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Öğe 4-aminothiophenol-intercalated montmorillonite: Organic-inorganic hybrid material as an immobilization support for biosensors(Elsevier Science Sa, 2020) Yilmaz, Yahya Yasin; Yalcinkaya, Esra Evrim; Demirkol, Dilek Odaci; Timur, SunaHybrid materials containing organic and inorganic structures are very important because they have the advantages of each of their components. Intercalation of the organic molecule to inorganic structures such as clay allows the preparation of multifunctional new immobilization matrices that contain both the strength properties of the clays and the properties of the organic molecule such as its functional groups (amine, carboxyl or hydroxyl etc.). in this study, 4-aminothiophenol intercalated montmorillonite (4ATP-Mt) was prepared and used as an immobilization layer for the pyranose oxidase (PyOx) enzyme on a glassy carbon (GC) electrode. Firstly, 4ATP intercalation of Mt was carried out, and the success of intercalation was proven using Fourier-Transform Infrared Spectroscopy (FTIR), X-ray Diffractometer (XRD), and Thermogravimetric Analysis (TGA) techniques. Then PyOx was immobilized using 4ATP-Mt, BSA and glutaraldehyde as a cross-linker on the surface of GC electrodes. To show the coating steps for the preparation of 4ATP-Mt/PyOx biosensors, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques were applied, and surface morphology was visualized by scanning electron microscopy (SEM). After optimization of working conditions, analytical performance parameters were determined for glucose detection. the 4ATP-Mt/PyOx biosensor exhibited a wide linear concentration range between 0.01 and 0.5 mM (LOD: 1.0 mu M) for glucose. Additionally, the fabricated 4ATP-Mt/PyOx was assayed for the analysis of glucose in artificial body fluids and drinks.Öğe Amine-intercalated montmorillonite matrices for enzyme immobilization and biosensing applications(Royal Soc Chemistry, 2012) Seleci, Muharrem; Ag, Didem; Yalcinkaya, Esra Evrim; Demirkol, Dilek Odaci; Guler, Cetin; Timur, SunaClay based biosensors were developed using montmorillonite (Mont) modified with methyl (M) and dimethylamine (DM). X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric measurements were used to characterize the modified clays. After immobilization of glucose oxidase (GOx) via clay on the glassy carbon electrode, its application as a glucose biosensor was investigated in detail. The best response characteristics were obtained by DM-Mont and optimization of enzyme amount, reproducibility of biosensor fabrication, repeatability of measurements and operational stability were all evaluated. The optimized biosensor showed a very good linearity between 0.05 mM and 1.0 mM, a 7 s response time and a limit of detection to glucose of 0.038 mM. Also, kinetic parameters and stabilities were determined. Apparent K-m and I-max values were found as 0.73 mM and 2.955 mu A, respectively. As well as batch configuration, the DM-Mont/GOx biosensor was successfully applied in the flow injection analysis mode. Finally, the performance of the DM-Mont/GOx biosensor to analyze glucose in a wine sample was compared with HPLC.Öğe 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, SunaThe 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.Öğe Application of Biofunctionalized Magnetic Nanoparticles Based-Sensing in Abused Drugs Diagnostics(Amer Chemical Soc, 2020) Sanli, Serdar; Ghorbani-Zamani, Faezeh; Moulahoum, Hichem; Gumus, Zinar Pinar; Coskunol, Hakan; Demirkol, Dilek Odaci; Timur, SunaReal-time detection of substance use is an approach of high interest leading to the optimization of behavioral interventions and drug abuse intervention. the current methods in use suffer many limitations and need high logistical and laboratory requirements. Biosensors have shown a great potential in overcoming these limitations. in the present study, the electrochemical biosensor composed of a screen-printed electrode (SPE) was designed for the detection of synthetic cannabinoid (SC). Antibody-immobilized magnetic nanoparticles were also used to create a surface on the transducer with magnetic interactions in order to detect JWH-073 as a SC model. the use of immobilized magnetic nanoparticles to create working surfaces makes the electrode a reusable SPE which can be reutilized after the cleansing. To examine and observe any possible changes on the surface due to its interaction with the analyte, different electrochemical techniques such as differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectrometry were applied. Based on the obtained results, the linearity of the biosensor was found between 5 and 400 ng/mL, and the detection limit was calculated as 22 ng/mL (n = 6) using the 3 Sb/m formula. the biosensor functionality was studied in the presence of some related interferents that showed lower responses than JWH-073, thus demonstrating the good selectivity of the prepared biosensor. Finally, the sensory platform was used to test synthetic urine sample, and the results were compared with obtained results from liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS), which showed that the proposed method could be utilized to identify abuse drugs.Öğe Bienzymatic fluorescence detection based on paraoxonase and laccase on anthracene-sequestered polyamic acid films: A novel approach for inhibition-based sensors(Elsevier, 2020) Esen, Elif; Yazgan, Idris; Demirkol, Dilek OdaciA fluorescence assay based on paraoxonase (PO) and laccase (Lac) immobilized on anthracene-sequestered polyamic acid films is now being reported for the first time for ciprofloxacin (CFx) detection. in enzymatic reaction, PO converts phenyl acetate (PA) to acetic acid and phenol. The formed phenol is further oxidized by laccase using oxygen as a co-substrate. For indirectly fluorescence measurements of PA hydrolysis, increased fluorescence intensity was measured after oxygen consumption by laccase. This is because oxygen is quencher of anthracene (Ant) incorporated in the sequestered poly(amic) acid (PAA) film. The detection mechanism was based on inhibition of PO activity by CFx. Using PAA provided the advantage of controlling the film thickness. Firstly, morphology of PAA-Ant polymeric film was characterized by scanning electron microcopy (SEM) and the success of PO-Lac immobilization on PAA-Ant was proven by SEM plus Energy-dispersive X-ray spectroscopy (SEM-EDX) and fluorescence measurements. Then Ant-PAA/PO/Lac is calibrated for PA and CFx without any interfering of some potential interferences. All results make it a promising tool for monitoring CFx at minute levels in samples.Öğe Bioconjugation and Applications of Amino Functional Fluorescence Polymers(Wiley-V C H Verlag Gmbh, 2017) Geyik, Caner; Guler, Emine; Gumus, Zinar Pinar; Barlas, Firat Baris; Akbulut, Huseyin; Demirkol, Dilek Odaci; Timur, Suna; Yagci, YusufSynthesis and novel applications of biofunctional polymers for diagnosis and therapy are promising area involving various research domains. Herein, three fluorescent polymers, poly(p-phenylene-co-thiophene), poly(p-phenylene), and polythiophene with amino groups (PPT-NH2, PPP-NH2, and PT-NH2, respectively) are synthesized and investigated for cancer cell targeted imaging, drug delivery, and radiotherapy. Polymers are conjugated to anti-HER2 antibody for targeted imaging studies in nontoxic concentrations. Three cell lines (A549, Vero, and HeLa) with different expression levels of HER2 are used. In a model of HER2 expressing cell line (A549), radiotherapy experiments are carried out and results show that all three polymers increase the efficacy of radiotherapy. This effect is even more increased when conjugated to anti-HER2. In the second part of this work, one of the selected polymers (PT-NH2) is conjugated with a drug model; methotrexate via pH responsive hydrazone linkage and a drug carrier property of PT-NH2 is demonstrated on neuroblastoma (SH-SY5Y) cell model. Our results indicate that, PPT-NH2, PPP-NH2, and PT-NH2 have a great potential as biomaterials for various bioapplications in cancer research.Öğe Biofunctional quantum dots as fluorescence probe for cell-specific targeting(Elsevier Science Bv, 2014) Ag, Didem; Bongartz, Rebecca; Dogan, Leyla Eral; Seleci, Muharrem; Walter, Johanna-G.; Demirkol, Dilek Odaci; Stahl, Frank; Ozcelik, Serdar; Timur, Suna; Scheper, ThomasWe describe here the synthesis, characterization, bioconjugation, and application of water-soluble thioglycolic acid TGA-capped CdTe/CdS quantum dots (TGA-QDs) for targeted cellular imaging. Antihuman epidermal growth factor receptor 2 (HER2) antibodies were conjugated to TGA-QDs to target HER2-overexpressing cancer cells. TGA-QDs and TGA-QDs/anti-HER2 bioconjugates were characterized by fluorescence and UV-Vis spectroscopy, X-ray diffraction (XRD), hydrodynamic sizing, electron microscopy, and gel electrophoresis. TGA-QDs and TGA-QDs/anti-HER2 were incubated with cells to examine cytotoxicity, targeting efficiency, and cellular localization. The cytotoxicity of particles was measured using an MIT assay and the no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50), and total lethal concentration (TLC) were calculated. To evaluate localization and targeting efficiency of TGA-QDs with or without antibodies, fluorescence microscopy and flow cytometry were performed. Our results indicate that antibody-conjugated TGA-QDs are well-suited for targeted cellular imaging studies. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.Öğe Biofunctionalization of PAMAM-montmorillonite decorated poly (epsilon-caprolactone)-chitosan electrospun nanofibers for cell adhesion and electrochemical cytosensing(Elsevier Advanced Technology, 2018) Kirbay, Fatma Ozturk; Yalcinkaya, Esra Evrim; Atik, Gozde; Evren, Gizem; Unal, Betul; Demirkol, Dilek Odaci; Timur, SunaThe construction and biofunctionalization of the poly (C-caprolactone) (PCL)-chitosan (CHIT) nanofibrous mats, which included Polyamidoamine (PAMAM) dendrimer modified montmorillonite (Mt), for the cell adhesion and electrochemical cytosensing were accomplished in this report. After the intercalation of the PAMAM generation zero dendrimer into the Mt, PAMAM-Mt decorated PCL-CHIT electrospun nanofibers were formed. The addition of PAMAM caused the decrease of contact angle of PCL-CHIT nanofibers. The covalent immobilization of a tripeptide namely Arginylglycylaspartate (RGD) on both the PCL-CHIT/Mt and PCL-CHIT/PAMAM-Mt surface was carried out. U87-MG and HaCaT (negative control) cell lines were incubated on the PCL-CHIT/Mt/RGD and PCL-CHIT/PAMAM-Mt/RGD. The proliferation studies and imaging of the cells were carried out on these fibers. Finally, electrochemical measurements were performed after each modification step by differential pulse/cyclic voltammetry and electrochemical impedance spectroscopy. U87-MG cells were grown better than HaCaT cells on the PCL-CHIT/PAMAM-Mt/RGD surfaces. To the best of our knowledge, there is no study that developed electrochemical cytosensor using electrospun nanofibers as a cell adhesion platform.Öğe BIOFUNCTIONALIZED NANOMATERIALS FOR TARGETING CANCER CELLS(Elsevier Science Bv, 2017) Guler, Emine; Demir, Bilal; Guler, Bahar; Demirkol, Dilek Odaci; Timur, Suna; Ficai, A; Grumezescu, AMÖğe Biomimetic-electrochemical-sensory-platform for biomolecule free cocaine testing(Elsevier Science Bv, 2018) Sengel, Tulay Yilmaz; Guler, Emine; Arslan, Mustafa; Gumus, Z. Pinar; Sanli, Serdar; Aldemir, Ebru; Akbulut, Huseyin; Demirkol, Dilek Odaci; Coskunol, Hakan; Timur, Suna; Yagci, YusufA biomimetic cocaine sensor was fabricated by using poly(p-phenylene) (PPP) with cyclodextrin (CD) units in the backbone and poly(ethylene glycol) (PEG) side chains (PPP-CD-g-PEG). The sensory platform was constructed by one step surface modification of glassy carbon electrode with PPP-CD-g-PEG by drop coating. The electrochemical measurements are based on the formation of CD-cocaine inclusion complex on the surface resulting in a significant decrease in electron transfer capacity of the selected redox probe. The changes in the surface features due to cocaine binding were explored via electrochemical techniques such as differential pulse voltammetry, cyclic voltammetry and electrochemical impedance spectrometry. The sensor exhibited linearity in the range of 25-200 nM cocaine, LOD was calculated as 28.62 nM (n = 5) according to 3Sb/m formula. Finally, the sensory platform was successfully applied for the cocaine analysis in synthetic urine samples and correlated with the chromatographic method.Öğe Brilliant green sequestered poly(amic) acid film for dual-mode detection: Fluorescence and electrochemical enzymatic biosensor(Elsevier Science Sa, 2018) Maiga, Mohomodou; Yazgan, Idris; Kariuki, Victor M.; Demirkol, Dilek Odaci; Sadik, Omowunmi A.; Timur, SunaHerein, we report a facile technique to fabricate fluorescent polymeric structure, brilliant-green sequestered poly(amic) acid film (BG-PAA), as enzyme support-material for biosensor applications. The structure and fluorescence properties of the fabricated BG-PAA membrane were investigated using H-1 NMR, scanning electron microscopy (SEM) and fluorescence microscopy. Glucose oxidase (GOx) was used as a model enzyme that immobilized on BG-PAA membrane using glutaraldehyde. The created BGPAA/GOx membrane was utilized to fabricate dual-purpose as fluorescent and electrochemical biosensors for the determination of glucose in beverages. Utilization of the dissolved oxygen in GOx mediated glucose oxidation resulted in alteration of the measured fluorescence and current intensity. In the fluorescence assay, the decreased concentration of oxygen causes the increased fluorescence intensity due to the elimination of quenching effect of oxygen on BG fluorescence. In amperometric assay, decrease in oxygen concentration was followed at -0.7 V. After optimization of working conditions linearity, limit of detection and repeatability of system were determined. Finally, BG-PAA/GOx was tested to analyze glucose in beverages. (C) 2017 Elsevier B.V. All rights reserved.Öğe Caffeic Acid Detection Using an Inhibition-Based Lipoxygenase Sensor(Springer, 2012) Demirkol, Dilek Odaci; Gulsunoglu, Baran; Ozdemir, Caglar; Dincer, Ayse; Zihnioglu, Figen; Timur, SunaAn 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.Öğe Calixarene modified montmorillonite: a novel design for biosensing applications(Royal Soc Chemistry, 2014) Sonmez, Burak; Sayin, Serkan; Yalcinkaya, Esra Evrim; Seleci, Didem Ag; Yildiz, Huseyin Bekir; Demirkol, Dilek Odaci; Timur, SunaHere we report the synthesis, characterization and application of calixarene (Calix) modified montmorillonite (Mt) as a platform for bio-applications such as biomolecule immobilization and biosensing technologies. This modification enhanced the biomolecule immobilization capability of Mt. Initially, amino-functionalised calixarenes (Calix-NH2) were synthesized and used as a modifier. X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric analysis were performed to verify the modification of the clay minerals. For the biosensor construction, Calix-NH2 modified Mt (Calix-NH2/Mt), bovine serum albumin (BSA), glutaraldehyde (GA) and pyranose oxidase were immobilized on the surface of a glassy carbon electrode which was then referred to as a CalixNH(2)/ Mt/PyOx biosensor. After optimization of the enzyme amount and pH, analytical characteristics were investigated in detail.Öğe Carbon Nanotube Modified Screen Printed Electrodes: Pyranose Oxidase Immobilization Platform for Amperometric Enzyme Sensors(2017) Demirkol, Dilek Odaci; Özdemir, Çağlar; Pılloton, Roberto; Timur, SunaHere, a novel enzymatic biosensor was developed using multiwalled carbon nanotube including screen printed electrodes (MWCNT?SPE). Pyranose oxidase (PyOx) was immobilized on the electrode surface by way of gelatin membrane and then cross?linked using glutaraldehyde. Glucose was detected at ? 0.7 V (vs. Ag/AgCl) by watching consumed oxygen in enzymatic reaction after addition substrate. After optimization of pH and enzyme loading, the linearity was found in the range of 0.1–1.0 mM of glucose. After that, the effect of MCNT on the current was tested. Also the enzymatic biosensor including glucose oxidase instead of pyranose oxidase was prepared and the biosensor response followed for glucose. Furthermore, this system was tested for glucose analysis in soft drinks.Öğe Catalase-conjugated surfaces: H2O2 detection based on quenching of tryptophan fluorescence on conducting polymers(Pergamon-Elsevier Science Ltd, 2021) Gelen, Sultan Sacide; Munkhbat, Tuvshinjargal; Rexhepi, Zuale; Kirbay, Fatma Ozturk; Azak, Hacer; Demirkol, Dilek OdaciConducting polymers are promising materials used to prepare electrochemical and optical detection platforms for bioanalytical systems. After conjugation of biomolecules onto electmpolymerized monomers for preparation of multifunctional surfaces, they can be used to easily monitor small molecules, macromolecules, and cells. in this study, multifunctional monomer with indole (necessary for fluorescence detection of H2O2) and carboxyl functional groups (necessary for covalent immobilization of biological material) was synthesized, electropolymerized, modified with biomolecules (catalase) and then applied for the selective detection of target analyte (H2O2). Tryptophan sequestered dithione [3,2-b:2',3'-d] pyrmle (DTP-Trp) was synthesized and electropolymerized on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates, which is a transparent support. Afterward, catalase (CAT) was immobilized on the Poly(DTP-Trp) using a zero-length crosslinker, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC), via covalent bonds between carboxyl groups of CAT and amino groups of Poly(DTP-Trp). Surface characterization of Poly(DTP-Trp)/CAT was done by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). The presence of Poly(DTP-Trp)/CAT on ITO-PET surfaces were also confirmed by electrochemical methods to show the success of support modification. Determination of H2O2 was investigated using fluorescence spectrometry based on quenching mechanism of H2O2 on the fluorescence of tryptophan. After optimization of working conditions of Poly(DTPTrp)/CAT, H2O2 detection in synthetic samples was done without any interference of the matrices.Öğe Cells-on-nanofibers: Effect of polyethyleneimine on hydrophobicity of poly-epsilon-caprolacton electrospun nanofibers and immobilization of bacteria(Elsevier Science Inc, 2019) Gordegir, Meleknur; Oz, Sultan; Yezer, Irem; Buhur, Merve; Unal, Betul; Demirkol, Dilek OdaciAmong other synthetic polymers, poly-E-caprolacton (PCL) nanofibers are one of the most popular ones, especially in tissue engineering application due to its distinct mechanical and chemical properties. However, in some cases, lacking functional group on polymer structure obstructs the covalent modification of the PCL nanofibers for the aim. Herein, polyethyleneimine (PEI) was blended with PCL polymer to provide functional amino groups on the surface of the nanofiber mat. PCL-PEI nanofiber was successfully constructed and preparation parameters were optimized. Scanning electron microscopy (SEM) and contact angle measurements were carried out to characterize the PCL-PEI nanofiber. After characterization, Gluconobacter oxydans was immobilized on the surface by the help of glutaraldehyde chemistry. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements were carried out to prove the success of surface modification. In addition, scanning electron microscopy images were also taken after the immobilization of G. oxydans on PCL-PEI nanofiber mat. For the first time in this study, one microorganism was immobilized onto the electrospun nanofiber mat by covalent modification. In conclusion, PCL-PEI/G. oxydans whole-cell biosensor was tested for sensing of glucose as a model analyte.Öğe Cellulose acetate-chitosan based electrospun nanofibers for bio-functionalized surface design in biosensing(Springer, 2020) Yezer, Irem; Demirkol, Dilek OdaciProduction of multifunctional biomaterials in nanoscale is one of the most popular topics in nanotechnology related to biological applications because of its biocompatibility and biodegradability. Herein, cellulose acetate (CA) was blended with chitosan (CS) for the formation of non-soluble electrospun nanofibers in aqueous medium. Amine-functionalized nanofiber surfaces were obtained using carbohydrates, which is an advantage for biomolecule immobilization by covalent bonds. Different solvent systems and CA-CS feeding ratio were examined to obtain ultrafine non-beaded nanofibers. After showing the surface characteristics of CA-CS nanofibers, glucose oxidase (GOx) was immobilized on CA-CS coated electrode by covalent conjugation. Cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy measurements were carried out to prove the surface modification. Finally, CA-CS/GOx platform was investigated to detect glucose in samples and some potential interfering compounds were tested to find out the performance of CA-CS/GOx. CA-CS electrospun nanofibers were well-characterized and applied successfully to fabricate repeatable electrochemical enzymatic biosensor for the first time in this paper.Öğe Chitosan matrices modified with carbon nanotubes for use in mediated microbial biosensing(Springer Wien, 2011) Demirkol, Dilek Odaci; Timur, SunaWe describe a microbial sensor based on Pseudomonas fluorescens cells that was prepared by modifying graphite electrodes with chitosan and carbon nanotubes. Chronoamperometry was performed at +0.3 V in the presence of hexacyanoferrate as a mediator and revealed a good response to glucose which is linear in the 1.0 to 5.0 mM concentration range. Linearity was defined by the equation of y = 102.120x-13.279 (R (2) = 0.998) (y shows current density as nA.cm(-2) and x shows glucose concentration in mM). The effect of the CNTs on the response was compared to that of electrodes made without CNTs.Öğe Chitosan-ferrocene film as a platform for flow injection analysis applications of glucose oxidase and Gluconobacter oxydans biosensors(Elsevier Science Bv, 2012) Yilmaz, Ovgu; Demirkol, Dilek Odaci; Gulcemal, Suleyman; Kilinc, Ali; Timur, Suna; Cetinkaya, BekirChitosan-ferrocene (CHIT-Fc) hybrid was synthesized through covalent modification and its electrochemical properties in immobilized form were studied by using cyclic voltammetry. The hybrid film exhibited reversible electrochemistry with a formal potential of +0.35V (vs. Ag/AgCl) at pH 5.5. The Fc in CHIT matrix retained its electrocatalytic activity and did not diffuse from the matrix. This redox-active hybrid was further employed as a support for immobilization of glucose oxidase (GOx) and whole cells of Gluconobacter oxydans using glutaraldehyde on a glassy carbon electrode (GCE). The experimental conditions were optimized and the analytical characteristics of enzyme and microbial biosensors were evaluated for glucose in flow injection analysis (FIA) system. Under optimized conditions, both enzyme and microbial biosensors exhibited wide linear ranges for glucose from 2.0 to 16.0 mM and from 1.5 to 25.0 mM, respectively. Moreover, the biosensors have the advantages of relatively fast response times, good reproducibility and stability in FI mode. It was demonstrated that CHIT-Fc provides a biocompatible microenvironment for both bioctalysts and an electron transfer pathway. Additionally, integration of the enzyme and microbial biosensors into the FIA system has several advantages including capability of automation and high throughput at low cost. This promising redox hybrid can be utilized as an immobilization matrix for biomolecules in biosensor systems. (C) 2012 Elsevier B.V. All rights reserved.Öğe Comparative cell adhesion properties of cysteine extended peptide architectures(Royal Soc Chemistry, 2016) Soylemez, Saniye; Demir, Bilal; Eyrilmez, Gizem Oyman; Kesici, Seckin; Saylam, Aytul; Demirkol, Dilek Odaci; Ozcubukcu, Salih; Timur, Suna; Toppare, LeventThis study presents the comparative cell attachment investigation of TAT and well-known RGD peptide modified surfaces. Initially, cysteine containing arginine-glycine-aspartic acid (RGD) and TAT peptides, a class of cell penetration peptides, were synthesized. Gold film coated indium tin oxide (gold/ITO) surfaces were coated with RGD and TAT peptides and used for cell culture applications. Thiol groups on the peptides provide post-modification of the surface. The efficient bonding of the peptides with the modified surface brings proper attachment of the cells. The peptide modified surfaces were tested for adhesion of several cell lines such as monkey kidney epithelial cell (Vero), human cervical carcinoma cell (HeLa), human glioblastoma cell (U87-MG) and human immortalized skin keratinocyte cell (HaCaT) lines. These cells were cultured on RGD and TAT modified gold/ITO surfaces. Cell imaging studies were performed on these surfaces using fluorescence microscopy technique. Scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and contact angle measurements were carried out for the surface characterization. The results indicate that the RGD and TAT modified surfaces exhibited better cell adhesion. Therefore, besides RGD as a well-known adhesion peptide, TAT functionalized substrates were found to be efficient bio-sensing candidates for further studies.