Studies On The Synthesis Of Silver Nanoparticles And Their Antimicrobial Mechanism

Silver nanoparticles synthesized based on nanotechnology are new antimicrobial products of more stable physical and chemical properties than Ag+. Silver nanoparticles have incomparable antimicrobial activity to traditional inorganic antimicrobial reagents due to their quantum size effect and quite large surface-to-volume ratio. In addition, they have properties of long-term antimicrobial activity, high safety and low risk for drug resistance. Biosynthesis of silver nanoparticles is high safety, low-cost and green method with broad application in the future. In this study, we synthesized silver nanoparticles by chemical and biological methods and investigated the antimicrobial mechanism.Ag NO3 was reduced by ascorbic acid and coated by silicon dioxide(Si O2) to obtain Ag-Si O2 core-shell nanoparticles(Ag-Si O2 NPs). The average diameter of Ag-Si O2 NPs was 92.9 nm. We investigated the antimicrobial activity of Ag-Si O2 NPs and found the nanoparticles had growth inhibitive effects on Candida albicans and Fusarium oxysporum. Moreover, we detected IC50 of Ag-Si O2 NPs against C. albicans(2 μg/ml) by broth dilution method and MIC against F. oxysporum(4 μg/m) by cylinder plate method.In the study, we synthesized silver nanoparticles using extracts of Taxus chinensis cell culture for the first time and obtained silver nanoparticles of 3-5 nm diameter. To evaluate antimicrobial activity of the silver nanoparticles, we investigated MIC values against gram positive(Staphylococcus aureus and Bacillus subtilis) and gram negative bacterias(Escherichia coil and Salmonella paratyphi B). The silver nanoparticles exhibited strong antibacterial activity especially against gram positive bacteria. The IC50 values against S. aureus and B. subtilis were 1 μg/ml while those were 8 μg/ml against E. coil and 4 μg/ml against S. paratyphi B.We investigated the antimicrobial activity mechanism of silver nanoparticles against C. albicans and F. oxysporum provide the theoretical basis for broad application of silver nanoparticles. The results showed: 1. Ag-Si O2 NPs could slowly release Ag+ due to its unique core-shell structure. When we added chelating agent cysteine, Ag-Si O2 NPs still exhibited strong antimicrobial activity. The results demonstrated that the antimicrobial activity of silver nanoparticles resulted from Ag+ and quantum size effect. 2. We further investigated the growth inhibition of C. albicans biofilm and the results demonstrated Ag-Si O2 NPs not only inhibited the formation of biofilm but also the mature biofilm and the inhibition effects were not hindered by extracellular matrix. 3. The mycelium of F. oxysporum was in un-normal state and could not produce conidia and infect plants when treated by Ag-Si O2 NPs. 4. Reactive oxygen species(ROS) were detected by flow cytometry when treating C. albicans with Ag-Si O2 NPs. The membrane potential of mitochondria △Ψm decreased significantly in a time and dosage dependent pattern. In addition, activities of antioxidant enzymes CAT, SOD and POD in F. oxysporum exhibited a decline trend after an initial ascent. These results showed that Ag-Si O2 NPs stimulated ROS production in C. albicans and F. oxysporum to significantly change redox state and decreased △Ψm resulting in death of C. albicans and F. oxysporum.In conclusion we synthesized silver nanoparticles by chemical and biological methods and investigated the antimicrobial activity. It is worth mentioning that, we synthesized silver nanoparticles using Taxus chinensis cell for the first time. We investigated their antimicrobial mechanism, and the results demonstrated Ag-Si O2 NPs stimulated ROS production, destructed the structure of biofilm formation, and inhibited spore germination and growth which resulting in cell aberration and death of C. albicans and F. oxysporum. Our results provide the new synthesis methods of silver nanoparticles and the antimicrobial mechanism was analysis, deeply and scientifically.