Researcher:
Durmuşoğlu, Emek Göksu

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PhD Student

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Emek Göksu

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Durmuşoğlu

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Durmuşoğlu, Emek Göksu

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2016 - 20207

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Now showing 1 - 7 of 7
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    A new substrate for glutathione reductase: glutathione coated Ag2S quantum dots
    (Elsevier, 2019) N/A; N/A; N/A; Department of Chemistry; N/A; Aydemir, Duygu; Hashemkhani, Mahshid; Durmuşoğlu, Emek Göksu; Acar, Havva Funda Yağcı; Ulusu, Nuriye Nuray; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Health Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; School of Medicine; N/A, N/A; N/A; 178902; 6807
    Glutathione (GSH), a key player in various cellular processes including detoxification, anti-oxidant defense system and cell proliferation is also a potentially good coating material for luminescent quantum dots. GSH is oxidized to oxidized glutathione (GSSG) under oxidative stress and then reduced back by glutathione reductase (GR) enzyme to maintain the balance of GSH/GSSG ratio. In this frame, GSH stabilized quantum dots (QDs) have never been evaluated as GR substrate. Here, GSH coated Ag2S QDs, luminescent in the medical window, were prepared and their GR activity were tested. We have shown by spectrophotometric methods that GSH-Ag2S acted as a substrate-analog for GR enzyme that had lower activity compared to the original substrate GSSG. These results provide a new perspective in the evaluation of QDs in medical applications, enzyme activity or level detection as well as possible means to study enzymes.
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    Production of small, stable PbS/CdS quantum dots via room temperature cation exchange followed by a low temperature annealing processes
    (American Chemical Society (ACS), 2017) Yıldızhan, Melike M.; Gulgun, Mehmet A.; N/A; Department of Chemistry; Durmuşoğlu, Emek Göksu; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178902
    Here, we discuss a simple low temperature process for the synthesis of small and stable PbS/CdS QDs with emission below 1100 nm. For this, small PbS QDs with emission below 1100 nm synthesized from PbCl2 in oleylamine with 1-dodecanethiol, as reported by our group recently, were used. A thin CdS shell was grown on PbS at room temperature (RT) via cation exchange (CE), which is a self-limiting process providing about 100 nm blue shift in the emission maxima, hence is quite practical for reaction control and production of predictable particles. RTCE process provides 6-9 times stronger emission than original PbS with better optical stability. Annealing of the PbS/CdS QDs in solid state at mild temperatures (50-100 degrees C) improves crystallinity of the particles. Final ligand exchange on the annealed PbS/CdS with 1-dodecanethiol (DT) enhances the long-term stability of particles further. The optimum overall process is determined as RTCE followed by annealing at 50 degrees C for 1 h and finished with ligand exchange with DT. Influence of these processes on QD structure and optical properties were studied as well as stability in chloroform and petroleum products (diesel and gasoline) for possible optical tagging applications of such liquids. Overall, a simple, controllable, and scalable method is developed to produce highly stable, bright, size-tunable PbS/CdS QDs with emission detectable with low cost semiconductor detectors.
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    Green synthesis of strongly luminescent, ultrasmall pbs and pbse quantum dots
    (Amer Chemical Soc, 2017) N/A; Department of Chemistry; Department of Chemistry; Durmuşoğlu, Emek Göksu; Türker, Yurdanur; Acar, Havva Funda Yağcı; PhD Student; Researcher; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 178902
    Although size tunable synthesis of PbS between 3 and 10 nm with emission in the NIR. II region is well-known, there is no well-established method to produce smaller particles with emission below 1000 nm, which is easier to detect with less costly and more widely available Si and extented PMT-detectors. Here, we demonstrate synthesis of PbS QDs in sizes between 2.4 and 3.2 nm using PbCl2, elemental S, dodecanethiol (DT), and a toluene/oleylamine mixture at low temperatures (65-80 C-omicron). It was shown that addition of DT enhances the solubility of S and DT binds to the crystal surface during the growth, hence reducing the size with enhanced luminescence intensity. Use of toluene as a cosolvent reduces the viscosity and provides an additional reduction in the size. Using these variables, size tunable synthesis of highly luminescent QDs were achieved. Furthermore, we applied additional DT ligand exchange as a postprocess that increases the long-term stability of particles. The photoluminescence lifetime investigation provided insight into the luminescence properties of OLA/DT and DT-capped PbS QDs. Finally, we successfully expanded our synthesis method to the synthesis of small PbSe QDs.
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    Discovery of an exceptionally strong luminescence of polyethyleneimine-superparamagnetic iron oxide nanoparticles
    (Wiley-V C H Verlag Gmbh, 2018) Erdem, Emre; Ow-Yang, Cleva W.; N/A; Department of Chemistry; Department of Chemistry; N/A; N/A; Department of Chemistry; Ünal, Özlem; Yurtsever, İsmail Ersin; Khodadust, Rouhollah; Yağcı, Mustafa Barış; Durmuşoğlu, Emek Göksu; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Other; Researcher; N/A; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; College of Sciences; N/A; 7129; N/A; N/A; N/A; 178902
    Polyethyleneimine (PEI) is rarely recognized as a luminescent polymer but is frequently used for the production of cationic nanoparticles and tagged with an organic fluorophore to be tracked optically. Herein, a strongly luminescent, branched PEI-superparamagnetic iron oxide nanoparticle (bPEI-SPION) without a traditional fluorophore is reported. A tremendous enhancement (1200 times) in the weak blue luminescence of bPEI is achieved only if it is adsorbed on a SPION during the synthesis of nanoparticles, which is improved further upon protonation, irreversibly. This is quite unexpected since SPIONs are strong absorbers in the visible region. All reaction parameters, different synthetic methods, as well as protonation are studied as independent factors to understand the origin of such enhancement. Detailed spectroscopic analysis and density functional theory calculations indicate that partial amine oxidation and Fe3+ reduction takes place during the synthesis, which significantly contributes to the luminescence enhancement. In addition, PEI-SPION exhibits excitation wavelength dependent emission and maintains its magnetic properties.
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    PublicationOpen Access
    Luminescent PbS and PbS/CdS quantum dots with hybrid coatings as nanotags for authentication of petroleum products
    (American Chemical Society (ACS), 2019) Durmuşoğlu, Emek Göksu; Türker, Yurdanur; Acar, Havva Funda Yağcı; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; 178902
    There is an urgent need to tag some valuable liquid products, such as petroleum products, for authentication. However, it is a challenging task because of the strong autofluorescence of liquid petroleum products in the visible range and the chemically active and harsh medium. Therefore, strongly luminescent, near-infrared (NIR) fluorophores with long-term stability are needed. The use of NIR quantum dots (QDs), such as lead chalcogenides, seems to be the best approach; however, most widely used coatings do not provide enough stability, and QDs are quenched in a short time in liquid petroleum products. Here, we report for the first time the synthesis of highly luminescent, ultrasmall, NIR-emitting PbS and PbS/CdS QDs with a hybrid coating consisting of oleylamine (OLA), 1-dodecanethiol (DT), and poly(methacrylic acid) (PMAA), adopting a simple, greener synthetic method. The photoluminescence (PL) emission wavelengths of these QDs were tuned between 700 and 1100 nm for detection with low-cost, widely used silicon detectors, which allows easy translation of such QDs as luminescent nanotags to serve as a means for the authentication of goods, such as petroleum. In the nanoparticle design, a thin layer of a CdS shell deposited by a cation-exchange process was adopted to enhance the emission intensity and stability of PbS QDs. The influence of postsynthetic ligand exchange of OLA with DT on the stability is also shown. PMAA in the coating provided a significant blue shift in the peak maxima, enhanced the luminescence intensity, and, most importantly, improved the long-term stability of QDs, especially in liquid petroleum products (oil, gasoline, and diesel). Such stability and size tunability was utilized to create binary barcodes. Hence, these QDs are shown as promising luminescent nanotags for liquid petroleum products. The development of such stable QD-based nanotags offers an invaluable use of nanotechnology for optical barcode generation.
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    PublicationOpen Access
    Impact of reaction variables and PEI/L-cysteine ratio on the optical properties and cytocompatibility of cationic Ag2S quantum dots as NIR bio-imaging probes
    (Royal Society of Chemistry (RSC), 2016) Department of Chemistry; Duman, Fatma Demir; Khodadust, Rouhollah; Durmuşoğlu, Emek Göksu; Yağcı, Mustafa Barış; Acar, Havva Funda Yağcı; PhD Student; Other; Researcher; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; N/A; N/A; N/A; N/A; 178902
    Near-infrared emitting semiconductor quantum dots (NIRQDs) are popular fluorescent probes due to better penetration depth and elimination of tissue autofluorescence. Here, we demonstrate one pot aqueous synthesis of cytocompatible, strongly luminescent, cationic Ag2S NIRQDs utilizing a mixed coating composed of branched polyethyleneimine (PEI)-25 kDa and L-cysteine (Cys) as in vitro luminescent tags and in vivo optical imaging agents. Ultrasmall sizes, a clear first excitonic peak in the absorption spectra, relatively narrow emission peaks with maxima between 730 and 775 nm and a Stokes shift less than 100 nm were obtained. Lifetime measurements indicate excitonic and defect-related emissions. Interestingly, not the emission maxima but the intensity was influenced by the Cys amount more dramatically. PEI/Cys 60/40 mol ratio provided the highest quantum yield reported until now for Ag2S NIRQD (157%) emitting at such a short wavelength. Low molecular weight PEI failed to produce luminescent QDs. Cytotoxicity evaluation of the most strongly luminescing NIRQDs, revealed the PEI/Cys (mol mol(-1)) 50/50 composition as the non-toxic composition below 2.4 mu g Ag per mL concentration. Others had low-toxicity. In vitro microscopy experiments showed endosomal distribution of NIRQDs in Hela cells and strong NIR signal. In vivo imaging study demonstrated that Ag2S NIRQDs could effectively be used as strong optical imaging agents.
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    PublicationOpen Access
    Synergistic effect of plasmonic gold nanoparticles decorated carbon nanotubes in quantum Dots/TiO2 for optoelectronic devices
    (Wiley, 2020) Selopal, Gurpreet Singh; Mohammadnezhad, Mahyar; Besteiro, Lucas, V.; Liu, Jiabin; Zhang, Hui; Navarro-Pardo, Fabiola; Liu, Guiju; Wang, Maorong; Sun, Shuhui; Zhao, Haiguang; Wang, Zhiming M.; Department of Chemistry; N/A; Acar, Havva Funda Yağcı; Çavuşlar, Özge; Durmuşoğlu, Emek Göksu; Faculty Member; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; 178902; N/A; N/A
    Here, a facile approach to enhance the performance of solar-driven photoelectrochemical (PEC) water splitting is described by means of the synergistic effects of a hybrid network of plasmonic Au nanoparticles (NPs) decorated on multiwalled carbon nanotubes (CNTs). The device based on TiO2–Au:CNTs hybrid network sensitized with colloidal CdSe/(CdSexS1−x)5/(CdS)1 core/alloyed shell quantum dots (QDs) yields a saturated photocurrent density of 16.10 ± 0.10 mA cm−2 [at 1.0 V vs reversible hydrogen electrode (RHE)] under 1 sun illumination (AM 1.5G, 100 mW cm−2), which is ≈26% higher than the control device. The in-depth mechanism behind this significant improvement is revealed through a combined experimental and theoretical analysis for QDs/TiO2–Au:CNTs hybrid network and demonstrates the multifaceted impact of plasmonic Au NPs and CNTs: i) hot-electron injection from Au NPs into CNTs and TiO2; ii) near-field enhancement of the QDs absorption and carrier generation/separation processes by the plasmonic Au NPs; iii) enhanced photoinjected electron transport due to the highly directional pathways offered by CNTs. These results provide fundamental insights on the properties of QDs/TiO2–Au:CNTs hybrid network, and highlights the possibility to improve the performance of other solar technologies.