Browsing by Author "Ertekin K."
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Item Photophysical and photochemical characteristics of an azlactone dye in sol-gel matrix; a new fluorescent pH indicator(2003) Ertekin K.; Karapire C.; Alp S.; Yenigül B.; Içli S.The photophysical and photochemical properties of an azlactone derivative, 4-(p-N,N-dimethylaminophenylmethylene)-2-phenyl-5-oxazolone, (DPO) in a sol-gel matrix have been examined. The fluorescence quantum yield, radiative lifetime, fluorescence lifetime, fluorescence rate constant and singlet energy values of the DPO dye were determined in a modified tetraethyl orthosilicate (TEOS) solid matrix by absorption and emission spectroscopy and obtained data were compared with the results of measurements in acetonitrile (MeCN) and tetrahydrofuran (THF) solution. The sol-gel matrix enhanced the fluorescence quantum yield (Qf=0.296) and fluorescence emission lifetime (τf=0.47 ns) compared to Qf=0.0027-0.0025 and τf=0.02-0.03 ns for solutions in MeCN and THF. The acidity constant of DPO was found to be as pKa=5.1 in the transparent sol-gel matrix. The dye doped sol-gel exhibited a pH sensitivity in pH range 3.0-7.0. © 2002 Elsevier Science Ltd. All rights reserved.Item Characterization of a reservoir-type capillary optical microsensor for pCO2 measurements(Elsevier, 2003) Ertekin K.; Klimant I.; Neurauter G.; Wolfbeis O.S.A reservoir type of capillary microsensor for pCO2 measurements is presented. The sensor is based on the measurement of the fluorescence intensity of the anionic form of the pH indicator 1-hydroxy-3,6,8-pyrenetrisulfonate in the form of its ion pair with a quaternary ammonium base in an ethyl cellulose matrix. The glass capillary containing the reservoir sensor was prepared by immersing the tip of the optical fiber into the sensing agent very close to the sensor tip thus providing a very small volume for the sensing reaction. The purpose of the sensing approach is to regenerate the dye/buffer system by diffusion, which may be poisoned by interfering acids, or bleach by photolysis. The fresh cocktail from the reservoir takes the place of protonated form of the dye. The internal buffer system also makes the protonation-deprotonation equilibria reversible. The distal tip of the internal buffer containing reservoir is coated with a gas-permeable but ion-impermeable teflon membrane. The dynamic range for the detection of pCO2 is between 1 and 20 hPa, which corresponds to the range of dissolved CO2 in water. The response time is 15 s and the detection limit is 1 hPa of pCO2. The recovery performance of this sensor can be improved by means of mechanical adjustment of the sensor tip in a micrometric scale. © 2002 Elsevier Science B.V. All rights reserved.Item Enhanced optical oxygen sensing using a newly synthesized ruthenium complex together with oxygen carriers(Elsevier, 2003) Ertekin K.; Kocak S.; Ozer M.S.; Aycan S.; Cetinkaya B.In this article, an emission based, simple and fast method is proposed for the determination of gaseous oxygen. A newly synthesized fluorophore, dichloro-{2,6-bis[1-(4-dimethylamino-phenylimino) ethyl]pyridine}ruthenium(II) has been used for oxygen sensing together with oxygen carrier perfluorochemicals (PFCs) in silicon matrix. It should be noted that the solubility of oxygen in fluorocarbons is about three to ten times large as that observed in the parent hydrocarbons or in water, respectively. Employed PFCs are chemically and biochemically inert, have high dissolution capacities for oxygen, and, once doped into sensing film, considerably enhance the response of sensing agent. © 2003 Elsevier B.V. All rights reserved.Item Glucose sensing employing fluorescent pH indicator: 4-[(p-N,N-dimethylamino)benzylidene]-2-phenyloxazole-5-one(2005) Ertekin K.; Cinar S.; Aydemir T.; Alp S.The proton sensitive azlactone derivative; 4-[(p-N,N-dimethylamino) benzylidene]-2-phenyloxazole-5-one (DPO) exhibits high quantum yield, excellent photostability, and high molar absorptivity in a sol - gel matrix. In this work, two different DPO containing constructions were tested and evaluated as glucose sensors. In the first, both glucose oxidase (GOx) and azlactone derivative were incorporated into a single tetraethylorthosilicate (TEOS) based sol - gel phase. In the second, TEOS and 3-aminopropyltriethoxysilane (APTEOS) containing dye-doped sol - gel layer was covered with GOx entrapped sol - gel (the two-layer configuration). The monolayer configuration has the fastest response time (τ90 = 20 s) but suffers from leaching upon prolonged use. Response time and dynamic working range of the cross-linking agent containing two-layer configuration are 40 s and 0.1-15 mM glucose, respectively. The resulting glucose sensor was characterized by high sensitivity, low interference from acidogenic species, and a working lifetime of at least 90 days. © 2004 Elsevier Ltd. All rights reserved.Item Determination of pK a values of clinically important perfluorochemicals in nonaqueous media(2008) Hakli O.; Ertekin K.; Ozer M.S.; Aycan S.Perfluorochemicals (PFCs) are clinically and biotechnologically important species. In this work, the potentiometric titration method in nonaqueous media is proposed for the determination of acidity constant values of six different perfluorinated compounds. The saturated and nonsaturated perfluoroacids, perfluorocarnosine, and perfluoroalkyl-β-alanine were potentiometrically titrated in acetonitrile, N,N-dimethylformamide, acetone, ethanol, methanol, and pyridine with tetrabutylammonium hydroxide. The half-neutralization potentials and acidity constants of PFCs have been calculated from the titration curves by using the computerized derivative method. Except for RF-Carnosine, all of the potentiometric titration curves of the PFCs exhibited one stoichiometric and well-defined endpoints in all of the solvents employed. The reproducibility and sensitivity of the method were evaluated. © 2008 MAIK Nauka.Item Sol-gel synthesized Sr4Al14O25:Eu2+/Dy3+ blue–green phosphorous as oxygen sensing materials(Elsevier B.V., 2016) Aydin I.; Ertekin K.; Demirci S.; Gultekin S.; Celik E.In this study, we utilized newly synthesized Sr4Al14O25:Eu2+/Dy3+ blue–green phosphors along with silver nanoparticles (AgNPs) for fabrication of oxygen sensitive materials. To the best of our knowledge oxygen sensing mechanism of the offered design is totally different from the previously published works. One-component silicone: poly (1-trimethylsilyl-1-propyne), two component phenyl bearing silicone, plasticized polymethylmethacrylate, and ethylcellulose (EC) were tested as matrix materials. Electrospun fibers, porous and smooth thin films were produced by electrospinning or knife coating technique. Oxygen induced luminescence of the phosphors at 544 nm was followed as the analytical signal. Utilization of silver nanoparticles in silicone along with phosphors resulted with a 7.14 fold enhancement in the signal intensity and significant spectral response towards oxygen competing with the signals of the oxygen sensors utilizing metalloporphyrins or ruthenium complexes. We observed high sensitivity and stability, increased surface area and an enhancement in all sensor dynamics. Linearity of the calibration plots was superior for the pO2 range of 0.0–20.0% with respect to the previously reported ones. When stored at the ambient air of the laboratory there was no significant drift in signal intensity after 12 months. Our sensitivity and stability tests are still in progress. © 2016 Elsevier B.V.Item Luminescent properties of scintillator nanophosphors produced by flame spray pyrolysis(Elsevier B.V., 2017) Yildirim S.; Karsu Asal E.C.; Ertekin K.; Celik E.In the present work flame spray pyrolysis synthesis and characterization of the nano-scale phosphors; M′-YTaO4 and M′-Y(Ta0.85Nb0.15)O4 have been studied for the first time. Phase and elemental analysis of the produced nanophosphors were carried out by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) measurements, respectively. The surface morphology and particle size of the nanophosphors were identified using scanning electron microscopy (SEM). The XRD results reveal that the nanophosphors have monoclinic M′-YTaO4 and M′-Y(Ta0.85Nb0.15)O4 phases belonging to the presence of M´-form of fergusonite structure. The particle sizes of the nanophosphors were found to be in the range of 50–100 nm. The spectroscopic characterization was performed by both radioluminescence (RL) and thermally stimulated luminescence (TSL) measurements after exposure to X-ray irradiation. Also, photoluminescence and decay times were investigated under UV excitation. The nanophosphors can be concluded as appropriate emissive materials for imaging, display and scintillator applications due to the efficient photoluminescence, moderate radioluminescence (RL) and thermally stimulated luminescence characteristics. © 2017 Elsevier B.V.Item Structural and luminescent properties of Er3+ and Tb3+-doped sol–gel-based bioactive glass powders and electrospun nanofibers(Springer, 2021) Deliormanlı A.M.; Rahman B.; Oguzlar S.; Ertekin K.In this study, sol–gel-based erbium (Er3+), terbium (Tb3+) and Er3+: Tb3 co-doped 1393 bioactive glass powders and electrospun nanofibers were prepared. Structural and morphological properties of the bioactive glasses as well as the photoluminescence characteristics were investigated in detail. The median particle size and average diameter of the prepared glass powders and fibers were in the range of ~ 1.5–3.5 μm and 280–660 nm, respectively. The steady-state photoluminescence and decay kinetics of the samples were investigated under excitation (374 nm) where only Er3+ and Tb3+ ions close to Si nanoclusters can be excited. All the samples prepared in the study exhibited bright green emission upon excitation at 374 nm. Results showed that the dopant concentration and the sample morphology have significant influence on the photoluminescence and decay properties of the glasses. Sol–gel-derived bioactive glass particles exhibited stronger emission intensity, whereas electrospun nanofibers showed extended decay times. In vitro bioactivity experiments revealed that Er3+ and Tb3+ doping did not inhibit the conversion of the glass samples to hydroxyapatite treated in simulated body fluid for 30 days. It was concluded that Er3+ and Tb3+-containing 1393 bioactive glasses have a potential to be used in tissue engineering applications as well as bioimaging studies. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Photoluminescence and decay characteristics of cerium, gallium and vanadium - containing borate-based bioactive glass powders for bioimaging applications(Elsevier Ltd, 2021) Deliormanlı A.M.; Oguzlar S.; Ertekin K.Biomaterials having photoluminescent properties play a crucial role in real-time bioimaging after in vivo implantation. In this study, photoluminescence properties and decay characteristics of the borate-based 13–93B3 glasses containing different concentrations of cerium, gallium, and vanadium oxides were investigated for biomedical applications. The borate-based bioactive glass powders were prepared using melt-quench technique and size reduction was performed through planetary ball milling. Bioactivity of the prepared powders was investigated in simulated body fluid at 37 °C under static conditions. The photoluminescent properties and decay kinetics of the as-prepared and the SBF-treated bioactive glass powders were analyzed by steady-state and time-resolved photoluminescence measurements. Results revealed that the cerium activated glasses exhibited an intense luminescence centered at 538 nm. Broad-band emission of the gallium and vanadium doped samples was centered at 440 and 572 nm, respectively. All of the SBF-treated glasses exhibited enhanced lifetimes and bi-exponential decays both in nanosecond and microsecond regime measurements. It was concluded that depending on the dopant concentration, bioactive glass particles prepared in the study showed remarkable photoluminescence and have potential to be used in bioimaging applications. © 2020 Elsevier Ltd and Techna Group S.r.l.Item Emission based response of Er3+, Tb3+, and Er3+-Tb3+ co-doped 1393 bioactive glasses along with HPTS towards CO2(Elsevier B.V., 2025) Ulucan U.; Oguzlar S.; Deliormanlı A.M.; Ertekin K.The HPTS serves as a versatile tool in pH and CO2 sensing studies, as well as in cell biology studies of various processes. However, the long-term photostability of HPTS as a fluorescent dye is an important consideration in its use, especially for long-term applications. In this work, sol–gel synthesized Er3+, Tb3+ and Er3+: Tb3+ co-doped 1393 bioactive glass particles were incorporated with the HPTS in the presence of ionic liquid in an ethyl cellulose matrix. The interaction of the bioactive glasses with the HPTS was investigated by steady-state luminescence and excited-state lifetime measurements. The prepared composites showed linearizable responses when exposed to different CO2 concentrations. High I0/I100 values (87, 109 and 115) were obtained for the binary blends of HPTS and bioactive glasses. When the imidazolium-based IL was used together with the offered composites, we observed improved stability and longevity for the HPTS up to 315 days. The incorporation of imidazolium-based ionic liquids as additives in HPTS-based fluorescence assays together with the bioactive glasses holds promise for enhancing the photostability of the HPTS and improving the reliability and longevity of fluorescence signals in various research applications. © 2024 Elsevier B.V.