Preparation Of A Self-activated Hybrid Nanocatalyst Based On MIL88B-NH₂ And Its Antibacterial Effect

Bacterial infections have become a serious threat to human health,and a variety of methods have emerged for treating of bacterial infections.Especially the combination of various methods based on bacteria characteristics has become a key direction of current research.With the intensive research and rapid development of nanomedicine,chemodynamic therapy（CDT）using highly toxic hydroxyl radicals（·OH）has shown substantial promise for application.However,its antimicrobial efficacy is hampered by insufficient H₂O₂levels,the tendency of GSH to phagocytose hydroxyl radicals,and the low efficiency of Fe³⁺to Fe²⁺biotransformation.This results in the blockage of·OH production by rapid Fe²⁺depletion in the initiation phase and the near-neutral pH of the infection site.To address this set of problems,we immobilized glucose oxidase（GOx）on the surface of MIL88B-NH₂（MIL NPs）encapsulated with Fe₃O₄nanoparticles and successfully constructed a glucose-fueled,H₂O₂self-supplied cascade catalyti·OH nanoreactor GOx-Fe₃O₄@MIL88-NH₂（GFM NRs）.MIL88B-NH₂（MIL NPs）with peroxidase-mimetic enzymatic activity immobilizes and protects GOx while synergistically enhancing the chemical kinetic therapeutic effect of Fe₃O₄nanoparticles.GOx continuously converts glucose to gluconic acid and H₂O₂.The former lowers the pH to about 4,when Fe₃O₄-MIL88-NH₂（Fe₃O₄@MILNPs）exhibits the highest reactivity.Continuously generated H₂O₂is used for the subsequent catalysis of activated Fe₃O₄@MIL NPs to produce highly toxic hydroxyl radicals for bactericidal action.This avoids the direct use of relatively high concentrations and toxicity of H₂O₂.The first chapter of this thesis reviews the current status of bacterial infections and related therapeutic tools,details the antimicrobial mechanism of nanodrug delivery systems and their application in antimicrobial applications,introduces the application of metal-organic frameworks（MOFs）in the field of antimicrobial,and presents the background and significance of the research in the thesis.In the second chapter,we designed and synthesized glucose-fueled cascade catalytic nanoreactors,GFM NRs,based on solving pH and H₂O₂concentration problems,and successfully verified the synthesis of GFM NRs by various characterization methods.We also demonstrated that the synthesized GFM NRs have improved peroxidase activity and glucose oxidase dual enzyme activity,and can generate large amounts of·OH after adding glucose,which can address the problem of insufficient endogenous H₂O₂and unsuitable pH in chemodynamic therapy（CDT）.In addition,it was demonstrated that with the addition of an appropriate amount of glutathione（GSH）,the conversion of Fe³⁺to Fe²⁺was accelerated and accompanied by a gradual decrease in GSH content,which solved the problem of GSH phagocytosis of·OH in CDT and reduced CDT efficiency.Chapter 3 of the thesis demonstrated by plate counting,live-dead staining experiments and scanning electron microscopy（SEM）morphological observation that·OH production by GFM NRs in the presence of glucose compared to control PBS,glucose,Fe₃O₄@MIL NPs+glucose,GFM NRs,GOx+glucose on Escherichia coli（E.coli）,the Methicillin-resistant Staphylococcus aureus（MRSA）and multi-drug resistant Acinetobacter baumannii（MDR-AB）,with 98%,93%and 92%bactericidal rates for the three bacteria,respectively.The bactericidal effect of GFM NRs in glucose presence was also positively correlated with concentration.4μg/m L of GFM NRs achieved 98%for E.coli,5μg/m L of GFM NRs achieved 96%for MRSA,and 60μg/m L of GFM NRs achieved 93%for MDR-AB.SEM and staining of live-dead bacteria was used to visualize them.SEM pictures showed that bacteria treated with GFM NRs+glucose had serious morphological destruction.The red fluorescence representing dead bacteria was significantly stronger than the green fluorescence representing live bacteria in the GFM NRs+glucose treated bacteria in the live-dead bacteria staining experiment.The experiments in this chapter demonstrate that GFM NRs efficiently produce·OH in the presence of glucose and exhibit broad-spectrum bactericidal activity in the in vitro experiments.In Chapter 4 of the thesis,the biocompatibility of GFM NRs was firstly evaluated at the cellular level and animal level by cytotoxicity assay,hemolysis assay,blood items of Kunming rats after GFM NRs injection,blood biochemical parameters,body weight changes,and tissue section analysis of major organs.Then,a multidrug-resistant Acinetobacter baumannii wound infection model was constructed with Balb/c mice to verify the in vivo bactericidal effect of GFM NRs in the presence of glucose.The therapeutic experiments demonstrated that the bactericidal effect of GFM NRs+glucose was more obvious than that of glucose oxidase（GOx）+glucose,indicating that the·OH generated by the cascade catalytic reaction of GFM NRs fueled by glucose has a better bactericidal effect in vivo than H₂O₂generated by GOx in the presence of glucose,accelerates wound healing,and shows promise as a treatment for drug-resistant bacterial infections.Chapter 5 of the thesis summarizes the overall experimental study and suggests further scientific and technical issues to be addressed in this field.