Browsing by Author "Okyay, Tugba O."
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Item Antibacterial properties and mechanisms of toxicity of sonochemically grown ZnO nanorods(RSC Advances, 2015) Okyay, Tugba O.; Bala, Rukayya K.; Nguyen, Hang N.; Atalay, Ramazan; Bayam, Yavuz; Rodrigues, Debora F.In this study, we present a simple, fast and cost-effective sonochemical growth method for the synthesis of zinc oxide (ZnO) nanorods. ZnO nanorods were grown on glass substrates at room temperature without the addition of surfactants. The successful coating of substrates with ZnO nanorods was demonstrated by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The antimicrobial properties of ZnO nanorods against the planktonic Bacillus subtilis and Escherichia coli and their respective biofilms were investigated. The cytotoxicity of ZnO nanorods were evaluated using the NIH 3T3 mammalian fibroblast cell line. Moreover, to understand the possible mechanisms of ZnO nanorod toxicity, glutathione oxidation, superoxide production, and release of Zn2+ ions by the ZnO nanorods were determined, and the LIVE/DEAD assay was employed to investigate cell membrane damage. The results showed that sonochemically grown ZnO nanorods exhibited significant antimicrobial effects to both bacteria and prevented biofilm formation. ZnO nanorods did not present any significant toxicity to fibroblast cells. The main anti-microbial mechanisms of ZnO nanorods were determined to be H2O2 production and cell membrane disruption.Item The synergism of temperature, pH and growth phases on heavy metal biosorption by two environmental isolates(Journal of Hazardous Materials, 8/30/2014) Fan, Jingjing; Okyay, Tugba O.; Rodrigues, Debora F.In real environmental applications, such as heavy metal bioremediation, microorganisms are generally not kept at their optimum growth conditions; therefore, it is imperative to investigate their heavy metal removal performance under diverse environmental conditions. The present study aims to investigate the effects of pH, temperature and growth phases on the removal of Cu2+ and Cr6+ by two environmental isolates identified as Ochrobactrum intermedium LBr and Cupriavidus metallidurans CH34. Results showed that cells in logarithmic phase presented better biosorption capacity than cells in stationary phase for both isolates. The Cr6+ metal was removed more efficiently by live O. intermedium LBr than dead cells; while dead C. metallidurans CH34 biosorbed better than live ones. It was also found that the pH and temperature affected the biosorption capacity. The optimum temperatures were determined to be 37 °C and 27 °C, and the optimum pH values were 6 and 7 for O. intermedium LBr and C. metallidurans CH34, respectively. Additionally, both microorganisms preferentially adsorbed Cu2+ in Cu2+/Cr6+ mixtures. The main mechanism of adsorption was determined to be through carboxylic, hydroxyl, and amino functional groups.