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Publication Metadata only A novel magnetomechanical pump to actuate ferrofluids in minichannels(Begell House, Inc, 2011) Bilgin, Alp; Kurtoglu, Evrim; Erk, Hadi Cagdas; Sesen, Muhsincan; Kosar, Ali; Department of Chemistry; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; College of Sciences; 178902An improvement in the current methods of ferrofluid actuation was presented in this paper. A novel magnetomechanical microfluidic pump design was implemented with a ferrofluid as the active working fluid. Obtained flow rates were comparable to previous results in this research line. It was also seen that the basic pump architecture, which the subject pump is based on, enables much more room for further development.Publication Metadata only A universal method for the preparation of magnetic and luminescent hybrid nanoparticles(American Chemical Society (ACS), 2010) Topal, Uğur; N/A; N/A; Department of Chemistry; Kaş, Recep; Sevinç, Esra; Acar, Havva Funda Yağcı; Master Student; Master Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 178902Hybrid nanoparticles (MDOTs) composed of luminescent quantum dots (QDs) and superparamagnetic iron oxides (SPIOs) were prepared by the ligand-exchange mechanism in a simple and versatile extraction method. In this method, aqueous QDs (CdS or CdTe) coated with carboxylated ligands exchange the fatty acid (lauric acid) coating of SPIOs in a water chloroform extraction process. QDs form a coating around SPIOs and transfer them into the aqueous phase in high efficiency. The method worked successfully with both small and polymeric coating molecules selected as cysteine, 2-mercaptopropionic acid, and a poly(acrylic acid)/mercaptoacetic acid mixture. The original properties of the nanoparticles were well-preserved in the hybrid structures: All MDOTS showed ferrofluidic behavior and had a luminescence in the original color of the QD. Magnetic properties and the luminesence intensity of MDOTs can be easily tuned with the SPIO/QD ratio. All particles are small and show very good stability (optical and colloidal) over months. For stable MDOTs with good luminescence properties, highly luminescent aqueous QDs (CdS or CdTe) with the mentioned coatings were prepared. The first examples of CdTe coated with 2MPA emitting from green to red and CdTe-PAA/MAA were provided as well.Publication Metadata only Anticancer use of nanoparticles as nucleic acid carriers(Amer Scientific Publishers, 2014) Gozuacik, D.; Akkoc, Y.; Kosar, A.; Dogan-Ekici, A. Isin; Ekici, Sinan; Department of Chemistry; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; College of Sciences; 178902Advances in nanotechnology opened up new horizons in the field of cancer research. Nanoparticles made of various organic and inorganic materials and with different optical, magnetic and physical characteristics have the potential to revolutionize the way we diagnose, treat and follow-up cancers. Importantly, designs that might allow tumor-specific targeting and lesser side effects may be produced. Nanoparticles may be tailored to carry conventional chemotherapeutics or new generation organic drugs. Currently, most of the drugs that are commonly used, are small chemical molecules targeting disease-related enzymes. Recent progress in RNA interference technologies showed that, even proteins that are considered to be "undruggable" by small chemical molecules, might be targeted by small RNAs for the purpose of curing diseases, including cancer. In fact, small RNAs such as siRNAs, shRNAs and miRNAs can drastically change cellular levels of almost any given disease-associated protein or protein group, resulting in a therapeutic effect. Gene therapy attempts were failing mainly due to delivery viral vector-related side effects. Biocompatible, non-toxic and efficient nanoparticle carriers raise new hopes for the gene therapy of cancer. In this review article, we discuss new advances in nucleic acid and especially RNA carrier nanoparticles, and summarize recent progress about their use in cancer therapy.Publication Metadata only Bacterial physiology is a key modulator of the antibacterial activity of graphene oxide(Royal Society of Chemistry (RSC), 2016) Karahan, H. Enis; Wei, Li; Goh, Kunli; Liu, Zhe; Dehghani, Fariba; Xu, Chenjie; Wei, Jun; Chen, Yuan; Department of Chemistry; Birer, Özgür; Researcher; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; N/ACarbon-based nanomaterials have a great potential as novel antibacterial agents; however, their interactions with bacteria are not fully understood. This study demonstrates that the antibacterial activity of graphene oxide (GO) depends on the physiological state of cells for both Gram-negative and -positive bacteria. GO susceptibility of bacteria is the highest in the exponential growth phase, which are in growing physiology, and stationary-phase (non-growing) cells are quite resistant against GO. Importantly, the order of GO susceptibility of E. coli with respect to the growth phases (exponential >> decline > stationary) correlates well with the changes in the envelope ultrastructures of the cells. Our findings are not only fundamentally important but also particularly critical for practical antimicrobial applications of carbon-based nanomaterials.Publication Metadata only Development of color tunable aqueous cds-cysteine quantum dots with improved efficiency and investigation of cytotoxicity(Amer Scientific Publishers, 2010) N/A; N/A; Department of Chemistry; Department of Chemistry; Öztürk, Sinan S.; Selçukbiricik, Fatih; Acar, Havva Funda Yağcı; Master Student; N/A; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 178902Cysteine capped aqueous CdS quantum dots with improved luminescence and excellent colloidal-luminescence stability were developed in a simple one pot aqueous method from safer precursors at low temperatures. Investigation of size and luminescence as a function of cysteine amount, pH and temperature revealed an optimum value for all these variables to maximize the quantum yield. Cysteine:Cd ratio of 2, reaction pH of 9.5 and synthesis at room temperature-30 degrees C emerged as the best conditions for the highest QY of 19%. Yet, QY can be improved up to 55% if QDs are cleaned from excess cysteine and ions and redispersed in pH 7 medium. Size of the QDs, therefore the color of luminescence, can be tuned by the reaction temperature in this simple process. Higher temperatures provide larger particles. Cell uptake and cell viability studies in a wide range of doses and different incubation times with MCF-7 and HeLa cell lines revealed cell dependent differences. MCF-7 cells uptake more ODs but are much more viable than HeLa cells. At low doses such as 0.025 mg QD/ml all cells are viable. At 24 h incubation times MCF-7 cells demonstrate viability above 75% up to 0.15 mg QD/ml. On the other hand HeLa cells loose viability with increasing dose.Publication Metadata only Development of highly stable and luminescent aqueous CdS quantum dots with the poly(acrylic acid)/mercaptoacetic acid binary coating system(Amer Scientific Publishers, 2009) Lieberwirth, I.; Department of Chemistry; N/A; Department of Chemical and Biological Engineering; Acar, Havva Funda Yağcı; Çelebi, Serdar; Serttunalı, Nazlı İpek; Faculty Member; Master Student; Undergraduate Student; Department of Chemistry; Department of Chemical and Biological Engineering; College of Sciences; Graduate School of Sciences and Engineering; College of Engineering; 178902; N/A; N/AHighly stable and luminescent CdS quantum dots (QD) were prepared in aqueous solutions via in situ capping of the crystals with the poly(acrylic acid) (PAA) and mercaptoacetic acid (MAA) binary mixtures. The effect of reaction temperature and coating composition on the particle size, colloidal stability and luminescence were investigated and discussed in detail. CdS QDs coated with either PAA or MAA were also prepared and compared in terms of properties. CdS-MAA QDs were highly luminescent but increasing reaction temperature caused an increase in the crystal size and a significant decrease in the quantum yield (QY). Although less luminescent and bigger than CdS-MAA, CdS-PAA QDs maintained the room temperature size and QY at higher reaction temperatures. CdS-MAA QDs lacked long term colloidal stability whereas CdS-PAA QDs showed excellent stability over a year. Use of PAA/MAA mixture as a coating for CdS nanoparticles during the synthesis provided excellent stability, high QY and ability to tune the size and the color of the emission. Combination of all of these properties can be achieved only with the mixed coating. CdS coated with PAA/MAA at 40/60 ratio displayed the highest QY (50% of Rhodamine B) among the other compositions.Publication Metadata only Development of near-infrared region luminescent N-acetyl-L-cysteine-coated Ag2S quantum dots with differential therapeutic effect(Future Medicine Ltd, 2019) Erkısa, Merve; Arı, Ferda; Ulukaya, Engin; Department of Chemistry; N/A; N/A; Department of Chemistry; Buz, Pelin; Demirci, Gözde; Duman, Fatma Demir; Acar, Havva Funda Yağcı; Undergraduate Student; PhD Student; Master Student; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Science and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 178902Aim: N-acetyl-L-cysteine (NAC) is a free radical scavenger. We developed NAC-coated Ag2S (NAC-Ag2S) quantum dot (QD) as an optical imaging and therapeutic agent. Materials & methods: QDs were synthesized in water. Their optical imaging potential and toxicity were studied in vitro. Results: NAC-Ag2S QDs have strong emission, that is tunable between 748 and 840 nm, and are stable in biologically relevant media. QDs showed significant differences both in cell internalization and toxicity in vitro. QDs were quite toxic to breast and cervical cancer cells but not to lung derived cells despite the higher uptake. NAC-Ag2S reduces reactive oxygen species (ROS) but causes cell death via DNA damage and apoptosis. Conclusion: NAC-Ag2S QDs are stable and strong signal-generating theranostic agents offering selective therapeutic effects.Publication Metadata only Effect of Al2O3 and ZrO2 filler material on the microstructural, thermal and dielectric properties of borosilicate glass-ceramics(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Karaahmet, Oğuz; Çiçek, Buğra; N/A; Department of Chemistry; Arıbuğa, Dilara; Balcı, Özge; PhD Student; Researcher; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 295531Various glass-ceramics are widely used or considered for use as components of microelectronic materials due to their promising properties. In this study, borosilicate glass was prepared using the powder metallurgical route and then mixed with different amounts of Al2O3 and ZrO2 filler materials. Glass-ceramics are produced by high-energy ball milling and conventional sintering process under Ar or air. In this study, the effects of different filler materials and different atmospheres on the microstructural, thermal and dielectric properties were investigated. The data showed that ZrO2 filler material led to better results than Al2O3 under identical working conditions and similar composite structures. ZrO2 filler material significantly enhanced the densification process of glass-ceramics (100% relative density) and led to a thermal conductivity of 2.904 W/K.m, a dielectric constant of 3.97 (at 5 MHz) and a dielectric loss of 0.0340 (at 5 MHz) for the glass with 30 wt.% ZrO2 sample. This paper suggests that prepared borosilicate glass-ceramics have strong sinterability, high thermal conductivity, and low dielectric constants, making them promising candidates for microelectronic devices.Publication Metadata only Emergence of 2MPA as an effective coating for highly stable and luminescent quantum dots(American Chemical Society (ACS), 2009) Özen, Can; Lieberwirth, Ingo; Department of Chemistry; N/A; Department of Chemistry; Acar, Havva Funda Yağcı; Kaş, Recep; Yurtsever, İsmail Ersin; Faculty Member; Master Student; Faculty Member; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; 178902; N/A; 71293-Mercaptopropionic acid (3MPA) is a popular coating material for the preparation of aqueous quantum dots, yet its isomer 2-mercaptopropionic acid (2MPA) has not been much studied. Here, we present a detailed study on the aqueous synthesis of CdS quantum dots with a 2MPA coating. Reaction variables Such as the Cd/S ratio, 2MPA/Cd ratio, pH, and temperature were individually studied to evaluate the influence of these variables on particle size and luminescence. At the optimum ratios and reaction conditions, a quantum yield (QY) as high as 54% was achieved. These quantum dots (QDs) have exhibited excellent colloidal and photostability over eight months of study. The color of the emission can be tuned by the reaction temperature and/or Cd/S ratio. 3MPA-coated US nanoparticles were prepared at various 3MPA/Cd ratios for comparison. The highest QY achieved for CdS-3MPA was 15%, and the luminescence decreased dramatically overtime. Ab initio calculations and spectroscopic characterization did not reveal a significant difference in the structure or particle-coating interaction between 2MPA- and 3MPA-coated QDs. Luminesence lifetime measurements indicated longer lifetimes and a larger contribution of the surface-related emission, indicating better removal of quenching defects froth the surface in 2MPA-coated particles compared to that of CdS-3MPA. On the basis of the provided evidence, we report 2MPA as a new and better alternative to the widely used 3MPA for superior luminescence and long-term photo and colloidal stability.Publication Metadata only Facile synthesis of graphene aerogel supported nickel/nickel oxide core−shell nanoparticles: efficient electrocatalysts for oxygen evolution reactions(Amer Chemical Soc, 2019) Beyazay, Tugce; Department of Chemistry; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; Researcher; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; College of Sciences; N/A; 42079Graphene aerogels decorated with nickel/nickel oxide core-shell nanoparticles are synthesized via a one-pot hydrothermal reaction followed by thermal reduction. Nickel loading is varied from 1.5 to 40 wt % in a highly controlled fashion by simply tuning Ni2+ to graphene oxide ratio in the hydrothermal reaction mixture. In fact, graphene aerogel loaded with 40 wt % Ni has a BET surface area of 560 m(2) g(-1) due to the preservation of the porous structure with the aid of supercritical CO2 drying. The thermal reduction applied for the growth of nanoparticles induces deoxygenation of graphene aerogel structure simultaneously. Valence band spectroscopy results reveal an increase in metallicity with a gradual increase in the nickel loading, which has a direct impact on the final electrocatalytic performance. For the evaluation of the electrocatalytic activity of Ni/NiO loaded aerogels toward oxygen evolution reaction, cyclic voltammetry (coupled with a rotating disk electrode) is utilized. In fact, 40 wt % Ni loaded graphene aerogel requires a low overpotential of 320 mV for the supply of 10 mA cm(-2) (with a Tafel slope of 61 mV dec(-1) and a TOF of 0.11 s(-1)), which outperforms most of the Ni-based electrocatalysts reported in the literature.