| In response to the wide spreading of infectious diseases caused by pathogen,antibacterial materials that can effectively inhibit the growth of microorganisms haveattracted significant research interests. To date, sodium hypochlorite, ozone, chlorineoxide, metal ions, quaternary ammonium salts, quaternary phosphonium salts,peptides, guanidinium, N-halamines, etc., have been used in the development ofantibacterial materials. Among them, N-halamine antibacterial materials have receivedintensive interest because of their unique properties, such as antibacterial efficacy,stability in aqueous solution and in dry storage, regenerability upon exposure towashing cycles, lack of corrosion, low toxicity, and relatively low expense. Due tothese characteristics, the application of N-halamine antibacterial materials rangesacross the area of medical devices, hospitals, water purification systems, foodpackaging, food storage, hygienic products, etc. The antibacterial mechanism ofN-halamine materials involves the direct transfer of halogen from the N-halamine tobacterial cells, and the halogen has a strong tendency to participate in ionic reactions,thereby leading to destruction or inhibition of metabolic processes in microorganisms.Antibacterial performances of N-halamine materials strongly depend on theiractivated surface area. N-halamine materials with larger surface area can provide moreN-halamine functional sites to contact with the bacteria, and the N-halamineincrement can lead to the enhanced antibacterial efficiency.Nanomaterials with the size ranged from few nanometers to more than a hundrednanometers can present superior physical, chemical, and mechanical properties.Because of their small particle size and large surface area, nanomaterials possessremarkable potential and prospect. Therefore, to enhance antibacterial efficacy,fabrication of N-halamine materials with nanostructure to enlarge activate surface areais advisable. However, there is a major drawback to the application ofnanometer-sized N-halamine materials originating from the separation. Antibacterialperformance of N-halamine materials is usually conducted in an aqueous suspension,which requires an additional separation step to separate N-halamine nanomaterials from suspension, and separation of such fine nanostructures from a large volume ofsolution involves further expense.The recent successful synthesis of magnetic nanoparticles provides a convenienttool for exploring magnetic separation technique due to their specific characteristics.Magnetic separation is a technology involving the transport of magnetic ormagnetically susceptible particles in a gradient magnetic field. This technology can beemployed to recover desired species of submicron dimensions from solutioncontaining suspended solid particles or other biological particulates in a rapid andeasy way. Therefore, magnetic separation has been widely applied to various aspectsin biotechnology and biomedicine, such as cell sorting, enzyme immobilization, drugdelivery, and protein separation. The advantage of magnetic separation technology isto maximize the amount of target particles removed from the suspension whileminimizing the amount of time to carry out the separation process.In this thesis, a series of N-halamine-based antibacterial nanocomposite materialswere synthesized, and their antibacterial performances against Gram-positive andGram-negative bacteria were investigated. In addition, magnetic separation techniquewas introduced to facilitate the separation process of the N-halamine-basedantibacterial nanocomposite materials. The details are as follows:1. N-halamine-functionalized SiO2@PS core-shell nanoparticles(SiO2@PS-N-halamine) were prepared, and the effect of reaction condition onmorphology was studied. The excellent antibacterial activity of SiO2@PS-N-halaminenanoparticles against E. coli and S. aureus was assayed via the minimum inhibitionconcentration (MIC) method. Antibacterial test indicated that SiO2@PS-N-halaminenanoparticles displayed2-8times higher biocidal activity than the micrometer-sizedN-halamine, and these powerful and stable nano-sized biocides had higherantibacterial efficacy against S. aureus than E. coli. Finally, the long-term stability ofN-halamine structural biocide was confirmed.2. Four kinds of monodisperse SiO2@N-halamine core-shell nanoparticles weresynthesized, and their structure, morphology, and component were characterizedsubsequently. All these nanoparticles have legible spherical shapes and obviouscore-shell structures, and no significant differences were observed in the morphologyamong them. Diameters of SiO2@N-halamine nanoparticles were controlled viaadjusting the size of silica template. Chlorine contents of SiO2@N-halamine nanoparticles were determined by the aid of iodometric/thiosulfate titration method.Effects of particle size, chlorine content, and contact time on antibacterial efficiencywere investigated. The regenerability feature of N-halamine-based materials wastestified by FTIR measurement. Hydantoin structure appeared after antibacterialperformance can convert to N-halamine via chlorination treatment.3. Monodisperse Fe3O4@SiO2@N-halamine nanoparticles were fabricated andcharacterized by a series of measurement. Antibacterial test revealed that both themicrometer-sized N-halamine and Fe3O4@SiO2@N-halamine nanoparticles possessedantibacterial property, and Fe3O4@SiO2@N-halamine nanoparticles showed higherantibacterial capacity than micrometer-sized counterpart. The antibacterial kinetic testconfirmed that the antibacterial efficiency of Fe3O4@SiO2@N-halamine nanoparticlesincreased with chlorine content. Magnetism study revealed thatFe3O4@SiO2@N-halamine nanoparticles have super-paramagnetic property, whichcan make them magnetically separable from the aquaeos solution.4. PSA@Fe3O4@SiO2-N-halamine core-shell nanoparticles were prepared, andeffects of reaction parameters on morphology and content were studied. Antibacterialtest revealed that both micrometer-sized N-halamine andPSA@Fe3O4@SiO2-N-halamine nanoparticles have antibacterial activity against S.aureus and P. aeruginosa, while PSA@Fe3O4@SiO2nanopartices without N-halaminemodification displayed no antibacterial property, indicating that antibacterialperformance of PSA@Fe3O4@SiO2-N-halamine nanoparticles is provided by theN-halamine structure. Both these two N-halamine-structural materials have higherantibacterial efficacy against P. aeruginosa than S. aureus. Magnetism investigationshowed that PSA@Fe3O4@SiO2-N-halamine nanoparticles have super-paramagneticproperty and magnetic response, and they can be separated readily by the aid of anexternal magnetic field.In summary, several N-halamine-based antibacterial nanocomposite materialswere synthesized, and their antibacterial performances were enhanced effectivelythrough particle size decrease. In addition, magnetic separation technology wasintroduced to facilitate the separation process of N-halamine-based materials.
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