The Preparation And Application Studies Of New Nano-antimicrobial

With the combined effect of natural evolution and antibiotic misuse,the chance of bacterial resistance mutations greatly increases.The emergence of superdrug-resistant bacteria is also a reminder of the need to study new antimicrobials.Nano materials developed from singular material to composite material,having special properties that are different from macroscopic materials,such as quantum size effect,small size effect,surface and boundary effect,and so on.Nano-silver has both catalysis and extensive antimicrobial activity,within an catalyze a variety of chemical reactions and inhibit most of the bacteria.As a non-antibiotic antibacterial agent,nano-silver directly destroys the cell structure of bacteria,and the bacteria can hardly resists.Moreover,Ag nanomaterials showed low toxicity to human body and are widely applied in water purification systems,wound dressings,surgery instruments,and implantable materials.The magnetic microcomposites are superparamagnetic,which can be easily recycled under the effect of magnetic field,with a low cost.Recently,the Ag modified magnetic composites have gained increasing attention and showed application.However,the development of Ag modified magnetic composites is considerably restricted by three factors.First,the current synthetic methods of magnetic nanomaterials is complicated.Second,nanoparticles,which have small size and exhibit high surface energy,resulting in serious stability issues in the water environment.Third,the irregular aggregation of magnetic composite materials induced by magnetic attraction.Therefore,we purpose to design a Ag modified magnetic nanomaterial with novel structure and stable performance.This study mainly consists of two parts.First,we developed a simple,effective and reproducible approach for synthesis of 3D flower-like Ag-coated magnetic microspheres?Fe₃O₄@SiO₂@Ag microflowers?with the size of 800nm as a highly active and easily recyclable catalyst.The synthesis of Fe₃O₄@SiO₂@Ag microflowers was developed based on our scheduled seed growth approach with some modifications,which include four steps.Fe₃O₄@SiO₂@Ag microflowers is mainly composed of the three parts.The microscale Fe₃O₄ core ensures the quick separation and recovery of the catalyst,and the highly-branched Ag shell provides a large surface area and numerous catalytically active site.The size and morphology of the flower-like Ag shell of the as-prepared microflowers could be easily controlled by varying the experimental parameters.In that the particle diameter of Fe₃O₄@SiO₂@Ag microflowers can not be detected for the size,TEM,SEM,XRD,EDS and TGA were applied to characterize the morphology of the Fe₃O₄@SiO₂@Ag microflowers.We investigated the catalytic ability of the highly-branched microflowers for reduction of 4-NP and MB in water,NaBH₄ as the reducing agent.To gain insights into the effect of the surface morphology of Ag microcomposites on catalytic properties,we synthesis four kinds of composite materials with different surface morphology.The catalytic rate can be treated as a pseudo-first order reaction kinetics,and the rate constant of the reaction can be calculated using the equation.Compare the catalytic activity of Fe₃O₄@SiO₂@Ag microflowers with others in the reduction of 4-NP.The large specific surface area and the high number of catalytic sites on the highly branched structure led to stronger catalytic activity.Evaluate the catalysis of Fe₃O₄@SiO₂@Ag microflowers by comparing with other catalysts.The Fe₃O₄@SiO₂@Ag microflowers were used for six magnetic separation cycles to evaluate stability and reusability.The Fe₃O₄@SiO₂@Ag microflower with long petals could be successfully recycled and reused for six successive cycles of reaction,with stable conversion efficiency of 96.6%and 93.4%in the reduction of 4-NP and MB,respectively.These studies focused on synthesis of different antibiotic-functional nanostructures and investigated their enhanced antibacterial activity.Second,we propose the use of a novel vancomycin-modified Fe₃O₄@SiO₂@Ag microflowers for rapid and effective killing of pathogenic bacteria in solutions.For the preparation of vancomycin modified Fe₃O₄@SiO₂@Ag microflowers,the microflowers were carboxyl-group-functionalized by MUA first and then conjugated with vancomycin according to a coupling reaction.As a multi-function carrier,the highly-branched flower-like Ag shell with good dispersity,uniform structure,sufficient magnetic responsiveness,and provides larger surface area for effective Ag ion release and bacterial contact.Vancomycin was selected for binding to the Fe₃O₄@SiO₂@Ag microflowers to maximize the bactericidal potential.We confirm the coupling of vancomycin molecule to Fe₃O₄@SiO₂@Ag microflowers with TEM,UV-vis and element mapping analyze.We test the sterilizing effect of the synthesized van/Fe₃O₄@SiO₂@Ag microflowers on E.coli and MRSA,and compared with bare Fe₃O₄@SiO₂@Ag microflowers and free-form vancomycin.The minimuminhibitionconcentrations?MIC?ofthevancomycin-modified Fe₃O₄@SiO₂@Ag microflowers are 10?g m L^-1 for E.coli and 20?g m L^-1 for MRSA.Moreover,the antibacterial ability of van/Fe₃O₄@SiO₂@Ag microflowers is significantly higher than that of the non-modified microflowers and vancomycin.Recyclability tests were performed with E.coli and MRSA using plate counting method.The antimicrobial effect of van/Fe₃O₄@SiO₂@Ag microflowers remains above 90%after 5 cycles.New Zealand rabbits were selected as experimental animals,and the skin stimulation experiments of Fe₃O₄@SiO₂@Ag microflowers and van/Fe₃O₄@SiO₂@Ag microflowers on the skin surface of rabbits were conducted.There was no erythema,edema,dermal irritation and death in all casas after the skin stimulation experiments of Fe₃O₄@SiO₂@Ag microflowers and van/Fe₃O₄@SiO₂@Ag microflowers.New Zealand rabbits all going well.We confirmed that the synthesized Fe₃O₄@SiO₂@Ag microflowers by using seed-mediated growth method has stronger catalytic performance in comparision with other catalysts.The vancomycin-modified Fe₃O₄@SiO₂@Ag microflowers has stronger antibacterial effect.The efficiency of Fe₃O₄@SiO₂@Ag microflowers and van/Fe₃O₄@SiO₂@Ag microflowers remains above 90%after several magnetic separation cycles.In this study,we provide a new idea for new nanomaterial.