Browsing by Author "Nguyen, Hang N."
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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 Chronic toxicity of graphene and graphene oxide in sequencing batch bioreactors: A comparative investigation(Journal of Hazardous Materials, 2/5/2018) Nguyen, Hang N.; Rodrigues, Debora F.The present study investigates the chronic toxicity of graphene (G) and graphene oxide (GO) in activated sludge. Sequencing batch bioreactors were fed with influents containing 0, 1 and 5 mg L?1 of GO or G (12 h cycles) for ten days. Reduction in performance of the bioreactors in relation to chemical oxygen demand, ammonia and phosphate removals was observed after three days in the bioreactors fed with 5 mg L?1 of nanomaterials. After about eight days, these reactors reached a steady state nutrient removal, which corresponded to recovery of certain groups of ammonia oxidizing bacteria and phosphate accumulating bacteria despite the increasing accumulation of nanomaterials in the sludge. These results suggested that biological treatment can be affected transiently by initial exposure to the nanomaterials, but certain groups of microorganisms, less sensitive to these nanomaterials, can potentially strive in the presence of these nanomaterials. Results of 16S rRNA gene deep sequencing showed that G and GO affected differently the microbial communities in the activated sludge. Between the two nanomaterials investigated, GO presented the highest impact in nutrient removal, gene abundance and changes in microbial population structures.Item Designing polymeric adhesives for antimicrobial materials: poly(ethylene imine) polymer, graphene, graphene oxide and molybdenum trioxide – a biomimetic approach(Journal of Materials Chemistry B, 5/10/2017) Nguyen, Hang N.; Nadres, Enrico T.; Alamani, Bryan G.; Rodrigues, Debora F.The synthesis of biocompatible polymers for coating applications has gained significant attention in recent years due to the increasing spread of infectious diseases via contaminated surfaces. One strategy to combat this problem is to apply antimicrobial coatings to surfaces prone to microbial contamination. This study presents a series of biomimetic polymers that can be used as adhesives to immobilize known antimicrobial agents on the surfaces as coatings. Several polymers containing dopamine methacrylate as co-polymers were synthesized and investigated as adhesives for the deposition of an antimicrobial polymer (polyethyleneimine) and antimicrobial nanoparticles (graphene, graphene oxide and molybdenum trioxide) onto glass surfaces. The results showed that different antimicrobials required different types of adhesives for effective coating. Overall, the coatings fabricated from these composites were shown to inactivate E. coli and B. subtilis within 1 h. These coatings were also effective to prevent biofilm growth and demonstrated to be non-toxic to the human corneal epithelial cell line (htCEpi). Leaching tests of the coatings proved that the coatings were stable under biological conditions.Item Influence of environmental factors on tenuazonic acid production by Epicoccum sorghinum: An integrative approach of field and laboratory conditions(Science of the Total Environment, 6/1/2018) Oliveira, Rodrigo C.; Nguyen, Hang N.; Mallmann, Carlos A.; Freitas, Rogerio S.; Correa, Benedito; Rodrigues, Debora F.Sorghum is the fifth most cultivated and consumed grain in the world. However, this grain is frequently contaminated with toxins from fungi. The present study evaluated the effects of environmental factors on tenuazonic acid (TeA) production by Epicoccum sorghinum in the field and in controlled laboratory conditions. In this study, 50 sorghum grain samples were collected from summer and autumn growing seasons and analyzed for TeA contamination using LC-MS/MS. To further understand the ecophysiology of this fungus, an isolated strain of E. sorghinum from the field was investigated for its development and TeA production under controlled environmental conditions in the laboratory. In the ecophysiological investigation, the effects of water activity (0.90, 0.95, 0.99) and temperature (18, 22, 26 and 30?°C) were evaluated on the radial growth, enzymatic production and expression of TAS1, which is the gene involved in TeA production. Results showed that in the field, the summer season presented the highest TeA average level in the grains (587.8??g/kg) compared to level found in the autumn (440.5??g/kg). The ecophysiological investigation confirmed that E. sorghinum produces more actively TeA under environmental conditions simulating the summer season. Optimum growth, maximum TAS1 gene expression, and higher extracellular enzymatic production were observed at 26?°C with a water activity of 0.99. Pearson correlation analyses showed that the production of TeA highly correlates with fungal growth. The present study demonstrates that abiotic factors in a combined approach of field and laboratory conditions will assist in predicting the driving environmental factors that could affect growth of E. sorghinum and TeA production in sorghum grains.Item Response surface methodology as a powerful tool to optimize the synthesis of polymer-based graphene oxide nanocomposites for simultaneous removal of cationic and anionic heavy metal contaminants(RSC Advances, 3/28/2017) Perez, Jem Valerie; Nadres, Enrico T.; Nguyen, Hang N.; Dalida, Maria Lourdes P.; Rodrigues, Debora F.Nanocomposites containing graphene oxide (GO), polyethyleneimine (PEI), and chitosan (CS) were synthesized for chromium(VI) and copper(II) removal from water. Response surface methodology (RSM) was used for the optimization of the synthesis of the CS–PEI–GO beads to achieve simultaneous maximum Cr(VI) and Cu(II) removals. The RSM experimental design involved investigating different concentrations of PEI (1.0–2.0%), GO (500–1500 ppm), and glutaraldehyde (GLA) (0.5–2.5%), simultaneously. Batch adsorption experiments were performed to obtain responses in terms of percent removal for both Cr(VI) and Cu(II) ions. A second-order polynomial equation was used to model the relationship between the synthesis conditions and the adsorption responses. High R2 values of 0.9848 and 0.8327 for Cr(VI) and Cu(II) removal, respectively, were obtained from the regression analyses, suggesting good correlation between observed experimental values and predicted values by the model. The optimum bead composition contained 2.0% PEI, 1500 ppm GO, and 2.08% GLA, and allowed Cr(VI) and Cu(II) removals of up to 91.10% and 78.18%, respectively. Finally, characterization of the structure and surface properties of the optimized CS–PEI–GO beads was carried out using X-ray diffraction (XRD), porosity and BET surface area analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), which showed favorable adsorbent characteristics as given by a mesoporous structure with high surface area (358 m2 g?1) and plenty of surface functional groups. Overall, the synthesized CS–PEI–GO beads were proven to be effective in removing both cationic and anionic heavy metal pollutants.