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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Motion of single terrylene molecules in confined channels of poly(butadiene)-poly(ethylene oxide) diblock copolymer(Amer Chemical Soc, 2009) N/A; Department of Physics; Department of Chemistry; Yorulmaz, Mustafa; Kiraz, Alper; Demirel, Adem Levent; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 22542; 6568The motion of terrylene probe molecules in confined PB channels of an asymmetric PB-PEO diblock copolymer has been investigated by single molecule tracking. The one-dimensional diffusion coefficients were found to be significantly smaller and had a narrower distribution compared to two-dimensional diffusion coefficients in PB. The trajectories of some single molecules showed unusual behavior of directed motion where mean square displacement had a parabolic dependence oil lag time. The likely origin of this behavior is discussed in terms of local variations in the PB channel width and the resulting change in the local density. The results show the effect of nonuniformities and heterogeneities in the channels on the motion of single molecules and demonstrate the sensitivity of single molecule tracking in characterizing self-assembled block copolymer morphologies.Publication Metadata only Investigation of the factors affecting the photothermal therapy potential of small iron oxide nanoparticles over the 730-840 nm spectral region(Royal Soc Chemistry, 2018) N/A; N/A; N/A; Department of Physics; Department of Chemistry; Bilici, Kübra; Muti, Abdullah; Duman, Fatma Demir; Sennaroğlu, Alphan; Acar, Havva Funda Yağcı; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 23851; 178902The use of superparamagnetic iron oxide nanoparticles (SPIONs) as a sensitizer in photothermal therapy (PTT) is relatively new and the origin of such a phenomenon is not known. Usually, large crystals and aggregated particles are preferred in the literature, suggesting that these increase the absorbance of particles at the irradiation wavelength, and hence, provide a larger temperature increase. This study has two major goals: identification of the key factors that affect the photo-induced temperature increase in well-controlled experiments and the influence of laser irradiation on nanoparticle properties. Small, biocompatible poly(acrylic acid) coated SPIONs (PAA/SPIONs) were used since they are more practical for future medical use than large aggregates. We studied the impact of three major laser-dependent variables, namely the wavelength (between 728 and 838 nm), intensity (1.85-9.76 W cm(-2)) and power (105-800 mW) as well as attenuation at the irradiation wavelength, on photothermal heating achieved with PAA/SPIONs. Within the studied range of these variables, only the laser power plays a critical role on the magnitude of photothermal heating in solutions. There is no strong correlation between the attenuation at the excitation wavelength and the temperature increase. In addition, extensive characterization of SPIONs before and after irradiation revealed no significant difference, which supports the re-usability of SPIONs. Lastly, the PTT potential of these small PAA/SPIONs was demonstrated in vitro on HeLa cells. At these low laser powers no temperature increase in SPION-free water or cell death in SPION-free cells was detected. Hence, this study provides a new insight into the photothermal effect of SPIONs, provides a clear and repeatable experimental procedure and demonstrates great potential for small SPIONs to be exploited in PTT.Publication Metadata only Reversible switching of wetting properties and erasable patterning of polymer surfaces using plasma oxidation and thermal treatment(Elsevier Science Bv, 2018) Soydan, Seren; Jonas, Alexander; N/A; Department of Chemistry; N/A; Department of Chemistry; Department of Physics; Department of Chemistry; Rashid, Muhammed Zeeshan; Atay, İpek; Yağcı, Mustafa Barış; Yılgör, Emel; Kiraz, Alper; Yılgör, İskender; PhD Student; Post Doctorate Student; Researcher; Researcher; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; N/A; College of Sciences; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; N/A; N/A; 40527; 22542; 24181Polymer surfaces reversibly switchable from superhydrophobic to superhydrophilic by exposure to oxygen plasma and subsequent thermal treatment are demonstrated. Two inherently different polymers, hydrophobic segmented polydimethylsiloxane-urea copolymer (TPSC) and hydrophilic poly(methyl methacrylate) (PMMA) are modified with fumed silica nanoparticles to prepare superhydrophobic surfaces with roughness on nanometer to micrometer scale. Smooth TPSC and PMMA surfaces are also used as control samples. Regardless of their chemical structure and surface topography, all surfaces display completely reversible wetting behavior changing from hydrophobic to hydrophilic and back for many cycles upon plasma oxidation followed by thermal annealing. Influence of plasma power, plasma exposure time, annealing temperature and annealing time on the wetting behavior of polymeric surfaces are investigated. Surface compositions, textures and topographies are characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and white light interferometry (WLI), before and after oxidation and thermal annealing. Wetting properties of the surfaces are determined by measuring their static, advancing and receding water contact angle. We conclude that the chemical structure and surface topography of the polymers play a relatively minor role in reversible wetting behavior, where the essential factors are surface oxidation and migration of polymer molecules to the surface upon thermal annealing. Reconfigurable water channels on polymer surfaces are produced by plasma treatment using a mask and thermal annealing cycles. Such patterned reconfigurable hydrophilic regions can find use in surface microfluidics and optofluidics applications. (C) 2018 Elsevier B.V. All rights reserved.Publication Metadata only Solid state sensor for simultaneous measurement of total alkalinity and ph of seawater(Amer Chemical Soc, 2017) Briggs, Ellen M.; Sandoval, Sergio; Takeshita, Yuichiro; Kummel, Andrew C.; Martz, Todd R.; Department of Physics; Erten, Ahmet Can; Teaching Faculty; Department of Physics; College of Sciences; 233923A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity (A(T)) using ion sensitive field effect transistor (ISFET) technology to provide a simplified means of characterization of the aqueous carbon dioxide system through measurement of two "master variables": pH and A(T). ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanographic applications. A modified ISFET is demonstrated to perform a nanoliter-scale acid base titration of A(T) in under 40 s. This method of measuring A(T), a Coulometric Diffusion Titration, involves electrolytic generation of titrant, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e., OH-, HCO3-, B(OH)(4)(-), PO43-) of seawater A(T). The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in A(T) over the range of seawater A(T) of similar to 2200-2500 mu mol kg(-1) which demonstrates great potential for autonomous sensing.Publication Metadata only High average-power diode-pumped femtosecond Cr3+: LiCAF laser(Association for Computational Linguistics, 2008) Kärtner, Franz X.; Fujimoto, James G.; Demirbaş, Ümit; Benedick, Andrew; Siddiqui, Aleem; Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 2385167-fs pulses with an average power of 300 mW and pulse repetition rate of 120 MHz were obtained from a diode-pumped Cr3+: PLiCAF laser. A semiconductor saturable absorber mirror enabled stable and self-starting mode-locked operation.Publication Metadata only Survival probability in a quantum walk on a one-dimensional lattice with partially absorbing traps(American Scientific Publishers, 2013) Gonulol, Meltem; Aydiner, Ekrem; Shikano, Yutaka; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674Time dependence of the survival probability in a one dimensional lattice with randomly distributed and partial absorbing traps is analyzed as a function of concentration and absorption probability of the traps. The short and long time behaviors of the non-interacting quantum walks are identified with stretched exponentials. Dynamical scaling laws of the short and long time regimes as well as the crossover time between them are characterized. It is found that the short time behavior is more sensitive to the absorption probability and the crossover takes longer time for more transparent traps. Moreover, the stretching exponents increase with the transparency of the traps.Publication Metadata only Acousto-optic mode-locking of a Cr2+: ZnSe laser(Optica Publishing Group, 2000) Carrig, Timothy J.; Wagner, Gregory J.; Jeong, Jay Y.; Pollock, Clifford R.; Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851Acousto-optic mode-locking of a Cr2+:ZnSe laser that produces 4.4 psec duration, transform-limited, Gaussian shaped pulses is described. The laser outputs 82 mW of output power at an 81 MHz pulse repetition frequency.Publication Metadata only Luminescent Nd3+ doped thermoplastic silicone-urea copolymers(Amer Chemical Soc, 2006) Department of Chemistry; N/A; Department of Physics; Department of Physics; Department of Chemistry; Yılgör, İskender; Demirbaş, Ümit; Sennaroğlu, Alphan; Kurt, Adnan; Yılgör, Emel; Faculty Member; Master Student; Faculty Member; Teaching Faculty; Researcher; Department of Physics; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; 24181; 20328; 23851; 194455; N/AA simple method for the preparation of rare earth ion-doped polymers, which display luminescence, is reported. For this purpose silicone–urea copolymers were doped with Nd(NO3)3·6H2O. Various structural and physicochemical properties of the resultant materials were investigated. FTIR studies indicated strong interaction of Nd3+ ions with urea groups, but no interaction with siloxane backbone, which is expected. Absorption measurements in the visible and near infrared region were performed and the radiative decay rates and branching ratios for the meta-stable 4F3/2 level were determined by using Judd–Ofelt theory. The samples were also excited at 800nm and emission spectra were observed in the near infrared at 905, 1059, and 1331nm. In Nd3+ doped silicone–urea systems the highest emission cross section at 1059nm was determined to be 60.7×10−21cm2. Spectroscopic parameters determined in this study suggest that Nd3+ doped silicone–urea copolymers are promising candidates for the development of fiber lasers or amplifiers near 1.06 and 1.3μm.Publication Metadata only Preparation and spectroscopy of novel er(iii) doped polyurethaneureas for broadband uv-to-visible conversion(American Chemical Society (ACS), 2008) Department of Chemistry; Department of Chemistry; Department of Physics; Department of Physics; Department of Physics; Yılgör, Emel; Yılgör, İskender; Çankaya, Hüseyin; Kılcı, Reyhane; Sennaroğlu, Alphan; Reseacher; Faculty Member; PhD Student; Master Student; Faculty Member; Department of Chemistry; Department of Physics; College of Sciences; College of Sciences; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; 40527; 24181; N/A; N/A; 23851[No abstract available]Publication Metadata only Ag2S-Glutathione quantum dots for NIR image guided photothermal therapy(Royal Soc Chemistry, 2020) N/A; N/A; N/A; N/A; Department of Physics; Department of Chemistry; Hashemkhani, Mahshid; Bilici, Kübra; Muti, Abdullah; Sennaroğlu, Alphan; Acar, Havva Funda Yağcı; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 23851; 178902Aqueous synthesis of glutathione (GSH) coated Ag2S quantum dots (QD) with strong emission in the medical imaging window (700-900 nm) was performed from AgNO3. Variations in temperature, time, pH and sulfur source (Na2S and thioacetamide) were studied to tune the emission wavelength and intensity of the QDs. The optimum synthesis conditions to produce the smallest QDs (ca. 7 nm) with the highest quantum yield (70%) and excellent stability were determined as 50 degrees C and pH 10 where Na2S was used in 2 h reactions. The cytotoxicity was evaluated with MTT assay on the HT29 and MCF7 cancer cell lines and indicated no significant toxicity of the QDs up to 200 mu g mL(-1). The Photothermal Therapy (PTT) potential was first investigated using a 795 nm, continuous-wave fiber coupled diode laser using aqueous solutions of QDs and then on HT29 and MCF7 cells. QD (150 mu g mL(-1)) treated MCF7 cells almost quantitatively died after 10 min irradiation at 795 nm (700 mW, 1.82 W cm(-2)) and the viability of HT29 cells dropped to 40%. Most cell death was late apoptotic/necrotic. This study indicates that such a laser irradiation procedure and the QDs are safe, yet their combination provides dramatic cell death upon short laser treatment. PTT coupled with strong intracellular optical signal promotes Ag2S-GSH QDs as potential theranostic nanoparticles.