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Öğe Alcohol Biosensing by Polyamidoamine (PAMAM)/Cysteamine/Alcohol Oxidase-Modified Gold Electrode(Wiley, 2010) Akin, Mehriban; Yuksel, Merve; Geyik, Caner; Odaci, Dilek; Bluma, Arne; Hoepfner, Tim; Beutel, Sascha; Scheper, Thomas; Timur, SunaA highly stable and sensitive amperometric alcohol biosensor was developed by immobilizing alcohol oxidase (A OX) through Polyamidoamine (PAMAM) dendrimers on a cysteamine-modified gold electrode surface. Ethanol determination is based on the consumption of dissolved oxygen content due to the enzymatic reaction. The decrease in oxygen level was monitored at -0.7 V vs. Ag/AgCl and correlated with ethanol concentration. Optimization of variables affecting the system was performed. The optimized ethanol biosensor showed a wide linearity from 0.025 to 1.0 mM with 100 s response time and detection limit of (LOD) 0.016 mM. In the characterization studies, besides linearity some parameters such as operational and storage stability, reproducibility, repeatability, and substrate specificity were studied in detail. Stability studies showed a good preservation of the bioanalytical properties of the sensor, 67% of its initial sensitivity was kept after 1 month storage at 4 degrees C. The analytical characteristics of the system were also evaluated for alcohol determination in flow injection analysis (FIA) mode. Finally, proposed biosensor was applied for ethanol analysis in various alcoholic beverage as well as offline monitoring of alcohol production through the yeast cultivation. (C) 2010 American Institute of Chemical Engineers Biotechnol. Prog., 26: 896-906, 2010Öğe A new set up for multi-analyte sensing: At-line bio-process monitoring(Elsevier Advanced Technology, 2011) Akin, Mehriban; Prediger, Andreas; Yuksel, Merve; Hoepfner, Tim; Demirkol, Dilek Odaci; Beutel, Sascha; Timur, Suna; Scheper, ThomasA multi-analyte sensing device is described, for simultaneous at-line monitoring of glucose, ethanol, pO(2)-value and cell density. It consists of a dual biosensor, a modified microscope and a fiber optical pO(2)-sensor that are integrated into a flow analysis (FA) system. The biosensor is based on a conventional thin layer flow-through cell equipped with a gold (Au) dual electrode (serial configuration). The biosensors with no cross-talking were produced by modifying the electrochemical transducers. Each Au surface was initially modified by self-assembled monolayer (SAM) of cysteamine. Alcohol oxidase (AOx) and pyranose oxidase (PyOx) were immobilized each onto a gold surface by means of PAMAM (polyamidoamine) dendrimer via glutaraldehyde cross-linking. The responses for glucose and ethanol were linear up to 0.5 mM. The operational stability of the biosensors was very promising, after 11 h continuous operation, only 6.0% of the initial activity was lost. The potential of the described biosensor was demonstrated by parallel determination of ethanol and glucose in yeast fermentation process. Simultaneously the cell density of the culture was monitored with an in situ microscope (ISM), which was integrated into the FA system. Both the used in situ microscope and the image processing algorithm used for the analysis of the acquired image data are described. Furthermore the pO(2)-value was monitored using a fiber optical sensor, which was embedded in a flow cell. The multi-sensor device allows the at-line monitoring of several process values without the need for further sampling or time consuming offline measurements. (C) 2011 Elsevier B.V. All rights reserved.Öğe 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, ThomasThis 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, 2011Öğe PAMAM-functionalized water soluble quantum dots for cancer cell targeting(Royal Soc Chemistry, 2012) Akin, Mehriban; Bongartz, Rebecca; Walter, Johanna G.; Demirkol, Dilek Odaci; Stahl, Frank; Timur, Suna; Scheper, ThomasHerein, the phase-transfer reaction of quantum dots (QDs) with amine-terminated polyamidoamine (PAMAM) dendrimers with controllable ligand molar ratios was achieved. The unique properties of PAMAM allowed us to build up structurally and electrostatically stabilized water soluble QD complexes. Synthesized conjugates were characterized in terms of fluorescence and UV-Vis profiles, hydrodynamic size, number of surface dendrimer groups, and stability. Cytotoxic effects of conjugates for MCF-7, A-549 and HEP-G2 cancer cells were assessed based on cell viability using MTT assay. Cytotoxicity results were expressed as no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50) and total lethal concentration (TLC) values (mu M). Furthermore, HER2 receptor-mediated targeting efficiency of antibody labelled P/QDs conjugates was evaluated by successful staining of MCF-7 cells with bioconjugates. Uniquely, effective cell internalization was achieved with well-characterized antibody coupled P/QDs in contrast to antibody free P/QDs conjugates. Fluorescence microscopy images demonstrated that the designed PAMAM-derivatized QDs nanoparticles show great potential in the areas of cellular imaging and targeted therapy.Öğe Synthesis and application of poly-SNS-anchored carboxylic acid: a novel functional matrix for biomolecule conjugation(Royal Soc Chemistry, 2011) Ekiz, Fulya; Oguzkaya, Funda; Akin, Mehriban; Timur, Suna; Tanyeli, Cihangir; Toppare, LeventHere we report the synthesis of a novel conducting polymer and its properties as an immobilization platform for biosensor application. The conducting polymer has functional groups used for the formation of amide bonding with the enzyme immobilized on the polymer surface. After covalent immobilization of glucose oxidase (GOx) on the polymeric matrix, its application for glucose biosensing was investigated in detail. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to monitor the surface properties of the polymer before and after biomolecule conjugation. The optimized biosensor showed a very good linearity between 0.01 mM and 1.2 mM, a 13 s response time and a detection limit (LOD) of 0.004 mM to glucose. Also, kinetic parameters, operational and storage stabilities were determined. Apparent Michaelis constant (K-m(app)) and I-max values of 1.17 mM and 11.28 mu A, respectively, were obtained.