Synthesis And Antibacterial Properties Of Ag-Based Magnetic Core-Shell Structural Antibacterial Agents

Although the demands for hygiene in public health care are increasing, the infectious pathogenic bacteria is still greatly threaten public health. At the meanwhile, the emergence of drug-resistant strain has also became a serious pubic health problem. Therefore, it's urgent to develop and research new antimicrobial agent against bacterial resistance. At present, Ag-based nano-antibacterial agent can play a crucial role in antibacterial applications. Research in this area has shown that silver nanoparticles ?AgNPs? have an important advantage as it can kills all pathogenic microorganisms, and no organism has ever been reported to readily develop resistance to it. However, the pure silver nanopaticles are limited in practical application because of their nanoparticles agglomeration, poor stability and difficult recycling use. In this paper, they were designed to be deposited onto the surface of SiO3 or TiO₂ to to build Fe₃O₄@SiO₂/AgNPs and Fe₃O₄@SiO₂@TiO₂/AgNPs core/shell structures which can inhibit the aggregation of AgNPs and enhance their stability and antibacterial activity. In addition, by the combination of magnetic material with antibacterial properties to form a magnetic core-shell structure antimicrobial agent, the antibacterial agent could target a certain area or be magnetically separated under the external magnetic field. By using the minimal inhibitory concentration method, the inhibition zone method and the plate method, we studied the antibacterial activities of these two kinds of silver-based antibacterial agents. The antibacterial mechanism of the silver-based antibacterial agents and TiO₂ photocatalytic antibacterial agents were explored, and the intrinsic relationships between the photocatalytic activity and the antibacterial properties of TiO₂ photocatalytic antibacterial agents were discussed. The specific contents of this paper were illustrated as below:1? Ag nanoparticles-decorated Fe₃O₄@SiO₂ core-shell nanospheres:morphology controlled preparation and antibacterial activityIn the DEG solvent system, the Fe₃O₄ magnetic microspheres with high crystallinity were prepared use FeCl3·6H2O as a precursor. The effects of the reactants FeCl3·6H2O concentration and temperature on the morphology of Fe₃O₄ were investigated. Furthermore, we also explored its formation mechanism. It was followed by preparation of Fe₃O₄@SiO₂ core-shell structure by using Fe₃O₄ as core materials.The influence of the SiO₂ shell thickness on the magnetic properties of Fe₃O₄ were studied. Finally, by using a seed-mediated growth approach, the Ag nanocrystals were used as seeds to realize the morphology controlled preparation of Ag-deposited Fe₃O₄@SiO₂ nano-antibacterial agent. The minimal inhibitory concentration and the inhibition zone showed that the size and the deposition density of the silver nanoparticles played a decisive role in the antimicrobial activity. AgNPs with smaller size and higher decoration density may exert higher toxicity due to their higher specific surface area and associated faster Ag- release rate compared to larger AgNPs. Antibacterial experimental results show that the AgNPs can be oxidized in the tested bacterial solution by dissolved oxygen, resulting in the further release of Ag+ under this slightly acidic condition. These released Ag ions can easily accumulate around the living bacterial cells and interact with the thiol group of the cysteine chain to form -S-Ag, which impede the enzymatic function of the protein and deactivate the microorganism cells. Secondly, under sunlight irradiation, photo-induced electron-hole pairs are generated in Ag nanoparticles due to surface plasmon resonance. Then the photo-induced electrons are scavenged by dissolved oxygen molecules to yield superoxide radical anions ?·O₂^-?.The radical anions can also combine with H+ to form OOH, and OOH radicals and the trapped electrons combine to produce H2O₂, finally forming OH radicals. Hydroxyl radical ?OH? and O₂^- species possessing strong oxidation abilities exhibit the collapsing force which leads to the bacterial death. In the reaction system, the most noteworthy is that in magnetically recycling conditions, after 9 times, the antibacterial capacity of Fe₃O₄@SiO₂/AgNPs samples was getting worse with the increase of cycles, which indicates that the Fe₃O₄ magnetic core can increase the stability of the silver nanoparticles and reduce loss rate of product.2?Synthesis of Fe304@Si02@TiO₂/AgNPs photocatalytic antibacterial agent and its photocatalytic antibacterial properties.A series of Fe₃O₄@SiO₂@TiO₂/AgNPs heterostructural photocatalytic antibacterial materials were prepared by changing the concentration of TBOT and AgNO3 on the basis of the above mentioned Fe₃O₄@SiO₂, which used as a magnetic nano-core. Photodegradation and photocatalytic antibacterial results showed that when the added content of TBOT was 0.3 mL and concentration of AgNO3 was 0.30 mol, the obtained samples showed the best photocatalytic activity. At the same time, it also shows that there is a internal relation between the photocatalytic activity and its antibacterial activity, typically, it's a positive proportion between them. And under the condition of external magnetic recovery, after a continuous cycle 6 times, the photocatalytic activity degradation rate of the heterogeneous composite nanomaterials did't change much, the result suggested that the sample pocesses a good stability. And the heterogeneous photocatalytic antibacterial agents showed a better antibacterial activity under UV light. This is mainly due to metal silver can effective capture the photo-electron of TiO₂ under the UV irradiation, to realize the effective separation of electrons and holes, enhance the production of ROS, and ultimately to enhance its antibacterial activity. The main active groups in the process of photocatalytic antibacterial activity were detected by using tert butyl alcohol and potassium bromate. The results showed that the main active groups were generated -O₂^- by the reation of photoinduced electrons and oxygen molecules on the surface of metal silver.