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Öğe 1,10-Phenanthroline Derivatives as Mediators for Glucose Oxidase(Elsevier Advanced Technology, 2010) Öztekin, Yasemin; Krikstolaityte, Vida; Ramanaviciene, Almira; Yazıcıgil, Zafer; Ramanavicius, ArunasThis study is focused on possible application of some 1,10-phenanthroline derivatives (PDs) in the development of biosensors and biofuel cells Differently from some other studies, the PDs that were not involved into structures of metal complexes were investigated. Five PDs [1,10-phenanthroline monohydrate (PMH), 5-nitro-1,10-phenanthroline (5NP), 5-amino-1,10-phenanthroline (5AP), 5-amino,6-nitro-1.10-phenanthroline (5A6NP) and 5,6-diamino-1,10-phenanthroline (56DAP)] were selected for this study Bioelectrochemical responses of PDs and glucose oxidase (GOX)-modifiecl graphite rod electrodes (GREs) were studied amperometrically and potentiometrically The best redox mediators for GOX were found on PDs containing amino groups SAP and 56DAP Amperometrical measurements have shown that 5NP derivative was also acting as a redox mediator but activity of 5NP was approximately four times lower than 5AP and three times lower than 56DAP This study clearly illustrates that some PDs can be applied as redox mediators for oxidases and are suitable for the development of reagent-less biosensors and biofuel cells. Since amino groups can be very easily involved in the formation of chemical bounds, the amino-PDs are interesting compounds for the development of nanobiotechnological tools by bottom-up technique.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 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 An electrochemical and computational study for discrimination of D- and L-cystine by reduced graphene oxide/beta-cyclodextrin(ROYAL SOC CHEMISTRY, 2015) Zor, Erhan; Bingöl, Haluk; Ramanaviciene, Almira; Ramanavicius, Arunas; Ersöz, 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 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 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 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 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 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 Molecularly Imprinted Polypyrrole for DNA Determination(WILEY-V C H VERLAG GMBH, 2013) Ratautaite, Vilma; Topkaya, Seda Nur; Mikoliunaite, Lina; Ozsoz, Mehmet; Oztekin, Yasemin; Ramanaviciene, Almira; Ramanavicius, ArunasIn this study graphite electrodes modified by a thin DNA-imprinted polypyrrole layer, which was able to bind specific target-DNA, are reported. For this aim, electrochemical synthesis of polypyrrole was performed on a pencil graphite electrode by cyclic voltammetry (CV) or by potential pulse sequences (PPS). The modified electrode surface was used for electrochemical determination of target-DNA by differential pulse voltammetry. According to our best knowledge this is a first report on the application of DNA-imprinted polymer for the determination of target-DNA. The results showed that the molecularly imprinted polypyrrole (MIPPy) layer that formed on the carbon electrode surface was sensitive for target-DNA, while the nonimprinted polypyrrole layer was not sensitive to the same target-DNA. Comparison of electrodes modified using PPS and CV techniques is presented.Öğe Polyphenol-modified glassy carbon electrodes for copper detection(ELSEVIER SCIENCE SA, 2011) Oztekin, Yasemin; Yazicigil, Zafer; Ramanaviciene, Almira; Ramanavicius, ArunasThe present work reports the preparation of electrochemically polymerized flavone - luteolin and flavonol - kaempferol modified glassy carbon (GC) electrodes (PolyLut/GC and PolyKae/GC, respectively). Electrochemical polymerization was performed by electrochemical oxidation of luteolin and kaempferol by potential cycling in aqueous media. Cyclic voltammograms of luteolin on the GC electrode indicated one clear oxidation peak at +475 mV, which can be assigned to the oxidation of 3'-hydroxyl and 4'-hydroxyl groups in the B-ring of the luteolin molecule. The cyclic voltammograms of kaempferol on the GC electrode contained two oxidation peaks, one at about +390 mV, which is assigned to the oxidation of 4'-hydroxyl and 3-hydroxyl groups of the B-ring and C-ring of the kaempferol molecule, and second oxidation peak at about +710 mV, which is assigned to the 7-hydroxyl group of the A-ring. The interaction of PolyLut/GC and PolyKae/GC electrodes with copper(II) (Cu(II)) ions were investigated by differential pulse voltammetry (DPV). It was determined that PolyLut/GC and PolyKae/GC electrodes showed sensitivity towards Cu(II) with good reproducibility and stability of analytical signal. The effect of the interfering ions on the voltammetric measurements of Cu(II) was examined. (c) 2010 Elsevier B.V. All rights reserved.Öğe Square wave voltammetry based on determination of copper (II) ions by polyluteolin- and polykaempferol-modified electrodes(ELSEVIER SCIENCE BV, 2011) Oztekin, Yasemin; Yazicigil, Zafer; Ramanaviciene, Almira; Ramanavicius, ArunasApplicability of square wave voltammetry for the determination of Cu(II) ions by PolyLut/GC and PolyKae/GC electrodes was evaluated in this study. For this luteolin and kaempferol were electrochemically polymerized on glassy carbon (GC) electrode surface in order to get polyluteolin and polykaempferol-modified glassy carbon electrodes (PolyLut/GC and PolyKae/GC, correspondingly). The formation of polyphenol layer on the GC electrode surface was evidenced by atomic force microscopy. Square wave voltammetry was found to be more sensitive in comparison with differential pulse voltammetry. It was determined that PolyLut/GC and PolyKae/GC electrodes offered great sensitivity towards Cu(II) ions with very low limit of detection, good reproducibility, sufficient stability and excellent selectivity of analytical signal. (C) 2011 Elsevier B.V. All rights reserved.Öğe Visualization of red-ox proteins on the gold surface using enzymatic polypyrrole formation(SPRINGER WIEN, 2011) Ramanaviciene, Almira; Kausaite-Minkstimiene, Asta; Oztekin, Yasemin; Carac, Geta; Voronovic, Jaroslav; German, Natalija; Ramanavicius, ArunasWe describe a new method for the visualization of the activity of red-ox proteins on a gold interface. Glucose oxidase was selected as a model system. Surfaces were modified by adhesion of glucose oxidase on (a) electrochemically cleaned gold; (b) gold films modified with gold nanoparticles, (c) a gold surface modified with self-assembled monolayer, and (d) covalent immobilization of protein on the gold surface modified with a self-assembled monolayer. The simple optical method for the visualization of enzyme on the surfaces is based on the enzymatic formation of polypyrrole. The activity of the enzyme was quantified via enzymatic formation of polypyrrole, which was detected and investigated by quartz microbalance and amperometric techniques. The experimental data suggest that the enzymatic formation of the polymer may serve as a method to indicate the adhesion of active redox enzyme on such surfaces.
