K. Woo, Y-S Ko, S-H Park, J-H Lee, J. Hwang
Korea Insitute of Science and Technology,
Keywords: silver nanoparticle, silica, hybrid, microparticle, biofouling
Summary:Pathogenic bacteria and viruses cause health problems and occasionally, lead to pandemic. Thus, global demand for clean air and safe water is increasing. Filtering systems have been utilized to provide clean air and water. However, the pathogenic microorganisms filtered on the medium can proliferate and be a source of contamination when an appropriate nutritional condition is reached by the filtered dust materials (i.e., biofouling). Recent advances in nanoscience and nanotechnology afford nanoparticles (NPs) that can exhibit antimicrobial activity. However, those NPs have some drawbacks in practical utilization as an anti-biofouling agent. For example, silver nanoparticles (AgNPs) exhibit anti-microbial effects most effectively when their surface is exposed to the microorganisms. However, the AgNPs without ligands aggregate seriously upon their contact, limiting their utilization as an anti-biofouling coating material on a filter medium. In situ production and coating of naked AgNPs in a gas phase needs complicated equipment and high cost. Besides, the nanoparticles can be released to the environment and exhibit toxicity. Hybrid microparticles with coated AgNPs can be an alternative because the microparticles are well dispersible without ligands and easily collectable by a conventional centrifugation and furthermore, the nanoparticles coated on the microparticle can exhibit nano-properties. Here we introduce silver nanoparticle-coated silica (AgNPs@SiO2) hybrid particles synthesized by seed-mediated growth method and their applications as a biocidal coating material for air and water filtration system. Aminopropyl-functionalized silica colloids with sub-micron sizes were used as a substrate material to coat AgNPs. The AgNP-coating was achieved by growing Ag seeds up to ~30 nm in size on the silica surface where the Ag seeds remained spaciously through seeding and sorting-out process. The hybrid microparticles were collectable by a conventional centrifugation and re-dispersible, and the hybrid structure was stable for more than one year, promising as a coating material for air and water filtering systems. For the antibacterial test on air filtering medium, the AgNPs@SiO2 particles were aerosolized and coated on a commercial air filter. The target bacteria are gram-negative bacteria, Escherichia coli, and gram-positive bacteria, Staphylococcus epidermidis. These bacteria were found to be trapped by AgNPs@SiO2, which was observed by scanning electron microscopy. The trapped bacteria appeared unable to escape without rupturing their cellular membrane, eventually leading to cell death. For the antibacterial test on water filtering medium, the AgNPs@SiO2 particles were immobilized on a commercial polyamide-based membrane. The membrane surface was functionalized with cysteamine as a linker for the immobilization of AgNPs@SiO2 particles. Due to the strong chemical bonding between Ag and sulfur, the hybrid particles could be fixed robustly on the membrane, providing a good stability against leaching of Ag. This AgNPs@SiO2-immobilized membrane also showed excellent antibacterial activity. In these regards, the AgNPs@SiO2 hybrid structure can open a way for practical utilization of AgNPs. Moreover, the availability of scale-up synthesis (50 g/batch) of AgNPs@SiO2 may facilitate practical applications ranging from household appliances to industrial products.