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Öğe Chitosan modified graphite electrodes developed for electrochemical monitoring of interaction between daunorubicin and DNA(Elsevier B.V., 2019) Congur G.; Eksin E.; Erdem A.Chitosan (CHIT) modified single-use electrodes were developed for the first time in the present study and applied for electrochemical monitoring of anticancer drug-DNA interaction. Under this aim, pencil graphite electrode (PGE) was used as the biosensor platform and the modification of PGEs using biopolymer, CHIT was performed by passive adsorption process. Microscopic and electrochemical characterizations of CHIT modified PGEs were performed. An anticancer drug, Daunorubicin (DNR) was analyzed by using both PGEs and CHIT-PGEs. Moreover, the effect of CHIT modification on biosensor development upon to the sensitivity of voltammetric detection of DNR and DNA was also investigated. The interaction between DNA and DNR was then performed and accordingly, the voltammetric measurements were performed before/after interaction process by using differential pulse voltammetry (DPV) technique. © 2018Öğe Development of ionic liquid modified disposable graphite electrodes for label-free electrochemical detection of DNA hybridization related to Microcystis spp(MDPI AG, 2015) Sengiz C.; Congur G.; Erdem A.In this present study, ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate (IL)) modified pencil graphite electrode (IL-PGEs) was developed for electrochemical monitoring of DNA hybridization related to Microcystis spp. (MYC). The characterization of IL-PGEs was performed using microscopic and electrochemical techniques. DNA hybridization related to MYC was then explored at the surface of IL-PGEs using differential pulse voltammetry (DPV) technique. After the experimental parameters were optimized, the sequence-selective DNA hybridization related to MYC was performed in the case of hybridization between MYC probe and its complementary DNA target, noncomplementary (NC) or mismatched DNA sequence (MM), or and in the presence of mixture of DNA target: NC (1:1) and DNA target: MM (1:1). © 2015 by the authors; licensee MDPI, Basel, Switzerland.Öğe Electrochemical assay for determination of gluten in flour samples(Elsevier Ltd, 2015) Eksin E.; Congur G.; Erdem A.Herein, an electrochemical assay developed by differential pulse voltammetry (DPV) in combination with the disposable pencil graphite electrode (PGE) was progressed for sensitive and selective detection of gluten. Under the optimum experimental conditions, a linear concentration range of gluten was obtained from 20 to 100 µg/mL and consequently the detection limit was found to be 7.11 µg/mL. In addition, this electrochemical assay was successfully employed for the detection of gluten in different flour samples. Applicability of our method was also tested in the commercial samples of vinegar and baker's yeast. © 2015 Elsevier Ltd. All rights reserved.Öğe Electrochemical biosensors for screening of toxins and pathogens(2012) Erdem A.; Muti M.; Karadeniz H.; Congur G.; Canavar E.Many important technological advances have been still progressed for the development of advanced sensors to monitor specific biointeractions and -different recognition events of biomolecules in solution and at the solid substrates. Some of typical applications on screening of selected toxins and pathogens have been overviewed herein for environmental, agriculture, food monitoring and control with coming important features of electrochemical sensor strategies. © 2012 Springer Science+Business Media B.V.Öğe Electrochemical monitoring of indicator-free DNA hybridization by carbon nanotubes-chitosan modified disposable graphite sensors(2012) Erdem A.; Muti M.; Karadeniz H.; Congur G.; Canavar E.Single walled carbon nanotubes (SWCNT)-chitosan (CHIT) modified pencil graphite electrodes (PGEs) were developed for monitoring of DNA hybridization. SWCNT-chitosan modified PGE (CNT-CHIT-PGE), Chitosan modified PGE (CHIT-PGE) and unmodified PGE (bare-PGE) were firstly characterized by using scanning electron microscopy (SEM), and their electrochemical behaviors were investigated using electrochemical impedance spectroscopy (EIS). The concentrations of CHIT, carbon nanotube (CNT) and also amino linked DNA probe etc. were respectively optimized in order to obtain the better working conditions of CNT-CHIT modified PGE in DNA analysis. The sequence selective DNA hybridization related to Hepatitis B virus (HBV) was then explored in the case of hybridization between amino linked HBV probe and its complementary (target), or noncomplementary (NC), or mismatch (MM) sequences, and also hybridization in mixture sample. © 2012 Elsevier B.V.Öğe Electrochemical monitoring of the interaction between Temozolamide and nucleic acids by using disposable pencil graphite electrodes(Elsevier B.V., 2015) Altay C.; Eksin E.; Congur G.; Erdem A.Abstract Temozolomide (TMZ) is an anticancer drug used for the treatment of adult brain tumour and skin cancer. The biomolecular interaction between TMZ and DNA was investigated for the first time in this study using disposable pencil graphite electrodes (PGEs) in combination with electrochemical techniques. The surface confined interactions between TMZ and different type of nucleic acids were performed. Before/after surface confined interaction process, the oxidation signals of TMZ, guanine and adenine were measured using differential pulse voltammetry (DPV) and PGE and accordingly, the changes at the oxidation signals were evaluated. The detection limit (DL) was also estimated based on the oxidation signal of TMZ. The interaction of TMZ with single stranded poly [A], poly [G], or double stranded poly [A]-poly[T] and poly [G]-poly[C] was also explored. Moreover, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were utilized for detection the interaction between TMZ and DNA. The features of this single-use electrochemical sensor was discussed in comparison to other reports that were developed for TMZ detection. © 2015 Elsevier B.V.Öğe Estrone specific molecularly imprinted polymeric nanospheres: Synthesis, characterization and applications for electrochemical sensor development(2013) Congur G.; Senay H.; Turkcan C.; Canavar E.; Erdem A.; Akgol S.The aim of this study is (i) to prepare estrone-imprinted nanospheres (nano-EST-MIPs) and (ii) to integrate them into the electrochemical sensor as a recognition layer. N-methacryloyl-(l)-phenylalanine (MAPA) was chosen as the complexing monomer. Firstly, estrone (EST) was complexed with MAPA and the EST-imprinted poly(2-hyroxyethylmethacrylate-co-N-methacryloyl-(l)- phenylalanine) [EST-imprinted poly(HEMA-MAPA)] nanospheres were synthesized by surfactant-free emulsion polymerization method. The specific surface area of the EST-imprinted poly(HEMA-MAPA) nanospheres was found to be 1275 m2/g with a size of 163.2 nm in diameter. According to the elemental analysis results, the nanospheres contained 95.3 mmole MAPA/g nanosphere. The application of EST specific MIP nanospheres for the development of an electrochemical biosensor was introduced for the first time in our study by using electrochemical impedance spectroscopy (EIS) technique. This nano-MIP based sensor presented a great specificity and selectivity for EST. © 2013 Bentham Science Publishers.Öğe Impedimetric Detection of microRNA at Graphene Oxide Modified Sensors(Elsevier Ltd, 2015) Congur G.; Eksin E.; Erdem A.Abstract The graphene oxide (GO) modified pencil graphite electrodes (PGEs) were utilized for electrochemical monitoring of microRNA-34a (miRNA-34a) in this study. The GO concentration was firstly optimized after its modification onto the surface of disposable PGE by passive adsorption. The electrochemical behaviour of GO-PGEs was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) as well as microscopic characterization by using scanning electron microscopy (SEM). The impedimetric detection of hybridization between miRNA-34a target and its complementary DNA probe was recognized under the optimum conditions. The selectivity of the impedimetric genosensor was furtherly studied against to other miRNA sequences; such as; miRNA-15a, miRNA-155 and miRNA-660 in PBS (pH 7.40) or fetal bovine serum (FBS): PBS (1:1) diluted solution. © 2015 Elsevier Ltd.Öğe Indicator-free electrochemical biosensor for microRNA detection based on carbon nanofibers modified screen printed electrodes(Elsevier B.V., 2015) Erdem A.; Eksin E.; Congur G.Carbon nanofibers (CNFs) are fiber-structured nano-sized carbon materials, which have excellent mechanical, thermal and electrical properties. CNFs possess a wide range of application especially in biorecognition area. In this study, we developed an indicator-free voltammetric biosensor for detection of miRNA-34a target RNA by using carbon nanofiber enriched disposable screen printed electrodes (CNF-SPEs). The sensitive and selective recognition of miRNAs has been an attractive topic due to they have been defined as small RNAs and play major roles in regulating the translation and degradation of messenger RNAs. The characterization of CNF-SPEs in contrast to unmodified ones was firstly performed by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) techniques. The amino linked DNA probe, that was the complementary sequence of miRNA-34a, was immobilized onto the surface of CNF-SPEs. After measuring the guanine oxidation signal measured by differential pulse voltammetry (DPV), the detection of sequence-selective hybridization was then investigated between probe and miRNA-34a RNA target, or other miRNA sequences; miRNA-15a, or miRNA-660, which were chosen as noncomplementary sequences (NC). The detection limit was corresponded to 10.98 µg/mL (54 pmol in 35 µL sample) in the linear concentration range of target miRNA-34a from 25 to 100 µg/mL by using CNF-SPEs. The features of this present study was comprehensively discussed by means of the unique characteristics of single-use CNF-SPEs and importance of miRNA monitoring. © 2015 Elsevier B.V. All rights reserved.Öğe Iron(III) and nickel(ii) complexes as potential anticancer agents: Synthesis, physicochemical and structural properties, cytotoxic activity and DNA interactions(Royal Society of Chemistry, 2015) Bal-Demirci T.; Congur G.; Erdem A.; Erdem-Kuruca S.; Özdemir N.; Akgün-Dar K.; Varol B.; Ülküseven B.Template reactions of 2-hydroxy-R-benzaldehyde-S-methylisothiosemicarbazones (R = 3-methoxy or 4-hydroxy) with the corresponding aldehydes in the presence of FeCl3 and NiCl2 yielded N1,N4-disalicylidene chelate complexes. The compounds were characterized by means of elemental and spectroscopic methods. The structure of complex 1 was determined by X-ray single crystal diffraction. Crystal data (Mo K?; 296 K) are as follows: monoclinic space group P21/c, a = 12.9857(8) Å, b = 7.8019(4) Å, c = 19.1976(12) Å, ß = 101.655(5)°, Z = 4. Cytotoxic effects of the compounds were evaluated by the MTT assay in K562 leukemia, ECV304 endothelial and normal mononuclear cells, and DNA fragmentation analysis using the diphenylamine reaction was performed. The DNA binding capacity of thiosemicarbazones at IC50 and different concentrations was investigated. The DNA fragmentation percentage of compound treated cells was higher than that of non-treated control cells but was higher for compound 3 (84%) compared to the others. The interaction of compounds 1-4 and DNA was investigated voltammetrically by using nucleic acid modified electrodes after the double stranded fish sperm DNA (fsDNA), or poly(dA)·poly(dT), was immobilized onto the surface of pencil graphite electrodes (PGEs). Accordingly, the oxidation signals of DNA bases, guanine and adenine, were measured by using differential pulse voltammetry (DPV). The changes in the signals of guanine and adenine were evaluated before and after the interaction process. The results indicated that compound 3 was cytotoxic at very low concentrations in K562 leukemia cells unlike other cells and that could damage the DNA double stranded form, specifically the adenine base. Therefore, it may have a selective antileukemic effect and drug potential. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015.Öğe Multiwalled Carbon Nanotubes-Chitosan Modified Single-Use Biosensors for Electrochemical Monitoring of Drug-DNA Interactions(Wiley-VCH Verlag, 2015) Sengiz C.; Congur G.; Eksin E.; Erdem A.A multiwalled carbon nanotubes (CNT)-chitosan (CHIT) modified pencil graphite electrode (CNT-CHIT/PGE) was developed for the first time herein for electrochemical monitoring of the interaction of an anticancer drug, mitomycin C (MC) and DNA. The characterization of unmodified PGE, CHIT/PGE, CNT/PGE and CHIT-CNT/PGE were performed by scanning electron microscopy and cyclic voltammetry techniques. The oxidation signals of MC and guanine were measured before and after interaction at the surface of CNT-CHIT/PGEs using differential pulse voltammetry. Electrochemical impedance spectroscopy technique was also successfully utilized for monitoring of the interaction process at the surface of CNT-CHIT/PGEs in different interaction times. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
