was applied to the determination of SC in pharmaceutical and plasma samples.
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    Synthesis, characterization, and application of silver nanoparticle-thiophenol nanocomposite film on the glassy carbon surface
    (Wiley, 2013) Güzel, Remziye; Ekşi, Haslet; Üstündağ, Zafer; Solak, Ali Osman
    In this study, 4-thiophenol modified glassy carbon electrode was prepared by the reduction of 4-diazothiophenol tetrafluoroborate salt. Silver nanoparticles were attached to the thiophenol modified surface to prepare a thiophenol-silver nanoparticle composite film. 4-Aminothiopenol molecules were deposited by self-assembling technique to form multi-layered nanofilms of TP/SNP/PhNH2 on glassy carbon substrate. These surfaces were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, reflectance-absorption infrared spectroscopy, and ellipsometry at each multilayer film growth process. Atomic force microscopic images of GC/TP/SNP/PhNH2 surfaces were also acquired. The characterization methods show that the amine group containing surface permits the subsequent modification by a variety of coupling reactions for the immobilization of more complex systems. An application of the electrode modification for the determination of uric acid with a significantly lower detection limit is described. Copyright (c) 2013 John Wiley & Sons, Ltd.