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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 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 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 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 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.
