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    Construction of an Amperometric Cholesterol Biosensor Based on DTP(aryl)aniline Conducting Polymer Bound Cholesterol Oxidase
    (WILEY-V C H VERLAG GMBH, 2018) Cevik, Emre; Cerit, Alaaddin; Gazel, Nilay; Yildiz, Huseyin Bekir
    In this study, an amperometric cholesterol biosensor was constructed based on cholesterol oxidase immobilized on a conducting 4-(4H-dithienol[3,2-b:2,3-d]pyrrole-4)aniline polymer, (DTP(aryl)aniline). Glassy carbon electrodes were covered with P(DTP(aryl)aniline) which is used for the wiring of enzyme to the electrode surface by using electro-polymerization. The electron transfer was successfully made by the bio-catalytic activity and possession of the unique morphology of the polymer allowed efficient immobilization of the cholesterol oxidase enzyme. Analytical performances; linear range, detection limit, limit of quantification and the Michaelis-Menten constant (K-m) of biosensor electrodes were obtained 2.0M-23.7M, 0.27M, 0.82M, 17,81M respectively. Biosensor optimization parameters: optimum pH, optimum temperature, stability test and response time were evaluated. The real sample and recovery studies were also performed in order to show applicability of the biosensing electrodes.
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    Electrospun Polyvinyl Borate/Poly(methyl methacrylate) (PVB/PMMA) Blend Nanofibers
    (TAYLOR & FRANCIS AS, 2014) Koysuren, Ozcan; Karaman, Mustafa; Yildiz, Huseyin Bekir; Koysuren, H. Nagehan; Dinc, Havva
    The aim of this study was to prepare polyvinyl borate (PVB)/poly(methyl methacrylate) (PMMA) blend nanofibers by electrospinning process. Polyvinyl borate was synthesized by the condensation reaction of polyvinyl alcohol and boric acid. FTIR analyses showed that boron atoms were found to be integrated into the polymer network. Blending PMMA with PVB decreased the fiber diameter and enhanced the surface roughness of PVB/PMMA blend nanofiber mats. The water wetting property of the nanofiber mats was influenced by the surface roughness. The blend composition with the highest polyvinyl borate content was found to be suitable for thermally stable nanofiber formation.
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    Immobilization of tyrosinase and alcohol oxidase in conducting copolymers of thiophene functionalized poly(vinyl alcohol) with pyrrole
    (ELSEVIER SCIENCE BV, 2007) Yildiz, Huseyin Bekir; Sahmetlioglu, Ertugrul; Boyukbayram, Ayse Elif; Toppare, Levent; Yagci, Yusuf
    Immobilization of tyrosinase and alcohol oxidase is achieved in the copolymer of pyrrole with vinyl alcohol with thiophene side groups (PVATh-co-PPy) which is a newly synthesized conducting polymer. PVATh-co-PPy/alcohol oxidase and PVATh-co-PPy/tyrosinase electrodes are constructed by the entrapment of enzyme in conducting copolymer matrix during electrochemical copolymerization. For tyrosinase and alcohol oxidase enzymes, catechol and ethanol are used as the substrates, respectively. Kinetic parameters: maximum reaction rates (V-max) and Michaelis-Menten constants (K-m) are obtained. V-max and K-m are found as 2.75 mu mol/(min electrode) and 18 mM, respectively, for PVATh-coPPy/alcohol oxidase electrode and as 0.0091 mu mol/(min electrode) and 40 mM, respectively, for PVATh-co-PPy/tyrosinase electrode. Maximum temperature and pH values are investigated and found that both electrodes have a wide working range with respect to both temperature and pH. Operational and storage stabilities show that although they have limited storage stabilities, the enzyme electrodes are useful with respect to operational stabilities. (c) 2007 Elsevier B.V. All rights reserved.
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    Phenol biosensor based on electrochemically controlled integration of tyrosinase in a redox polymer
    (SPRINGER WIEN, 2007) Yildiz, Huseyin Bekir; Castillo, Jaime; Guschin, Dmitrii A.; Toppare, Levent; Schuhmann, Wolfgang
    An amperometric biosensor for the detection of phenolic compounds was developed based on the immobilization of tyrosinase within an Os-complex functionalized electrodeposition polymer. Integration of tyrosinase within the redox polymer assures efficient catechol recycling between the enzyme and the polymer bound redox sites. The non-manual immobilization procedure improves the reproducibility of fabrication process, greatly reduces the desorption of the enzyme from the immobilization layer, and, most importantly prevents fast inactivation of the enzyme by its substrate due to fast redox cycling. A two-layer sensor architecture was developed involving ascorbic acid oxidase entrapped within an electrodeposition polymer in a second layer on top of the redox polymer/tyrosinase layer. Using this sensor architecture it was possible to eliminate the current interference arising from direct ascorbate oxidation up to a concentration of 630 mu M ascorbic acid. The effects of the polymer thickness, the enzyme/polymer ratio, and the applied potential were evaluated with respect to optimal sensor properties. The sensitivity of the optimized sensors for catechol was 6.1 nA mu M-1 with a detection limit of 10 nM, and for phenol 0.15 nA mu M-1 with a detection limit of 100 nM.
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    A photoelectrochemical device for water splitting using oligoaniline-crosslinked [Ru(bpy)(2)(bpyCONHArNH(2))](+2) dye/IrO2 nanoparticle array on TiO2 photonic crystal modified electrode
    (PERGAMON-ELSEVIER SCIENCE LTD, 2016) Yildiz, Huseyin Bekir; Carbas, Buket Bezgin; Sonmezoglu, Savas; Karaman, Mustafa; Toppare, Levent
    This article describes the construction of photoelectrochemical cell system splitting water into hydrogen and oxygen using UV-vis light under constant applied voltage. Oligoaniline-crosslinked 2-(4-aminobenzyl)malonic acid functionalized IrO2 center dot nH(2)O nanoparticles and visible light absorbing dye, [Ru(bpy)(2)(bpyCONHArNH(2))(+2)] arrays on titanium dioxide (TiO2) photonic crystals modified electrodes were used as photoanode, and nanostructures based on bonding of Pt nanoparticles by using electropolymerization on poly 4-(2,5-di(thiophene-2-il)-1H-pyrrol-1-il)benzenamine P(SNS-NH2) conducting polymer modified gold electrode acted as cathode. Each component in anode and cathode of the system was characterized successfully using the methods related. Some optimization studies such as the molar concentration ratio of [Ru(bpy)(2)(bpyCONHArNH(2))(+2)] dye to IrO2 center dot nH(2)O nanoparticles, the optimum cycle number of each components and thickness of TiO2 film were performed in order to investigate the system performance. Furthermore, the photocurrent generation capacity of the photoanode against oxygen resulting and UV stability experiments of photoanode were also investigated. After obtained all necessary informations and improvements of the system, the cell was constructed, and corresponding hydrogen gas evolution from water splitting was calculated as 1.25 x 10(-8) mol/cm(2) by using a gas chromatography (GC). The cell generated a photocurrent with a quantum yield of 3.5%. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.