2 The presence
of Ag nanoparticles leads to the breakage of the cell
membrane at endocytosis and other parts, through which
nanoparticles or ions penetrate into the cells. Subsequently,
Ag nanoparticles react with other species in the cell matrix,
such as proteins or glutathione to generate ROS or hydroxyl
radicals via Fenton reactions. The excess of generated ROS
eventually leads to cell death through the destruction of several
species inside the cell matrix, as shown in Fig. 5.272 For
instance, the generated ROS could damage the DNA by the
inhibition of cell growth, by the activation of signaling cascades
in mitochondrial pathway or by lipid peroxidation.272
The mechanism of antibacterial activity at the molecular level
has been further investigated by the identification of biomolecules
in comparison with model compounds through SERS.
The SERS results suggest that there is a significant interaction
of Ag nanoparticles with proteins through metabolic processes
of purine.276 Besides, Li et al. investigated the mechanism for the antibacterial activity of Ag nanoparticles
on Escherichia coli using transmission electron microscopy.267
They have found that the presence of Ag nanoparticles
leads to the destruction of the cell membrane and
hinders the activity of some enzymes, which cause the bacteria
to eventually die.