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    Amine intercalated clay surfaces for microbial cell immobilization and biosensing applications
    (Royal Soc Chemistry, 2013) Demir, Bilal; Seleci, Muharrem; Ag, Didem; Cevik, Serdar; Yalcinkaya, Esra Evrim; Demirkol, Dilek O.; Anik, Ulku; Timur, Suna
    Trimethylamine (TM) intercalated montmorillonite (Mont) clay was prepared and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric measurements. Gluconobacter oxydans cells were immobilized on the micro-structured matrix and used in microbial sensor applications. Sensor responses were based on the respiratory activity of the cells and the consumption of oxygen was monitored at 20.7 V (vs. Ag/AgCl and platinum electrodes) by using glucose as a substrate. Stabilization of the bacteria was performed on the Mont using glutaraldehyde. Optimization of the TM-Mont/G. oxydans sensor and examination of the electrochemical mechanism were carried out in a batch system. Measurements concerning analytical characteristics, operational stability, repeatability and substrate specificity depending on the carbon source in the culture were investigated in a flow injection analysis (FIA) system. Linear ranges were found between 0.15 and 5.0 mM for the batch mode and 0.1 and 5.0 mM for the FIA system, respectively. Finally, real samples were analyzed and were compared with the results of a spectrophotometric method as reference.
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    Amine intercalated clay surfaces for microbial cell immobilization and biosensing applications
    (Royal Soc Chemistry, 2013) Demir, Bilal; Seleci, Muharrem; Ag, Didem; Cevik, Serdar; Yalcinkaya, Esra Evrim; Demirkol, Dilek O.; Anik, Ulku; Timur, Suna
    Trimethylamine (TM) intercalated montmorillonite (Mont) clay was prepared and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric measurements. Gluconobacter oxydans cells were immobilized on the micro-structured matrix and used in microbial sensor applications. Sensor responses were based on the respiratory activity of the cells and the consumption of oxygen was monitored at 20.7 V (vs. Ag/AgCl and platinum electrodes) by using glucose as a substrate. Stabilization of the bacteria was performed on the Mont using glutaraldehyde. Optimization of the TM-Mont/G. oxydans sensor and examination of the electrochemical mechanism were carried out in a batch system. Measurements concerning analytical characteristics, operational stability, repeatability and substrate specificity depending on the carbon source in the culture were investigated in a flow injection analysis (FIA) system. Linear ranges were found between 0.15 and 5.0 mM for the batch mode and 0.1 and 5.0 mM for the FIA system, respectively. Finally, real samples were analyzed and were compared with the results of a spectrophotometric method as reference.
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    Amino acid intercalated montmorillonite: electrochemical biosensing applications
    (Royal Soc Chemistry, 2014) Demir, Filiz; Demir, Bilal; Yalcinkaya, Esra E.; Cevik, Serdar; Demirkol, Dilek Odaci; Anik, Ulku; Timur, Suna
    The present work is the first that includes the use of glycine (Gly), lysine (Lys) and glutamic acid (Glu) modified clay mineral matrices in the biosensors. For this purpose, initially, Gly, Lys and Glu were intercalated with montmorillonite (Mt), thus, various modified Mts were obtained. These modified materials were then characterized via X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric analysis (TGA/DTG) and scanning electron microscopy (SEM). In order to investigate the applicability of amino acid modified clay minerals in biosensor areas, glucose oxidase (GOx) was selected as the model enzyme and a GOx based biosensor was prepared. After immobilizing the enzyme with amino acid modified Mt onto a glassy carbon electrode, working conditions like pH and modifier type were optimized. Among the modified Mts, Gly-Mt was the optimum clay mineral type and pH 4.0 was the optimum pH value. Then analytical characteristics were examined under optimum experimental conditions. The linear range of optimum sensor design was 0.1-1.0 mM within the kinetic parameters of an immobilized enzyme K-m(app) m = 0.7 mM, I-max = 107.8 nA. Finally, the developed biosensor was applied to real samples where the results were compared with a spectrophotometric reference method.
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    Biocentri-voltammetric biosensor for acetylcholine and choline
    (Springer Wien, 2012) Cevik, Serdar; Timur, Suna; Anik, Ulku
    We report on the determination of choline and acetylcholine via biocentrivoltammetry. This method combines centrifugation and voltammetry and is based on a carbon paste electrode modified with acetylcholinesterase and choline oxidase. The electrode was placed at the bottom of a biocentrivoltammetric cell. Acetylcholine and choline are accumulated on the enzyme electrode via centrifugative forces, upon which a direct voltammetric scan is applied. Reaction time, pH values, quantities of enzyme and centrifugation parameters were optimized. A linear response is obtained in the 0.07 to 10 mu M concentration range of acetylcholine, and a limit of detection as low as 0.5 mu M. The linear range is between 0.1 and 500 mu M for choline. The method was applied to the determination of acetylcholine and choline in spiked serum samples.
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    Biocentri-voltammetry for the enzyme assay: a model study
    (Royal Soc Chemistry, 2012) Cevik, Serdar; Timur, Suna; Anik, Ulku
    This work constitutes the first biocentri-voltammetric application for acetylcholinesterase (AChE) activity assay. After the optimization of working conditions like reaction time, centrifugation speed and time and enzyme amount, the analytical characteristics were investigated. As a result, the linear range of 1.0-350 mu M was obtained with an equation of y = 0.0004x + 0.0163. The correlation coefficient is equal to (R-2) 0.99 +/- 0.001815 (n = 3) and the RSD value was calculated as 3.6% (n = 4). Then Donepezil-based drug analysis was also conducted by using the developed method and an inhibition of 80% was calculated.
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    Bismuth Film Combined with Screen-Printed Electrode as Biosensing Platform for Phenol Detection
    (Wiley-V C H Verlag Gmbh, 2010) Merkoci, Arben; Anik, Ulku; Cevik, Serdar; Cubukcu, Meliha; Guix, Maria
    Mushroom tissue was immobilized onto plain screen printed electrode (SPE) and multiwalled carbon nanotube (MWCNT) modified SPE (SPE/MWCNT) via bismuth (Bi) deposition. By this way. SPE/Bi/Tissue and SPE/MWCNT/Bi/Tissue biosensors for phenol detection were obtained. UV-visible spectroscopy and SEM were utilized for explain the immobilization procedure. After optimizing working parameters, both biosensors were compared in terms of analytical characteristics. Linear range of response were found as 5-100 mu M for SPE/Bi/Tissue and 2- 200 mu M for SPE/MWCNT/Bi/Tissue while detection limits were calculated as 0.48 mu M and 1.1.7 mu M for SPE/Bi/ Tissue and SPE/MWCNT/Bi/Tissue respectively. Developed systems were also applied for phenol detection in synthetically prepared waste water sample and very promising results were obtained.
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    Bismuth Film Electrode as Sensing Platform for IgE-anti-IgE Interactions
    (Wiley-Blackwell, 2011) Anik, Ulku; Cevik, Serdar; Timur, Suna
    In this study, a bismuth film was used as a sensing platform for immunoreaction assay which includes the interactions between IgE and anti-IgE molecules. For preparing this assay, IgE was deposited on a carbon paste electrode via bismuth(III) cations without using any membrane or functional reagent. The immobilized reagents and interaction of anti-IgE on this formation were monitored by using atomic force microscopy technique and electrochemical impedance spectroscopy. Then some experimental parameters like the effect of IgE amount and the IgE anti-IgE interaction time were optimized. Under the optimal experimental conditions, the binding of anti-IgE was also examined by following current decrease in differential pulse voltammograms of neutral red.
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    Usage of Bismuth Film Electrode as Biosensor Transducer for Alkaline Phosphatase Assay
    (Wiley-V C H Verlag Gmbh, 2010) Anik, Uelkue; Cubukcu, Meliha; Cevik, Serdar; Timur, Suna
    A biosensor for monitoring alkaline phosphatase (ALP) enzyme activity was developed by using bismuth film electrode (BiFE) as transducer. The aim was to test the possible applications of BiFE as transducer in this biosensing platform. ALP was immobilized onto the BiFE electrode by means of gelatin which was then crosslinked by glutaraldehyde. The measurement was based on monitoring of p-nitrophenol which was released after enzymatic reaction of p-nitrophenyl phosphate (pNPP) substrate. The effect of enzyme activity (in Unit) was examined for 100 mu M of pNPP substrate and a good linearity was observed between 1.28 and 4.26 U activities with the equation of y = 0.214x - 0.201 and R(2) = 0.998 where x and y show enzyme activity in unit and current response in mu A respectively. Analytical characteristics were also examined after the optimization of experimental parameters.