Nano-Ag is currently the most widely used antimicrobial
nanomaterial. Its strong antimicrobial activity, broad antimicrobial
spectrum, low human toxicity, and ease of use make it
a promising choice for water disinfection and microbial control.
It is now well accepted that the antimicrobial activity of
nano-silver largely stems from the release of silver ions. Silver ions can bind to thiol groups in vital
proteins, resulting in enzyme damage. It also
has been reported that silver ions can prevent DNA replication
and induce structural changes in the cell envelope . Thus, the release rate and bioavailability of silver ions is
crucial for the toxicity of nano-Ag. Studies have suggested
that physicochemical properties of nano-Ag play an important
role in its antimicrobial activity. However, the influence
of the size, shape, coating, and crystallographic facet appears
to be mainly related to different release kinetics of silver ions.
The presence of common ligands reduces the bioavailability of
silver ions and mitigates its toxicity . A recent
study found that low concentration (sublethal) of silver ions or
nano-Ag enhances E. coli growth, suggesting a hormetic
response that could be counterproductive to its antimicrobial
applications .
CNTs kill bacteria by causing physical perturbation of the
cell membrane, oxidative stress, or disruption of a specific
microbial process via disturbing/oxidizing a vital cellular
structure/component upon direct contact
with bacterial cells. Graphene and graphite materials exhibit
antimicrobial properties through similar mechanisms . The cytotoxicity of CNTs strongly depends on
their physicochemical properties. Short, dispersed, and
metallic CNTs with small diameters are more toxic