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    A New Approach to Synthesis of Highly Dispersed Gold Nanoparticles via Glucose Oxidase-Immobilized Hydrogel and Usage in The Reduction of 4-Nitrophenol
    (Wiley-V C H Verlag Gmbh, 2020) Ozay, Hava; Tarimeri, Nur; Gungor, Zeynep; Demirbakan, Burcak; Ozcan, Burcu; Sezgintürk, Mustafa Kemal; Özay, Özgür
    In this study, for the first time in the literature, synthesis of Au(0) nanoparticles supported by a crosslinked gel structure was performed via enzyme-mediated reduction of Au(III) ions without using any chemical reductant. In our newly-developed method, glucose oxidase enzymes immobilized in the crosslinked gelatine structure ensured simultaneous reduction of the Au(III) ions diffused within the gel to Au(0). The Au@Gel obtained was structurally characterised with TEM (Transmission electron microscopy), EDX (Energy dispersive X-ray analysis) elemental mapping, XPS (X-Ray photoelectron spectroscopy) and XRD (X-Ray Diffraction) analyses. The catalytic activity of Au(0) particles with nearly 8 nm size in the Au@Gel was investigated for the reduction of 4-nitrophenol (4-NP) as a model compound in the presence of NaBH(4)as reducing agent. The activation parameters for the reduction reaction of 4-nitrophenol in the presence of Au@Gel catalyst were determined as E-a= 30.16 kJmol(-), Delta H= 27.52 kJmol(-)and Delta S= -197.45 Jmol(-)K(-). The Au@Gel catalyst system, with good catalytic activity, simultaneously has nearly perfect reusability.
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    A novel label free immunosensor based on single-use ITO-PET electrodes for detection MAGE1 protein
    (Elsevier Science Sa, 2017) Ozcan, Burcu; Sezgintürk, Mustafa Kemal
    This study is aimed to design a label free biosensor based on transparent ITO-PET (Indium tin oxide-polyethylene terephthalate) electrode to determine MAGE1 protein. Firstly, indium tin oxide (ITO) electrodes were modified with NH4OH/H2O2/H2O to obtain the OH groups on the surface. Later, the surface of ITO electrodes were treated with 3-glycidoxypropyltriethoxysilane (3-GOPE). After SAM formation, anti-MAGE1 protein was covalently immobilized on modified ITO electrodes. The parameters such as SAMs concentration, the concentration and incubation time of anti-MAGE1 solution were optimized. For determining the immobilization steps and optimization of the biosensor, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were utilized. To determine analytical characterization of designed biosensor; linear range, repeatability, reproducibility, regeneration processes were studied. In optimum conditions, the linear range of the biosensor was determined as 0.01 pg-1.28 pg mL(-1). Square wave voltammetry technique was applied to the biosensor. These steps were realized in K-3[Fe (CN)(6)]/K/4[Fe(CN)(6)] redox probe. Moreover, Single frequency technique was used to understand the interaction between antiMAGE-1 and MAGE-1 protein. This step was realized in pH 7 phosphate buffer. And also, shelf life of designed biosensor was investigated. SEM (Scanning Electron Microscope) technique was used to determine the morphology of the surface in every step. The other important parameter for this study was Kramer's Kronig transform. It is used to determine whether the impedance spectra of the designed biosensor are affected from the deviation obtained because of external factors. Lastly, the designed biosensor was applied to real human serum and the results were compared with ELISA (Enzyme-Linked ImmunoSorbent Assay) test. (C) 2017 Elsevier B.V. All rights reserved.
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    Early detection of the ovarian cancer with a label-free and disposable ITO-PET based immunosensor platform
    (Elsevier, 2024) Ozcan, Burcu; Özay, Hava; Özay, Özgür; Sezgintürk, Mustafa Kemal
    Alpha fetoprotein (AFP), a popular biomarker for ovarian cancer, was the target of this study to create an immunosensor based on electrochemical impedance spectroscopy (EIS). For this purpose, a disposable Indium tin oxide coated PET (In2O3/SnO2, ITO-PET) electrode was used as a basic electrode for working of the triple electrode system and the electrodes were modified with 3-(Trimethoxy silyl) propyl methacrylate (3- TMSPM) silanization agent. Although there are studies on the determination of AFP, the determination of AFP with a cheap, flexible and sensitive electrode system such as ITO-PET in this study makes the study remarkable. With the designed biosensors, AFP protein determination at a wide concentration range (0.05 pg/mL-100 pg/mL) could be successfully performed. To prove that the designed immunosensor was constructed correctly, linear range, repeatability, reproducibility and regeneration capacity (characterization studies) were investigated. Obtaining successful results in the storage capacity studies of the biosensor, which has high reproducibility and repeatability, showed that it also has potential for commercial use. The high specificity of the biosensor also proves its reliability. Finally, the performance of the biosensor in commercial human serum samples was also evaluated.
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    Fabrication of an ultrasensitive and single-use graphite paper based immunosensor for Neuropeptide Y detection: A promising biosensing system for early detection of childhood obesity
    (Elsevier, 2022) Ozcan, Burcu; Sezgintürk, Mustafa Kemal
    The purpose of this study was to develop a label-free impedimetric immunosensing system as an analysis technique for hypothalamic Neuropeptide Y hormone with the goal of determining childhood obesity. A novel process for producing a bioelectrode modified with reduced graphene oxide and its biocompatibility with neu-ropeptide Y was discussed. The immobilization process is based on the adsorption of reduced graphene oxide (dispersed in dimethylformamide solution) onto a novel graphite paper electrode. Anti-neuropeptide Y anti-bodies were covalently immobilized on the reduced graphene oxide modified electrode surface using ethyl (dimethylaminopropyl) carbodiimide / N-Hydroxysuccinimide coupling chemistry. Electrochemical impedance spectroscopy and cyclic voltammetry techniques were used to monitor and evaluate all immobilization stages, optimization studies, and analytical characterization of the biosensor. The scanning electron microscopy was used to observe the surface morphology during the immobilization steps of the biosensor. The applicability of the designed biosensor to real serum samples was evaluated for clinical use. The biosensor demonstrated high sensitivity for determining neuropeptide Y in real serum samples. The developed immunosensor had a large linear range (0.005-10 pg/mL) and a low limit of detection for neuropeptide Y antigen (0.11 fg mL-1). Addi-tionally, the designed immunosensor demonstrated high repeatability, reproducibility, long storage stability (after the fifth week, up to 87% of initial activity), and reusability (20 times).
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    Highly sensitive and cost-effective ITO-based immunosensor system modified by 11-CUTMS: Analysis of SOX2 protein in real human serum
    (Elsevier Science Bv, 2019) Ozcan, Burcu; Sezgintürk, Mustafa Kemal
    In this study it is aimed to construct an immunosensor system for detection of Sex-determining region Y-box 2 (SOX2) antigen by using Indium tin oxide- polyethylene terephthalate (ITO-PET) as working electrode. Firstly, ITO-PET electrode surfaces were hydroxylated by using NH4OH/H2O2/H2O and were incubated with 11-cyanoundecyltrimethoxysilane (11-CUTMS), respectively. After silanization process, anti- SOX2 was immobilized on modified ITO-PET electrodes. All immobilization processes were examined with Electrochemical impedance spectroscopy (EIS) and Cyclic voltammetry (CV). The basic parameters such as 11-CUTMS and anti-SOX2 concentrations, anti-SOX2 and SOX2 incubation period were optimized. The immunosensor prepared under optimal conditions gave a response for a wide concentration range of SOX2 protein (0.02 pg 2 pg mL(-1)) and the limit of detection was determined as low as 0.013 pg And also, the immunosensor had good repeatability, reproducibility, reusability and long shelf life. Scanning Electron Microscope (SEM) method was utilized to observe the morphologies of the electrode surfaces belonging to all steps. Lastly, seven different real human serum were analyzed with the constructed immunosensor and Enzyme-Linked ImmunoSorbent Assay (ELISA). The results found with these methods were analogised with each other. (C) 2019 Elsevier B.V. All rights reserved.
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    The Evaluation of Clinical Applications for the Detection of the Alzheimer's Disease Biomarker GFAP
    (Taylor & Francis Inc, 2024) Özçelikay-Akyıldız, Göksu; Karadurmuş, Leyla; Çetinkaya, Ahmet; Uludağ, İnci; Ozcan, Burcu; Ünal, Mehmet Altay; Sezgintürk, Mustafa Kemal
    One of the most prevalent neurodegenerative diseases is Alzheimer's disease (AD). The hallmarks of AD include the accumulation of amyloid plaques and neurofibrillary tangles, which cause related secondary diseases, progressive neurodegeneration, and ultimately death. The most prevalent cell type in the human central nervous system, astrocytes, are crucial for controlling neuronal function. Glial fibrillary acidic protein (GFAP) is released from tissue into the bloodstream due to astrocyte breakdown in neurological diseases. Increased levels of GFAP in the serum can function as blood markers and be an effective prognostic indicator to help diagnose neurological conditions early on, from stroke to neurodegenerative diseases. The human central nervous system (CNS) is greatly affected by diseases associated with blood GFAP levels. These include multiple sclerosis, intracerebral hemorrhage, glioblastoma multiforme, traumatic brain injuries, and neuromyelitis optica. GFAP demonstrates a strong diagnostic capacity for projecting outcomes following an injury. Furthermore, the increased ability to identify GFAP protein fragments helps facilitate treatment, as it allows continuous screening of CNS injuries and early identification of potential recurrences. GFAP has recently gained attention due to data showing that the plasma biomarker is effective in identifying AD pathology. AD accounts for 60-70% of the approximately 50 million people with dementia worldwide. It is critical to develop molecular markers for AD, whose number is expected to increase to about 3 times and affect humans by 2050, and to investigate possible targets to confirm their effectiveness in the early diagnosis of AD. In addition, most diagnostic methods currently used are image-based and do not detect early disease, i.e. before symptoms appear; thus, treatment options and outcomes are limited. Therefore, recently developed methods such as point-of-care (POC), on-site applications, and enzyme-linked immunosorbent assay-polymerase chain reaction (ELISA-PCR) that provide both faster and more accurate results are gaining importance. This systematic review summarizes published studies with different approaches such as immunosensor, lateral flow, POC, ELISA-PCR, and molecularly imprinted polymer using GFAP, a potential blood biomarker to detect neurological disorders. Here, we also provide an overview of current approaches, analysis methods, and different future detection strategies for GFAP, the most popular biosensing field.
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    Ultra-sensitive detection of parathyroid hormone in human serum: a cheap and practical biosensing platform modified by an epoxy ended-silane agent
    (Taylor & Francis Ltd, 2020) Ozcan, Burcu; Hanbaba, Muhammet Ali; Sezgintürk, Mustafa Kemal
    In this study, we designed an impedimetric immunosensor by modification of disposable ITO-PET (indium tin oxide-polyethylene terephthalate) electrode surface with 3-glycidoxypropyltriethoxysilane (3-GOPE). 3-GOPE silanization agent generates a suitable platform on the ITO-PET working electrode surface for antibody immobilisation and allows a wide determination range for analyte concentrations with the fabricated biosensor. All immobilisation processes, investigation of optimum parameters and characterisation studies of the developed immunosensor were evaluated and followed by Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV). Furthermore, the interactions between anti-parathyroid hormone (anti-PTH) and Parathyroid hormone (PTH) were simultaneously analysed with the Single Frequency Impedance (SFI) technique. All parameters which affect the biosensor response were optimised. A great wide concentration range (1 fg mL(-1)-2500 fg mL(-1)) and ultra-low detection limit (0.89 fg mL(-1)) were obtained under optimum conditions. Moreover, the impedimetric biosensor allowed high sensitivity in the detection of PTH in human serum. It was proved that the fabricated biosensor system has some advantages such as long-term storage life, very low limit of detection, ability to detect the PTH concentrations at femtogram level (1 fg mL(-1)- 2500 fg mL(-1)), excellent reproducibility and repeatability, reusability and ultra-high sensitivity.