3.4 Comparative antibacterial potential at sub-10 nm scale
As mentioned earlier, the bactericidal efficacy of silver nanoparticles over a range of 5–100 nm is significantly enhanced as
the size of nanoparticles is reduced below 10 nm. Therefore, a size-dependent antibacterial efficacy was tested against three bacterial strains where the nanoparticles taken were of size 5, 7 and 10 nm, designated as Ag(5), Ag(7), and Ag(10), respectively. For comparison, the concentration of individual nanoparticles was considered at their MBC concentration for a particular microbial strain, which inhibited bacterial growth. The initial bacterial concentration was adjusted to 105 to 106 CFU ml1 in 50 ml nutrient broth while the time period for the antibacterial activity was evaluated up to 3 hours, as the minimum time necessary to achieve $99% (bacteriostatic effect) and $99.9% bacterial killing (bactericidal effect) is expected to fall within this duration.