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    A novel impedimetric biosensor based on graphene oxide/gold nanoplatform for detection of DNA arrays
    (Elsevier Science Sa, 2013) Gupta, Vinod Kumar; Yola, Mehmet Lutfi; Qureshi, Munewar Saeed; Solak, Ali Osman; Atar, Necip; Ustundag, Zafer
    A highly sensitive method for detection of DNA hybridization was developed. This method was based on the modification of glassy carbon electrode with gold nanoparticles (AuNPs) involving p-aminothiophenol (ATP) functionalized graphene oxide (GO). This GO was used as a platform for impedimetric genosensing using 5'-TA GGG CCA CTT GGA CCT-(CH2)(3)-SH-3' single-stranded probe (ss-DNA), 5'-AGG TCC AAG TGG CCC TA-3'(target DNA), 5'-SH-C-6-TAG GGC CA-3'(non-complementary-1) and 5'-SH-C-6-TGC CCG TTA CG 3-' (non-complementary-2) oligonucleotide sequences. The film exhibited excellent properties for immobilizing DNA probes and sensing DNA hybridization. The DNA immobilization and hybridization on the film were studied by cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), and found that the charge transfer resistance (R-ct) of the electrode increased with the concentration of the target DNA hybridized with the ss-DNA. The linear detectionrange was from 1.0 x 10(-13) M to 1.0 x 10(-7) M and the detection limit was 1.10 x 10(-14) M (n = 6). Compared with the other electrochemical DNA biosensors, the proposed biosensor showed its own performance of simplicity, good stability, and high sensitivity. (C) 2013 Elsevier B. V. All rights reserved.
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    A novel magnetic Fe@Au core-shell nanoparticles anchored graphene oxide recyclable nanocatalyst for the reduction of nitrophenol compounds
    (Pergamon-Elsevier Science Ltd, 2014) Gupta, Vinod Kumar; Atar, Necip; Yola, Mehmet Lutfi; Ustundag, Zafer; Uzun, Lokman
    In this study, a novel catalyst based on Fe@Au bimetallic nanoparticles involved graphene oxide was prepared and characterized by transmission electron microscope (TEM), and x-ray photoelectron spectroscopy (XPS). The nanomaterial was used in catalytic reductions of 4-nitrophenol and 2-nitrophenol in the presence of sodium borohydride. The experimental parameters such as temperature, the dosage of catalyst and the concentration of sodium borohydride were studied. The rates of catalytic reduction of the nitrophenol compounds have been found as the sequence: 4-nitrophenol>2-nitrophenol. The kinetic and thermodynamic parameters of nitrophenol compounds were determined. Activation energies were found as 2.33 kcal mol(-1) and 3.16 kcal mol(-1) for 4-nitrophenol and 2-nitrophenol, respectively. The nanomaterial was separated from the product by using a magnet and recycled after the reduction of nitrophenol compounds. The recyclable of the nanocatalyst is economically significant in industry. (C) 2013 Elsevier Ltd. All rights reserved.
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    A novel sensitive Cu(II) and Cd(II) nanosensor platform: Graphene oxide terminated p-aminophenyl modified glassy carbon surface
    (Pergamon-Elsevier Science Ltd, 2013) Gupta, Vinod Kumar; Yola, Mehmet Lutfi; Atar, Necip; Ustundag, Zafer; Solak, Ali Osman
    Graphene oxide (GO) based glassy carbon (GC) electrode has been prepared. Firstly, p-nitrophenyl (NP) modified GC (NP/GC) electrode was prepared via the electrochemical reduction of its tetraflouroborate diazonium salt. After the formation of NP/GC electrode, the negative potential was applied to NP/GC electrode to reduce the nitro groups to amine. p-Aminophenyl (AP) modified GC (AP/GC) electrode was immersed into a graphene oxide solution containing 1-ethyl-3(3-(dimethlyamino)propyl)-carbodiimide. Hence, we constructed GO terminated AP modified GC (GO/AP/GC) electrode. NP/GC, AP/GC and GO/AP/GC electrodes were characterized sequentially using cyclic voltammetry (CV) in the presence of 1.0 mM of potassium ferricyanide in 0.1 M KCl. In addition, GO and GO/AP/GC surfaces were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The GO/AP/GC electrode was used for the analysis of Cd(II) and Cu(II) ions by adsorptive stripping voltammetry. The linearity range and the detection limit of Cd(II) and Cu(II) ions were 1.0 x 10(-11)-5.0 x 10(-10) M and 3.3 x 10(-12) M (SIN=3), respectively. (C) 2013 Elsevier Ltd. All rights reserved.
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    A novel voltammetric sensor based on p-aminothiophenol functionalized graphene oxide/gold nanoparticles for determining quercetin in the presence of ascorbic acid
    (Elsevier Science Sa, 2013) Yola, Mehmet Lutfi; Atar, Necip; Ustundag, Zafer; Solak, Ali Osman
    In this study, gold nanoparticles (AuNPs) with the diameters of maximum 25 nm were self-assembled onto the surfaces of p-aminothiophenol functionalized graphene oxide (ATPGO) sheets simply by mixing their aqueous dispersions. The prepared graphene oxide (GO), ATPGO and AuNPs-ATPGO composites were characterized by a transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), reflection-absorption infrared spectroscopy (RAIRS), the X-ray diffraction (XRD) method and Raman spectroscopy. The electrochemical determination of quercetin (QR) has been studied using square wave voltammetry (SWV) on glassy, carbon electrode (GCE) modified with AuNPs-ATPGO composite (AuNPs-ATPGO/GCE). QR gave rise to a single oxidation peak in the potential interval from 200 to 600 mV in 0.1 M acetate buffer (pH 5.5). The well-defined peaks were observed at the optimized instrumental parameters for SWV such as frequency, amplitude and potential increments. The developed method was validated according to the ICH guideline and found to be linear, sensitive, specific, precise and accurate. The linearity range of QR was 1.0 x 10(-12)-1.0 x 10(-11) M with the detection limit (S/N = 3) of 3.0 x 10(-13) M under optimum conditions. The validated method was applied successfully for the determination of QR in pharmaceutical preparations. (C) 2013 Elsevier B.V. All rights reserved.
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    Biosynthesis of silver nanoparticles using chitosan immobilized Bacillus cereus: Nanocatalytic studies
    (Elsevier, 2013) Gupta, Vinod Kumar; Atar, Necip; Yola, Mehmet Lutfi; Darcan, Cihan; Idil, Onder; Ustundag, Zafer; Suhas
    In this paper, the biosynthesis study of silver nanoparticles (AgNPs) using chitosan immobilized on the Bacillus cereus (Bc-C) was performed via bioreduction without any reducing agent. Transmission electron microscopy (TEM) showed that the AgNPs were formed as uniformly sized and shaped in the range of 10-30 nm. Scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction patterns (XRD) confirmed the formation of the Bc-C-Ag. XRD diffraction patterns revealed that the Ag+ on the Bc-C was reduced to Ag (0). This situation shows successful AgNPs synthesis using Bc-C In the bioreduction studies, the effects of operating variables such as initial metal concentration, pH and contact time were also investigated. The AgNPs formed on Bc-C (Bc-C-Ag) were used as a bionanocatalyst for the reduction of 4-nitrophenol (4-NP). The kinetic models and the thermodynamic parameters were investigated to reveal the reduction mechanism. (C) 2013 Elsevier B.V. All rights reserved.
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    Electrochemical studies on graphene oxide-supported metallic and bimetallic nanoparticles for fuel cell applications
    (Elsevier Science Bv, 2014) Gupta, Vinod Kumar; Yola, Mehmet Lutfi; Atar, Necip; Ustundag, Zafer; Solak, Ali Osman
    A fuel cell is an electrochemical cell that converts a source fuel into an electrical current It generates electricity inside a cell through reactions between a fuel and an oxidant, triggered in the presence of an electrolyte. Fuel cells have been attracting more and more attention in recent decades due to high-energy demands, fossil fuel depletions, and environmental pollution throughout world. In this study, different sized metallic and bimetallic nanoparticles (AuNPs, Fe@AuNPs, Ag@AuNPs) were synthesized on graphene oxide sheets and their electrocatalytic activities for methanol oxidation were investigated. All the catalysts were characterized by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical measurements are performed to compare the catalytic efficiencies of methanol oxidation. Experimental results demonstrated that graphene oxide-supported bimetallic nanoparticles enhanced electrochemical efficiency for methanol electro-oxidation with regard to diffusion efficiency, oxidation potential and forward oxidation peak current. Graphene oxide-supported Ag@AuNPs, in comparison to graphene oxide-supported Fe@AuNPs and AuNPs, showed the more efficiency for methanol electro-oxidation. (C) 2013 Elsevier B.V. All rights reserved.
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    Electrochemically grafted etodolac film on glassy carbon for Pb(II) determination
    (Elsevier Science Sa, 2012) Yola, Mehmet Lutfi; Atar, Necip; Qureshi, Munewar Saeed; Ustundag, Zafer; Solak, Ali Osman
    This study reports the electrochemical modification of glassy carbon (GC) surface with etodolac (ETO), the characterization of this ETO modified glassy carbon (ETO/GC) electrode and its electroanalytical application for the determination of Pb(II) ions. Binding type of the etodolac with the glassy carbon surface was investigated and found that it was through the etheric linkage revealed from the reflection-absorption infrared spectroscopy (RAIRS). The ETO/GC electrode was characterized by cyclic voltammetry (CV), reflection-adsorption IR spectroscopy, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The ETO/GC electrode was found to be suitable for selective determination of Pb(II) by adsorptive stripping voltammetry in the solutions of the mixture of heavy metal ions, such as Cu(II) and Cd(II) and showed high stability and reproducibility. The stability and the potential range of the ETO/GC electrode were also studied. The developed method was validated according to the ICH guideline and found to be linear, sensitive, selective, precise and accurate. The linearity range of Pb(II) was 5.0 x 10(-10) to 1.0 x 10(-8) M with the detection limit (S/N = 3) of 1.67 x 10(-10) M. The validated method was applied successfully for the determination of Pb(II) in real samples. (c) 2012 Elsevier B.V. All rights reserved.
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    Electrochemically modified sulfisoxazole nanofilm on glassy carbon for determination of cadmium(II) in water samples
    (Pergamon-Elsevier Science Ltd, 2013) Gupta, Vinod Kumar; Yola, Mehmet Lutfi; Atar, Necip; Solak, Ali Osman; Uzun, Lokman; Ustundag, Zafer
    Sulfisoxazole (SO) was grafted to glassy carbon electrode (GCE) via the electrochemical oxidation of SO in acetonitrile solution containing 0.1 M tetrabutylammoniumtetra-fluoroborate (TBATFB). The prepared electrode was characterized by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), reflection-absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). The ellipsometric thickness of SO nanofilm at the glassy carbon surface was obtained as 14.48 +/- 0.11 nm. The stability of the SO modified GCE was studied. The SO modified GCE was also utilized for the determination of Cd(II) ions in water samples in the presence of Pb(II) and Fe(II) by adsorptive stripping voltammetry. The linearity range and the detection limit of Cd(II) ions were 1.0 x 10(-1) to 5.0 x 10(-8) M and 3.3 x 10(-11) M (S/N = 3), respectively. (C) 2013 Elsevier Ltd. All rights reserved.
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    Molecular imprinted polypyrrole modified glassy carbon electrode for the determination of tobramycin
    (Pergamon-Elsevier Science Ltd, 2013) Gupta, Vinod Kumar; Yola, Mehmet Lutfi; Ozaltin, Nuran; Atar, Necip; Ustundag, Zafer; Uzun, Lokman
    Over the past two decades, molecular imprinted polymers have attracted a broad interest from scientists in sensor development. In the preparation of molecular imprinted polymers the desired molecule (template) induces the creation of specific recognition sites in the polymer. In this study, the glassy carbon electrode (GCE) based on molecularly imprinted polypyrrole (PPy) was fabricated for the determination of tobramycin (TOB). The developed electrode was prepared by incorporation of a template molecule (TOB) during the electropolymerization of pyrrole on GCE in aqueous solution using cyclic voltammetry (CV) method. The performance of the imprinted and non-imprinted electrodes was evaluated by square wave voltammetry (SWV). The effect of pH, monomer and template concentrations, electropolymerization cycles on the performance of the imprinted and non-imprinted electrodes was investigated and optimized. The non-modified and TOB-imprinted surfaces were characterized by using atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and CV. The linearity range of TOB was 5.0 x 10(-10)-1.0 x 10(-8) M with the detection limit of 1.4 x 10(-10) M. The developed nanosensor was applied successfully for the determination of TOB in egg and milk. (C) 2013 Elsevier Ltd. All rights reserved.