There is a significant need for materials that promptly exhibit antimicrobial activity upon contact. The large-scale fabrication of monodisperse silver nanoparticle (AgNP)-decorated silica (AgNP@SiO) hybrid particles, and their prompt and synergistic antibacterial activity against both the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus epidermidis on air filtration units are presented. Monodisperse aminopropyl-functionalized silica colloids (406 nm) were used as a support material and were hybridized with AgNPs using a seeding, sorting-out, and growing strategy with Ag seeds (1-2 nm) into ∼30 nm AgNPs, successfully yielding 51 g of AgNP@SiO hybrid particles. Medium filter samples (glass fiber material, 4 × 4 cm) were coated with AgNP@SiO particles and tested for antibacterial efficacy. SEM characterization of the bacterial morphology suggested prompt and synergistic antibacterial activity against both classes of bacteria. Moreover, antibacterial efficacies >99.99% for both bacteria were obtained using a filter sample with a coating areal density of 1 × 10 particles per cm. Solutions of AgNP@SiO at 1.3% were stable even after 8 months. The hybrid particle AgNP@SiO and the air filter system coated with the particles are expected to be useful for future green environment applications.