The Synthesis Of Silver-based Nanomaterials Stabilized By Coordination Polymers And Their Antibacterial Properties And Antibacterial Mechanisms

Pathogenic bacterial infection poses a serious threat to human health and life.In recent years,the increasing number of drug-resistant bacteria has led to the decline of antibiotic efficacy,especially the emergence of"superbacteria",which has brought new threats and challenges to human health.The development of new and effective antimicrobial agents is imminent.Recent studies have shown that silver nanomaterials have excellent broad-spectrum resistance and become one of the most promising antibacterial agents.Although silver nanoparticles have superior antimicrobial properties,they are easy to aggregate,to some extent,which reduces their antimicrobial activity and limits their application.At present,many strategies are used to improve the antibacterial properties of silver nanoparticles,including the use of inorganic/organic materials,graphene oxide and polymers to stabilize silver nanoparticles.Poly?N-isopropyl acrylamide??PNIPAM?as an environment-responsive polymer has been broadly studied in the biomedical fields such as gene and drug delivery,and tissue engineering due to its good biocompatibility,temperature sensitivity and flexible structural tunability.Current studies have shown that PNIPAM has become one of the best candidates for the preparation of smart antimicrobial materials with low cytotoxicity,and can endow the antibacterial material with a temperature-controllable selective antibacterial function.However,the application of PNIPAM in antibacterial field is just in the beginning.In this study,we developed a novel highly efficient silver-based antimicrobial nanomaterial based on a thermo-sensitive copolymer P?NIPAM-co-MQ?with coordination ability as stabilizer.Two kinds of silver nanoparticle composites,Ag NPs@P and GO@P@Ag NPs,were successfully synthesized,and their antibacterial properties and mechanisms were studied in detail.The specific research contents and results are as follows:Methods:P?NIPAM-co-MQ?copolymer was prepared through a classical free radical polymerization from the two monomers of NIPAM and MQ.Two new silver based nanomaterials,Ag NPs@P and GO@P@Ag NPs,were synthesized with P?NIPAM-co-MQ?and GO@P as stabilizers,respectively.The materials were characterized and analyzed by ¹H NMR,FTIR,UV-Vis,XPS,ICP-AES and TEM.MIC and MBC assay,optical density method and flat colony counting were used evaluated the antibacterial properties of the nanomaterials.The antibacterial mechanism of nanomaterials was studied based on fluorescence detection,scanning electron microscopy?SEM?and intracellular ROS analysis.Result:1.In this study,three small sizes of Ag NPs@P₁?3.91 nm?,Ag NPs@P₂?2.29 nm?and Ag NPs@P₃?1.59 nm?with uniform dispersion were successfully synthesized using a thermo-sensitive P?NIPAM-co-MQ?copolymer with coordination ability as a stabilizer.The copolymer stabilized silver nanoparticles?Ag NPs@P?displayed good thermo-sensitive characteristics and solution stability at p H=6.5-8.0.And the antibacterial properties of the nanomaterials were systematically evaluated,the results showed that Ag NPs@P possessed high-efficiency and long-term antimicrobial properties for Gram-positive bacteria?S.aureus?and Gram-negative bacteria?E.coli?.The MIC values of the three nanomaterials is between 4.05-21.6?g/m L,and the MBC values is between 8.01-27?g/m L.In particular,Ag NPs@P₃with ultrasmall size exhibited better antimicrobial activity against both normal bacteria and antibiotic-resistant bacteria with a very low MIC value of 4.05?g/m L.Moreover,Ag NPs@P also exhibited an interesting temperature-dependent antibacterial activity mainly owing to the effect of thermo-sensitive copolymer on Ag NPs.It was also found that the antibacterial activity of the Ag NPs@P also was affected by the proportion of thermo-sensitive copolymer,temperature and sizes of nanoparticles.In the experiment,we further studied the antibacterial mechanism of Ag NPs@P.The result showed that the antibacterial mechanism of Ag NPs@P involved a variety of ways including destroying cell membranes,internalization of silver nanoparticles and generation of ROS.Our study further reveals that the higher content of internalized silver and intracellular ROS levels may contribute more to the bactericidal activity of Ag NPs@P at low concentration,while at high concentration,the bactericidal effect of Ag NPs@P was mainly attributed to membrane damage.This study provides a new perspective for the preparation of effective nanosilver antimicrobial agents.2.The second part of this thesis is to synthesize GO@P@Ag NPs nanocomposites with GO@P as stabilizer.Through TEM analysis,we can see clearly that PNIPAM can control the size and stability of silver nanoparticles and improve the loading amount of silver nanoparticles on GO compared with GO@Ag NPs.Further antibacterial experiments show that the GO@P@Ag NPs nanocomposites have good antibacterial activity against Gram-negative E.coli and Gram-positive S.aureus.The antibacterial properties of GO@P@Ag NPs are temperature and concentration dependent,and also related to the species of tested bacteria.At a certain concentration,GO@P@Ag NPs can completely kill the tested bacteria within one hour.At the same time,GO@P@Ag NPs have a good long-term cyclic antibacterial effect.After 5cycles of use,the sterilization rate of GO@P@Ag NPs can still reach 70-80%.The results of PI/DAPI staining,SEM analysis and intracellular ROS detection showed that the antibacterial mechanism of GO@P@Ag NPs was mainly due to the damage of cell membrane and the production of intracellular ROS.Conclusion:In this article,two kinds of silver based nano antibacterial agents,Ag NPs@P and GO@P@Ag NPs,were successfully synthesized.The results show that both of them have good broad-spectrum antibacterial activity.The antibacterial activities are affected by the properties of thermo-sensitive polymer,the size of silver nanoparticles and the characteristics of the tested bacteria.The nanosilver-based antibacterial materials can kill bacteria through various mechanisms.This study lays a good foundation for the development and application of new and high-efficiency antibacterial agents.