Preparation Of Silver Nanostructures With Different Shapes And Its Antibacterial Activity

Drinking water security is closely linked to human health. It is indicated that highconcentration of bacteria is the main reason for water insanitation in our country. However,defects exist in all the techniques of drinking water disinfection. Better disinfectant ordisinfect techniques need to be developed to improve the drinking water quality. It is ofgreat practical significance to develop new methods and materials for drinking watersterilization.As a new bactericidal nanomaterials, silver nanoparticles is efficient、broad-spectrum andsecurity in water disinfection and has a potential application prospect in drinking watersterilization. Research show that the properties of silver nanocrystal have a strongco-relationship with its shape, however, the co-relationship between the particle shape and itsbactericidal performance remain obscure. In order to provide the basis for drinking watersterilization of silver nanoparticles, we here studied the shape control synthetic andantibacterial activity of silver nanoparticles. We mainly got the following achievements.Silver nanostructure could be synthesized via microwave-assisted method, with20mL ofethylene glycol (EG) as reductant and90mg of AgNO3as silver precursor. Silvernanostructure with different shapes could be selectively synthesized by adding Cl-to controlthe reaction rate and well control the synthetic time. At low addition level of NaCl (less than0.1mg)，the products were qusi-spherical nanoparticles; at medium addition level of NaCl(about1mg)，the products were mainly nanocubes; at medium addition level of NaCl (about5mg)，the products were mainly nanowires. The optimum parameters for nanocubes were:0.5-1mg of NaCl and2min, while5mg of NaCl and3min30s for nanowires. SEM, TEM,XRD, UV-Vis and SAED was used to characterize the silver nanostructure with differentshapes. Results showed that spherical particles were monocrystals with60±15nm in diameter,nanocubes were single crystals with55±10nm in edge length and nanowires were twinnedstructure with60±10nm in diameter and2-4um in length.All the three types of AgNPs showed antibacterial activity and the antibacterial activityincreased with increased concentration and reaction time. Silver nanocubes showed thestrongest bactericidal performance while nanowires showed the weakest antibacterial activity.At a cell density of1×106CFU/mL, the MIC of silver nanocubes and nanospheres towards E.coli were75ug/mL and100ug/mL respectively, while there was no MIC for nanowires even at100ug/mL. With1min reaction,25ug/mL siver nanocubes and100ug/mL spheres could killedall the bacterias while nanowires could not kill all the bacterias even at a concentration of 100ug/mL.The bactericidal performance of AgNPs is both shape-dependent and facet-dependent.Due to special one-dimensional nanostructure with high aspect ratio, nanowires showed wrosecontact with E. coli cells which led to weak bactericidal performance compare to silvernanocubes and nanospheres. The cubic nanoparticles mainly bounded by high reactivity {100}facets showed stronger antibacterial activity than the quasi-spherical nanoparticles boundedby relatively stable {111} facets.All the three types of AgNPs coulgenerated reactive oxygen species (ROS) and oxidizedpartial GSH. Oxidative stress generated by the formation of ROS was one of the mainmechanisms for the toxicity of Ag-NPs to bacteria. The introduction of cysteine could greatlyhindered the bactericidal performance of AgNPs and the release of Ag+was anothermechanism for the toxicity of Ag-NPs. It was proposed that the difference in the release ofAg+was led to different bactericidal performance of AgNPs with different shapes.