The Antibacterial Activity Of Graphene And Its Effect On Biofilm Formation

Nano-science developed newly in the late 1980s, and it was listed as the most promising scientific and technological fields in the 21st century together with life science and information science. Because of its nanostructures and nanoscale, nanomaterials have good magnetic properties, electrical conductivity, optical properties, reactivity etc., and their development and application is prompting a growing number of revolutionary changes in industry. Carbon nanomaterials is a large branch of nanomaterials, while graphene is a major new carbon nano-material with rapid development in recent years. Graphene is used in electronics, telecommunications, energy and medicine, therefore graphene and graphene-related products will inevitably enter the environment through various means in the process of production, use and disposal, its unique physical and chemical properties may bring unpredictable ecological impact to the environment. Therefore, researchers is paying more and more attention to its possible negative ecological and environmental effects as enjoying the positive sides of graphene.Similar to other environmental contaminants, graphene poured into the environment also proceed a series of complex migration and conversion processes in hydrosphere, atmosphere, pedosphere and life system. Graphene will occur many complex environmental behavior in the water:they may disperse and suspend stably, and may also agglomerate and settle in the mud. Whatever it exists in any form, graphene will have an impact on the water environment and aquatic organisms.Biofilms are bacteria growing on certain interfaces in order to adapt the living environment in the growth process, they are a corresponding form to suspension cells. The environment of microorganism growth will change as graphene entering water, and bacterial growth state may have corresponding change in order to deal with this situation, which may also affect the formation of biofilm. Facing these problems, there is little literature about the effects of graphene on biofilm at present, so it is imminent to understand the antimicrobial properties of graphene and its influence on biofilm. In this research, we adopted different concentrations of graphene and graphene oxide (0,10,20,40,80,160 mg/L) to study their impacts on Gram-negative and Gram-positive bacteria:Escherichia coli and Bacillus subtilis. The results are as follow:(1)Graphene and graphene oxide had strong antibacterial properties, which were enchanced with the increase of their concentrations.(2)Graphene and graphene oxide also have influence on the biofilm formation: low concentrations of them promoted the biofilm formation, while high concentrations of graphene and graphene oxide inhibited biofilm formation.(3)We discussed the antimicrobial mechanism of graphene material through XTT experiment and glutathione (GSH) oxidation experiment:XTT experiments showed no absorption, which suggested that the nanomaterial did not produce free oxygen radicals; While GSH was oxidized by different concentrations of graphene and graphene oxide, so we knew that graphene did not produce active oxygen free radicals to cells.(4)We did the dead cells experiment to verify the mechanism of the effects of graphene nanomaterial on bacterial biofilm formation, and got the probable conclusions:When the concentration of graphene and graphene oxide were low, they existed as uniform dispersion at first and the number of nanoparticles were less, and partial planktonic cells contacted the nanoparticles, then these cells gathered to form chain to resist, but graphene and graphene oxide will reunite after a period of time, and cells in the chain will deposite on the surface of the nanoparticles and nanoparticles can produce membrane stress and oxidative stress to them, so the cells were damaged and produced dead cells, which provided protective barrier for the living cells, and living cells continue to grow to form biofilm. But when the concentration of graphene and graphene oxide became high, the amount of nanoparticles in the solution exceeded the number cells can bear, and nearly all living cells would be killed, so no living cells could continue to grow and suppressed the growth of biofilm.