Physicochemical properties of NPs including surface morphology, size, crystal structure, charge and zeta potential regulate their antibacterial actions. Bacterial strains, exposure time and environmental conditions also impact the potency of antimicrobial drugs. Some of the crucial factors that govern the antibacterial mechanism of NPs are summarized below Size and surface charge of NPs affect the antimicrobial potential. Length and breadth of nanotubes can extend the release of given antimicrobial. Large specific surface area of NPs increases the prospect of closeness, contact, and interaction with microbial membrane [56, 57] Shapes of nanomaterials are the basis of wavering degrees of damage to pathogens through periplasmic enzymes. For example, ZnONPs of various shapes (sphere, pyramid, and plate) exhibit varied photocatalytic activities with β-galactosidase leading to functional and conformational change in the enzyme [58]. Prismatic-shaped Y2O3 NPs show better activity against P. desmolyticum and S. aureus, which may be due to direct interaction of Y2O3 NPs and bacterial cell membrane surfaces, causing leakage of the cellular components [59]

Roughness of NPs can decrease the adhesion of microbes, as the size and surface area-to-mass ratio stimulate the adsorption of bacterial proteins [60] Zeta potential of NPs resiliently impacts microbial adhesion because of electrostatic attraction generation due to negative charge on bacterial membrane and positively charged NPs [61]. For example, Mg(OH)2_NPs, being positively charged are adsorbed on microbial surfaces and this accumulation at the site of infection ascends the permeability [62] Doping modifications allow proper dispersal of NPs in hydrophilic or aqueous environments. For example, nanocomposites framed with a combination of Au and ZnO show enhanced photocatalytic property and ROS formation as Au allows enriched light absorption (Surface Plasmon Resonance) and ZnO with transformed band gap width increases electron transport efficiency and charge carrier separation [63]. Cr doping on the ZnONPs significantly enhanced their antimicrobial activity against a wide range of pathogenic bacteria [64] Environmental conditions impact the antimicrobial potency of NPs. For example, most bacterial enzymes cannot function beyond optimum temperature and NPs targeting these enzymes would be ineffective. Reduced pH shows high dissolution of ZnONPs and adhesion of NPs on the bacterial membrane of MRSA and E. coli [65]