Polydopamine-assisted Preparation Of Ag-based Antibacterial Nanocomposite And Study On Their Antibacterial Activities

Infection by pathogenic bacteria and outbreak of antibiotic resistant bacteria have greatly threatened public health.Therefore,it is necessary to create new,effective,and alternative antimicrobials.The rapid development of nanotechnology opens up a new opportunity in antibacterial research fields,many nano-structured materials have been considered as promising candidates for antibacterial applications.These engineered nanoparticles including ZnO,TiO2,silver nanoparticle(Ag NP),Au nanopartilce and CuO nanopartilce.Particularly,Ag nanoparticle is probably the most promising one among the antibacterial nanostructures reported so far,due to its broad-spectrum antimicrobial activity and low propensity to induce bacteria resistance.However,the practical application of Ag NPs is frequently limit by the critical problem of tendency to aggregate due to colloidal instability.To overcome this shortcoming,various nanomaterials such as silica,carbon,iron oxide,and graphene oxide(GO),have been employed as substrates to immobilize Ag NPs.Unsatisfactory,inspite of these strategies can effectively prevent the aggregation of Ag NPs and enhance their stability and antibacterial activity,but these synthesis processes are usually complex and use of toxic chemical reducing agents such as hydrazine and sodium borohydride.An easy and environment friendly preparation of the silver-based nanocomposite should be highly desired.Dopamine,a small molecule that acts in many ways similar to adhesive proteins of mussels.It can undergo self-polymerization in aerated basic solutions,leading to polydopamine(PDA)films adherent to virtually any surface.Additionally,similar to natural adhesive proteins,PDA shows good biocompatibility and low toxicity to the environment.Probably more important for the goal of preparing antibacterial nanocomposite,PDA offers ample active catechol and amine groups that are able to serve as reducing and binding agent for the formation of metallic nanoparticles from mother salt solutions.In this work,we developed a facile and environment friendly method to fabricate Ag-based antibacterial nanocomposite via in situ reduction of silver ion using PDA thin films deposited on curcumin crystals sacrificial template and magnetic nanoparticles hard template.The successful preparation of the nanocomposites were characterizated and the antibacterial activities of those nanocomposites were evaluated on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus.Moreover,cytotoxicities of the nanocomposites were further studied.Followings are results we got in this study:(1)The successful synthesis of Ag@PDA-NTs nanocomposites was characterized by TEM,XRD,XPS and FTIR.Various methods such as bacterial growth curve,inhibitory zone test,viable bacterial colonies count,and live/dead bacterial fluorescence stain were used to evaluate the antibacterial activities of the nanocomposite.Results showed that the nanocomposite possessed excellent antibacterial activities against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus with respective minimum inhibitory concentration(MIC)to be 60 and 80 ?g/mL.The Ag@PDA-NTs nanocomposites have good stability,and did not show significant cytotoxicity to QSG-7701 human normal liver cells.(2)The successful synthesis of reusable Fe3O4-PDA-Ag nanocomposites was characterized by TEM,XRD,Raman and FTIR.Various methods such as bacterial growth curve,inhibitory zone test,viable bacterial colonies count,and live/dead bacterial fluorescence stain were used to evaluate the antibacterial activities of the nanocomposite.Results showed that the nanocomposite possessed excellent antibacterial activities against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus,with MIC values to be 40 and 60?g/mL.Furthermore,over 60%of the original antibacterial activity of the nanocomposite was retained after 6 cycles of reuse.In addition,the nanocomposite did not show significant cytotoxicity to HEK293T human embryonic kidney cells.In summary,we have prepared two Ag-based antibacterial nanocomposites by the help of polydopamine.The successful synthesis of these nanocomposites was characterized,and the antibacterial activities and cytotoxicities of them were further studied.