It has been reported that the nanoparticles of 5 nm size are characterized by an excess energy at the surface as their
band gap energy abruptly increases. These properties are attributed to lattice contractions which favor confinement of electrons and are responsible for the “electronic effects” of silver nanoparticles which thereby, enhance their direct
interaction with bacterial cells. Results are consistent with that of earlier studies where, the smallest AgNPs
demonstrated the best antibacterial activity against both pathogenic and non-pathogenic bacterial strains, and activity was attributed to the maximum contact area associated with them. Although, the probable reason for antibacterial activity of AgNPs cannot be fully explained by either release of Ag+ ions or by direct contact, significant enhancement in their antibacterial effect, particularly below the 10 nm size range is predominantly attributed to the contact mode killing mechanism.