Magnetic hybrid colloids decorated with Ag nanoparticles bite away bacteria and chemisorb viruses

Abstract

Magnetic hybrid colloids (MHCs) decorated with different-sized Ag nanoparticles (Ag07@MHC, Ag15@MHC, and Ag30@MHC denote MHCs decorated with similar to 7 nm, similar to 15 nm, and similar to 30 nm AgNPs, respectively) are synthesized and used to investigate their antimicrobial efficacy and mechanism. An MHC (diameter similar to 0.6 mu m) is a cluster of superparamagnetic Fe3O4 nanoparticles (similar to 10 nm) encapsulated with a silica shell (thickness similar to 0.1 mu m). The Ag30@MHC was prepared using the seed-growth method with Ag seeds self-assembled on the aminopropyl-functionalized MHC, and its surface is covered with AgNPs and Ag+ ions. The Ag07@MHC and Ag15@MHC were prepared using the seeding, coalescing, and growing strategy with Au seeds, and these MHCs released substantially less Ag+ ions than Ag30@MHC due to the contribution of the Au core. The Ag30@MHC exhibited the greatest antimicrobial efficacy towards E. coli CN13 (6-log reduction) and the bacteriophage MS2 (2-3 log reduction) due to the synergistic effect of the 3D architecture decorated with AgNPs and Ag+ ions as well as the already-known effects of free AgNPs. On the 3D architecture, the AgNPs abstract Mg2+ or Ca2+ ions from the bacterial membrane and the Ag+ ions grab the microorganisms by forming a complex with the thiol groups imbedded in the membrane, which bites away bacteria and completely ruptures the cell structure. The Ag30@MHC is easily collectible from the reaction mixture using an external magnet without detachment of AgNPs, and it is re-dispersible. Overall, Ag30@MHC is believed to be a promising antimicrobial material for practical applications.