Comparative Antibacterial Mechanisms of Metal Oxide Nanoparticles (Zno, Nio, Ceo2, And Fe2O3): A Critical Review of Structure-Activity Relationships and Emerging Applications

The global problem of the increase of antibiotic resistance has motivated several studies on alternative bactericidal agents. The promising materials include metal oxide nanoparticles (MONPs) due to their multi-mechanistic antibacterial action, chemical stability, and customizable physicochemical features. In this review, we critically and comparatively examined the antibacterial mechanisms of four extensively studied MONPs, namely zinc oxide (ZnO), nickel oxide (NiO), cerium oxide (CeO2), and iron oxide (Fe2O3), emphasizing the impact of particle size, morphology, surface area, crystal phase, and synthesis route on their biological activity.The four bactericidal processes addressed here, ROS generation , membrane rupture , metal ion release , and intracellular DNA damage , are comparatively analyzed across the oxide systems with emphasis on mechanistic contrasts and overlaps. The action against Gram-positive and Gram-negative bacteria is established in parallel to the demonstrated efficacy against resistant clinical infections, especially MRSA. MIC statistics reported are extensively reviewed and cytotoxicity profiles essential for biological translation are assessed for each substance.This review provides an integrated view of mechanistic, structural and biological data to identify major knowledge gaps and to propose directions for further research, in particular on standardization of antibacterial testing protocols and the importance of strong in vivo efficacy studies.