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Öğe Electrocatalytic oxidation of NADH using a pencil graphite electrode modified with quercetin(Elsevier, 2013) Dilgin, Yusuf; Kizilkaya, Bayram; Dilgin, Didem Giray; Gokcel, H. Ismet; Gorton, LoIn the present study, the electrocatalytic oxidation of reduced beta nicotinamide adenine dinucleotide (NADH) was investigated using a pencil graphite electrode modified with quercetin (PGE/QH(2)). The PGE/QH(2) was prepared through two steps: (i) the pre-treatment of PGE at 1.40V vs. Ag vertical bar AgCl vertical bar KCl(sat.) in pH 7.0 phosphate buffer containing 0.1 M KCl for 60 s and (ii) adsorption of QH(2) on the PGE via immersion of PGE into a 1.0 mM QH(2) solution (in ethanol) for 60 s. Cyclic voltammetric studies show that the peak potential of NADH oxidation shifts from +500 mV at bare PGE to +300 mV at PGE/QH(2). The electrocatalytic currents obtained from amperometric measurements at +300 mV vs. Ag vertical bar AgCl vertical bar KCl(sat.) and in phosphate buffer solution at pH 7.0 containing 0.1 M KCl were linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 0.5 mu M to 100 mu M. The limit of detection was found to be 0.15 mu M. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.Öğe Photoelectrocatalytic Oxidation of NADH at a Graphite Electrode Modified with a New Polymeric Phenothiazine(Wiley-V C H Verlag Gmbh, 2009) Gligor, Delia; Dilgin, Yusuf; Popescu, Ionel Catalin; Gorton, LoA new approach for photoelectrocatalytic oxidation of NADH is described, based on a graphite electrode (G) modified with a new phenothiazine derivative, polyphenothiazine formaldehyde (PPF). Electrochemical measurements reveal that G/PPF presents a quasireversible voltammetric response, corresponding to a 2e(-)/2H(+) transfer and that G/PPF modified electrodes show electrocatalytic activity for NADH oxidation. When the surface of the G/PPF modified electrode was irradiated with a light source (250 W Halogen lamp), a significant increase in the electrocatalytic current was observed. The second order electrocatalytic rate constant (k(obs,[NADH]=0) = 3.9 x 10(3) M-1 s(-1), pH 7.0) was calculated from rotating disk electrode experiments, performed at various NADH concentrations. From amperometric measurements, it was noticed that, in the presence of light irradiation, the sensitivity of NADH detection (calculated as I-max/K-M ratio) increased ca. 3 times.Öğe Photoelectrocatalytic oxidation of NADH with electropolymerized Toluidine Blue O(Wiley-V C H Verlag Gmbh, 2007) Dilgin, Yusuf; Gorton, Lo; Nisli, GurelA poly(Toluidine Blue O) (poly-TBO) modified electrode was successfully prepared by repeated sweeping the applied potential from -0.6 to + 0.8 V (vs. SCE) on a glassy carbon electrode (GCE) in borate buffer solution at pH 9.1 containing 0.1 M NaNO3 and 0.4 mM Toluidine Blue 0 (TBO). The poly-TBO modified GCE shows electrocatalytic activity toward NADH oxidation in phosphate buffer solution at pH 7.0, with an overpotential of ca. 350 mV lower than that at the bare electrode. The photoelectrocatalytic oxidation of NADH at this electrode was also successfully investigated by using cyclic voltammetry and amperometry at constant potential. When the modified electrode surface was irradiated with a 250 W halogen lamp, a photoelectrocatalytic effect was observed for NADH oxidation and the current was increased about 2.2 times. The applied potential was selected at +100mV for amperometric and photoamperometric detection of NADH. A linear calibration graph for NADH was obtained in the range between 1.0 x 10(-5) and 1.0 x 10(-3) M and between 5.0 x 10(-6) and 1.0 X 10(-3) M for amperometric and photoamperometric studies, respectively. The effect of some interfering compounds, such as ascorbic acid and dopamine on the electrocatalytic and photoclectrocatalytic oxidation of NADH was tested.Öğe Photoelectrochemical Communication between Thylakoid Membranes and Gold Electrodes through Different Quinone Derivatives(Wiley-V C H Verlag Gmbh, 2014) Hasan, Kamrul; Dilgin, Yusuf; Emek, Sinan Cem; Tavahodi, Mojtaba; Akerlund, Hans-Erik; Albertsson, Per-Ake; Gorton, LoPhotosynthesis is a sustainable process for the conversion of light energy into chemical energy. Thylakoids in energy-transducing photosynthetic membranes are unique in biological membranes because of their distinguished structure and composition. The quantum trapping efficiency of thylakoid membranes is appealing in photobioelectrochemical research. In this study, thylakoid membranes extracted from spinach are shown to communicate with a gold-nanoparticle-modified solid gold electrode (AuNP-Au) through a series of quinone derivatives. Among these, para-benzoquinone (PBQ) is found to be the best soluble electron-transfer mediator, generating the highest photocurrent of approximately 130 mu Acm(-2) from water oxidation under illumination. In addition, the photocurrent density is investigated as a function of applied potential, the effect of light intensity, quinone concentration, and amount of thylakoid membrane. Finally, the source of photocurrent is confirmed by using 3-(3,4-dichlorophenyl)-1,1-dimethylurea (known by its trade name, Diuron), an inhibitor of photosystem II, which decreases the total photocurrent by 50%.Öğe Poly-phenothiazine derivative-modified glassy carbon electrode for NADH electrocatalytic oxidation(Pergamon-Elsevier Science Ltd, 2009) Gligor, Delia; Dilgin, Yusuf; Popescu, Ionel Catalin; Gorton, LoElectropolymerization of a new phenothiazine derivative (bis-phenothiazin-3-yl methane; BPhM) on glassy carbon (GC) electrode generates a conducting film of poly-BPhM. in stable contact with the electrode surface. The heterogeneous electron-transfer process corresponding to the modified electrode is characterized by a high rate constant (50.4 s(-1), pH 7). The CC/poly-BPhM electrode shows excellent electrocatalytic activity toward NADH oxidation. The rate constant for catalytic NADH oxidation, estimated from rotating disk electrode (RDE) measurements and extrapolated to zero concentration of NADH, was found to be 9.4 x 10(4) M-1 s(-1) (pH 7). The amperometric detection of NADH, at +200 mV vs. SCE, is described by the following electroanalytical parameters: a sensitivity of 1.82 mA M-1, a detection limit of 2 mu M and a linear domain up to 0.1 mM NADH. (c) 2008 Elsevier Ltd. All rights reserved.
