Functionalization And Antibacterial Activity Of Gold Nanoclusters Against Oral Pathogens

Background and Objective:In order to seek better antibacterial effect against oral pathogens,different nanomaterials are getting more and more attention.Gold nanoclusters,also known as nanogold cluster,as a new type of nanomaterials,have attracted wide attention due to their unique properties.Gold nanoclusters are stable molecular aggregates composed of several to dozens of gold atoms under the protection of a certain molecular layer.Its ultra-small size,large Stokes shift,strong light luminescence and other characteristics make it have excellent application prospects in biological imaging and monitoring.At the same time,gold nanoclusters also have a variety of nano-enzyme activities,such as superoxide dismutase activity,peroxidase activity.By selecting and modifying the ligands on the surface of the gold nanoclusters,the enzyme activities of the clusters can be better exerted.Among them,the choice of polypeptide as the gold cluster ligand has many advantages,such as mild reaction,green environment,etc.The gold nanoclusters synthesized with polypeptide ligands have multiple properties,among which,the peptides themselves have partial antibacterial activity,and the peroxidase activity of the gold nanoclusters can also produce an inhibitory effect on bacteria.In addition,the gold nanoclusters have fluorescence properties.Based on this,two kinds of gold nanoclusters with polypeptide as ligands were synthesized in this project,and the correlation between their antibacterial ability,antibacterial performance and enzyme activity was studied in order to make new breakthroughs in oral materials.Methods:We designed and synthesized two kinds of polypeptides with different structures,namely membrane-breaking polypeptide and DNA-binding polypeptide.Using the two kinds of polypeptide as templates,two kinds of red fluorescence gold nanoclusters,namely membrane-breaking polypeptide gold nanoclusters A(gold nanoclusters A)and DNA-binding polypeptide gold nanoclusters B(gold nanoclusters B),were synthesized by template method.Then,by adjusting the synthesis time and the ratio of chloro-auric acid to polypeptide,we optimized the synthesis conditions of gold nanoclusters according to the fluorescence intensity.At the same time,TMB solution was used to detect the enzyme activity of the two gold clusters by color change and absorbance value.The relationship between the activity of peroxidase and these two factors was investigated by changing the ratio of synthesis of gold nanoclusters and environmental p H.Then,Staphylococcus aureus,Escherichia coli and Streptococcus mutans were used as research models to explore the effect of the concentration of gold nanoclusters on the production of reactive oxygen species using the reactive oxygen species detection kit in the way of co-culture for 1h.At the same time,we used the same coculture method to detect the effects of each component of the gold nanoclusters on Escherichia coli using reactive oxygen species kit.Finally,we used live bacteria/dead bacteria staining kit to test the co-culture of gold nanoclusters A with Escherichia coli for 1h to explore the correlation between antibacterial properties and membrane damage.Results:1.We synthesized two kinds of gold nanoclusters,namely,Au NCs A and B.The optimal reaction ratio of Au NCs A is 1:2 for 16 h,and the optimal reaction ratio of Au NCs B is 1:1 for 6 h.The enzyme activity of Au NCs A synthesized with 1:2 ratio and Au NCs B synthesized with 1:1 ratio was the highest.2.Au NCs A had inhibitory effects on all three bacteria in the range of 12.5 μM to200 μM,while Au NCs B had no obvious effect.3.Au NCs A was positively correlated with the enzyme activity in the range of12.5 μM to 200 μM.The higher the concentration,the more reactive oxygen species were produced and the better the antibacterial performance was.4.The membrane-breaking polypeptide ligands can play a synergistic role with the gold nanoclusters and damage the bacterial membrane.Conclusions:Au NCs A with membrane-breaking polypeptide as ligand has obvious antibacterial activity,which can increase the level of reactive oxygen species.It not only inherits the dual function of gold nanoclusters and membrane-breaking peptide,but also has enhanced synergic antibacterial effect.However,Au NCs B with DNAbinding polypeptide as ligand could not achieve the expected antibacterial effect.