Yavuz Onganer - Academia.edu (original) (raw)

Papers by Yavuz Onganer

Social Science Research Network, 2022

Journal of Colloid and Interface Science, 1998

Granular activated carbon was utilized as adsorbent for the removal of Fe(III) ions from aqueous ... more Granular activated carbon was utilized as adsorbent for the removal of Fe(III) ions from aqueous solutions at different temperatures and fixed pH. The batch adsorption kinetics has been described by the Lagergren equation which is a pseudo-first-order rate expression; the surface mass transfer coefficients and diffusion coefficients have been calculated at different temperatures. The intraparticle transport of Fe(III) within the pores of activated carbon was found to be the rate-limiting step, while the process of uptake obeyed the Langmuir model of adsorption.

Synthetic Metals, 2018

In this study, fluorescence resonance energy transfer (FRET) between CdS quantum dots (QDs) and R... more In this study, fluorescence resonance energy transfer (FRET) between CdS quantum dots (QDs) and Rhodamine 101 was investigated in reverse micelles. CdS QDs as donor were synthesized by using reverse micelle method. The particle sizes of CdS QDs were found as 1.18 ± 0.05 for QD1 and 2.11 ± 0.25 nm for QD2 with TEM measurements. It was determined that the fluorescence intensity of the QDs quenched as the concentration of Rh101 increased. The effect of the concentration of dye on the quenching of the fluorescence intensity of QDs was evaluated by the Stern-Volmer approach and K SV and k q values were calculated. It was observed that the quenching was not diffusion controlled. The FRET parameters were also calculated by using fluorescence spectroscopy. The distances between donor-acceptor (r) were also calculated as 4.74 nm for QD1 and 2.26 nm for QD2. The steady-state transfer efficiencies were calculated as 0.24 and 0.53 for QD1 and QD2, respectively. The time-resolved transfer efficiencies were also determined as 0.11 for QD1 and 0.48 for QD2. The results demonstrated that the novel donor-acceptor pairs may play an important role in the applications of many research areas such as FRET-based nanosensors and light harvesting devices.

Journal of Photochemistry and Photobiology A: Chemistry, 2021

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021

Colloids and Surfaces B: Biointerfaces, 2021

Graphene oxide (GO), one of the popular materials in recent years, has been synthesized according... more Graphene oxide (GO), one of the popular materials in recent years, has been synthesized according to the modified Hummers' method. Stable dispersions of different amounts of negatively charged GO were prepared in aqueous media. The GO/dye composites were prepared in deionized water by a simple method with the positively charged Safranin T compound (SfT), which is known to have strong fluorescence properties. By changing the GO/dye ratio, it was obtained stable composites in aqueous media. It was investigated the interaction of SfT with GO in an aqueous solution under the critical micelle concentration (CMC), at the CMC and above the CMC by adding sodium dodecyl sulfate (SDS). It was clarified the formation of GO-SfT composites by using spectroscopic techniques. In these composites, the effect of GO layers on the SfT's photophysical properties was examined by absorption and fluorescence spectroscopy techniques. The change in the quenching effect of GO was monitored both adding a stabilizing electrolyte (NaCl) to the media and changing the pH of the medium. The evaluation was on the probability of the GO-SfT-SDS ternary system being a pH sensing biological sensor material. As a result of this study, it was thought that the GO-SfT-SDS system could be functionalized as a fluorescent pH sensor by taking advantage of GO's sensitivity to pH.

Journal of Photochemistry and Photobiology A: Chemistry, 2020

Aggregation of the cationic dyes pyronin B (PyB) and pyronin Y (PyY) in aqueous solution containi... more Aggregation of the cationic dyes pyronin B (PyB) and pyronin Y (PyY) in aqueous solution containing anionic polyelectrolyte polystyrene sulfonate (PSS) has been studied by using steady-state and time-resolved fluorescence and UV-vis absorption spectroscopy techniques. Although H-aggregates of these pyronin dyes have been previously observed in colloidal suspension, this is the first report of their J-aggregates obtained as a function of dye concentration by using constant concentration of PSS in solution. The best dye concentrations for the Jaggregates were determined as 2.4 × 10 −5 M and 1.2 × 10-4 M for PyB and PyY, respectively. Moreover, aggregation equilibrium constants (K D) and thermodynamic functions were determined as a function of temperature for H-type aggregation. By employing the exciton theory, angle (α) between the molecular transition dipole moments and the long aggregate axis, and the intermolecular distance (R) were also calculated for each dye aggregates. In addition, the fluorescence lifetime values were determined from fluorescence decay measurements for the monomer and aggregated species of pyronin compounds in polyelectrolyte aqueous solution.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2019

Langmuir films of cationic octadecylamine (ODA +) has been prepared by Langmuir-Blodgett (LB) fil... more Langmuir films of cationic octadecylamine (ODA +) has been prepared by Langmuir-Blodgett (LB) film technique and is used as an immobilization matrix for polyphenol oxidase (PPO). The immobilization areas of PPO were demonstrated by an electrostatic surface potential map. PPO-ODA complexes were transferred onto ITO electrode which was then characterized for its catalytic and optical properties. Very high and maintained PPO activity of PPO-ODA/ITO bio-electrode was shown by UV-vis absorption studies. The highly sensitive and stability biosensor behavior of the bio-electrode was shown via cyclic voltammetry studies. The stability, sensitivity, LOD and, LOQ values of the prepared sensor were calculated as 94.83% (after two weeks), 1.839 μAmM −1 cm −2 , 0.644 μM and, 0.214 μM, respectively for pyrocatechol in a wide linear range (10-100 mM). Successful prepare of the bio-electrode was confirmed from SEM and FT-IR techniques. This study revealed that the immobilization with LB film techniques contributes to the stability and recycling of PPO and its use in biological systems is superior to other film techniques mentioned in the literature. In this study, disadvantages that are observed in enzyme-based sensors were minimized. The first application of the bio-electrodes can be a promising tool towards enzymatic studies and opens a new path for industrial applications such as removing and transforming toxic compounds in industrial processes, decolorization, and drug industry such as biotechnological production of L-DOPA.

Dyes and Pigments, 2018

Please cite this article as: Şenol AyşMerve, Metin Ö, Onganer Y, A facile route for the preparati... more Please cite this article as: Şenol AyşMerve, Metin Ö, Onganer Y, A facile route for the preparation of silver nanoparticles-graphene oxide nanocomposites and their interactions with pyronin Y dye molecules, Dyes and Pigments (2018), doi:

Journal of Molecular Structure, 2018

The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse... more The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse micelle systems by using molecular UV-Vis absorption, steady-state and timeresolved fluorescence spectroscopy techniques. For this purpose, the fluorescence spectra of C120 dye in reverse micelle systems with different values of W 0 (from 0 to 45) were examined. The bathochromic shift from 400 nm to 439 nm was observed for the fluorescence maxima of C120. It was found that intramolecular arrangements occurred in the structure of C120 molecule due to specific solute-solvent interactions. Fluorescence lifetime measurements were carried out and quantum yield values, radiative (k r) and non-radiative rate constants (k nr) were calculated. The data compared with the values reported in the literature. Steady-state anisotropy (r) studies were done to explain the microenvironment around the C120 molecules. Anisotropy data varying 0.048 to 0.030 with varying W 0 displayed that the microenvironment for the C120 dye in water pools of reverse micelles was different than C120 dye in pure water which is 0.009. The microviscosity and rotational relaxation time values were calculated as a function of W 0. We have determined that C120 dye is a useful probe for the definition the microviscosity of reverse micelles with different water pool sizes.

Luminescence, 2018

The photophysical properties and photodynamics of Pyronin Y (PyY) dye compound in seven polar pro... more The photophysical properties and photodynamics of Pyronin Y (PyY) dye compound in seven polar protic solvents (n-alcohols) were examined as a function of temperature by using UV-visible, steady-state and time-resolved fluorescence spectroscopy techniques. To understand dye-solvent interactions, photophysical parameters including Stokes' shifts, fluorescence quantum yields and fluorescence lifetimes were determined. To examine the effect of solvent polarity, the difference between the ground state dipole moment and the excited state dipole moment was determined. For this purpose, the multiple regression analysis and the Kamlet-Taft technique were used. Moreover, photodynamic parameters, rotational relaxation times and steady-state anisotropy were calculated. The result showed that the specific interactions of PyY with the solvent molecules take place through hydrogen bonding. As the hydrocarbon chain of the alcohols gets longer, photophysical parameters diminish, probably because of weaker hydrogen bonding. Furthermore, it was found out that the dipole moment of excited states (μ e) is higher than that of the ground state (μ g). In addition, Brownian motions increased with the increasing temperature that weakened the fluorescence character of PyY. It was also revealed that the rotation of PyY increased with a prolonged hydrocarbon chain of alcohol series, due to the lesser extent of hydrogen bonding.

Dyes and Pigments, 2017

The monitoring of bovine serum albumin (BSA) and deoxyribonucleic acid (DNA) in physiological pH ... more The monitoring of bovine serum albumin (BSA) and deoxyribonucleic acid (DNA) in physiological pH were studied comparatively by using coumarin 35 dye (C35). For this aim, the binding constant and binding number sites for the interactions of the dye with BSA and DNA were determined by Scatchard method. According to the spectroscopic data, fluorescence intensity of C35 was 30-fold and 8.5-fold increased with the presence of BSA and DNA, respectively. Effects of metal ions on the interactions between BSA-C35 and DNA-C35 systems were also studied in terms of metal ion sensor properties. Therefore, the effect of thirteen cations (

Sensors and Actuators B: Chemical, 2017

Polyethyleneimine (PEI)-modified reduced graphene oxide (rGO) based fluorescent sensor is reporte... more Polyethyleneimine (PEI)-modified reduced graphene oxide (rGO) based fluorescent sensor is reported for metal-ion sensing. PEI-rGO nanocomposites are synthesized by a facile and controllable method using hydrazine hydrate as a main reducing agent and PEI that is a reducing agent, surface modifier and polymer host. The formation of PEI-rGO nanocomposites is confirmed with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV-vis spectroscopy, Zeta potential measurements and Dynamic Light Scattering (DLS) analysis. Afterward, the interaction of fluorescein (FL) with PEI-rGO nanocomposites in aqueous dispersion, leading to the formation of FL/PEI-rGO ternary system, are studied at various conditions by using UV-vis absorption, steady-state and time-resolved fluorescence spectroscopies. It is observed that the photophysical properties of FL are dependent on the amount of both FL and PEI-rGO nanocomposites. The sensing ability of FL/PEI-rGO ternary system are examined in the detection of metal ions as a fluorescent sensor. The spectroscopic data reveal that the FL/PEI-rGO ternary system shows high sensitivity and selectivity for Fe 3+ ions in aqueous solution. The detection limit for Fe 3+ are determined to be 1.12 M.

AIP Conference Proceedings, 2016

Thin films of pyronin dye mixed with poly(vinyl alcohol) (PVA) on glass substrate were prepared b... more Thin films of pyronin dye mixed with poly(vinyl alcohol) (PVA) on glass substrate were prepared by using spin-coating technique. The optical and morphological properties of the thin films were studied by UV-Vis., steady-state fluorescence spectroscopies and atomic force microscopy (AFM). The thin films on glass substrate were fabricated at various [PVA]/[dye] (P/D) ratios. Hence, the monomeric and H-aggregates thin films of pyronin dye mixed with PVA were formed as a function of the dye and PVA concentration. It was determined that while the monomeric thin films showed strong fluorescence, the formation of H-aggregates in the thin film caused to decreasing the fluorescence intensity. AFM studies demonstrated that the morphology of the thin film was drastically varied with changing the optical property of the thin film such as monomeric and H-aggregates thin films.

Applied Surface Science, 2015

Abstract The present study focused on the adsorption and photophysical properties of pyronin B (P... more Abstract The present study focused on the adsorption and photophysical properties of pyronin B (PyB) in bentonite aqueous dispersion. The photophysical properties of PyB in the aqueous dispersion were studied by using UV–vis absorption, steady-state and time-resolved fluorescence spectroscopy techniques. In this concept, the interaction of the dye with bentonite particles in the aqueous dispersion was spectroscopically followed depending on certain parameters such as interaction time, pH and the dye concentration. Obtained spectral data revealed that the aggregate structures (H-type) of PyB in the aqueous dispersion were formed in the dye concentration range studied. The non-fluorescence nature of H-aggregates and the clay minerals governed the fluorescence property of PyB. The mentioned non-radiative processes caused the fluorescence lifetime of the dye to decrease compared to that in water. The adsorption process of PyB on bentonite was examined depending on contact time and initial adsorbate concentration. An adsorption isotherm was good-fitted by the Freundlich model with a linear regression correlation value of 0.999. The adsorption of PyB on bentonite particles was in agreement with pseudo second-order kinetics.

Sensors and Actuators B: Chemical, 2016

Abstract We report a controllable molecular aggregation of Merocyanine 540 (MC 540) with the assi... more Abstract We report a controllable molecular aggregation of Merocyanine 540 (MC 540) with the assistance of polyethylenimine (PEI) in aqueous solution and its application in the detection of metal ions as a colorimetric sensor. Photophysical properties of MC 540 in aqueous solution was studied by using UV–Vis and fluorescence (steady-state and time-resolved) spectroscopies under various conditions. The spectroscopic data revealed that the interaction of MC 540 with PEI in aqueous solution triggered the formation of its nonfluorescence H-aggregates. The formation of H-aggregates of MC 540 was followed with photophysical parameters such as fluorescence quantum yield and fluorescence lifetime values along with spectroscopic measurements. It was concluded that H-type aggregation was mainly dependent on both MC 540 and PEI concentrations. The effects of pH, temperature and metal ions on H-aggregates of MC 540 in aqueous solution were explored in detail. Interestingly, it was observed that H-aggregates of MC 540 were destroyed and converted to its H-dimer states in the presence of Ni 2+ , Cu 2+ , Al 3+ , Fe 3+ , Sn 4+ ions. Consequently, the controllable aggregation state of MC 540 with Ni 2+ , Cu 2+ , Al 3+ , Fe 3+ , Sn 4+ ions was designed as a colorimetric sensor.

Journal of Molecular Structure, 2016

Abstract The thin films of pyronin B (PyB) and pyronin Y (PyY) mixed with poly(vinyl sulphate) (P... more Abstract The thin films of pyronin B (PyB) and pyronin Y (PyY) mixed with poly(vinyl sulphate) (PVS) on glass substrate from aqueous solution were fabricated using a simple spin-coating film technique. The photophysical properties of the thin films were examined by UV–Vis, steady-state fluorescence and time-resolved fluorescence spectroscopy techniques. The dye thin films on the glass substrate were prepared at various [PVS]/[dye] ratios. The interactions of pyronin dyes with PVS caused the formation of monomeric and H-aggregate thin films of the dyes. H-aggregates of pyronin dyes in the thin film quenched their fluorescence intensities while the monomeric dye films have strong fluorescence. Moreover, the presence of H-aggregates in the thin film also decreased the fluorescence lifetimes of dyes. The morphological variations in the thin films depending on the dye concentration were investigated by AFM. The morphological analysis of the thin films revealed that the thin films including H-aggregates were predominant in fibril-like structures while the monomeric thin films displayed the same morphologies compared to that observed in pristine PVS film. When the spectroscopic and morphological results were evaluated, it was concluded that H-aggregates of pyronin dyes were formed due to the adsorption of the dyes on PVS backbone.

Applied Surface Science, 2015

Highlights ►Fluorescent carbon dots (C-dots) are synthesized by a facile method. ►The as-prepared... more Highlights ►Fluorescent carbon dots (C-dots) are synthesized by a facile method. ►The as-prepared C-dots have strong fluorescence between 350-550 nm. ►In a wide pH and temperature range, the C-dots are stable and show fluorescence property. ►The C-dots can be used to detect Fe +3 as a fluorescence sensor. Liquid nitrogen-assisted synthesis of fluorescent carbon dots from Blueberry and their performance in Fe 3+ detection

Social Science Research Network, 2022

Journal of Colloid and Interface Science, 1998

Granular activated carbon was utilized as adsorbent for the removal of Fe(III) ions from aqueous ... more Granular activated carbon was utilized as adsorbent for the removal of Fe(III) ions from aqueous solutions at different temperatures and fixed pH. The batch adsorption kinetics has been described by the Lagergren equation which is a pseudo-first-order rate expression; the surface mass transfer coefficients and diffusion coefficients have been calculated at different temperatures. The intraparticle transport of Fe(III) within the pores of activated carbon was found to be the rate-limiting step, while the process of uptake obeyed the Langmuir model of adsorption.

Synthetic Metals, 2018

In this study, fluorescence resonance energy transfer (FRET) between CdS quantum dots (QDs) and R... more In this study, fluorescence resonance energy transfer (FRET) between CdS quantum dots (QDs) and Rhodamine 101 was investigated in reverse micelles. CdS QDs as donor were synthesized by using reverse micelle method. The particle sizes of CdS QDs were found as 1.18 ± 0.05 for QD1 and 2.11 ± 0.25 nm for QD2 with TEM measurements. It was determined that the fluorescence intensity of the QDs quenched as the concentration of Rh101 increased. The effect of the concentration of dye on the quenching of the fluorescence intensity of QDs was evaluated by the Stern-Volmer approach and K SV and k q values were calculated. It was observed that the quenching was not diffusion controlled. The FRET parameters were also calculated by using fluorescence spectroscopy. The distances between donor-acceptor (r) were also calculated as 4.74 nm for QD1 and 2.26 nm for QD2. The steady-state transfer efficiencies were calculated as 0.24 and 0.53 for QD1 and QD2, respectively. The time-resolved transfer efficiencies were also determined as 0.11 for QD1 and 0.48 for QD2. The results demonstrated that the novel donor-acceptor pairs may play an important role in the applications of many research areas such as FRET-based nanosensors and light harvesting devices.

Journal of Photochemistry and Photobiology A: Chemistry, 2021

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021

Colloids and Surfaces B: Biointerfaces, 2021

Graphene oxide (GO), one of the popular materials in recent years, has been synthesized according... more Graphene oxide (GO), one of the popular materials in recent years, has been synthesized according to the modified Hummers' method. Stable dispersions of different amounts of negatively charged GO were prepared in aqueous media. The GO/dye composites were prepared in deionized water by a simple method with the positively charged Safranin T compound (SfT), which is known to have strong fluorescence properties. By changing the GO/dye ratio, it was obtained stable composites in aqueous media. It was investigated the interaction of SfT with GO in an aqueous solution under the critical micelle concentration (CMC), at the CMC and above the CMC by adding sodium dodecyl sulfate (SDS). It was clarified the formation of GO-SfT composites by using spectroscopic techniques. In these composites, the effect of GO layers on the SfT's photophysical properties was examined by absorption and fluorescence spectroscopy techniques. The change in the quenching effect of GO was monitored both adding a stabilizing electrolyte (NaCl) to the media and changing the pH of the medium. The evaluation was on the probability of the GO-SfT-SDS ternary system being a pH sensing biological sensor material. As a result of this study, it was thought that the GO-SfT-SDS system could be functionalized as a fluorescent pH sensor by taking advantage of GO's sensitivity to pH.

Journal of Photochemistry and Photobiology A: Chemistry, 2020

Aggregation of the cationic dyes pyronin B (PyB) and pyronin Y (PyY) in aqueous solution containi... more Aggregation of the cationic dyes pyronin B (PyB) and pyronin Y (PyY) in aqueous solution containing anionic polyelectrolyte polystyrene sulfonate (PSS) has been studied by using steady-state and time-resolved fluorescence and UV-vis absorption spectroscopy techniques. Although H-aggregates of these pyronin dyes have been previously observed in colloidal suspension, this is the first report of their J-aggregates obtained as a function of dye concentration by using constant concentration of PSS in solution. The best dye concentrations for the Jaggregates were determined as 2.4 × 10 −5 M and 1.2 × 10-4 M for PyB and PyY, respectively. Moreover, aggregation equilibrium constants (K D) and thermodynamic functions were determined as a function of temperature for H-type aggregation. By employing the exciton theory, angle (α) between the molecular transition dipole moments and the long aggregate axis, and the intermolecular distance (R) were also calculated for each dye aggregates. In addition, the fluorescence lifetime values were determined from fluorescence decay measurements for the monomer and aggregated species of pyronin compounds in polyelectrolyte aqueous solution.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2019

Langmuir films of cationic octadecylamine (ODA +) has been prepared by Langmuir-Blodgett (LB) fil... more Langmuir films of cationic octadecylamine (ODA +) has been prepared by Langmuir-Blodgett (LB) film technique and is used as an immobilization matrix for polyphenol oxidase (PPO). The immobilization areas of PPO were demonstrated by an electrostatic surface potential map. PPO-ODA complexes were transferred onto ITO electrode which was then characterized for its catalytic and optical properties. Very high and maintained PPO activity of PPO-ODA/ITO bio-electrode was shown by UV-vis absorption studies. The highly sensitive and stability biosensor behavior of the bio-electrode was shown via cyclic voltammetry studies. The stability, sensitivity, LOD and, LOQ values of the prepared sensor were calculated as 94.83% (after two weeks), 1.839 μAmM −1 cm −2 , 0.644 μM and, 0.214 μM, respectively for pyrocatechol in a wide linear range (10-100 mM). Successful prepare of the bio-electrode was confirmed from SEM and FT-IR techniques. This study revealed that the immobilization with LB film techniques contributes to the stability and recycling of PPO and its use in biological systems is superior to other film techniques mentioned in the literature. In this study, disadvantages that are observed in enzyme-based sensors were minimized. The first application of the bio-electrodes can be a promising tool towards enzymatic studies and opens a new path for industrial applications such as removing and transforming toxic compounds in industrial processes, decolorization, and drug industry such as biotechnological production of L-DOPA.

Dyes and Pigments, 2018

Please cite this article as: Şenol AyşMerve, Metin Ö, Onganer Y, A facile route for the preparati... more Please cite this article as: Şenol AyşMerve, Metin Ö, Onganer Y, A facile route for the preparation of silver nanoparticles-graphene oxide nanocomposites and their interactions with pyronin Y dye molecules, Dyes and Pigments (2018), doi:

Journal of Molecular Structure, 2018

The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse... more The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse micelle systems by using molecular UV-Vis absorption, steady-state and timeresolved fluorescence spectroscopy techniques. For this purpose, the fluorescence spectra of C120 dye in reverse micelle systems with different values of W 0 (from 0 to 45) were examined. The bathochromic shift from 400 nm to 439 nm was observed for the fluorescence maxima of C120. It was found that intramolecular arrangements occurred in the structure of C120 molecule due to specific solute-solvent interactions. Fluorescence lifetime measurements were carried out and quantum yield values, radiative (k r) and non-radiative rate constants (k nr) were calculated. The data compared with the values reported in the literature. Steady-state anisotropy (r) studies were done to explain the microenvironment around the C120 molecules. Anisotropy data varying 0.048 to 0.030 with varying W 0 displayed that the microenvironment for the C120 dye in water pools of reverse micelles was different than C120 dye in pure water which is 0.009. The microviscosity and rotational relaxation time values were calculated as a function of W 0. We have determined that C120 dye is a useful probe for the definition the microviscosity of reverse micelles with different water pool sizes.

Luminescence, 2018

The photophysical properties and photodynamics of Pyronin Y (PyY) dye compound in seven polar pro... more The photophysical properties and photodynamics of Pyronin Y (PyY) dye compound in seven polar protic solvents (n-alcohols) were examined as a function of temperature by using UV-visible, steady-state and time-resolved fluorescence spectroscopy techniques. To understand dye-solvent interactions, photophysical parameters including Stokes' shifts, fluorescence quantum yields and fluorescence lifetimes were determined. To examine the effect of solvent polarity, the difference between the ground state dipole moment and the excited state dipole moment was determined. For this purpose, the multiple regression analysis and the Kamlet-Taft technique were used. Moreover, photodynamic parameters, rotational relaxation times and steady-state anisotropy were calculated. The result showed that the specific interactions of PyY with the solvent molecules take place through hydrogen bonding. As the hydrocarbon chain of the alcohols gets longer, photophysical parameters diminish, probably because of weaker hydrogen bonding. Furthermore, it was found out that the dipole moment of excited states (μ e) is higher than that of the ground state (μ g). In addition, Brownian motions increased with the increasing temperature that weakened the fluorescence character of PyY. It was also revealed that the rotation of PyY increased with a prolonged hydrocarbon chain of alcohol series, due to the lesser extent of hydrogen bonding.

Dyes and Pigments, 2017

The monitoring of bovine serum albumin (BSA) and deoxyribonucleic acid (DNA) in physiological pH ... more The monitoring of bovine serum albumin (BSA) and deoxyribonucleic acid (DNA) in physiological pH were studied comparatively by using coumarin 35 dye (C35). For this aim, the binding constant and binding number sites for the interactions of the dye with BSA and DNA were determined by Scatchard method. According to the spectroscopic data, fluorescence intensity of C35 was 30-fold and 8.5-fold increased with the presence of BSA and DNA, respectively. Effects of metal ions on the interactions between BSA-C35 and DNA-C35 systems were also studied in terms of metal ion sensor properties. Therefore, the effect of thirteen cations (

Sensors and Actuators B: Chemical, 2017

Polyethyleneimine (PEI)-modified reduced graphene oxide (rGO) based fluorescent sensor is reporte... more Polyethyleneimine (PEI)-modified reduced graphene oxide (rGO) based fluorescent sensor is reported for metal-ion sensing. PEI-rGO nanocomposites are synthesized by a facile and controllable method using hydrazine hydrate as a main reducing agent and PEI that is a reducing agent, surface modifier and polymer host. The formation of PEI-rGO nanocomposites is confirmed with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV-vis spectroscopy, Zeta potential measurements and Dynamic Light Scattering (DLS) analysis. Afterward, the interaction of fluorescein (FL) with PEI-rGO nanocomposites in aqueous dispersion, leading to the formation of FL/PEI-rGO ternary system, are studied at various conditions by using UV-vis absorption, steady-state and time-resolved fluorescence spectroscopies. It is observed that the photophysical properties of FL are dependent on the amount of both FL and PEI-rGO nanocomposites. The sensing ability of FL/PEI-rGO ternary system are examined in the detection of metal ions as a fluorescent sensor. The spectroscopic data reveal that the FL/PEI-rGO ternary system shows high sensitivity and selectivity for Fe 3+ ions in aqueous solution. The detection limit for Fe 3+ are determined to be 1.12 M.

AIP Conference Proceedings, 2016

Thin films of pyronin dye mixed with poly(vinyl alcohol) (PVA) on glass substrate were prepared b... more Thin films of pyronin dye mixed with poly(vinyl alcohol) (PVA) on glass substrate were prepared by using spin-coating technique. The optical and morphological properties of the thin films were studied by UV-Vis., steady-state fluorescence spectroscopies and atomic force microscopy (AFM). The thin films on glass substrate were fabricated at various [PVA]/[dye] (P/D) ratios. Hence, the monomeric and H-aggregates thin films of pyronin dye mixed with PVA were formed as a function of the dye and PVA concentration. It was determined that while the monomeric thin films showed strong fluorescence, the formation of H-aggregates in the thin film caused to decreasing the fluorescence intensity. AFM studies demonstrated that the morphology of the thin film was drastically varied with changing the optical property of the thin film such as monomeric and H-aggregates thin films.

Applied Surface Science, 2015

Abstract The present study focused on the adsorption and photophysical properties of pyronin B (P... more Abstract The present study focused on the adsorption and photophysical properties of pyronin B (PyB) in bentonite aqueous dispersion. The photophysical properties of PyB in the aqueous dispersion were studied by using UV–vis absorption, steady-state and time-resolved fluorescence spectroscopy techniques. In this concept, the interaction of the dye with bentonite particles in the aqueous dispersion was spectroscopically followed depending on certain parameters such as interaction time, pH and the dye concentration. Obtained spectral data revealed that the aggregate structures (H-type) of PyB in the aqueous dispersion were formed in the dye concentration range studied. The non-fluorescence nature of H-aggregates and the clay minerals governed the fluorescence property of PyB. The mentioned non-radiative processes caused the fluorescence lifetime of the dye to decrease compared to that in water. The adsorption process of PyB on bentonite was examined depending on contact time and initial adsorbate concentration. An adsorption isotherm was good-fitted by the Freundlich model with a linear regression correlation value of 0.999. The adsorption of PyB on bentonite particles was in agreement with pseudo second-order kinetics.

Sensors and Actuators B: Chemical, 2016

Abstract We report a controllable molecular aggregation of Merocyanine 540 (MC 540) with the assi... more Abstract We report a controllable molecular aggregation of Merocyanine 540 (MC 540) with the assistance of polyethylenimine (PEI) in aqueous solution and its application in the detection of metal ions as a colorimetric sensor. Photophysical properties of MC 540 in aqueous solution was studied by using UV–Vis and fluorescence (steady-state and time-resolved) spectroscopies under various conditions. The spectroscopic data revealed that the interaction of MC 540 with PEI in aqueous solution triggered the formation of its nonfluorescence H-aggregates. The formation of H-aggregates of MC 540 was followed with photophysical parameters such as fluorescence quantum yield and fluorescence lifetime values along with spectroscopic measurements. It was concluded that H-type aggregation was mainly dependent on both MC 540 and PEI concentrations. The effects of pH, temperature and metal ions on H-aggregates of MC 540 in aqueous solution were explored in detail. Interestingly, it was observed that H-aggregates of MC 540 were destroyed and converted to its H-dimer states in the presence of Ni 2+ , Cu 2+ , Al 3+ , Fe 3+ , Sn 4+ ions. Consequently, the controllable aggregation state of MC 540 with Ni 2+ , Cu 2+ , Al 3+ , Fe 3+ , Sn 4+ ions was designed as a colorimetric sensor.

Journal of Molecular Structure, 2016

Abstract The thin films of pyronin B (PyB) and pyronin Y (PyY) mixed with poly(vinyl sulphate) (P... more Abstract The thin films of pyronin B (PyB) and pyronin Y (PyY) mixed with poly(vinyl sulphate) (PVS) on glass substrate from aqueous solution were fabricated using a simple spin-coating film technique. The photophysical properties of the thin films were examined by UV–Vis, steady-state fluorescence and time-resolved fluorescence spectroscopy techniques. The dye thin films on the glass substrate were prepared at various [PVS]/[dye] ratios. The interactions of pyronin dyes with PVS caused the formation of monomeric and H-aggregate thin films of the dyes. H-aggregates of pyronin dyes in the thin film quenched their fluorescence intensities while the monomeric dye films have strong fluorescence. Moreover, the presence of H-aggregates in the thin film also decreased the fluorescence lifetimes of dyes. The morphological variations in the thin films depending on the dye concentration were investigated by AFM. The morphological analysis of the thin films revealed that the thin films including H-aggregates were predominant in fibril-like structures while the monomeric thin films displayed the same morphologies compared to that observed in pristine PVS film. When the spectroscopic and morphological results were evaluated, it was concluded that H-aggregates of pyronin dyes were formed due to the adsorption of the dyes on PVS backbone.

Applied Surface Science, 2015

Highlights ►Fluorescent carbon dots (C-dots) are synthesized by a facile method. ►The as-prepared... more Highlights ►Fluorescent carbon dots (C-dots) are synthesized by a facile method. ►The as-prepared C-dots have strong fluorescence between 350-550 nm. ►In a wide pH and temperature range, the C-dots are stable and show fluorescence property. ►The C-dots can be used to detect Fe +3 as a fluorescence sensor. Liquid nitrogen-assisted synthesis of fluorescent carbon dots from Blueberry and their performance in Fe 3+ detection