*3.1.2 Damage to the wall-cell membrane due to electrostatic interaction and accumulation*

The electronegative groups of the polysaccharides in the bacterial membrane have an attraction sites by metal cations. The difference in charge between bacterial membranes and the NPs of metal oxides leads to electrostatic attraction and thus accumulates on the bacteria surface, altering the structure and permeability of the cell membrane. Gram-negative bacteria have a higher negative charge than Gram-positive bacteria and therefore the electrostatic interaction will be stronger in Gram-negative strains. The pores of the membranes are in the order of nanometers, therefore the smaller the particle size and the greater the surface area, the greater the efficiency of the metal oxide nanoparticles. In the same way, the cations extracted from the NPs of the metal oxides and their accumulation in the cell wall, create pits in it, leading to a change in permeability due to the sustained release of lipopolysaccharides, membrane proteins and intracellular factors. In addition, this mechanism has been linked to the interruption of the replication of adenosine triphosphate (ATP) and the deoxyribonucleic acid (DNA) of the bacterium, leading to its death. One study indicates that the action of NPs depends on the components and structure of the bacterial cell. The unique components of Gram-negative bacteria, such as LPS, can prevent the adhesion of metal oxides NPs to the barrier of bacterial cells and regulate the flow of ions in and out of the bacterial cell membrane.
