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    Conductive polymer-based electrochemical aptasensor for sensitive detection of cylindrospermopsin in water resources
    (Royal Soc Chemistry, 2026) Kesici-Meco, Ece; Unur-Yilmaz, Ece
    Increasing environmental pollution and climate change intensify the occurrence of harmful cyanobacterial blooms. These blooms release cyanotoxins, such as cylindrospermopsin (CYN), a hepatotoxic compound that threatens freshwater ecosystems, ecological stability, and human health. Addressing this challenge requires effective monitoring strategies aligned with the United Nations Sustainable Development Goal 6 (Clean Water and Sanitation). In this study, pencil graphite electrode (PGE) and conductive polymer based electrochemical aptasensor systems were developed for the selective and sensitive detection of CYN in both laboratory (deionized water) and environmental (lake water) samples. The proposed sensors provide low-cost, rapid, and reliable analytical platforms for environmental monitoring and sustainable water management. Poly(3,4-ethylenedioxythiophene) (PEDOT), and polypyrrole (PPy) were electropolymerized onto PGEs to enhance conductivity and provide effective CYN-specific aptamer (cynApt) immobilization. The surface morphologies and elemental compositions of bare PGE, PGE/PEDOT, and PGE/PPy were characterized by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), while their electrochemical properties were systematically evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Functional groups formed after polymer deposition and subsequent aptamer immobilization were analyzed using Fourier transform infrared (FT-IR) spectroscopy. The first system, PGE/PEDOT/cynApt, achieved detection limits of 0.23 +/- 0.005 ng mL-1 (0.55 +/- 0.013 nM) and 0.27 +/- 0.008 ng mL-1 (0.65 +/- 0.018 nM) for CYN in deionized and lake water, respectively, using CV. The second system, PGE/PPy/cynApt, exhibited superior performance, reaching detection limits of 0.18 +/- 0.005 ng mL-1 (0.43 +/- 0.012 nM) in deionized water and 0.24 +/- 0.009 ng mL-1 (0.58 +/- 0.022 nM) in lake water, respectively, using EIS. Conductive polymer modifications, with PEDOT and PPy, significantly enhanced the analytical response. Both platforms exhibited high selectivity toward CYN over other environmentally relevant cyanobacterial toxins, including okadaic acid (OA), saxitoxin (STX), and anatoxin-a (ATX-a), which are known to co-occur with CYN in freshwater blooms. In addition, the developed aptasensors retained their functional performance over a 7-day storage period, indicating suitable stability for practical use. This practical approach for the early detection of CYN in aquatic environments contributes to the prevention of water-related health risks and supports sustainable agricultural practices.
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    Electrochemical Investigation of DNA Interactions with Cyanobacterial Toxins: Cylindrospermopsin and Saxitoxin
    (Wiley-V C H Verlag Gmbh, 2025) Kesici-Meco, Ece; Yilmaz, Mete; Unur-Yilmaz, Ece
    Anthropogenic eutrophication threatens freshwater sources used for agricultural irrigation and increases the occurrence risk of cyanotoxins, such as cylindrospermopsin (CYN) and saxitoxin (STX). These toxins accumulate in surface waters and pose significant health risks, with CYN primarily affecting the liver and STX targeting the nervous system. In this study, dsDNA was immobilized on a pencil graphite electrode (PGE), and its interactions with CYN and STX were investigated by means of electrochemical impedance spectroscopy (EIS). Experimental conditions, including DNA concentration, cyanotoxin concentration, and DNA-cyanotoxin interaction time, were optimized to generate the most significant electrochemical signal (i.e., charge transfer resistance). The optimized PGE/DNA system established the foundation for an electrochemical biosensor that can be utilized for detection of cyanotoxins and detection limits of 0.12 ng mL-1 and 0.043 ng mL-1 were achieved for CYN and STX, respectively. The system was further analyzed using FTIR, UV-vis, and X-ray photoelectron spectroscopy (XPS), providing a comprehensive structural analysis of toxin-induced DNA alterations. The electrochemical system developed in this study by immobilizing DNA onto PGE allowed thorough investigation of the genotoxic effects of CYN and STX, as well as their sensitive detection.
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    Enhancing glass durability with acidic coatings: a comparative study on corrosion prevention efficiency
    (Springer Int Publ Ag, 2025) Erserin, Salih; Elgin, Fulya; Unur-Yilmaz, Ece
    Soda lime silicate float glass, the world's most extensively produced glass type, is highly susceptible to corrosion, especially when stored or transported in humid and high-temperature environments. This study investigates the corrosion prevention performance of three acidic aqueous coating systems: organic acid (OAS), polymeric (PS), and polymeric organic acid (POAS) solutions. Pristine glass substrates were spray-coated with each solution, and the resulting coatings were evaluated for surface uniformity (via white light interferometry, WLI) and water resistance (via contact angle measurements). The coated substrates were then subjected to accelerated weathering (500 h at 50 degrees C and 95% relative humidity), and changes in surface morphology and optical quality were assessed using atomic force microscopy (AFM), UV-Vis spectrophotometry, hazemeter, contact angle analysis, and methylene blue staining tests. The POAS coating, composed of poly(methacrylic acid) and sodium metabisulfite, provided the most effective protection, with minimal surface roughening and negligible optical degradation, attributed to strong hydrogen bonding and ionic interactions with surface silanol groups of glass, as well as redox stabilization during film formation. In contrast, PS coating exhibited lower interfacial adhesion due to the inert nature of polyethylene glycol, and OAS coating-composed of citric acid-suffered from ZnCl2-induced agglomeration in the absence of a polymeric matrix. These findings demonstrate that polymer chemistry, ionic content, and surface interaction mechanisms collectively govern coating properties and anticorrosive performance, underscoring the potential of acid-functional polymeric systems as practical and scalable solutions for glass protection during critical handling and storage periods.
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    Enzymatic electrochemical biosensor for glucose detection based on biomass-derived Fe3O4/C and PEDOT:PSS modification
    (Springer, 2024) Kesici-Meco, Ece; Unur-Yilmaz, Ece
    Enzyme-based electrochemical biosensors allow sensitive and selective detection of blood glucose levels and enable diabetes patients personalize their treatment plans. Biocompatible, low-toxic, abundant and electroactive iron oxide (Fe3O4) nanoparticles are widely used as biosensor electrode materials. Herein, Fe3O4/Carbon (Fe3O4/C) nanocomposite was obtained through hydrothermal carbonization and successive calcination of heteroatom-rich spirulina (Arthrospira platensis,SP) biomass on Fe3O4 nanoparticles. Functionality and electrical conductivity of the Fe3O4/C nanocomposite was further enriched by a conductive poly(3,4-ethylenedioxythiophene) polystyrenesulfonate coating (Fe3O4/C/PEDOT:PSS). Glucose oxidase (GOx) was physically immobilized on the electrodes and glucose was detected by means of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) methods. The glucose detection limits for the Fe3O4/C/GOx electrode were calculated as 0.73 mM (CV) and 1.04 mM (EIS) in the linear concentration range of 5-15 mM. The glucose detection limits for the Fe3O4/C/PEDOT:PSS/GOx electrode were calculated as 0.03 mM (CV) and 0.13 mM (EIS) in the linear concentration range of 0.5-1.5 mM. The selectivity of the biosensor was tested in the presence of ascorbic acid. Sensitive, selective, low-cost, and biocompatible electrodes provide a valuable tool in the management of diabetes.
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    Fe-doped densely stacked graphene for compact capacitive energy storage
    (Elsevier Science Sa, 2023) Sinan-Tatli, Neriman; Unur-Yilmaz, Ece
    Herein, we present iron oxide (& alpha;-Fe2O3) etching and simultaneous hydrothermal reduction approach to prepare densely stacked defect-rich graphene with abundant pseudocapacitive heteroatoms (18.1 wt% O and 1.2 wt% Fe). Electrochemical measurements were conducted in acidic (1 M H2SO4) and neutral (1 M Na2SO4) aqueous media. The Fe-doped densely stacked graphene (Fe-rGO) with a low specific surface area (32.9 m2 g-1) and high particle density (1.84 g cm-3) displayed high gravimetric and volumetric capacitances of 425 F g-1 and 780 F cm-3 at 0.25 A g-1, respectively, as well as outstanding rate performance (71 % capacitance retention at 20 A g-1 in 1 M H2SO4). Moreover, Fe-rGO exhibited high electrochemical and structural stability over 5000 cycles at 10 A g-1 without any loss in capacitance. An asymmetric supercapacitor (ASC) with Fe-rGO negative electrode and MnO2/PEDOT:PSS positive electrode was assembled with aqueous 1 M Na2SO4 electrolyte. The device exhibited 17.3 Wh kg-1 specific energy and a long cyclic stability (10,000 cycles at 1 A g-1). A practical application of the device was demonstrated by powering a light emitting diode.
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    Highly selective and cost-effective impedimetric biosensor for cylindrospermopsin detection using an aptamer-functionalized pencil graphite electrode
    (Pergamon-Elsevier Science Ltd, 2026) Kesici-Meco, Ece; Unur-Yilmaz, Ece
    Nutrient runoff from anthropogenic eutrophication, rising atmospheric CO2 levels, and global warming have significantly contributed to the proliferation of harmful cyanobacterial blooms in freshwater ecosystems. These blooms release cyanotoxins, such as cylindrospermopsin (CYN), which pose genotoxic and cytotoxic effects. The detection and monitoring of CYN in water are essential for protecting public health and reducing environmental risks. In this study, an electrochemical aptasensor was developed by effective immobilization of CYN-specific aptamer (cynApt) onto a highly conductive pencil graphite electrode (PGE), which offers a sustainable alternative to expensive gold and graphene-based sensors. CYN was detected through electrochemical impedance spectroscopy (EIS) by monitoring changes in charge transfer resistance. The detection limits for CYN using PGE/ cynApt electrodes were found to be 0.78 ng mL- 1 in deionized water and 0.97 ng mL- 1 in lake water, within a linear range of 1-20 ng mL- 1. The selectivity of the biosensor for CYN was also tested against other cyanotoxins, such as okadaic acid and saxitoxin, both in deionized and lake water.
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    PANI-grafted radially porous MnO2 for supercapacitor applications
    (Springer, 2024) Sinan-Tatli, Neriman; Unur-Yilmaz, Ece
    In this study, manganese carbonate (MnCO3) microspheres were used as self-templates for the synthesis of hollow and radially porous MnO2 via an oxidation-etching process. Then, in situ polymerization of aniline was conducted with and without 3-aminopropyl triethoxysilane (APTES) grafting agent, resulting in the formation of PANI-grafted MnO2 (MGP) and PANI-coated MnO2 (MP), respectively. The electrochemical performances were evaluated in a three-electrode configuration using a 1 M H2SO4 aqueous electrolyte solution. Both samples showed high-specific capacitances owing to the unique MnO2 structure with radial cavities, which facilitate ion diffusion and effectively accommodate volume expansion during cycling. The MGP exhibited similar to 30% higher specific capacitance (765 F g(-1) and 586 F g(-1) at 0.25 A g(-1)) and extended cycle life (80% retention after 14,000 cycles) compared to the MP. The results demonstrate that the charge transfer efficiency and structural stability of MGP are enhanced by the formation of covalent bonds between MnO2 and PANI through grafting.
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    Sustainable and Sensitive Aptasensor for Detection of Cylindrospermopsin Using Conductive Polymer PEDOT:PSS
    (Wiley-V C H Verlag Gmbh, 2025) Kesici-Meco, Ece; Unur-Yilmaz, Ece
    Cyanotoxins, produced by cyanobacteria, pose serious genotoxic, hepatotoxic, nephrotoxic, and neurotoxic risks in aquatic ecosystems. Among these, cylindrospermopsin (CYN), known for its high water solubility and bioaccumulation potential, significantly threatens public health and environmental safety. Anthropogenic eutrophication and climate-induced environmental changes have significantly intensified the frequency and severity of cyanobacterial blooms, thereby underscoring the necessity for rapid and reliable detection strategies for CYN. Aptamer-based electrochemical biosensors offer selective and sensitive detection, with performance reliant on effective aptamer immobilization and electrode conductivity. Pencil graphite electrodes (PGEs) provide a novel, low-cost, conductive, and easily modifiable alternative to commonly used noble-metal-based platforms, such as gold nanoparticles. This study reports the fabrication of an electrochemical aptasensor by modifying PGE with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) to increase surface area and enable effective immobilization of the CYN-specific aptamer (cynApt). Electrochemical characterization of the PGE/PEDOT:PSS/cynApt biosensor platform was conducted using cyclic voltammetry (CV), while CYN detection was performed using differential pulse voltammetry (DPV). The developed PGE/PEDOT:PSS/cynApt sensor achieved a limit of detection of 0.154 ng mL(-1) in deionized water and 0.224 ng mL(-1) in lake water, with a linear response range of 0.25 to 2.5 ng mL(-1). The sensor also demonstrated high selectivity against other cyanotoxins, such as okadaic acid and saxitoxin (STX). These results highlight the potential of the proposed aptasensor for sensitive and selective cylindrospermopsin (CYN) detection in environmental monitoring applications.