Study On The Inhibition And Removal Of Bacterial Biofilm By Nano-copper Oxide Food Contact Interface

Biofilms are infrequently removed by normal cleaning procedures and can contaminate food preparation surfaces.Normal anti-bacterial cleaning agents and antiseptic techniques include physical methods,e.g.,mechanical brushing,and chemical methods,e.g.,detergents and enzymes.Chemical disinfectants are widely used but may not penetrate an intact biofilm matrix and therefore not destroy biofilm living cellspathogens.Moreover,the use of antimicrobial agents may stimulate the growth of resistant strains,which necessitates alternative anti-biofilm agents or treatments,such as the local generation of reactive species,e.g.,reactive oxygen,chlorine,and nitrogen species?ROS,RCS,and RNS?for biofilm eradication.Although the literature regarding the anti-bacterial properties of ROS widespread,the anti-bacterial effects of RNS,e.g.,nitric oxide?NO?,and RCS,e.g.,chlorine and bleach?NaOCl?,is less mature.Two nanomaterials,V₂O₅ nanowires and CeO_2-x nanorods,have HPO-like activities and are functional coatings to prevent marine biofouling?seawater contains a high concentration of Cl^-and an appreciable level of Br^-?by brominating bacterial signaling molecules,such as N-acyl homoserine lactones.Herein,we constructed a CuO film on copper foil for the in situ generation of reactive chlorine species?RCS?for the contact killing of bacteria and biofilm suppression and dispersal.Additionally,we demonstrate the solid nano-CuO interface and not leached copper-ion-based Fenton chemistry is responsible for RCS generation and bacterial cytotoxicity.This process is modulated by the H₂O₂ and Cl^-concentrations in bacterial growth environment.A potential application for in situ generation of RCS might be the incorporation of CuO nanoparticles into functional food contact surfaces.The specific work is mainly carried out from the following four aspects:1.In-situ synthesis of Cu?CuO?foil by wet chemical method.The materials were characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The synthesized materials were proved to be stable by Inductively coupled plasma-Mass Spectrometry?ICP-MS?.2.Investigate the in situ production of reactive chlorine in nano-copper oxide food contact interface to inhibit and remove biofilm.In the experiment,eight groups of different reagents were prepared.The inhibitory effect of each reagent on planktonic bacteria was studied.With the prolongation of time,the antibacterial effect of each reagent became stronger and stronger.The killing effect of Cu?CuO?-H₂O₂-Cl^-on planktonic bacteria is stronger than that of Cu?CuO?,and stronger than that of Cu?CuO?-H₂O₂ binary system.There is a synergistic effect between the three reagents.The inhibition and removal of biofilms were studied by bicinchoninic acid method?BCA assay?,fluorescence microscopy and plate re-culture.It was found that with the increase of H₂O₂-Cl^-concentration,the membrane anti-film clearing effect was significant,and The presence or absence of Cu?CuO?foil at the same H₂O₂-Cl^-concentration was compared and found to be more effective in the Cu?CuO?foil group.The role of the nano-Cu?CuO?foil is to accelerate the reaction as a catalyst.The results of ICP-MS show that Cu?CuO?foil leaching Cu²⁺is a trace amount of CuO NPs,which plays a major role in the system.The experiment confirmed the production of active chlorine radicals by measuring the chlorination product of the 3-oxo-C8-HSL signal molecule.3.Investigate the in situ production of reactive nitrogen in nano-copper oxide food contact interface to inhibit and remove biofilm.Eight different groups of reagents were also prepared.It was found that the antibacterial effect of each reagent became stronger with time.The killing effect of Cu?CuO?-H₂O₂-NO₂^-on planktonic bacteria is stronger than that of Cu?CuO?,and stronger than that of Cu?CuO?-H₂O₂ binary system.There is synergy between the three reagents.Various methods were used to study its inhibitory and clearance effects on biofilms.It was found that with the increase of H₂O₂-NO₂^-concentration,the membrane-clearing effect of the system was significant.Cu?CuO?foil has a function as a catalyst to accelerate the progress of the reaction.ICP-MS demonstrated that CuO NPs(rather than leaching Cu²⁺)played a major bacteriostatic role.The reactive nitrogen produced in the system not only inhibits the growth of planktonic bacteria,but also inhibits and removes refractory biofilms.4.Studies on Cl^--NO₂^-promote the oxidation-reduction reaction on the surface of nano-Cu?CuO?foil for inhibiting and removing biofilms.The inhibition and scavenging effects of S.aureus and E.coli were studied by bicinchoninic acid method?BCA assay?,fluorescence microscopy and plate re-culture method.It was found that when Cl^--NO₂^-was present at the same time,the effects of inhibition,membrane inhibition and clearing were stronger than single agents,and the two had synergistic bactericidal effects instead of simple additive effects.