Synthesis Of Cascade-catalyzed Magnetic Graphitic Nanocapsules And Their Oral Antibacterial Applications

The oral environment is complex,and colonized microorganisms exist in the form of biofilms.Once the internal balance of the biofilm is out of balance and the pathogenic acid-producing bacteria dominate,it will cause tooth demineralization and then induce dental caries.Among common dental caries treatments,traditional antibacterial agents have little effect on biofilms,and high doses of hydrogen peroxide(H2O2)are high toxic and can damage oral health.Therefore,people turn their attention to the nanomaterials with enzyme-like activity—nanozymes.The highly toxic reactive oxygen species(ROS)generated by nanozymes catalyzing substrates(such as H2O2)can damage the biofilm structure and cause bacterial oxidative stress.So nanozymes become an emerging treatment for their excellent antibiofilm effect.However,the special acid environment of oral cariogenic biofilms will destroy the stability of nanozymes,and unfunctionalized nanozymes are easily removed by saliva,making it difficult to achieve effective therapeutic concentrations at the biofilm.,which greatly weakens the antibacterial effect of nanozymes.Therefore,developing a novel nanozyme with excellent stability and targeting ability is of great significance for oral antibacterial therapy.Based on the above problems,in this work,a cascade nanozyme(CoPt@Graphene@Glucose oxidase,CoPt@G@GOx)with high efficiency,stable catalysis and magneto actuated capability was prepared,which was composed of glucose oxidase(GOx)and cobalt-platinum graphitic nanocapsules(CoPt@G)composite.The catalytic process of the cascaded nanozyme was divided into two steps.First,GOx oxidized glucose to form H2O2,which avoided the direct use of high-concentration H2O2.Then,H2O2 was catalyzed by CoPt@G with peroxidase-like(POD)activity to generate high toxic free radicals·OH,exerting bactericidal properties.The presence of cobalt in CoPt@G enabled the particles to be magnetically actuated to target bacterial biofilms.Moreover,after the cobalt-platinum alloy was coated with the graphene shells,the corrosion of strong acid could be avoided,and the stability was enhanced to ensure the catalytic activity and magneto actuated ability.Therefore,the nanozyme has great potential in preventing and treating bacterial infections.Based on this,we explored its application in the treatment of oral cariogenic bacteria.The details of this work are as follows:(1)In Chapter 2,we prepared CoPt@G by the chemical vapor deposition(CVD),and adsorbed GOx on the surface of graphene shell through noncovalent interaction to obtain CoPt@G@GOx.Next,we characterized the morphology of the as-prepared CoPt@G@GOx,and verified the existence of GOx and its adsorption capacity.Further,we explored the properties of CoPt@G@GOx,including stability,magnetic properties,and cytotoxicity.The conclusion proves that the CoPt@G@GOx prepared by the facile method has uniform morphology,excellent stability,high magnetic actuated ability,and reasonable cytotoxicity.Therefore,we successfully prepared CoPt@G@GOx composite nanomaterials with excellent properties and stability.(2)In Chapter 3,we systematically explored the catalytic performance of CoPt@G@GOx.We found that CoPt@G possessed POD activity and could catalyze the generation of ROS from H2O2.Moreover,the composite nanoparticles CoPt@G@GOx could play a cascade catalytic activity.GOx oxidized glucose to generate H2O2,and CoPt@G catalyzed H2O2 to generate ROS.We conducted detailed studies on the factors affecting the catalysis of CoPt@G@GOx including the specific species of ROS generated,the effect of substrate channel effects,and particle acid stability.The catalytic performance was stable and excellent,the species of ROS generated is ·OH,and the catalytic activity of CoPt@G@GOx was four times higher than that of the simple mixed solution of CoPt@G and GOx.Therefore,CoPt@G@GOx.has high catalytic activity and stability,and avoid using high concentration of H2O2 directly,and is expected to be used in the treatment of bacterial infections.(3)In Chapter 4,we explored the therapeutic effect of CoPt@G@GOx on the cariogenic representative strain,Streptococcus mutans(S.mutans).We explored the antibacterial ability of CoPt@G@GOx against S.mutans plankton and biofilm,respectively.For planktonic bacteria,the gluconic acid produced by GOx catalyzed by glucose could reduce the pH of the solution and enhanced the POD activity of CoPt@G,thereby generating a large number of highly toxic free radicals,inhibiting the growth and reproduction of planktonic bacteria,slowing down or avoiding subsequent biofilm formation.For biofilm bacteria,the ·OH produced by CoPt@G@GOx could destroy the extracellular matrix,and the actuation of external magnetic field could improve the biofilm retention capacity and penetration depth of CoPt@G@GOx,thus exerting its excellent bactericidal activity against mature biofilms.The existence of GOx avoided the direct use of large doses of H2O2 and reduced the damage to oral tissues.Therefore,this highly stable,catalytically active and magnetically actuated cascade nanozyme provides a simple and effective method for the prevention and treatment of biofilminduced oral caries.