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    Caffeic Acid Detection Using an Inhibition-Based Lipoxygenase Sensor
    (Springer, 2012) Demirkol, Dilek Odaci; Gulsunoglu, Baran; Ozdemir, Caglar; Dincer, Ayse; Zihnioglu, Figen; Timur, Suna
    An inhibition based biosensing system was developed for the caffeic acid as lipoxygenase (LOX) inhibitor. LOX was immobilized in carbon paste electrode and the amperometric detection of hydroperoxy linoleic acid due to the enzymatic reaction using linoleic acid as a substrate was monitored at +0.9 V versus Ag/AgCl. The decrease in biosensor response in the presence of caffeic acid was found to be correlated with the inhibitor concentration. Diode array detector and LOX biosensor was used as an electrochemical detector for the analysis of this compound. All data were given as a comparison of two systems.
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    Design of Carbon Nanotube Modified Conducting Polymer for Biosensing Applications
    (Taylor & Francis Inc, 2011) Ozdemir, Caglar; Tuncagil, Sevinc; Demirkol, Dilek Odaci; Timur, Suna; Toppare, Levent
    An electrochemical biosensor with improved performance was designed through the immobilization of glucose oxidase (GOx) onto conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine (SNS-NH2) modified with carbon nanotubes (CNTs). For the optimization and characterization of the biosensor, pH profile, enzyme loading, reproducibility, operational stability experiments were carried out. It was found that the use of CNTs in a biosensing system enhanced the biosensor response. The linear relation was observed using glucose as the substrate in the range of 0.1-2.0 mM and defined by the equation; y = 8.582x + 2.945 (R2= 0.994, where y and x stand for concentration in mM and current signal as A/cm2). Finally, proposed biosensor was applied for glucose detection in real samples.
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    Gold nanoparticle modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrole-1-l) benzenamine for potential use as a biosensing material
    (Elsevier Sci Ltd, 2011) Tuncagil, Sevinc; Ozdemir, Caglar; Demirkol, Dilek Odaci; Timur, Suna; Toppare, Levent
    Gold nanoparticle (AuNP) modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine (SNS-NH2) was used as the biosensing platform for glucose analysis. Electrochemical measurements were carried out by following the consumed oxygen due to the enzymatic reaction of glucose oxidase (GOx) at -0.7 V vs Ag/AgCl. Optimisation of pH, enzyme loading, stability experiments were carried out. Effect of NP was investigated by monitoring the signal responses at different AuNP sizes and amounts. A linear relation of y = 1.597x + 0.264 (R-2 = 0.993) was found for glucose concentrations between 0.002 and 5.0 mM. The analytical characteristics of the system were also evaluated for glucose determination in flow injection analysis (FIA) mode. Finally, the system was checked for glucose detection on real samples. (C) 2011 Elsevier Ltd. All rights reserved.
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    In situ synthesis of biomolecule encapsulated gold-cross-linked poly(ethylene glycol) nanocomposite as biosensing platform: A model study
    (Elsevier Science Sa, 2010) Odaci, Dilek; Kahveci, Muhammet U.; Sahkulubey, Elif L.; Ozdemir, Caglar; Uyar, Tamer; Timur, Suna; Yagci, Yusuf
    In situ synthesis of poly(ethylene glycol) (PEG) hydrogels containing gold nanoparticles (AuNPs) and glucose oxidase (GOx) enzyme by photo-induced electron transfer process was reported here and applied in electrochemical glucose biosensing as the model system. Newly designed bionanocomposite matrix by simple one-step fabrication offered a good contact between the active site of the enzyme and AuNPs inside the network that caused the promotion in the electron transfer properties that was evidenced by cyclic voltammetry as well as higher amperometric biosensing responses in comparing with response signals obtained from the matrix without AuNPs. As well as some parameters important in the optimization studies such as optimum pH, enzyme loading and AuNP amount, the analytical characteristics of the biosensor (AuNP/GOx) were examined by the monitoring of chronoamperometric response due to the oxygen consumption through the enzymatic reaction at -0.7 V under optimized conditions at sodium acetate buffer (50 mM, pH 4.0) and the linear graph was obtained in the range of 0.1-1.0 mM glucose. The detection limit (LOD) of the biosensor was calculated as 0.06 mM by using the signal to noise ratio of 3. Moreover, the presence of AuNPs was visualized by TEM. Finally, the biosensor was applied for glucose analysis for some beverages and obtained data were compared with HPLC as the reference method to test the possible matrix effect due to the nature of the samples. (C) 2010 Elsevier B.V. All rights reserved.
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    Offline Glucose Biomonitoring in Yeast Culture by Polyamidoamine/Cysteamine-Modified Gold Electrodes
    (Wiley-Blackwell, 2011) Yuksel, Merve; Akin, Mehriban; Geyik, Caner; Demirkol, Dilek Odaci; Ozdemir, Caglar; Bluma, Arne; Hoepfner, Tim; Beutel, Sascha; Timur, Suna; Scheper, Thomas
    This article deals with the use of pyranose oxidase (PyOx) and glucose oxidase (GOx) enzymes in amperometric biosensor design and their application in monitoring fermentation processes with the combination of flow injection analysis (FIA). The amperometric studies were carried out at -0.7 V by following the oxygen consumption due to the enzymatic reactions for both batch and FIA modes. Optimization studies (enzyme amounts and pH) and analytical parameters such as linearity, repeatability, effect of interference, storage, and operational stabilities have been studied. Under optimized conditions, for the PyOx-based biosensor, linear graph was obtained from 0.025 to 0.5 mM glucose in phosphate buffer ( 50 mM) at pH 7.0 with the equation of y = 3.358x + 0.028 and R-2 = 0.998. Linearity was found to be 0.01-1.0 mM in citrate buffer (50 mM and pH 4.0) with the equation of y = 1.539x + 0.181 and R-2 = 0.992 for the GOx biosensor. Finally, these biosensor configurations were further evaluated in a conventional flow injection system. Results from batch experiments provide a guide to design sensitive, stable, and interference-free biosensors for FIA mode. Biosensor stability, dynamic range, and repeatability were also studied in FIA conditions, and the applicability for the determination of glucose in fermentation medium could be successfully demonstrated. The FIA-combined glucose biosensor was used for the offline monitoring of yeast fermentation. The obtained results correlated well with HPLC measurements. (C) 2011 American Institute of Chemical Engineers Biotechnol. Prog., 27: 530-538, 2011