الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
This study highlights a green approach for CS/AgNCs, Ag/SiO2NCs and rGO/AgNCs using the crude metabolite of Escherichia coli D8 (MF06257) strain as a reducing agent at sunlight and room temperature. The bacterial strain was obtained from the culture collection of Microbiology Laboratory, Faculty of Science, Damietta University, which had been isolated from the Egyptian environment. The AgNPs biosynthesis was detected in culture filtrate within 1-2 minutes. CS/AgNCs were synthesized by mixing the E. coli D8 supernatant with CS (pH 8) dissolved in 2 % acetic acid and sonication for 15 min in the presence of AgNO3 (1.5 mM). The mixture was stirred at 70 °C for 90 min and then centrifuged, washed with distilled water to remove excess solution, and finally re-dispersed in distilled water. For synthesis of Ag/SiO2NCs, AgNPs colloidal solution was added to SiO2 and mixed for 24 h. Finally, the solution was centrifuged, separated and dried. The rGO/AgNCs were prepared by oxidizing the graphite powder into GO and then ultrasonicated for 2 hrs followed by mixing with AgNO3 (1.5 mM) and E. coli D8 crude metabolite. The rGO/AgNCs powder was centrifuged and dried. The first indication for AgNPs and AgNCs formation was the color change into brown color. The AgNPs and AgNCs were assessed by UV-Vis spectroscopy, TEM, FT-IR spectroscopy, Zeta potential analyser and XRD analysis. Application of nanotechnology in creating new, effective medicines enables application of innovative solutions in fighting down pathogenic microorganism. Small dimensions of nanomaterials provide unique physicochemical and biological properties. Obtained polymer-silver nanocomposites met the requirements of potential medical application. Homogenously and finely dispersed over the whole AgNPs exhibited desired dimensions and their attachment in the polymer matrix was strong enough to keep the metallic silver in the polymer without releasing it to the environment. Their high antimicrobial activity coming from the biocide effect of AgNPs, silver ions and microbiostatic selected polymers were demonstrated against antibiotic resistant, biofilm forming strains of such as Staphylococcus aureus, E. coli, Klebsiella pneumoniae, Bacillus cereus and Candida albicans. In addition, the ultrastructure studies of the AgNCs-treated pathogenic bacterial strains confirmed the bactericidal action of the biosynthesized AgNCs. Also, the protein and dehydrogenase enzymes estimations confirmed the antimicrobial potential of CS/AgNCs. Sodium dodecyl sulfate and active polyacrylamide gel electrophoresis for proteins of CS/AgNCs treated pathogenic bacterial strains confirmed the toxic effects of the nanocomposite on their total protein content and enzymatic activities (MDH and GDH). Physicochemical analysis of the biosynthesized rGO/AgNCs revealed that they are sheet-like structure having embedded spherical shaped AgNPs. The anticancer activity of the rGO/AgNCs was studied using in vitro and in vivo tests. The rGO/AgNCs showed a dose-dependent cytotoxic effect on EAC cells. 50 μg/mL of rGO/AgNCs induced cytotoxic cell count in EAC cells reached to 87 %. The in vivo study was done using three groups of mice; rGO/AgNCs treated Ehrlich mice (intraperitoneally administered at doses of 10 mg/kg on the 8th), untreated Ehrlich mice and blank control mice. On the 14th day of treatment, silver was determined in kidney and liver by estimation of silver content, the ultrastructural and histopathological examinations. Histological sections of tumor tissue of mice treated with rGO/AgNCs showed their antiangiogenesis effect. The present study found that silver has the capability for penetration and accumulation inside liver and kidney tissues which appeared in the greater values of silver concentration for the treated mice compared to others. Moreover, the rGO/AgNCs showed a slow-release rate of silver ions from AgNPs surfaces, resulting in long-term toxicity effects. Mice bearing EAC tumor treated with rGO/AgNCs significantly ameliorated glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), albumin and creatinine compared to tumor group. These values were remained in the normal range, indicative of the rGO/AgNCs efficacy with less toxic effects. The overall results indicate that E. coli D8 (Accession number: MF06257) is a promising bacterial strain for the green synthesis of CS/AgNCs, Ag/SiO2NCs and rGO/AgNCs with antimicrobial potential and might be brought many biomedical applications throughout protecting human health (non-toxic to humans in minute concentrations). The rGO/AgNCs showed a hopeful result for the therapy of cancer. The antiangiogenesis mechanism of rGO/AgNCs and their side effects need to further work and more studies in the future.