In summary, it is clear that AgNPs are potent broad spectrum antimicrobials: minimum inhibitory concentrations of 2–4 lg/mL for AgNPs with diameters 45–50 nm against E. coli, V. cholerae, S.
flexneri, and at least one strain of S. aureus, have been reported,
which rivals the bactericidal properties of penicillin against nonresistant
strains [220].
Furthermore, that potency can be easily
manipulated through the unique physical effects offered by
nanomaterials. For instance, Akhaven and Ghaderi [244] showed
that when silver nanowires are subjected to external electric fields,
they have 18.5–63% better antimicrobial potency due to enhanced
silver ion production at the wire termini. Also, photoexcitation of
AgNPs coated with a thin (1–2 nm) layer of porous silica at visible
light frequencies which are in resonance with AgNP surface plasmon
bands has been shown by Fuertes et al. [245] to enhance antimicrobial
activity against E. coli significantly, either through
photosensitized ROS generation or photocatalyzed silver ion release;
this effect is also reversible, providing a portal into photoswitchable
antimicrobial behavior. Studies such as these imply
that if intelligently-designed silver nanostructures are incorporated
within food storage containers, the application of an external
electric field or light source might be able to be used as a controllable
and noninvasive sterilization method.