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Öğe COMPARISON OF BIODIESEL PRODUCTIVITIES OF DIFFERENT VEGETABLE OILS BY ACIDIC CATALYSIS(Assoc Chemical Eng, 2011) Sagiroglu, Ayten; Isbilir, Sebnem Selen; Ozcan, Hakki Mevlut; Paluzar, Hatice; Toprakkiran, Neslihan M.Biodiesel has become a subject which increasingly attracts worldwide attention because of its environmental benefits, biodegradability and renewability. Biodiesel production typically involves the transesterification of a triglyceride feedstock with methanol or other short-chain alcohols. This paper presents a study of transesterification of various vegetable oils, sunflower, safflower, canola, soybean, olive, corn, hazelnut and waste sunflower oils, with the acidic catalyst. Under laboratory conditions, fatty acid methyl esters (FAME) were prepared by using methanol in the presence of 1.85% hydrochloric acid at 100 degrees C for 1 h and 25 degrees C for 3 h. The analyses of biodiesel were carried out by gas chromatography and thin layer chromatography. Also, biodiesel productivities (%) were determined on basis of the ratio of ester to oil content (w/w). The biodiesel productivities for all oils were found to be about 80% and about 90% at 25 and 100 degrees C, respectively. Also, the results showed that the yield of biodiesel depended on temperature for some oils, including canola, sunflower, safflower Os, but it was not found significant differences among all of the oil types on biodiesel productivities.Öğe Detection of Parathyroid Hormone Using an Electrochemical Impedance Biosensor Based on PAMAM Dendrimers(Wiley, 2015) Ozcan, Hakki Mevlut; Sezginturk, Mustafa KemalThis paper presents a novel hormone-based impedimetric biosensor to determine parathyroid hormone (PTH) level in serum for diagnosis and monitoring treatment of hyperparathyroidism, hypoparathyroidism and thyroid cancer. The interaction between PTH and the biosensor was investigated by an electrochemical method. The biosensor was based on the gold electrode modified by 12-mercapto dodecanoic (12MDDA). Antiparathyroid hormone (anti-PTH) was covalently immobilized on to poly amidoamine dendrimer (PAMAM) which was bound to a 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide/N-hydroxysuccinimide (EDC/NHS) couple, self-assembled monolayer structure from one of the other NH2 sites. The immobilization of anti-PTH was monitored by electrochemical impedance spectroscopy, cyclic voltammetry and scanning electron microscope techniques. After the optimization studies of immobilization materials such as 12MDDA, EDC-NHS, PAMAM, and glutaraldehyde, the performance of the biosensor was investigated in terms of linearity, sensitivity, repeatability, and reproducibility. PTH was detected within a linear range of 10-60 fg/mL. Finally the described biosensor was used to monitor PTH levels in artificial serum samples. (C) 2015 American Institute of Chemical EngineersÖğe Fresh broad (Vicia faba) tissue homogenate-based biosensor for determination of phenolic compounds(Taylor & Francis Ltd, 2014) Ozcan, Hakki Mevlut; Sagiroglu, AytenIn this study, a novel fresh broad (Vicia faba) tissue homogenate-based biosensor for determination of phenolic compounds was developed. The biosensor was constructed by immobilizing tissue homogenate of fresh broad (Vicia faba) on to glassy carbon electrode. For the stability of the biosensor, general immobilization techniques were used to secure the fresh broad tissue homogenate in gelatin-glutaraldehyde cross-linking matrix. In the optimization and characterization studies, the amount of fresh broad tissue homogenate and gelatin, glutaraldehyde percentage, optimum pH, optimum temperature and optimum buff er concentration, thermal stability, interference effects, linear range, storage stability, repeatability and sample applications (Wine, beer, fruit juices) were also investigated. Besides, the detection ranges of thirteen phenolic compounds were obtained with the help of the calibration graphs. A typical calibration curve for the sensor revealed a linear range of 5-60 mu M catechol. In reproducibility studies, variation coefficient (CV) and standard deviation (SD) were calculated as 1.59%, 0.64 X 10(-3) M, respectively.Öğe A new biosensor for osteoporosis detection(Taylor & Francis Inc, 2019) Kabala, Sevilay Inal; Yagar, Hulya; Ozcan, Hakki MevlutOsteoporosis is a disease that is characterized by deterioration of bone tissue and increased risk of fracture as it leads to a decrease in bone mineral density, which is an important public health problem. Today, bone mineral density is measured by radiological techniques. Alternative techniques are needed because of the disadvantages such as excessive radiation intake, the cost of radiological techniques, and the necessity for specialist personnel for the devices. The quantitative determination of biochemical markers that play a role in bone mineralization may be a good alternative for the osteoporosis diagnosis and especially in the follow-up of treatment. In this study, a specific and sensitive immunological biosensor, which quantitatively determines the osteocalcin molecule, has been developed to be used in the early osteoporosis diagnosis and to evaluate the response to the drug treatment. Anti-osteocalcin antibody was immobilized onto gold electrode surface via covalent immobilization method by using 6-mercaptohexanol, 1,4-butanedioldiglycidyl ether, ethanolamine, and glutaraldehyde. Immobilization steps and biosensor characterization were specified by cyclic voltammetry and electrochemical impedance spectroscopy. The detection time and range of Ocn biosensor were determined as 45 min and 10-60 pg mu L-1 Ocn concentration, respectively. The Ocn biosensor was successfully applied in artificial serum samples spiked with Ocn.Öğe A new ITO-based A?42 biosensor for early detection of Alzheimer's disease(Elsevier Science Sa, 2023) Altay, Dilek Nur; Yagar, Hulya; Ozcan, Hakki MevlutIn this study, a novel label-free impedimetric immunosensor was fabricated for rapid, selective, and sensitive quantitative analysis of A & beta;42 protein for use in the diagnosis of Alzheimer's disease. The immunosensor was fabricated using inexpensive and disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrodes. After the electrodes were modified with 3-glycidoxypropyldimethoxymethylsilane (GPDMMS), the antibody specific to the A & beta;42 protein (anti-A & beta;42) was immobilized. The affinity interaction between anti-A & beta;42 and A & beta;42 in the immobilization steps in immunosensor fabrication and in the quantitation of A & beta;42 were analyzed using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) techniques. Additionally, the morphological changes occurring on the electrode surface during each immobilization step were imaged using scanning electron microscopy (SEM). The linear detection range of the immunosensor was determined as 1-100 pg/mL with the limit of detection value of 0.37 pg/mL. Analytical properties of the biosensor, including reproducibility, repeatability, storage stability, selectivity, and regeneration were investigated. The kinetic behavior of antibody-antigen complex formation was determined for the first time using single frequency impedance (SFI) analysis on an A & beta;42 biosensor. The potential for use of the immunosensor in clinical studies was demonstrated by analysis of A & beta;42 in commercially purchased human serum.Öğe A new PANI biosensor based on catalase for cyanide determination(Taylor & Francis Ltd, 2016) Ozcan, Hakki Mevlut; Aydin, TubaCyanide is one of the most widespread of compounds measured in environmental analysis due to their toxic effects on environment and health. We report a highly sensitive, reliable, selective amperometric sensor for determination of cyanide, using a polyaniline conductive polymer. The enzyme catalase was immobilized by electropolymerization. The steps during the immobilization were controlled by electrochemical impedance spectroscopy. Optimum pH, temperature, aniline concentration, enzyme concentration, and the number of scans obtained during electropolymerization, were investigated. In addition, the cyanide present in artificial waste water samples was determined. In the characterization studies of the biosensor, some parameters such as reproducibility and storage stability, were analyzed.Öğe A Novel Amperometric Biosensor Based on Banana Peel (Musa cavendish) Tissue Homogenate for Determination of Phenolic Compounds(Informa Healthcare, 2010) Ozcan, Hakki Mevlut; Sagiroglu, AytenIn this study the biosensor was constructed by immobilizing tissue homogenate of banana peel onto a glassy carbon electrode surface. Effects of immobilization materials amounts, effects of pH, buffer concentration and temperature on biosensor response were studied. In addition, the detection ranges of 13 phenolic compounds were obtained with the help of the calibration graphs. Storage stability, repeatability of the biosensor, inhibitory effect and sample applications were also investigated. A typical calibration curve for the sensor revealed a linear range of 10-80 mu M catechol. In reproducibility studies, variation coefficient and standard deviation were calculated as 2.69%, 1.44 x 10(-3) mu M, respectively.Öğe A NOVEL BIOSENSOR BASED ON Lactobacillus acidophilus FOR DETERMINATION OF PHENOLIC COMPOUNDS IN MILK PRODUCTS AND WASTEWATER(Taylor & Francis Inc, 2011) Sagiroglu, Ayten; Paluzar, Hatice; Ozcan, Hakki Mevlut; Okten, Suzan; Sen, BurhanDifferent branches of industry need to use phenolic compounds (PCs) in their production, so determination of PCs sensitively, accurately, rapidly, and economically is very important. For the sensitive determination of PCs, some biosensors based on pure polyphenol oxidase, plant tissu, e and microorganisms were developed before. But there has been no study to develop a microbial phenolic compounds biosensor based on Lactobacillus species, which contain polyphenol oxidase enzyme. In this study, we used different forms of Lactobacillus species as enzyme sources of biosensor and compared biosensor performances of these forms for determination of PCs. For this purpose, we used lyophilized Lactobacillus cells (containing L. bulgaricus, L. acidophilus, Streptococcus thermophilus), pure L. acidophilus, pure L. bulgaricus, and L. acidophilus-and L. bulgaricus adapted to catechol in Lactobacilli MRS Broth. The most suitable form was determined and optimization studies of the biosensor were carried out by using this form. For preparing the bioactive layer of the biosensor, the Lactobacillus cells were immobilized in gelatin by using glutaraldehyde. In the study, we used catechol as a substrate. Phenolic compound determination is based on the assay of the differences on the respiration activity of the cells on the oxygen meter in the absence and the presence of catechol. The microbial biosensor response depends directly on catechol concentration between 0.5 and 5.0 mM with 18 min response time. In the optimization studies of the microbial biosensor the most suitable microorganism amount was found to be 10 mg, and also phosphate buffer (pH 8.0; 50 mM) and 37.5 degrees C were obtained as the optimum working conditions. In the characterization studies of the microbial biosensor some parameters such as substrate specificity on the biosensor response and operational and storage stability were examine. Furthermore, the determination of PC levels in synthetic wastewater, industrial wastewater, and milk products was investigated by using the developed biosensor under optimum conditions.Öğe Production of Ricinoleic Acid from Castor Oil by Immobilised Lipases(Taylor & Francis Inc, 2009) Ozcan, Hakki Mevlut; Sagiroglu, AytenPorcine pancreatic lipase (PPL), Candida rugosa lipase (CRL), and Castor bean lipase (CBL) were immobilized on celite by deposition from aqueous solution by the addition of hexane. Lipolytic performance of free and immobilized lipases were compared and optimizations of lipolytic enzymatic reactions conditions were performed by free and immobilized derivatives using olive oil as substrate. Afterwards, the influence on lipolysis of castor oil of free lipases and immobilized lipase derivatives have been studied in the case of production of ricinoleic acid. All of the lipases performances were compared and enzyme derivative was selected to be very effective on the production of ricinoleic acid by lipolysis reaction. Various reaction parameters affecting the production of ricinoleic acid were investigated with selected the enzyme derivative. The maximum ricinoleic acid yield was observed at pH 7-8, 50C, for 3hours of reaction period with immobilized 1,3-specific PPL on celite. The kinetic constants Km and Vmax were calculated as 1.6 10-4mM and 22.2mM from a Lineweaver-Burk plot with the same enzyme derivative. To investigate the operational stability of the lipase, the three step lipolysis process was repeated by transferring the immobilized lipase to a substrate mixture. As a result, the percentange of conversion after usage decreased markedly.Öğe A simple immunosensor for thyroid stimulating hormone(Taylor & Francis Ltd, 2021) Ozcan, Hakki Mevlut; Aydin, Umut DenizDetermination of thyroid-stimulating hormone (TSH) level in serum or plasma is defined as a sensitive method for the diagnosis of hyperthyroidism and hypothyroidism and also in many diseases thought to be related to TSH levels. In this study, a novel simple impedimetric immunosensor based on polyamidoamine dendrimer was developed. Anti TSH antibody was immobilized on the gold electrode by using cysteamine self-assembled monolayer strategy. In constructing the immunosensor, a polyamidoamine dendrimer was used to increase the surface area in which Anti-TSH was immobilized and glutaraldehyde was used as a cross-linker. After each immobilization step, the electrode surface was monitored by electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy and energy-dispersive X-ray spectroscopy techniques and optimization studies were performed. The reproducibility, repeatability, linearity and sensitivity of the immunosensor were examined. Also, the interference experiments for glucose, salts and proteins in serum were performed. The limit of detection and limit of quantification values of the proposed immunosensor were 0.026 mIUL(-1) and 0.086 mIUL(-1), respectively and it was able to detect the amount of TSH within a linear range of 0.1-0.6 mIUL(-1).Öğe Ultrasensitive Impedimetric Biosensor Fabricated by a New Immobilisation Technique for Parathyroid Hormone(Springer, 2015) Ozcan, Hakki Mevlut; Yildiz, Kubra; Cakar, Cansu; Aydin, Tuba; Asav, Engin; Sagiroglu, Ayten; Sezginturk, Mustafa KemalThis paper presents a novel ultrasensitive and rapid impedimetric biosensor with new immobilisation materials for parathyroid hormone (PTH) with the aim to determine the PTH level in serum for the diagnosis and monitoring of parathyroid diseases such as hyperparathyroidism, adenoma, and thyroid cancer. The interaction between PTH and the biosensor was investigated with an electrochemical method. The biosensor was based on the gold electrode modified by mercaptohexanol (6-MHL). Anti-parathyroid hormone (anti-PTH) was covalently immobilised onto a self-assembled monolayer (SAM) by using epiclorhidrina (EPI) with ethanolamine (EA). The EPI-EA interaction represents the first use of these for the construction of biosensors in published reports. The immobilisation of the anti-PTH was monitored by electrochemical impedance spectroscopy, cyclic voltammetry and scanning electron microscopy (SEM) techniques. After the optimisation studies of immobilisation materials such as 6-MHL, EPI, EA and glutaraldehyde, linearity, repeatability and sensitivity of biosensor were evaluated as the performance of biosensor. PTH was detected within a linear range of 0.1-0.6 pg/ml, and the detection limit was 0.1 fg/ml. The specificity of the biosensor was also investigated. Finally, the described biosensor was used to detect the PTH levels in artificial serum samples.
