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Öğe 1,10-Phenanthroline-5,6-dione and 9,10-phenanthrenequinone as redox mediators for amperometric glucose biosensors(SPRINGER, 2014) Zor, Erhan; Oztekin, Yasemin; Mikoliunaite, Lina; Voronovic, Jaroslav; Ramanaviciene, Almira; Anusevicius, Zilvinas; Bingol, HalukIn this study, two ortho-quinoidal compounds, 1,10-phenanthroline-5,6-dione (PD) and 9,10-phenanthrenequinone (PQ), were examined as electron transfer mediators suitable for amperometric glucose biosensors. The dependences of the electrochemical responses of PD- and PQ-based amperometric glucose biosensors on varied concentrations of glucose were investigated under aerobic and anaerobic conditions. The PD-modified graphite rod (GR) electrode revealed a current response seven times higher than that of the PQ-modified GR electrode. The reactivity indices of ortho-quinoidals assessed by means of B3LYP functional method applying 6-311G(D) basis set showed that the electron-accepting potency for PD was markedly higher as compared with that of PQ. Compared to PQ, considerably higher reactivity of PD has been defined in the reactions with NADP(+)-ferredoxin reductase (FNR, EC 1.18.1.2) as a model single-electron transfer FAD-dependent enzyme, which provided an additional evidence for PD as a more efficient mediator compared to PQ. This study illustrates that PD can be applied as a redox mediator for glucose oxidase and it could be more suitable for a reagent-less biosensor design than PQ.Öğe Catalytic degradation of organic dye using reduced graphene oxide-polyoxometalate nanocomposite(ELSEVIER SCIENCE SA, 2017) Ucar, Asuman; Findik, Mukerrem; Gubbuk, I. Hilal; Kocak, Nuriye; Bingol, HalukSilicotungstic acid (SiW) decorated reduced graphene oxide (rGO) nanocomposite (rGO-SiW) has been prepared and evaluated as a heterogeneous nanocatalyst for the degradation reactions of methylene blue (MB) and rhodamine B (RhB). The structural and morphological properties of rGO-SiW nanocomposite were investigated by various techniques such as Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), Atomic force microscopy (AFM) and Scanning electron microscope (SEM), which revealed the homogeneous and noncovalent anchoring of SiW nanoparticles on rGO sheets. The catalytic activity of rGO-SiW nanocomposite on the degradations of MB and RhB has been monitored using UV-visible absorption spectrometry in the presence of NaBH4 as the reducing agent at room temperature in water. The reduction reactions followed pseudo-first order kinetics and degradation were achieved in 34 min for MB and 81 min for RhB using rGO-SiW as catalysts. (C) 2017 Elsevier B.V. All rights reserved.Öğe An electrochemical and computational study for discrimination of D- and L-cystine by reduced graphene oxide/beta-cyclodextrin(ROYAL SOC CHEMISTRY, 2015) Zor, Erhan; Bingol, Haluk; Ramanaviciene, Almira; Ramanavicius, Arunas; Ersoz, MustafaHere, we report a novel enantioselective electrochemical biosensor for the discrimination of cystine enantiomers (D- and L-cystine) using a chiral interface for the specific recognition of D- and L-cystine. The biosensor is based on reduced graphene oxide modified by beta-cyclodextrin (rGO/beta-CD) at the GCE surface. During the preparation of rGO/beta-CD/GCE, the modified electrode surfaces were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The electrochemical behaviours of the D- and L-cystine were investigated using the rGO/beta-CD/GCE by CV and compared to bare GCE. A clear separation between the oxidation peak potentials of D- and L-cystine was observed at 1.32 and 1.42 V, respectively. The electrochemical discrimination performance of the fabricated chiral sensor was also examined by differential pulse voltammetry (DPV) in a mixed solution of D- and L-cystine. In addition, the DPV technique was used for the determination of D- and L-cystine at low concentration values in the range of 1.0-10.0 mM. To investigate the amperometric response of rGO/beta-CD/GCE towards D- and L-cystine, the chronoamperometry technique was used in the concentration range of 10.0-100.0 mu M. The interactions of the enantiomers with rGO/beta-CD were modelled by molecular docking using AutoDock Vina, and the interaction energies were predicted to be -4.8 and -5.3 kcal mol(-1) for D- and L-cystine, respectively. The corresponding values of binding constants were calculated to be 3.32 x 10(3) and 7.71 x 10(3) M-1, respectively. The experimental and molecular docking results indicate that the rGO/beta-CD/GCE has a different affinity for each enantiomer.Öğe An electrochemical biosensor based on human serum albumin/graphene oxide/3-aminopropyltriethoxysilane modified ITO electrode for the enantioselective discrimination of D- and L-tryptophan(ELSEVIER ADVANCED TECHNOLOGY, 2013) Zor, Erhan; Patir, Imren Hatay; Bingol, Haluk; Ersoz, MustafaA new electrochemical biosensor based on the human serum albumin/graphene oxide/3-aminopropyl-triethoxysilane modified indium tin oxide electrode (ITO/APTES/GO/HSA) has been developed for the discrimination of tryptophan (Trp) enantiomers. The electrode has been characterized by scanning electron microscopy (SEM) and electrochemical techniques. The electrochemical behaviors of the enantiomeric pairs (D- and L-Trp) at the ITO/APTES/GO/HSA electrode have been investigated by cyclic voltammetry in the concentration range of 0.10-1.0 mM. A clear separation between the oxidation peak potentials of D- and L-Trp, at 0.86 and 1.26 V, respectively, has suggested that the ITO/APTES/GO/HSA electrode can be used as an electrochemical biosensor for the discrimination of Trp enantiomers. In order to find the percentage of an enantiomeric form of tryptophan in a mixture, the ITO/APTES/GO/HSA electrode is used for the simultaneous detection of D- and L-Trp which showed that the percentage of one enantiomeric form can be easily measured in the presence of the other. (c) 2012 Elsevier B.V. All rights reserved.Öğe Evaluation of 1,10-phenanthroline-5,6-dione as redox mediator for glucose oxidase(MAIK NAUKA/INTERPERIODICA/SPRINGER, 2016) Zor, Erhan; Oztekin, Yasemin; Ramanaviciene, Almira; Anusevicius, Zilvinas; Voronovic, Jaroslav; Bingol, Haluk; Barauskas-Memenas, DanaA low-cost and simply fabricated amperometric glucose biosensor based on glucose oxidase (GOx) and 1,10-phenanthroline-5,6-dione (PD) modified graphite rod electrode was developed. The electrode exhibited good electrocatalytic activity with a well-defined hyperbolic dependence of amperometric signal upon glucose concentration in the presence and in the absence of oxygen. The electrode showed a good reproducibility and repeatability with relative standard deviation of less than 3 and 5%, respectively. The interaction of GOx with PD mediator was confirmed by means of UV?Vis absorbance spectroscopy.Öğe Facilitated Proton Transfer by a Novel 2-Aminothiazole Derivative Across the Water/1,2-Dichloroethane Interface(SPRINGER/PLENUM PUBLISHERS, 2011) Bingol, Haluk; Coskun, AhmetThe behavior of proton transfer facilitated by a novel thiazole derivative, N-methyl-4-(4-phenoxyphenyl)thiazol-2-amine (MPPT), across the water/1,2-dichloroethane (1,2-DCE) interface was investigated electrochemically. The ionic partition diagram for MPPT was obtained from interpretation of the cyclic voltammograms. The apparent partition coefficient of MPPT was evaluated by the shaking-flask method under experimental conditions, while that for the protonated form of MPPT was calculated from its transfer potential obtained from the ionic partition diagram. It was suggested that the mechanism for transfer of MPPT across the water/1,2-DCE) interface depends on the pH of the aqueous phase. The parameters of the facilitated proton transfer across the water/1,2-DCE interface were evaluated as a quantitative measure of its lipophilicity.Öğe Fluorogenic ferrocenyl Schiff base for Zn2+ and Cd2+ detection(SPRINGER, 2017) Findik, Mukerrem; Ucar, Asuman; Bingol, Haluk; Guler, Ersin; Ozcan, EmineA novel sensor based on acetylferrocene-containing Schiff base (ASB) was synthesized by reaction of alpha-chloroacetylferrocene and N-(salicylidene)-l-valinmethylester. The structure of the compound was characterized by using elemental analysis and Fourier-transform infrared (FT-IR), H-1 nuclear magnetic resonance (NMR), and C-13 NMR spectroscopy. Its metal-cation-sensing properties were investigated spectrofluorometrically. ASB served as selective chemosensor for Zn2+ and Cd2+ towards alkali, alkaline-earth, and various heavy-metal ions. It showed significant fluorescence enhancement for Zn2+ and Cd2+ ions, stemming from C=N isomerization and chelation-enhanced fluorescence. The binding modes of the complexes were determined to have 1:1 complexation stoichiometry, and the binding constants were calculated as (6.93 +/- 0.25) x 10(6) M-1 for ASB center dot Zn (2+) and (7.49 +/- 0.18) x 10(5) M-1 for ASB center dot Cd (2+) using the nonlinear curve-fitting method.Öğe Graphene Quantum Dots-based Photoluminescent Sensor: A Multifunctional Composite for Pesticide Detection(AMER CHEMICAL SOC, 2015) Zor, Erhan; Morales-Narvaez, Eden; Zamora-Galvez, Alejandro; Bingol, Haluk; Ersoz, Mustafa; Merkoci, ArbenDue to their size and difficulty to obtain, cost/effective biological or synthetic receptors (e.g., antibodies or aptamers, respectively), organic toxic compounds (e.g., less than 1 kDa) are generally challenging to detect using simple platforms such as biosensors. This study reports on the synthesis and characterization of a novel multifunctional composite material, magnetic silica beads/graphene quantum dots/molecularly imprinted polypyrrole (mSGP). mSGP is engineered to specifically and effectively capture and signal small molecules due to the synergy among chemical, magnetic, and optical properties combined with molecular imprinting of tributyltin (291 Da), a hazardous compound, selected as a model analyte. Magnetic and selective properties of the mSGP composite can be exploited to capture and preconcentrate the analyte onto its surface, and its photoluminescent graphene quantum dots, which are quenched upon analyte recognition, are used to interrogate the presence of the contaminant. This multifunctional material enables a rapid, simple and sensitive platform for small molecule detection, even in complex mediums such as seawater, without any sample treatment.Öğe Green synthesis of reduced graphene oxide/nanopolypyrrole composite: characterization and H2O2 determination in urine(ROYAL SOC CHEMISTRY, 2014) Zor, Erhan; Saglam, Muhammed Esad; Akin, Ilker; Saf, Ahmet Ozgur; Bingol, Haluk; Ersoz, MustafaHere we report on a novel, simple and eco-friendly approach for the fabrication of a reduced Graphene Oxide/nanopolypyrrole (rGO/nPPy) composite material and its electrochemical performance for detection of hydrogen peroxide on a glassy carbon electrode. The characterization of the as-prepared rGO/nPPy composite was investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet-visible spectroscopy, scanning electron microscopy, contact angle measurement, cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques were used to investigate and optimize the performance of the developed electrochemical biosensor. The proposed biosensor showed excellent analytical response towards the quantification of H2O2 at pH 7.40. Under the optimized conditions, the biosensor shows a linear response range from 1.0 x 10(-7) to 4.0 x 10(-6) M concentrations of H2O2. The limit of detection was determined to be 34 nM. Reproducibility, sensitivity, stability and anti-interference capability of the fabricated biosensor for the detection of H2O2 were examined. The biological relevance of the developed electrochemical biosensor was further studied by the determination of H2O2 in urine samples. The real sample analysis of H2O2 was achieved before and after drinking coffee in urine samples. The successful and sensitive determination of H2O2 urine samples indicates that the proposed electrochemical biosensor can be applied to the quantification analysis of H2O2 in real samples.Öğe Green Synthesis of Reduced Graphene Oxide/Polyaniline Composite and Its Application for Salt Rejection by Polysulfone-Based Composite Membranes(AMER CHEMICAL SOC, 2014) Akin, Ilker; Zor, Erhan; Bingol, Haluk; Ersoz, MustafaIn this study, a novel, simple, and eco-friendly enzymatic-reaction-based approach to produce reduced graphene oxide/polyaniline (rGO/PANI) composite material was proposed. Glucose oxidase (GOx) was used as an effective catalyst producing hydrogen peroxide, in the presence of glucose, for the oxidative polymerization of aniline under ambient conditions. The prepared rGO/PANI composite was dispersed in polysulfone (PSf), and the mixed membranes were prepared by the phase inversion polymerization method. The morphology of membranes was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle (CA) techniques. The performance of membranes was studied in terms of salt rejection and pure water flux. The incorporation of rGO into the membrane matrix led to hydrophobic membrane surface with the enhanced macro-voids. On the contrary, the contact angle data revealed that the rGO/PANI-incorporated membrane surface is partly hydrophilic due to the PANI fibers in membrane, whereas SEM images showed the enhanced macro-voids. Membranes exhibited an improved salt rejection after rGO/PANI doping. The rGO/PANI-modified membrane loading exhibited a maximum of 82% NaCl rejection at an applied pressure of 10 bar. In addition, the results showed that the PSf-rGO/PANI composite membrane had the highest mean porosity and water flux.Öğe Organometallic chiral Schiff base for enantio-selective fluorescent recognition of methionine(SPRINGER INTERNATIONAL PUBLISHING AG, 2017) Ucar, Asuman; Findik, Mukerrem; Bingol, Haluk; Guler, Ersin; Ozcan, EmineHerein, the synthesis and characterization of a novel chiral Schiff bases derived from ferrocene, coded as 3, have been reported. The sensing behavior of the synthesized compound has been examined towards the enantiomers of some amino acids (methionine, alanine, serine, histidine, and threonine) by spectrofluorimetric method. The fluorescence response of compound 3 showed noticeable enhancement upon addition of d-methionine compared to l-methionine and kept nearly linear correlation with the concentration of d-methionine. The value of enantiomeric fluorescence difference ratio (ef) has been determined to be 1.54 when d - and l- methionine amount is 100 times more than compound 3. The results showed that the compound 3 can be used as a sensor for enantio-selective recognition of d-methionine.Öğe Preparation of a novel PSf membrane containing rGO/PTh and its physical properties and membrane performance(ROYAL SOC CHEMISTRY, 2015) Saf, Ahmet Ozgur; Akin, Ilker; Zor, Erhan; Bingol, HalukRecent advances in the fabrication of nanostructures such as graphene-related materials have received a lot of attention in membrane technology for the future of water supplies. Herein, we report the synthesis of a reduced graphene oxide/polythiophene (rGO/PTh) composite material using an in situ enzymatic polymerization reaction, which is an eco-friendly and a simple way to construct a nanocomposite material. Polysulfone (PSf) mixed matrix composite membranes containing rGO and rGO/PTh were prepared via a phase inversion method. The morphology of the membranes was evaluated by various characterization methods, including SEM, AFM, contact angle and porosity measurements. The performance and antifouling properties of the membranes were examined in detail. The PSf-rGO/PTh membrane showed a significant improvement in water flux permeability due to the enhancement of hydrophilicity and porosity. Moreover, the PSf-rGO/PTh membrane exhibited an approximately 10 times higher improved water flux than that of the rGO membrane as the pressure was increased. The fouling resistance ratio (FRR) and antifouling properties of the membranes were tested using two different protein solutions: bovine serum albumin (BSA) and cytochrome c (Ctc). The antifouling and FRR properties of the PSf-rGO/PTh membrane decreased due to not only the interactions between the functional groups on the membrane surface and fouling materials, but also the morphological properties of the membrane.Öğe Spectrophotometric and electrochemical behavior of a novel azocalix[4]arene derivative as a highly selective chromogenic chemosensor for Cr+3(PERGAMON-ELSEVIER SCIENCE LTD, 2011) Bingol, Haluk; Kocabas, Erdal; Zor, Erhan; Coskun, AhmetIn this study, a novel azocalix[4]arene derivative, 5,11,17-tris[(1-naphtyl)azo]-25,26,27,28-tetrahydroxycalix[4]arene (NAC4) bearing napthyl groups on the upper rim was synthesized. Its complexation behavior for alkali, alkaline-earth and various heavy metal ions (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Pb2+, Hg2+, Ni2+, Cd2+, Cu2+, Zn2+, Co2+, Fe2+, Cr3+, Ag+) was investigated by spectroscopic and voltammetric methods. This chemosensor exhibits decreased absorbance in the presence of Hg2+ and a unique absorbance quenching effect only for Cr3+. In addition, a new absorption band centered at 565 nm with the formation of the 1:1 host-guest complex (Cr3+-NAC4) was observed in the case of Cr3+, leading to an obvious color change from light orange to dark lilac. In voltammetric experiments, Cr3+ ions decreased voltammetric peaks of NAC4, whereas no significant changes occurred in the presence of the other metal ions. The Benesi-Hildebrand method was used to determine a logarithmic value of 3.76 for the association constant of the complex between Cr3+ and NAC4. (C) 2010 Elsevier Ltd. All rights reserved.Öğe Spectrophotometric and voltammetric characterization of a novel selective electroactive chemosensor for Mg2+(VERSITA, 2013) Zor, Erhan; Saf, Ahmet Ozgur; Bingol, HalukA novel azocalix[4]arene derivative, 5,11,17,23-tetrakis[(acetophenone)azo]-25,26,27,28-tetrahydroxycalix[4]arene (APC4), containing acetophenone azo groups at the upper rim was synthesized as a chemosensor. Its binding and sensing properties with alkali and alkaline earth metal ions (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+) were investigated by UV-vis spectrophotometric and voltammetric techniques. The stoichiometric ratio and the association constant were determined spectrophotometrically as 1:1 and (1.94 +/- 0.31)x10(5) L mol(-1) for the complex between Mg2+ and the chemosensor, respectively. Moreover, it was shown that the interaction between Mg2+ and the APC4 occurred by means of the phenol groups at the lower rim by voltammetric methods. The results of spectrophotometric and voltammetric experiments showed that the chromogenic chemosensor has high selectivity towards Mg2+ among the other used metal ions, especially the interfering Ca2+ ion.Öğe Synthesis of a Novel Thiadiazine Derivative and Electrochemical Properties for Pb2+ Transfer across Water/1,2-Dichloroethane Interface(PEKING UNIV PRESS, 2011) Baslak, Canan; Bingol, Haluk; Coskun, Ahmet; Atalay, TevfikThe transfer of Pb2+ facilitated by interfacial complexation with 5-(4-phenoxyphenyl)-6H-1,3,4-thiadiazin-2-amine (PPTA) at the polarized water/1,2-dicholoroethane (1,2-DCE) interface was investigated by cyclic voltammetry. We synthesized the thiadiazine derivative, PPTA, firstly. The transfer was performed at different metal concentrations and scan rates, and the obtained voltammetric transfer peaks toward Pb2+ ion over other divalent cations (Zn2+, Co2+, Ni2+, Cd2+, Hg2+, and Cu2+) were reversible. The dependence of the half-wave potentials of the Pb2+ ion on the concentration of PPTA in the organic phase indicates that the ion transfer is facilitated by the formation of 1:2 (metal: ligand) complex in the organic phase with the association constant (Ig beta(2)) of (17.1 +/- 0.2).Öğe Voltammetric discrimination of mandelic acid enantiomers(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2014) Zor, Erhan; Saf, Ahmet O.; Bingol, Haluk; Ersoz, MustafaWe report a novel electrochemical biosensor for direct discrimination of D- and L-mandelic acid (D- and L-MA) in aqueous medium. The glassy carbon electrode (GCE) surface was modified with reduced graphene oxide (rGO) and gamma-globulin (GLOB). Electrochemical characterization of the modified electrodes was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode surfaces were also characterized by scanning electron microscopy. Electrochemical response of the prepared electrode (GCE/rGO/GLOB) for discrimination of D- and L-MA enantiomers was investigated by cyclic voltammetry and was compared with bare GCE in the concentration range of 2 to 10 mM. Whereas the bare GCE showed no electrochemical response for the MA enantiomers, the GCE/rGO/GLOB electrode exhibited direct and selective discrimination with different oxidation potential values of 1.47 and 1.71 V and weak reduction peaks at potential values of -1.37 and -1.48 V, respectively. In addition, electrochemical performance of the modified electrode was investigated in mixed solution of D- and L-MA. The results show that the produced electrode can be used as electrochemical chiral biosensor for MA. (C) 2013 Elsevier Inc. All rights reserved.
