| Nanosilver is not a new material with 120 years applied history.One of the most important properties of nanosilver is broad-spectrum antibacterial ability,resulting in its many applications to,for example,food processing,cosmetics,clothing,biological medicine,water purification,and various household goods.Exposure risk of nanosilver to human and the environment increases definitely along with the rapid and increasing applications of nanosilver.Recent studies found that nanosilver killed not only pathogenic bacteria but also beneficial bacteria(such as azotobacter)in the environment,even inhibited the activity of human cell mitochondria.There were many bactericidal mechanisms about nanosilver,for example,nanosilver might bind to the cell wall of bacteria;nanosilver might interact with cysteine-containing membrane protein and enzymes,producing reactive oxygen species(ROS);the silver ions released from nanosilver might interact with DNA in bacterial cell.The debate on the bactericidal mechanism of nanosilver lasted for more than a century without a definite conclusion.If we want to use nanosilver more safely and scientifically,it is essential to understand its bactericidal mechanism and design safer nanosilver.During my MSc study,three kinds of 1-thiol sugar were synthesized and modified onto the surface of nanosilver.Then corresponding antibacterial effect was evaluated and possible bactericidal mechanism was discussed.It mainly includes the following aspects:Chapter 1.Summarizing the research status of nanosilver,including the research history of nanosilver,the synthesis and characterization of nanosilver,the application of nanosilver,and the antibacterial effects of nanosilver.Research proposal was thus made.Chapter 2.Designing and synthesizing three 1-thiol sugar,including 1-SH-glucose,1-SH-2-N-acetyl glucose and 1-SH-lactose.They were further modified onto the surface of nanosilver particles(AgNPs,nine kinds of nanosilver particles).In addition,glucose-and lactose-modified AgNPs were synthesized.Finally,all the synthesized AgNPs were characterized in different ways,such as TEM,DLS,infrared absorption and energy spectrum.Chapter 3.Exploring the release of Ag ion,antibacterial property,bacterial disruption and possible bactericidal mechanism of the prepared 11 kinds of AgNPs.The results show that AgNPs with the modification of thiol sugars released less Ag ions than those modified by simple sugars.Besides,when we modify different content of thiol sugar to the surface of AgNPs,we found that we could further regulate and control the release of Ag+ ions.In addition,AgNPs modified by glucose and lactose had stronger bactericidal property than those with thiol sugar.When different concentration of Ag+ions preconditioned bacteria,we found the bacterial activity gradually reduced with the increase of concentration of Ag+,suggesting that the bactericidal mechanism of AgNPs was determined by the release of Ag+.But for other nine kinds of thiol sugar modified AgNPs,the release of Ag+ was less,LacSH@AgNPs and GlcNAcSH@AgNPs still have bactericidal effect on bacteria,which may be influenced by sugar molecules that were modified onto the surface of AgNPs.The sugar molecules may interact with some of the receptor molecules on the surface of the bacteria,which further increase the endocytosis effect of AgNPs;once AgNPs enter into the interior of bacterial cell,they can further play a role of killing the bacteria.Scanning electron microscopy(SEM)can be used to see the seriously damaged bacterial cell walls.Therefore,it can be concluded that the bactericidal mechanism of AgNPs is determined by AgNP itself.Chapter 4.In order to explore the influence of surface modification to bacterial activity,BPEI@AgNP and BPEI@AuNP were designed and synthesized.It was found that the antibacterial property depended on AgNP itself,and the surface modification can only play an auxiliary role.Chapter 5.Summarizing the main research work of my thesis and outlining the perspectives in the future. |
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