Preparation Of Metal-organic Frameworks-based Novel Antibacterial Agents And Their Antibacterial Activity Evaluation

Diseases caused by pathogenic microorganisms remained an important public health issue.However,there are many limitations in traditional sterilization technology,including bacterial resistance,irreversible damage to the human body,high equipment requirements and so on.Therefore,it is urgent to develop novel low-cost,non-toxic or low-toxic antimicrobials to combat foodborne pathogens.Recently,the investigation of nanotechnology and the application of nanomaterials have aroused great interest of scientists all over the world.Among the nanomaterials,metal-organic frameworks(MOFs),as a unique subset of nanomaterials,have been extensively studied for various applications because of their high porosity,inherent biodegradability and excellent biocompatibility.Herein,the Gram-positive microbe S.aureus(ATCC 29213)and Gram-negative bacteria E.coli(ATCC 25922),which are responsible for most of the food-borne pathogens among the most common species,have been used as model bacteria.This work designed and synthesized two novel types of antibacterial agents based on metal-organic framework,which realized controlled release,powerful sterilization,and excellent biocompatibility in vitro and in vivo.The research contents and results are as follows:1.Preparation of chitosan loading copper metal-organic frameworks film and evaluation of its antibacterial properties:The HKUST-1/CS composite substrate was successfully synthesized via in-situ nucleation synthesized method,wherein the cupric ions undergo chelated to chitosan,followed by lyophilization,and then,the formed film was treated with an MOF ligand solution.The resultant film(namely,HKUST-1/CS)was characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),thermogravimetric analysis(TGA),and so on.The copper ion release rates were assessed and the results indicated that compared to Cu2+/CS,the stability of HKUST-1/CS was higher.HKUST-1/CS film is more conducive to storage and control of the slow release of copper ions.The antibacterial properties were determined by the disc diffusion and spread-plate methods and the results implied that with the increasing time,the HKUST-1/CS film displayed increased antibacterial activity against both the Gram-negative and the Gram-positive bacteria.HKUST-1/CS film showed a durable antibacterial performance.Moreover,fluorescent staining and morphological changes of the bacteria treated with the HKUST-1/CS film confirmed the antibacterial activity of the fabricated film.The bactericidal effect of the nano-antibacterial agent was positively correlated with the duration of action,and with the extension of time,the bacterial cell damage became more serious,and the cell membrane integrity became more unsatisfactory.The results of cytotoxicity studies implied that 0.1 mg mL-1 of Cu2+/CS exhibited obvious cytotoxicity and there was no observable cytotoxicity at 0.4 mg mL-1 of the HKUST-1/CS film.In conclusion,the as-prepared HKUST-1/CS film possessed versatile abilities such as slow release of copper ions and reduced cytotoxicity,which lays the foundation for the further application of copper-based metal organic framework fungicides in food systems.2.Synthesis and antibacterial evaluation of metal-organic framework peroxidase loading silver ions:A simple two-step synthesis method was used to construct the silver ion-loaded bactericide,namely NH2-MIL-88B(Fe)-Ag.Fourier transform infrared(FTIR)spectroscopy,X-ray photoelectron spectroscopy(XPS)and other methods verified that silver ions were successfully loaded in the metal-organic framework,and there was no obvious effect on the crystal structure of the metal-organic framework.The typical TMB chromogenic substrate and hydroxyl radical catcher terephthalic acid were used to evaluate the peroxidase activity.The results confirmed that the synthesized nano-bactericide exhibited good peroxidase activity,and its affinity for hydrogen peroxide was higher than that of horseradish peroxidase.Compared with hydrogen peroxide alone and NH2-MIL-88B(Fe)-Ag alone,the NH2-MIL-88B(Fe)-Ag assisted with hydrogen peroxide sterilization system showed a more outstanding bactericidal effect.In this sterilization system,the released silver ions and catalytic reaction between the peroxidase-like enzyme and H2O2 exhibited a synergetic effect,which effectively destroyed the bacterial cell membrane,and caused bacterial death.The results of in vivo and in vitro cytotoxicity studies indicated that the sterilization system showed high biocompatibility.The novel antibacterial agent of combining NH2-MIL-88B(Fe)-Ag and hydrogen peroxide achieved enhanced sterilization performance,which made it possible to avoid the toxicity of high concentration of H2O2 and Ag+as well as the waste of resources.This strategy paves the way for the application of nanozymes in the elimination of foodborne pathogen.