Synthesis And Antibacterial Application Of ZIF-8 Encapsulated Riboflavin Sodium Phosphate Submicron Particles

Foodborne diseases are considered as a critical public health problem all over the world.Hundreds of thousands of people have died from foodborne diseases every year.Microbial contamination is one of the important causes of foodborne diseases.Antibiotics are commonly used to prevent bacterial infections,but overuse and abuse of it results in the emergence and prevalence of drug-resistant bacteria.Therefore,it is imperative to develop new and efficient antibacterial agents.Previous researchers report that bacteria will not be easily able to develop resistance after treating by photodynamic sterilization.Hence,photodynamic sterilization has attracted increasing attention from researchers in the development of antimicrobial agents.Riboflavin is a photosensitizer and ultraviolet absorber,as well as an essential vitamin for human.The low solubility of riboflavin limits its application.Riboflavin sodium phosphate(RF),as a water-soluble formulation of riboflavin,has the same application effects as riboflavin.Therefore,riboflavin sodium phosphate is an ideal photosensitizer to substitute for riboflavin in this study.On the other hand,riboflavin sodium phosphate is prone to photodegradation under irradiation.And riboflavin sodium phosphate has no antibacterial effect without irradiation.There is a need for a carrier to improve the light stability and antibacterial activity of riboflavin sodium phosphate.ZIF-8 is a metal organic framework material,which has the property of p H-responsive.Under slightly acidic environment,ZIF-8 would degrade to release Zn²⁺.In this study,riboflavin sodium phosphate(RF)was a photosensitizer.Zeolite imidazole framework structure material(ZIF-8)was an ideal carrier to encapsulate riboflavin sodium phosphate.Therefore,RF@ZIF-8 had the synergy of the light responsiveness and p H-responsiveness.Then,blending RF@ZIF-8 with polycaprolactone(PCL)prepared for PCL/RF@ZIF-8 composite films.The characterization and antibacterial properties of RF@ZIF-8 submicron particles and PCL/RF@ZIF-8 composite films had been explored.The details were described as follows:1.The synthesis and characterization of RF@ZIF-8 submicron particles:RF@ZIF-8 was synthesized by the one-step method in the mixed system of water and methanol.The physical and chemical properties and the structures of RF@ZIF-8 was analyzed by X-ray diffraction(XRD),field emission scanning electron microscopy(SEM)and other experiments.Results showed that,riboflavin sodium phosphate loading capacity of RF@ZIF-8 was 18.4%.The structure of RF@ZIF-8 was consistent with ZIF-8.The particle sizes of RF@ZIF-8 increased after encapsulating riboflavin sodium phosphate into ZIF-8.The thermal stability of RF@ZIF-8 was improved compared to ZIF-8.According to UV-vis absorption spectra and fluorescence spectra,the typical peaks of RF@ZIF-8 were red-shifted compared to that of riboflavin sodium phosphate.After encapsulated riboflavin sodium phosphate into ZIF-8,the photostability of riboflavin sodium phosphate improved.Furthermore,RF@ZIF-8 collapsed to release Zn²⁺and riboflavin sodium phosphate under acidic conditions.2.The antibacterial properties and mechanism of RF@ZIF-8 submicron particles:the antibacterial effects of RF@ZIF-8,riboflavin sodium phosphate and ZIF-8 against E.coli and S.aureus were explored through the double dilution method,time-kill kinetics of photodynamic-sterilization and other experiments.Results revealed that,under irradiation,RF@ZIF-8 had lower minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)compared to that of riboflavin sodium phosphate and ZIF-8.Under365?375nm light irradiation,the inactivation time of RF@ZIF-8 were better than that of riboflavin sodium phosphate and ZIF-8.And the sterilization effects of RF@ZIF-8 was more efficient than riboflavin sodium phosphate and ZIF-8.Through PDT experiments,the detection of K⁺content and the morphology changes of cell,the sterilization mechanism of RF@ZIF-8was that,with the synergy of singlet oxygen and Zn²⁺,RF@ZIF-8 destroyed the cell membrane of bacteria,caused the intracellular material to flow out,and killed bacteria finally.3.The characterization and antibacterial properties of PCL/RF@ZIF-8 composite films:the degradable PCL/RF@ZIF-8 composite films were prepared by blending RF@ZIF-8 with PCL(the highest loading of RF@ZIF-8 in the matrix of PCL was 30wt%).The aim of this study was to explore the feasibly of the composite films to serve as food packaging.Through field emission scanning electron microscopy(SEM),X-ray diffraction(XRD)and Fourier infrared(FTIR),the integral structures of RF@ZIF-8 maintained well in the process of the preparation of PCL/RF@ZIF-8 composite films.And RF@ZIF-8 submicron particles dispersed well in the PCL matrix.Through optical transmittance,it was confirmed that adding RF@ZIF-8 into PCL matrix obstructed the transmission of ultraviolet light and visible light.However,the transparency of the composite films was not affected.Through antibacterial and anti-adhesion experiments,it was concluded that,PCL/RF@ZIF-8 composite films inactivated E.coli and S.aureus under irradiation.And PCL/RF@ZIF-8 composite films had excellent anti-adhesion of bacteria,preventing the growth of biofilm on the composite film under UVA lamp irradiation.In summary,this study developed a new type of biodegradable photodynamic antibacterial material,which had multiple-responsive antibacterial mechanisms.Furthermore,PCL/RF@ZIF-8 composite films had the potential to serve as an antibacterial food packaging material with a certain light blocking performance.