Lecithin molecule is a safe biological agent which capped the AgNPs with a bilayer structure. Figure 6, shows the formation of phospholipidsmembrane on the surface of silver nanoparticles. The presence of lecithin molecule bilayer leads to reduce the direct contact of
AgNPs to the bacterial cell membrane which results in lower killing rate of AgNPs. The silver nanoparticles should diffuse through the bilayer and contact to the bacterial cell membrane and cause the cell death. The killing rate is more decreased by an increase in lecithin concentration which leads to formation of multilayer structure on the AgNPs surface and prolong reaching time to the bacterial cell membrane.