Antiviral application of colloidal and immobilized silver nanoparticles

This study explored the application of colloidal and immobilized silver nanoparticles (AgNPs) for inactivation of bacteriophages. Coliphages that are commonly used as indicators for enteric viruses, were used in this study. Colloidal AgNPs were synthesized via a chemical reduction approach using sodium borohydride as reducing agent and trisodium citrate as stabilizing agent. AgNP-immobilized glass substrate was prepared by immobilizing AgNPs on amine-functionalized glass substrate by post-immobilization method. The AgNP-immobilized glass substrate was also tested so as to minimize the release of AgNPs in the treated water. The characterization of AgNPs and the AgNP-immobilized glass surface was done using field emission gun-transmission electron microscopy and scanning electron microscopy. Studies conducted with varying concentrations of colloidal AgNPs displayed good antiviral activity for MS2 and T4 bacteriophage. Colloidal AgNPs at a dose of 60 μg ml^-1 could completely inactivate MS2 and T4 bacteriophage within 30 and 50 min with an initial concentration of 10³ PFU ml^-1. Contaminated water (100 ml) in an unstirred batch reactor with an initial bacteriophage concentration of 10³ PFU ml^-1 could be inactivated by the AgNP-immobilized glass substrate (1 cm × 1 cm, containing 3.7 μg cm^-2 silver) suspended centrally in the batch reactor. Complete 3-Log bacteriophage inactivation was achieved within 70 and 80 min for MS2 and T4 bacteriophage, respectively, while the aqueous silver concentration was less than 25 μg l^-1. This is significantly lower than the recommended standard for silver in drinking water (i.e. 100 μg l^-1, US EPA). Thus, AgNP-immobilized glass may have good potential for generating virus-free drinking water.