Preparation And Antibacterial Properties Of Functionalized Graphene Oxide-loaded Silver Nanocomposites

Research background and purposeBacterial infection has always been a difficult problem to public health.The rise of bacterial resistance makes the effect of antibiotic treatment worse.Because of the increase of the number of drug-resistant bacteria,it urges people to speed up the development of biological antimicrobial materials.Among them,nanocomposites provide a feasible choice for the treatment of bacterial infection.As a currently popular material,graphene-based nanomaterials are widely used in antibacterial field.However,the instability of graphene-based nanomaterials in biological solutions such as cell culture media and serum severely limits their applications in the biological field.Therefore,functional modifications are needed to make up for this defect.Graphene oxide(GO)is the oxidized form of graphene.There are a large number of oxygencontaining functional groups on the base and edges of the sheet structure,such as epoxides,hydroxyl groups,carbonyl groups,and carboxyl groups,with a large specific surface area.Cyclodextrin has high biological stability and can selectively accommodate guests.The graphene-based nanosheets functionalized with cyclodextrin can be highly dispersed in a variety of physiological solutions.Graphene oxide composite materials modified by metal nanoparticles have also been studied in the antibacterial direction.Metal nanoparticles can replace antibiotics to fight bacterial infections because it’s not easy for them to develop drug resistance.Silver nanoparticles(Ag NPs)have excellent antibacterial properties and are widely used in antibacterial field.However,the cytotoxicity of Ag NPs itself and the toxicity of some stabilizers added during the synthesis process limit its application.At the same time,as the concept of environmental protection takes root deeply,there have been more and more reports of green synthesis.In order to solve the agglomeration issue of silver nanoparticles and reduce their cytotoxicity while maintaining antibacterial activity,the development of materials has become the focus of research considerations.When developing materials,it is important to choose the carrier which can not only reduce its toxicity but also make it disperse evenly.Research contentIn this project,GO was first synthesized by the improved Hummers method,and Sulfobutylether-beta-cyclodextrin(SBE-β-CD)was anchored on the GO sheet as the carrier GO-SBE-β-CD.Then the mild green polydopamine(PDA)was used as a reducing agent to reduce the precursor of metallic silver in situ.A uniform distribution of Ag NPs was generated on the surface of the carrier GO-SBE-β-CD sheet.Three(0.2 M/0.6 M/1.0 M)Ag NPs/GO-SBE-β-CD nanocomposites were successfully prepared.First,the carrier GO-SBE-β-CD was characterized by physical and chemical properties.The properties of GO-SBE-β-CD were determined by UV-visible spectra(UV-vis),stability test,X-ray powder diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),Confocal Raman spectroscopy(Raman),Transmission electron microscope(TEM).Afterwards,preliminary antibacterial properties and in vitro cytotoxicity tests were carried out.The synthesis of the carrier laid the foundation for subsequent loading of Ag NPs.Three(0.2 M/0.6 M/1.0 M)Ag NPs/GO-SBE-β-CD nanocomposites were synthesized in situ on the surface of GO-SBE-β-CD by PDA reduction.The structure and properties of Ag NPs/GO-SBE-β-CD were analyzed by UV-vis,particle size distribution,zeta potential,material stability test,XRD,FTIR,Raman,TEM,SEM and XPS,and the formation of Ag NPs was determined.Through a series of antibacterial experiments(including agar diffusion,colony number,live/dead staining and morphological observation of bacteria after treatment),the materials with better antibacterial properties were selected from 0.2 M/0.6M/1.0 M Ag NPs/GO-SBE-β-CD.Further studies were conducted to determine the cytotoxicity of the three nanocomposites in vitro and in vivo,including cytotoxicity test,cell fluorescence staining and in vitro animal experiments.According to the results of antibacterial effect and cytotoxicity in vitro and in vivo,the optimal antibacterial nanocomposites were selected.Research resultFirst,graphene oxide sheets were successfully synthesized.On this basis,GO was functionalized by SBE-β-CD.GO-SBE-β-CD was prepared as a carrier for subsequent loading of Ag NPs.The carrier GO-SBE-β-CD was stably dispersed in water for a long time and the thermal stability of GO was improved;The appearance of new absorption peaks in the Infrared spectrum and the increase of the Raman peak intensity showed that there is a hydrogen bond interaction between SBE-β-CD and GO;Scanning electron microscopy showed that the carrier GO-SBE-β-CD has a fold structure of GO sheet;Cytotoxicity experiments and preliminary antibacterial experiments showed that the carrier GO-SBE-β-CD does less damage to cells,and the antibacterial performance needs to be improved.Secondly,the mild green PDA was selected as the reducing agent,and Ag NPs were successfully synthesized in situ on the surface of the carrier GO-SBE-β-CD.The characterization results of the synthesized three nanocomposites 0.2 M/0.6 M/1.0 M Ag NPs/GO-SBE-β-CD showed that Ag NPs are uniformly distributed on the surface of the carrier GO-SBE-β-CD,and the average particle size is about 73 nm;Because Ag NPs had an enhanced Raman scattering effect,the XRD peak intensity of the material Ag NPs/GO-SBE-β-CD became larger;At the same time,the XPS results could clearly see the peaks corresponding to each crystal plane of Ag NPs;The results of antibacterial experiments showed that 0.2 M/0.6 M/1.0 M Ag NPs/GO-SBE-β-CD has good antibacterial activity against both the gram-negative bacterium Escherichia coli(E.coli)and the gram-positive bacterium Staphylococcus aureus(S.aureus);In vivo cytotoxicity test and animal test results could help screen out the best biocompatibility,which is 0.6 M Ag NPs/GO-SBE-β-CD.0.6M Ag NPs/GO-SBE-β-CD not only had the advantages of low antibacterial concentration,but also had good in vivo and in vitro biocompatibility.The cell viability was higher than85%.It was an excellent antibacterial nanocomposite material,which was expected to be used in the field of biological infections.