Design And Application Of Gold And Silver Nanoclusters-based Antibacterial Agents

Metal nanoclusters(MNCs)are a class of ultra-small particles composed of tens to hundreds of metal atoms.Their kernal size is less than 3 nm and they have a core-shell structure composed of metal core-organic ligand shells.In the scale of less than 3 nm,MNCs have discrete orbital energy levels due to strong quantum confinement effect,and exhibit interesting molecular like properties,including transition of highest and minimum occupied molecular orbitals,luminescence,intrinsic chirality,etc.In addition,due to its ultra-small size,good biocompatibility and rich and modifiable surface chemistry,MNCs are widely used in biomedical fields such as sensing,bioimaging,antibacterial and disease diagnosis and treatment.In recent years,as a new class of antibacterial agents,Au and Ag NCs have attracted extensive attention from researchers.They have the characteristics of broad-spectrum antibacterial property and non-drug resistance that traditional antibiotics cannot match.However,the current Au and Ag NCs-based antibacterial agents all rely on their own consumption to induce the generation of reactive oxygen species(ROS)for killing bacteria.Such low-efficiency antibacterial feature dooms their limitations in long-term antibacterial,and also limits their practical application in multiple application scenarios.Therefore,research efforts in both designing novel MNCs-based antibacterial agents with controlled release of antibacterial Au or Ag species,and devising a new type ofMNCs-based antibacterial agents to bypass the antibacterial mechanism of traditional ones,are extremely required.This may break through the short-acting antibacterial spell of the traditional MNCs-based antibacterial agents,and realize the downstream antimicrobial applications,showcasing great significance in both fundamental studies and practical applications.On the basis,this thesis mainly focuses on the following three aspects:1)In view of the short antibacterial efficacy caused by fast consumption of antibacterial agent,we report the design of a novel Ag NCs-based hydrogel(Ag NCs@BC)material by selecting natural hydrogel bacterial cellulose(BC)with adequate hydrophilicity,flexibility and good biocompatibility as support for in situ formation of Ag NCs.The as-fabricated Ag NCs@BC shows excellent broad-spectrum antibacterial activity against both gram-positive and gram-negative bacteria.In addition,due to its controlled release of Ag,Ag NCs@BC exhibits long-acting antibacterial properties compared to the original Ag NCs.In addition,Ag NCs@BC has good biocompatibility,which makes it promising in fighting bacterial infection.2)Encouraging with the achievement in addressing the short bactericidal efficacy of MNCs-based antibacterial agents obtained in the last chapter,we aim to design a novel MNCs-based antibacterial agent with purposes of thoroughly tackling the problem of consumption-caused short-acting antibacterial efficacy of tranditional analogues and catering the application demands of functional antibacterial agents.In this chapter we report the design of AIE-featured Au NCs for visible-light-driven antibacterial and deodorant applications.Owing to the intriguing AIE traits,the good harvest of visible light,and rich surface chemistry,the AIE-featured Au NCs unprecedentedly exhibit excellent visible-light-driven antibacterial activities against gram-positive(?98.5%)and gram-negative bacteria(?99.94%),which is resulted from their photodynamic producibility of abundant reactive oxygen species including O₂^·-,·OH and H₂O₂via O₂reduction and subsequent H₂O₂ oxidation.In addition,the Au NCs are demonstrated to be biocompatible,and easy to be deployed for downstream antibacterial and deodorant applications.For example,the Au NCs-modified domestic materials(e.g.,latex,ceramic glaze,organic fiber,and clothings)achieve long-lasting antibacterial efficiency of 99%and deodorant efficiency of>97.9%under visible-light irradiation.This work may shed light on designing novel AIE-featured metal NCs with photodynamic antibacterial and deodorant functions,enabling metal NCs and corresponding downstream materials to step into the photodynamic antibacterial and deodorant era.3)Wound infection caused by bacteria makes wound healing slow and has a huge negative impact on skin tissue engineering.In view of this,the photodynamic Au NCs-based antibacterial agent is integrated with chitosan and collagen to fabricate antibacterial nanofiber membrane via electrostatic spinning for wound healing.The composite fiber membrane has excellent biocompatibility,water retention and degradability.In addition,the composite fiber membrane also shows good broad-spectrum antibacterial properties,which can effectively eliminate bacterial infection.It is expected to have hemostasis,promote blood coagulation,promote wound healing and eliminate scars,which may enable it to be a multi-functional medical dressing that can eliminate bacterial infection,stop bleeding and promote skin tissue healing.This study lays a foundation for the application of multifunctional Au NCs-based nanofibers in skin tissue engineering and wound therapy.