The Synthesis And Characterization Of Carbon Dots Based Antibacterial Composites

Human health is seriously threatened by bacterial infection.Although many kinds of antibiotics have been developed for the treatment of bacterial diseases,the abuse and misuse of antibiotics lead to increasingly serious bacterial resistance.It is still a great challenge for people to explore antibiotic free treatment strategies to inactivate pathogens.Carbon dots（CDs）have been widely used in biomedical field due to their small size,stable luminescence,good water solubility,functionalization and good biosafety.In this thesis,we use carbon dots as functional units to prepare hydrogels,supramolecular assemblies and films by combining with other substances to achieve their applications in antibacterial and wound treatment.The work is listed as follows:Part Ⅰ:A series of negatively charged carbon dots were prepared using glutaraldehyde and polyethylene glycol as precursors.Among which,CD31 showed the strongest inhibition on E.coli and S.aureus.At the same time,CD31 andε-Polylysine were used to prepare injectable,self-healing,antibacterial hydrogels（CD-Plys）through Schiff base reaction.CD-Plys has significant broad-spectrum antibacterial activity,good wound healing ability and biocompatibility.CD-Plys can significantly accelerate wound healing,promote epithelia and angiogenesis.Therefore,CD-Plys has great application potential in bacteria-induced wound infection and tissue reconstruction.Part Ⅱ:We prepared carbon dots with positive and negative charges,and then the carbon dots assembled with boron dipyrromethene to prepare nanocomposites with positive（p-BDP）and negative charges（n-BDP）.The results show that both p-BDP and n-BDP have good water solubility,high colloidal stability and high photodynamic effect.In addition,p-BDP has higher antibacterial activity against S.aureus than n-BDP（their MIC is only 128 and 256 ng/mL）,and it can promote the healing of S.aureus infected wounds more than n-BDP.Therefore,the combination of carbon dots and photosensitizers can enhance the antibacterial activity.This work opens up a new prospect for the development of antibiotic free antibacterial nanoagents.Part Ⅲ:We used citric acid andε-Polylysine as the starting material to synthesize carbon dots with antibacterial activity.Polyvinyl alcohol was used as the matrix to prepare CD-PVA antibacterial composite films（PVA₃,PVA₅ and PVA₈）with smooth surface,uniform structure,excellent mechanical strength and flexibility.These films can be cut to any desired shapes according to the wound conditions.In addition,PVA₅ and PVA₈ have high antibacterial effect against E.coli and S.aureus.The results of wound treatment in vivo show that PVA₅ can effectively remove bacteria and is an ideal wound dressing to promote skin wound healing.In conclusion,the carbon dots based hydrogels,nanoparticles and films we prepared have good antibacterial activity.Our work provides a new method for exploring new nonantibiotic treatment modes,and also provides a new idea for the development of carbon dots based functional materials.