Engineering And Application Of Copper Nanocluster Based Antibacterial Agenents In Broad Spectrum

Bacteria are the pathogens of many human diseases.The development of antibacterial technology is of great significance to human health and environment.The wide-use of antibiotics has solved the problem of most bacterial infections,but it has also caused a crisis of bacterial resistance.Therefore,it’s urgent to the develop new and non-drug-resistant antibacterial agents.Metal nanoclusters（MNCs）are ultra-small metal nanoparticles smaller than 3 nm.MNCs have the advantage of size over traditional nanomaterials,allowing them to more easily cross the envolope（cell wall and membrane）of bacteria and enter the interior of bacteria,thus achieving efficient antibacterial activity.In addition,the abundant active sites on the surface of MNCs are beneficial to catalyze the biochemical reactions inside the bacteria,which further improves its antibacterial activity.At present,the precise synthesis and structural regulation of Au/Ag nanoclusters（Au/Ag NCs）have become mature,and have been successfully applied to broad-spectrum antibacterial activities.However,the abundance of Au and Ag elements is low,which limits their commercial application.Cu（belongs to IB group with Au and Ag）has a higher reserve on the earth,and has a broader industrialization prospect compared with Au and Ag.However,the synthesis of copper nanoclusters（Cu NCs）and their broad-spectrum antibacterial activities have been lagging behind.To sum up,this paper aims to solve the problem of drug-resistant bacteria infection by designing Cu based nanomaterials such as cysteine-protected Cu NCs（Cys-Cu（Ⅰ）NCs）,AIE-luminescent Cu（Ⅰ）complexes aggregates（PCuA）and AIE-luminescent Cu NCs（AIE-Cu NCs）.To investigate its efficacy in broad spectrum antibacteria and the treatment of wounds infected with methicillin-resistant Staphylococcus aureus（MRSA）.Specific works are as follows:（1）Firstly,low-cost Cys-Cu（Ⅰ）NCs were prepared by pH-mediated ligand reduction method and successfully applied in the treatment of drug-resistant bacterial infections.Antibacterial tests showed that Cys-Cu（Ⅰ）NCs had excellent broad-spectrum antibacterial activity against Gram-positive bacteria,Gram-negative bacteria and drug-resistant bacteria MRSA.In addition,due to the coordination of Cys,Cys-Cu（Ⅰ）NCs showed ultra-low cytotoxicity compared with Cu SO₄,reflecting its good biocompatibility.On this basis,we further revealed the bactericidal mechanism of Cys-Cu（Ⅰ）NCs.The results showed that Cys-Cu（Ⅰ）NCS could destroy the cell wall and membrane of bacteria,disturb the metabolism of bacteria,and finally kill bacteria through the dual mechanism of producing reactive oxygen species（ROS）and releasing copper ions.Based on the above work,we further prepared Cys-Cu（Ⅰ）NCs uniformly dispersed Carbomer transparent gel（Cys-Cu（Ⅰ）NCS-gel）and explored its effect as a wound dressing on wound healing in mice infected with MRSA（representative drug-resistant bacteria）.The results showed that Cys-Cu（Ⅰ）NCs-gel could effectively eradicate MRSA,showing excellent properties of promoting the wound healing of drug-resistant bacteria infection,providing a good paradigm for the treatment of drug-resistant bacteria infection by nanomaterials.（2）The above study found that although Cu NCs have excellent broad-spectrum antibacterial activity,due to its contact-released bactericidal mechanism,the series of antibacterial agents lack of long-term antibacterial performance,which is also a problem faced by most Cu-based antibacterial nano-agents.Au NCs（AIE-Au NCs）continuously produce bacteria-killing ROS through photocatalysis,which solves the problem of insufficient antibacterial persistence of MNCs.However,the high-cost of Au-based systems limits their commercial application.Therefore,in this paper,a rational design of AIE-mechanism luminescent Cu（Ⅰ）complex aggregate（PCuA）is proposed to solve the problem of antibacterial short-efficacy of Cu-based nanomaterials.Specifically,an atomically precise Cu（Ⅰ）complex was synthesized using p-mercaptobenzoic acid（p-MBA）.It was found that Cu（Ⅰ）-p-MBA complex was dispersed in alkaline aqueous environment and had no fluorescence.However,by decreasing the pH and introducing an ethanol solvent,the Cu（Ⅰ）-p-MBA complex appears to aggregate.With the increase of the volume fraction of ethanol in the solvent,the aggregation degree of Cu（Ⅰ）-p-MBA complex increased,and then AIE phenomenon appeared.However,the AIE property of Cu（Ⅰ）-p-MBA complex is dependent on the introduction of ethanol solvent,which limits its application in photodynamic broad-spectrum antibacteria.In order to get rid of the dependence on solvents,this study innovatively utilized the spatial limiting action of polymers such as polyethylene glycol（PEG）to successfully prepare PCuA which is stable in aqueous environment and has AIE-mechanism luminescence.The prepared PCuA showed not only photodynamic enhanced broad-spectrum antibacterial activity,but also good biocompatibility.Studies on antibacterial mechanism showed that PCuA with AIE mechanism had good visible light harvest,microsecond photogeneration carrier lifetime and reasonable energy level structure,which enabled it to produce ROS driven by visible light and improved antibacterial activity and long-term performance.This work provides a good paradigm for the preparation of AIE luminescent aggregates and the research of photodynamic broad-spectrum antibacteria.（3）The above study indicated that AIE-mechanism luminescent PCuA has a photodynamic enhanced broad-spectrum antibacterial activity,which alleviates the problem of short-efficacy of Cu-based antibacterial nano-agents.However,although the macromolecular confinement strategy achieves the stable existence of Cu（Ⅰ）complex（AIE-induced luminescence）in aqueous environment,the large size and difficult modification of PCuA limit the further improvement of antibacterial properties.As previously stated,MNCs-based antibacterial agents have the intrinsic advantages of ultra-small size and abundant and adjustable surface chemistry.Therefore,introducing AIE luminescence mechanism into Cu NCs can not only avoid the disadvantage of polymer confinement strategy,but also reduce the antibacterial cost and improve the antibacterial long-term performance of MNCs.Based on this,the atomically precise Cu（Ⅰ）-GSH complex is prepared in this chapter.The AIE activity of the Cu（Ⅰ）-GSH complex was discovered after the aggregation of the Cu（Ⅰ）-GSH complex was induced by decreasing pH and introducing undesirable solvents（DMF and ethanol）.In this chapter,based on the study of AIE of Cu（Ⅰ）-GSH complex,we successfully prepared AIE-mechanism luminescent Cu NCs（AIE-Cu NCs）under the condition of high temperature（80℃）,and realized simple pH-driven regulation of Cu（Ⅰ）-GSH complex aggregation on Cu（0）core surface.Thus,the fluorescence color of AIE-Cu NCs was modulated.Thanks to the AIE-luminescenct mechanism,AIE-Cu NCs can produce more ROS driven by visible light,showing a broad-spectrum antibacterial activity enhanced by photodynamics.In addition,AIE-Cu NCs also have good biocompatibility.On this basis,AIE-Cu NCs-gel containing AIE-Cu NCs was further prepared.Animal experiments showed that AIE-Cu NCs-gel showed excellent properties of photodynamic promoting healing of MRSA-infected wound.This work provides a paradigm for the design of antibacterial agents and the synthesis of MNCs.