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Öğe 1,10-Phenanthroline modified glassy carbon electrode for voltammetric determination of cadmium(II) ions(ELSEVIER SCIENCE SA, 2011) Oztekin, Yasemin; Ramanaviciene, Almira; Ryskevic, Natalija; Yazicigil, Zafer; Ustundag, Zafer; Solak, Ali Osman; Ramanavicius, ArunasThis study reports the electrochemical modification of glassy carbon (GC) electrode surface with the electro-polymerized form of 1,10-phenanthroline monohydrate (PMH), the characterization of this polyphenanthroline modified electrode (PPMH/GC) and the electroanalytical application suitable for the determination of Cd(II) ions. The PPMH/GC electrode was characterized by cyclic voltammetry, chronoamperometry and atomic force microscopy and formation of polyphenanthroline layer grafted to surface of GC electrode was evidenced. Selectivity of PPMH/GC electrode towards heavy metal ions was investigated by square wave voltammetry. The PPMH/GC electrode was found to be suitable for selective determination of Cd(II) in the solutions containing the mixture of heavy metal ions and showed high stability and reproducibility. The analytical methodology was successfully applied for monitoring the toxic metal ions in real samples. (C) 2011 Elsevier B.V. All rights reserved.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 Biofuel Cell Based on Anode and Cathode Modified by Glucose Oxidase(WILEY-V C H VERLAG GMBH, 2013) Krikstolaityte, Vida; Oztekin, Yasemin; Kuliesius, Jurgis; Ramanaviciene, Almira; Yazicigil, Zafer; Ersoz, Mustafa; Okumus, AytugA single compartment biofuel cell (BFC) based on an anode and a cathode powered by the same fuel glucose is reported. Glucose oxidase (GOx) from Aspergillus niger was applied as a glucose consuming biocatalyst for both anode and cathode of the BFC. The 5-amino-1,10-phenanthroline modified graphite rod electrode (GRE) with cross-linked GOx was used as the bioanode, and the GRE with co-immobilised horseradish peroxidase and GOx was exploited as the biocathode of the BFC. The open-circuit voltage of the designed BFC exceeded 450mV and a maximal power density of 3.5 mu W/cm(2) was registered at a cell voltage of 300mV.Öğe Copper nanoparticle modified carbon electrode for determination of dopamine(PERGAMON-ELSEVIER SCIENCE LTD, 2012) Oztekin, Yasemin; Tok, Mutahire; Bilici, Esra; Mikoliunaite, Lina; Yazicigil, Zafer; Ramanaviciene, Almira; Ramanavicius, ArunasThis paper reports the synthesis and characterization of copper nanoparticles (CuNPs) and application of copper nanoparticle-modified glassy carbon electrode for the electrochemical determination of dopamine. Electrochemical measurements were performed using differently modified glassy carbon (GC) electrodes. Bare, oxidized before modification and copper nanoparticle-modified glassy carbon electrodes (bare-GC, ox-GC and CuNP/GC electrodes, respectively) were characterized by cyclic voltammetry and electrochemical impedance spectroscopy in the presence of redox probes. Atomic force microscopy was used for the visualization of electrode surfaces. The CuNP/GC electrode was found to be suitable for the selective determination of dopamine even in the presence of ascorbic acid, uric acid, and p-acetamidophenol. The observed linear range of CuNP/GC for dopamine was from 0.1 nM to 1.0 mu M while the detection limit was estimated to be 50 pM. It was demonstrated that here reported glassy carbon electrode modified by copper nanoparticles is suitable for the determination of dopamine in real samples such as human blood serum. (C) 2012 Elsevier Ltd. All rights reserved.Öğe Development of poly(3-aminophenylboronic acid) modified graphite rod electrode suitable for fluoride determination(ELSEVIER SCIENCE BV, 2014) Ciftci, Hakan; Oztekin, Yasemin; Tamer, Ugur; Ramanaviciene, Almira; Ramanavicius, ArunasPoly(3-aminophenylboronic acid), (PAPBA) film was formed on the graphite rod surface by potential cycling. The PAPBA-modified graphite rod (PAPBA/GR) electrode prepared in this way was used for potentiometric fluoride determination. The linear calibration range was from 5 x 10(-4) to 5 x 10(-2) M with the slope of the linear part of the calibration curve of 42.5 mV/log C. No interference effect of the most common ions such as sodium, potassium, chloride, nitrate, iodide, calcium, zinc, aluminum, sulfate and sorbitol was observed during electrochemical determination of fluoride. On the other hand, the PAPBA/GR electrode showed not only good sensitivity and selectivity, but also relatively rapid response to changes of analyte concentrations in the range of 20 s. The sensor was successfully applied for fluoride determination in real sample - toothpaste. (C) 2014 Elsevier B.V. All rights reserved.Öğe Direct electron transfer from glucose oxidase immobilized on polyphenanthroline-modified glassy carbon electrode(ELSEVIER ADVANCED TECHNOLOGY, 2011) Oztekin, Yasemin; Ramanaviciene, Almira; Yazicigil, Zafer; Solak, Ali Osman; Ramanavicius, ArunasThis study reports direct electron transfer (DET) from immobilized glucose oxidase (GOx) via grafted and electropolymerized 1,10-phenanthroline monohydrate (PMH). The layer of poly-1,10-phenanthroline (PPMH) was gained via electrochemical deposition, which was used to create the PPMH-modified GC-electrode (PPMH/GC-electrode). Further, the GOx was immobilized on the PPMH/GC-electrode. The effect of surface-modification by the PPMH on the electron-transfer between enzyme and electrode-surface and some other electrochemical/analytical-parameters of newly designed enzymatic-electrode were evaluated. The PPMH/GC-electrode showed superior DET to/from flavine adenine dinucleotide cofactor of GOx, while some redox-compounds including ferrocene and K-3[Fe(CN)(6)] were completely electrochemically inactive on the PPMH/GC-electrode. It was also found that the resulting GOx/PPMH/GC-electrode functioned as a "direct response type" glucose-biosensor. The biosensor showed excellent selectivity towards glucose and demonstrated good operational-stability. According to our best knowledge, this study is the first scientific report on electrochemical-polymerization of PMH on the GC-electrode in non-aqueous media followed by its application in the design of glucose-biosensor. (C) 2010 Elsevier B.V. All rights reserved.Öğe The effect of colloidal solutions of gold nanoparticles on the performance of a glucose oxidase modified carbon electrode(SPRINGER WIEN, 2011) German, Natalija; Ramanavicius, Arunas; Voronovic, Jaroslav; Oztekin, Yasemin; Ramanaviciene, AlmiraThe aim of this work was to further evaluate the effect of colloidal solutions of gold nanoparticles (Au-NPs) on the performance of a carbon rod electrode modified with glucose oxidase. The amperometric response of the system at +0.3 V vs. Ag/AgCl was studied in the absence and in the presence of Au-NPs (6 nm and 13 nm in diameter) and in presence of N-methylphenazonium methyl sulfate (PMS) at pH 6.0. This study shows that the application of < 0.60 nmol L-1 concentrations of Au-NPs increases the rate of mediated electron transfer, and this effect does not depend on the diameter of Au-NPs. The analytical signal in the presence 0.60 nmol L-1 of Au-NPs (13 nm) and 2 mmol L-1 of PMS linearly depends on the concentration of glucose in the range from 0.1 to 10 mmol L-1, the limit of detection is as low as 0.05 mmol L-1.Öğe Electrochemical biosensor based on glucose oxidase encapsulated within enzymatically synthesized poly(1,10-phenanthroline-5,6-dione)(ELSEVIER SCIENCE BV, 2014) Ciftci, Hakan; Oztekin, Yasemin; Tamer, Ugur; Ramanaviciene, Almira; Ramanavicius, ArunasThis study is focused on the investigation of electrocatalytic effect of glucose oxidase (GOx) immobilized on the graphite rod (GR) electrode. The enzyme modified electrode was prepared by encapsulation of immobilized GOx within enzymatically formed poly(1,10-phenanthroline-5,6-dione) (pPD) film. The electrochemical responses of such enzymatic electrode (pPD/GOx/GR) vs. different glucose concentrations were examined chronoamperometrically in acetate-phosphate buffer solution (A-PBS), pH 6.0, under aerobic or anaerobic conditions. Amperometric signals of the pPD/GOx/GR electrode exhibited well-defined hyperbolic dependence upon glucose concentration. Amperometric signals at 100 mM of glucose were 41.17 and 32.27 mu A under aerobic and anaerobic conditions, respectively. Amperometric signals of the pPD/GOx/GR electrode decreased by 6% within seven days. The pPD/GOx/GR electrode showed excellent selectivity in the presence of dopamine and uric acid. Furthermore it had a good reproducibility and repeatability with standard deviation of 9.4% and 8.0%, respectively. (C) 2014 Elsevier B.V. All rights reserved.Öğe Electrochemical copper (II) sensor based on self-assembled 4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate(ELSEVIER SCIENCE SA, 2011) Oztekin, Yasemin; Ramanaviciene, Almira; Ramanavicius, ArunasA 4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate (AHMP)-based self-assembled monolayer (SAM) was formed on the gold electrode surface. Ellipsometric measurements evidenced the SAM formation on the gold electrode surface. The structural integrity of the modified gold electrode was also characterized by insulating properties of the SAM that were detected by cyclic voltammetry. The results of cyclic voltammetry showed that the SAM, which was formed by assembly of AHMP, was stable but did not completely block the redox-activity of ferrocene and K-3[Fe(CN)(6)]/K-4[Fe(CN)(6)]. In contrast completely blocked redox-activity was observed after the treatment of AHMP-based SAM with saturated solution of 4-formylphenylboronic acid in 1,4-dioxan. The modified electrodes exhibited a selective response towards Cu(II) ions in the presence of some interfering ions such as Cd(II), Co(II), Fe(II), Ni(II) and Pb(II). This study is the first scientific report on the application of AHMP-modified electrode as a selective Cu(II) sensor in the presence of some interfering cations. (C) 2011 Elsevier B.V. All rights reserved.Öğe Electrochemical determination of copper(II) using modified glassy carbon electrodes(DESALINATION PUBL, 2012) Bilici, Esra; Yazicigil, Zafer; Tok, Mutahire; Oztekin, YaseminElectrochemical modification of glassy carbon (GC) electrode surface via electrochemical oxidation of 1-aminoindan in acetonitrile including 100.0 mM of tetrabutylammonium tetrafluoroborate and applicability of electrode modified in this way for electrochemical determination of copper(II) (Cu(II)) were reported in this study. Electrochemical surface modification was performed by cyclic voltammetry in the potential range between +0.9 and +1.5V vs. Ag/Ag+ (10.0 mM of AgNO3) at the scan rate of 100 mV/s by 30 potential cycles. The modified electrode surface was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and contact angle measurement. The characterization results were compared with the characterization results of bare GC electrode. The results of the amperometric measurements of the modified GC electrode towards Cu(II) ions were investigated. It was determined that the modified electrode surface had electrochemical responses towards Cu(II) ions with high sensitivity, good selectivity, stability, reproducibility and repeatability. According to the results, it is believed that it will be possible to find an application area for this new surface in any industrial fields.Öğe Electrochemical Determination of Cu(II) Ions by 4-Formylphenylboronic Acid Modified Gold Electrode(WILEY-V C H VERLAG GMBH, 2011) Oztekin, Yasemin; Ramanaviciene, Almira; Ramanavicius, ArunasA self-assembled monolayer (SAM) modified by 4-formylphenylboronic acid was formed on the gold electrode, which was applied for the determination of trace concentrations of Cu(II). The formation of advanced SAM on the gold electrode was evidenced by electrochemical impedance spectroscopy, atomic force microscopy and contact angle measurements. Electrochemical determination of Cu(II) ions was performed by square wave voltammetry. Some mutual interferences caused by Cd(II), Co(II), Fe(II), Ni(II) and Pb(II) ions were investigated and it was demonstrated how the negative effects of these interfering ions could be eliminated by adjustment of proper parameters of square wave voltammetry.Öğe Electrochemical determination of Cu(II) ions using glassy carbon electrode modified by some nanomaterials and 3-nitroaniline(ELSEVIER SCIENCE BV, 2015) Dedelaite, Lina; Kizilkaya, Selin; Incebay, Hilal; Ciftci, Hakan; Ersoz, Mustafa; Yazicigil, Zafer; Oztekin, YaseminThe aim of this research was to investigate the effect of the several nanomaterials in electrochemical determination of Cu(II) ions. For this aim, firstly the deposition of graphene oxide (GO), graphene, magnetite (Fe3O4), gold-chitosan (AuChts) or multilayer carbon nanotubes (MWCNTs) on the glassy carbon (GC) electrode surface was performed. Then the electrochemical modification of electrode by poly-3-nitroaniline (poly-3NA) was performed by 100 potential cycles in the range between +0.9 V and +1.4 V vs. Ag/AgNO3 at the sweep rate of 100 mV/s. For electrochemical reduction of nitro groups present on modified GC electrode surface, potential cycling was performed in 100 mM HCl between -0.1 V and -0.8 V vs. Ag/AgCl/(KClsat.) at the sweep rate of 100 mV/s. Nanomaterial and poly-3NA modified electrodes were applied in the determination of Cu(II) ions by differential pulse voltammetry. It was determined that GC electrodes consecutively modified with MWCNTs, poly-3NA and then by electrochemical reduction of nitro groups were the most sensitive towards Cu(II) ions with detection limit of 0.5 x 10(-9) M. (C) 2015 Elsevier B.V. All rights reserved.Öğe Electrochemical Glutathione Sensor Based on Electrochemically Deposited Poly-m-aminophenol(WILEY-V C H VERLAG GMBH, 2011) Oztekin, Yasemin; Ramanaviciene, Almira; Ramanavicius, ArunasPreparation and characterization of electrodes suitable for determination of glutathione is reported in this study. For this poly-m-aminophenol (PmAP), poly-o-aminophenol, and poly-p-aminophenol were electrochemically deposited from aqueous solution on the surface of glassy carbon (GC) electrode by potential cycling in the range of +0.2-+1.0 V. The modified GC electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, contact angle measurement and ellipsometry. It was found that poly-m-aminophenol modified GC electrode (PmAP/GC-electrode) is most suitable for electroanalytical determination of glutathione. An electroanalytical system for the determination of glutathione based on the PmAP/GC-electrode was developed. The analytical system was characterized by low limit of detection, good stability, high sensitivity and wide linear detection range.Öğe The electrochemical investigation of salts partition with ion exchange membranes(ELSEVIER SCIENCE BV, 2008) Ata, Nejla; Yazicigil, Zafer; Oztekin, YaseminThe regenaration of acid and base from the solutions containing metallic salts was achieved by salt splitting method (SSM) using not only anion-exchange membranes (AEM) but also cation-exchange membrane (CEM). In these experiments, while the ion exchange membrane was anion-exchange membrane, acid solutions were used as an anolyte and different salts of potassium were used as a catholyte. In addition to these experiments, while the ion exchange membrane was cation-exchange membrane, base solutions were used as a catholyte and different salts of potassium were used as an anolyte. The effects of current density, initial concentrations of anolyte and catholyte solutions, the type of salt solution and the type of the ion-exchange membranes on the recovery ratio of bases and acids were investigated. The results of the experiments were investigated with the Statistical Package for Social Sciences (SPSS) program. The obtained results show that this technique can be used not only for recovering the acid and base wastes of industry but also for removing the impurities in order to obtain pure acids and bases in laboratory conditions. (c) 2008 Elsevier B.V. All rights reserved.Öğe Electrochemical stability and repulsion of polypyrrole film(ELSEVIER SCIENCE BV, 2013) Ratautaite, Vilma; Ramanaviciene, Almira; Oztekin, Yasemin; Voronovic, Jaroslav; Balevicius, Zigmas; Mikoliunaite, Lina; Ramanavicius, ArunasThis study reports the electrochemical synthesis of polypyrrole (Ppy) film on the gold surface and the evaluation of this film repulsion conditions from the electrode surface. It is known that overall stability of the conducting polymer layer on the electrode is critical for many applications including biosensors. It can be affected by many factors however electrochemical treatment of electrode is mostly well-known among them. This work was mainly based on the preparation of the polymeric layer and the investigation of its stability. Overoxidised polypyrrole film was synthesized on the gold electrode. Later this layer was treated by potential cycling in wide potential intervals. The stability of Ppy layers deposited on electrode was evaluated. It was determined that Ppy layer was stable within 0-0.9 V potential range, scan rate was 20 mV/s, vs. Ag/AgCl/KClsat. while it was repulsed from the gold electrode by 10 potential cycles within 0.0-1.0 V potential range at the same scan rate. Some possible future applications of repulsed Ppy films are predicted. (C) 2012 Elsevier B.V. All rights reserved.Öğe Enzymatic polymerization of polythiophene by immobilized glucose oxidase(ELSEVIER SCI LTD, 2014) Krikstolaityte, Vida; Kuliesius, Jurgis; Ramanaviciene, Almira; Mikoliunaite, Lina; Kausaite-Minkstimiene, Asta; Oztekin, Yasemin; Ramanavicius, ArunasIn this study 'green', environmentally friendly enzymatic reaction-based synthesis of conducting polymer polythiophene (PTP) is proposed. Glucose oxidase (GO(x)) was shown as an effective catalyst, which, in the presence of glucose, produces hydrogen peroxide suitable for the oxidative polymerization of PTP under ambient conditions at neutral pH. Enzymatically induced formation of the PTP layer over GO(x)-modified graphite rod electrode (GRE) was demonstrated and evaluated amperometrically and by attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectroscopy. Surface morphology of GO(x)- and PTP-modified GR electrodes was characterized by atomic force microscopy. It was clearly shown that the apparent kinetic Michaelis constant (K-M(app.)) of GO(x)/PTP-modified GRE increased by increasing the duration of polymerization reaction. Therefore, enzymatic polymerization could be applied in adjustment and/or tuning of K-M(app.) and other kinetic parameters of GO(x)-based electrodes used in biosensor design. (C) 2014 Elsevier Ltd. 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 Evaluation of Some Redox Mediators in the Design of Reagentless Amperometric Glucose Biosensor(WILEY-V C H VERLAG GMBH, 2014) Kausaite-Minkstimiene, Asta; Mazeiko, Viktor; Ramanaviciene, Almira; Oztekin, Yasemin; Solak, Ali Osman; Ramanavicius, ArunasThe influence of redox mediators (tetrathiafulvalene (TTF), tetrathiafulvalene-tetracyanoquinodimethane complex (TTF-TCNQ), phenazine methosulfate (PMS), 5,6-diamino-1,10-phenonthroline (5,6-DAP), potassium ferrocyanide (K4[Fe(CN)6]), methylene blue (MB) and toluidine blue (TB)) on the response of amperometric glucose biosensor was investigated in this research. Graphite rod electrode (GRE) modified by adsorbed mediator and glucose oxidase (GOx) cross-linked with glutaraldehyde was served as working electrode. The highest amperometric signals were observed by using TTF and TTF-TCNQ as mediators. The impact of amount of immobilized GOx, an optimal pH region for operation, stability and reproducibility of the analytic signal of designed biosensor using these mediators were investigated and discussed.Öğe Evaluation of the Redox Mediating Properties of 1,10-Phenanthroline-5,6-dione for Glucose Oxidase Modified Graphite Electrodes(ELECTROCHEMICAL SOC INC, 2014) Ramanavicius, Arunas; Genys, Povilas; Oztekin, Yasemin; Ramanaviciene, Almira1,10-Phenanthroline-5,6-dione and glucose oxidase modified and unmodified graphite rod electrodes (GRE) were investigated in buffer with 0.04 mol*L-1 of glucose by electrochemical impedance spectroscopy (EIS). The EIS was conducted under potentiostatic conditions and showed relatively good stability. The impedimetric results were evaluated using estimated equivalent circuit. The EIS based study demonstrated redox mediating properties of 1,10-phenanthroline-5,6-dione deposited on GRE. EIS characteristics observed in this study show that electrodes modified by both 1,10-phenanthroline-5,6-dione and glucose oxidase can be used as an impedimetric glucose biosensor. (C) 2013 The Electrochemical Society. All rights reserved.Öğe Investigation of the separation of metal mixtures using cation-exchange membranes(ELSEVIER SCIENCE BV, 2009) Yazicigil, Zafer; Oztekin, YaseminThe process, called electrodeposition, was used for recovery of metals from aqueous solutions. The aqueous solutions of the sulfate forms of copper and cobalt metals were used as the catholyte solution and 0.1 M NaNO3 was used as an anolyte solution. The effect of current density, metal concentration and type of the cation-exchange membrane to the recovery of metals were investigated, optimum conditions were obtained and % recovery value (%R) for each metal was calculated. At the end of this study, it was observed that, in general, for each metal the recovery of metal increased with current density and concentration. On the other hand, it was determined that %R value increased in the order of CMB >CMX >CMS membrane type. All experiments were carried out at room temperature and the concentration of metals was determined with an atomic absorption spectrophotometer.
