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Öğe Amperometric Glucose Biosensor Based on Glucose Oxidase, 1,10-Phenanthroline-5,6-dione and Carbon Nanotubes(Electrochemical Soc Inc, 2014) Zor, Erhan; Oztekin, Yasemin; Ramanaviciene, Almira; Anusevicius, Zilvinas; Bingol, Haluk; Barkauskas, Jurgis; Ersoz, MustafaA biosensor for glucose determination was fabricated by the immobilization of glucose oxidase (GOx) on carbon nanotubes (CNTs) and/or 1,10-phenanthroline-5,6-dione (PD) modified graphite rod electrodes (GOx/PD/CNTs/GR) and its amperometric response toward glucose was investigated under aerobic and anaerobic conditions. The sensitivity of the GOx/PD/CNTs/GR electrode was found to be higher compared to that of a PD-modified GR electrode without CNTs (GOx/PD/GR), implying that CNTs play an important role in the facilitation of electron transfer between the redox active site of GOx and the electrode surface. The GOx/PD/CNTs/GR biosensor exhibited a linear dependency on substrate concentration in a range from 0.0 until 50.0 mM of glucose with oxygen present and from 0.0 until 62.5 mM of glucose in the absence of oxygen. With oxygen present, the limit of detection (LOD) values were determined to be 5.4 and 8.0 mM, and the limit of quantitation values (LOQ) were calculated as 16.2 and 24 mM for GOx/PD/GR and GOx/PD/CNTs/GR, respectively. In the absence of oxygen, the LOD values were calculated as 4.2 and 10.7 mM, and the LOQ values were calculated as 12.6 and 32.1 mM for GOx/PD/GR and GOx/PD/CNTs/GR, respectively. When examining the interference effect of uric acid for GOx/PD/GR and GOx/PD/CNTs/GR electrodes, no significant changes in the amperometric response of the modified electrodes were observed up to 100.0 mM of uric acid. (C) 2014 The Electrochemical Society. All rights reserved.Öğe Arsenic(V) removal from underground water by magnetic nanoparticles synthesized from waste red mud(Elsevier Science Bv, 2012) Akin, Ilker; Arslan, Gulsin; Tor, Ali; Ersoz, Mustafa; Cengeloglu, YunusIn this study waste red mud (bauxite residue) sample obtained from Seydisehir (Konya, Turkey) was evaluated for the synthesis of Fe3O4 nanoparticles (NPs) in ammonia solution that can be used to remove As(V) from both synthetic and natural underground water samples. The synthesized Fe3O4-NPs were characterized by using TEM, VSM, XRD, SAXS,TGA and FT-IR spectroscopy. The Fe3O4-NPs assumed a near-sphere shape with an average size of 9 nm. The results showed that synthesized Fe3O4-NP5 from waste red mud have satisfactory magnetic properties and As(V) sorption capacity, especially at low equilibrium arsenate concentrations. (c) 2012 Elsevier B.V. All rights reserved,Öğe Chiral sensors(Elsevier Sci Ltd, 2019) Zor, Erhan; Bingol, Haluk; Ersoz, MustafaChirality has a crucial effect on clinical, chemical and biological research since most bioactive substances possess chirality in the natural world. Thus, new effective methods and/or (nano)materials are required to explain chiral recognition of chiral substances, which always become a hot topic in pharmaceutical and chemo/biological study. Recently, the researchers have developed new methods by using (nano) materials which can offer many advantages, and they have received considerable attention in chiral recognition. In this review, we report an overview of chiral sensors in a view of various transduction principles including electrochemical, QCM and optical measurements used for detection and discrimination of chiral molecules. We discuss the general aspects and the used materials for the construction of chiral sensors with selected studies between 2009 and 2019. Additionally, we explore the capabilities of how these materials can help to fabricate simple but efficient chiral sensors. Finally, we discuss the challenges and future outlooks. (c) 2019 Elsevier B.V. All rights reserved.Öğe An electrochemical and computational study for discrimination of D- and L-cystine by reduced graphene oxide/?-cyclodextrin(Royal Soc Chemistry, 2015) Zor, Erhan; Bingol, Haluk; Ramanaviciene, Almira; Ramanavicius, Arunas; Ersoz, MustafaHere, we report a novel enantioselective electrochemical biosensor for the discrimination of cystine enantiomers (D- and L-cystine) using a chiral interface for the specific recognition of D- and L-cystine. The biosensor is based on reduced graphene oxide modified by beta-cyclodextrin (rGO/beta-CD) at the GCE surface. During the preparation of rGO/beta-CD/GCE, the modified electrode surfaces were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The electrochemical behaviours of the D- and L-cystine were investigated using the rGO/beta-CD/GCE by CV and compared to bare GCE. A clear separation between the oxidation peak potentials of D- and L-cystine was observed at 1.32 and 1.42 V, respectively. The electrochemical discrimination performance of the fabricated chiral sensor was also examined by differential pulse voltammetry (DPV) in a mixed solution of D- and L-cystine. In addition, the DPV technique was used for the determination of D- and L-cystine at low concentration values in the range of 1.0-10.0 mM. To investigate the amperometric response of rGO/beta-CD/GCE towards D- and L-cystine, the chronoamperometry technique was used in the concentration range of 10.0-100.0 mu M. The interactions of the enantiomers with rGO/beta-CD were modelled by molecular docking using AutoDock Vina, and the interaction energies were predicted to be -4.8 and -5.3 kcal mol(-1) for D- and L-cystine, respectively. The corresponding values of binding constants were calculated to be 3.32 x 10(3) and 7.71 x 10(3) M-1, respectively. The experimental and molecular docking results indicate that the rGO/beta-CD/GCE has a different affinity for each enantiomer.Öğe An electrochemical biosensor based on human serum albumin/graphene oxide/3-aminopropyltriethoxysilane modified ITO electrode for the enantioselective discrimination of D- and L-tryptophan(Elsevier Advanced Technology, 2013) Zor, Erhan; Patir, Imren Hatay; Bingol, Haluk; Ersoz, MustafaA new electrochemical biosensor based on the human serum albumin/graphene oxide/3-aminopropyl-triethoxysilane modified indium tin oxide electrode (ITO/APTES/GO/HSA) has been developed for the discrimination of tryptophan (Trp) enantiomers. The electrode has been characterized by scanning electron microscopy (SEM) and electrochemical techniques. The electrochemical behaviors of the enantiomeric pairs (D- and L-Trp) at the ITO/APTES/GO/HSA electrode have been investigated by cyclic voltammetry in the concentration range of 0.10-1.0 mM. A clear separation between the oxidation peak potentials of D- and L-Trp, at 0.86 and 1.26 V, respectively, has suggested that the ITO/APTES/GO/HSA electrode can be used as an electrochemical biosensor for the discrimination of Trp enantiomers. In order to find the percentage of an enantiomeric form of tryptophan in a mixture, the ITO/APTES/GO/HSA electrode is used for the simultaneous detection of D- and L-Trp which showed that the percentage of one enantiomeric form can be easily measured in the presence of the other. (c) 2012 Elsevier B.V. All rights reserved.Öğe Graphene Quantum Dots-based Photoluminescent Sensor: A Multifunctional Composite for Pesticide Detection(Amer Chemical Soc, 2015) Zor, Erhan; Morales-Narvaez, Eden; Zamora-Galvez, Alejandro; Bingol, Haluk; Ersoz, Mustafa; Merkoci, ArbenDue to their size and difficulty to obtain, cost/effective biological or synthetic receptors (e.g., antibodies or aptamers, respectively), organic toxic compounds (e.g., less than 1 kDa) are generally challenging to detect using simple platforms such as biosensors. This study reports on the synthesis and characterization of a novel multifunctional composite material, magnetic silica beads/graphene quantum dots/molecularly imprinted polypyrrole (mSGP). mSGP is engineered to specifically and effectively capture and signal small molecules due to the synergy among chemical, magnetic, and optical properties combined with molecular imprinting of tributyltin (291 Da), a hazardous compound, selected as a model analyte. Magnetic and selective properties of the mSGP composite can be exploited to capture and preconcentrate the analyte onto its surface, and its photoluminescent graphene quantum dots, which are quenched upon analyte recognition, are used to interrogate the presence of the contaminant. This multifunctional material enables a rapid, simple and sensitive platform for small molecule detection, even in complex mediums such as seawater, without any sample treatment.Öğe Graphene-based hybrid for enantioselective sensing applications(Elsevier Advanced Technology, 2017) Zor, Erhan; Morales-Narvaez, Eden; Alpaydin, Sabri; Bingol, Haluk; Ersoz, Mustafa; Merkoci, ArbenChirality is a major field of research of chemical biology and is essential in pharmacology. Accordingly, approaches for distinguishing between different chiral forms of a compound are of great interest. We report on an efficient and generic enantioselective sensor that is achieved by coupling reduced graphene oxide with gamma-cyclodextrin (rGO/gamma-CD). The enantioselective sensing capability of the resulting structure was operated in both electrical and optical mode for of tryptophan enantiomers (D-/L-Trp). In this sense, voltammetric and photoluminescence measurements were conducted and the experimental results were compared to molecular docking method. We gain insight into the occurring recognition mechanism with selectivity toward D- and L-Trp as shown in voltammetric, photoluminescence and molecular docking responses. As an enantioselective solid phase on an electrochemical transducer, thanks to the different dimensional interaction of enantiomers with hybrid material, a discrepancy occurs in the Gibbs free energy leading to a difference in oxidation peak potential as observed in electrochemical measurements. The optical sensing principle is based on the energy transfer phenomenon that occurs between photo excited D-/L-Trp enantiomers and rGO/gamma-CD giving rise to an enantioselective photoluminescence quenching due to the tendency of chiral enantiomers to form complexes with gamma-CD in different molecular orientations as demonstrated by molecular docking studies. The approach, which is the first demonstration of applicability of molecular docking to show both enantioselective electrochemical and photoluminescence quenching capabilities of a graphene-related hybrid material, is truly new and may have broad interest in combination of experimental and computational methods for enantiosensing of chiral molecules. (C) 2016 Elsevier B.V. All rights reserved.Öğe Green synthesis of reduced graphene oxide/nanopolypyrrole composite: characterization and H2O2 determination in urine(Royal Soc Chemistry, 2014) Zor, Erhan; Saglam, Muhammed Esad; Akin, Ilker; Saf, Ahmet Ozgur; Bingol, Haluk; Ersoz, MustafaHere we report on a novel, simple and eco-friendly approach for the fabrication of a reduced Graphene Oxide/nanopolypyrrole (rGO/nPPy) composite material and its electrochemical performance for detection of hydrogen peroxide on a glassy carbon electrode. The characterization of the as-prepared rGO/nPPy composite was investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet-visible spectroscopy, scanning electron microscopy, contact angle measurement, cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques were used to investigate and optimize the performance of the developed electrochemical biosensor. The proposed biosensor showed excellent analytical response towards the quantification of H2O2 at pH 7.40. Under the optimized conditions, the biosensor shows a linear response range from 1.0 x 10(-7) to 4.0 x 10(-6) M concentrations of H2O2. The limit of detection was determined to be 34 nM. Reproducibility, sensitivity, stability and anti-interference capability of the fabricated biosensor for the detection of H2O2 were examined. The biological relevance of the developed electrochemical biosensor was further studied by the determination of H2O2 in urine samples. The real sample analysis of H2O2 was achieved before and after drinking coffee in urine samples. The successful and sensitive determination of H2O2 urine samples indicates that the proposed electrochemical biosensor can be applied to the quantification analysis of H2O2 in real samples.Öğe Green Synthesis of Reduced Graphene Oxide/Polyaniline Composite and Its Application for Salt Rejection by Polysulfone-Based Composite Membranes(Amer Chemical Soc, 2014) Akin, Ilker; Zor, Erhan; Bingol, Haluk; Ersoz, MustafaIn this study, a novel, simple, and eco-friendly enzymatic-reaction-based approach to produce reduced graphene oxide/polyaniline (rGO/PANI) composite material was proposed. Glucose oxidase (GOx) was used as an effective catalyst producing hydrogen peroxide, in the presence of glucose, for the oxidative polymerization of aniline under ambient conditions. The prepared rGO/PANI composite was dispersed in polysulfone (PSf), and the mixed membranes were prepared by the phase inversion polymerization method. The morphology of membranes was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle (CA) techniques. The performance of membranes was studied in terms of salt rejection and pure water flux. The incorporation of rGO into the membrane matrix led to hydrophobic membrane surface with the enhanced macro-voids. On the contrary, the contact angle data revealed that the rGO/PANI-incorporated membrane surface is partly hydrophilic due to the PANI fibers in membrane, whereas SEM images showed the enhanced macro-voids. Membranes exhibited an improved salt rejection after rGO/PANI doping. The rGO/PANI-modified membrane loading exhibited a maximum of 82% NaCl rejection at an applied pressure of 10 bar. In addition, the results showed that the PSf-rGO/PANI composite membrane had the highest mean porosity and water flux.Öğe Preparation of polymer inclusion membrane with sodium diethyldithiocarbamate as a carrier reagent for selective transport of zinc ions(Desalination Publ, 2017) Arslan, Gulsin; Yilmaz, Abdurrahman; Tor, Ali; Ersoz, MustafaThis study reports the design of a new type of polymer inclusion membrane (PIM) for selective transport of zinc ion. Sodium diethyldithiocarbamate (NaDDTC) was incorporated in the cellulose acetate-based membrane as a carrier for Zn(II) ion. The PIMs were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and contact angle measurements. The effects of parameters, including concentration of Zn(II) in the feed phase, HCl in the stripping phase and amount of NaDDTC incorporated in the membrane, on the transport of Zn(II) ion were studied. For 1 x 10(-4) M of Zn(II) ion in the feed phase at pH 5.04, 96% of Zn(II) ion was transported through the PIMs prepared with 1.0 (wt%) diethyldithiocarbamate via 0.5 M HCl as a stripping phase. The diffusion of Zn(II) ions through the membrane was governed by complex formation between Zn(II) ion and NaDDTC in the membrane. Moreover, selective transport of Zn(II) ion was achieved in the presence of divalent metal ions involving Cu(II), Pb(II) and Ni(II). The prepared PIM provided reproducible transport efficiency, and it can be efficiently used in separation processes.Öğe Solvent washing with toluene enhances efficiency and increases reproducibility in perovskite solar cells(Royal Soc Chemistry, 2016) Kara, Koray; Kara, Duygu Akin; Kirbiyik, Cisem; Ersoz, Mustafa; Usluer, Ozlem; Briseno, Alejandro L.; Kus, MahmutWe report a simple process for reproducibly fabricating perovskite solar cells. We emphasize that the solvent washing technique is the most practical method for successful uniform crystallization so it facilitates highly efficient reproducible perovskite solar cells. The critical parameter for tuning crystallinity is determined to be the type of washing solvent and the quantity dispensed. The amount of washing solvent strongly affects the particle size distribution resulting in better or worse interconnection between the crystal grains. We discovered that 20 mu l of toluene is the best washing solvent for device reproducibility. Our proposed parameters result in 90% reproducible perovskite solar cells with an average efficiency around 8%.Öğe Voltammetric discrimination of mandelic acid enantiomers(Academic Press Inc Elsevier Science, 2014) Zor, Erhan; Saf, Ahmet O.; Bingol, Haluk; Ersoz, MustafaWe report a novel electrochemical biosensor for direct discrimination of D- and L-mandelic acid (D- and L-MA) in aqueous medium. The glassy carbon electrode (GCE) surface was modified with reduced graphene oxide (rGO) and gamma-globulin (GLOB). Electrochemical characterization of the modified electrodes was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode surfaces were also characterized by scanning electron microscopy. Electrochemical response of the prepared electrode (GCE/rGO/GLOB) for discrimination of D- and L-MA enantiomers was investigated by cyclic voltammetry and was compared with bare GCE in the concentration range of 2 to 10 mM. Whereas the bare GCE showed no electrochemical response for the MA enantiomers, the GCE/rGO/GLOB electrode exhibited direct and selective discrimination with different oxidation potential values of 1.47 and 1.71 V and weak reduction peaks at potential values of -1.37 and -1.48 V, respectively. In addition, electrochemical performance of the modified electrode was investigated in mixed solution of D- and L-MA. The results show that the produced electrode can be used as electrochemical chiral biosensor for MA. (C) 2013 Elsevier Inc. All rights reserved.
