Post-Synthesis Modulation of the Physicochemical Properties of Green-Synthesized Iron Oxide Nanoparticles with Tween 80 to Enhance Their Antibacterial Activity and Biocompatibility

<b>Background</b>: Iron oxide nanoparticles (IONPs) have broad-spectrum antimicrobial activity, with negligible potential for resistance development, excellent biocompatibility, and therefore, could be promising alternatives to conventional antimicrobials. However, their industrial-scale production relies on chemical synthesis that involves toxic reagents, imposing potential environmental hazards. In contrast, green synthesis offers an eco-friendly alternative, but our previous study found that green-synthesized IONPs (IONPs-G) exhibited a lower antibacterial activity and a higher cytotoxicity compared to chemically synthesized counterparts, likely due to nanoparticle aggregation. <b>Objectives</b>: To address this challenge, the current study presents a simple, effective, economic, scalable, and eco-friendly strategy to optimize the physicochemical properties of IONPs-G post-production without requiring extensive modifications to synthesis parameters. <b>Methods</b>: IONPs-G were dispersed in a solvent mixture containing Tween 80 (Tw80). Subsequently, in vitro antimicrobial and in vivo cytotoxicity studies on rabbits' skin and eye were conducted. <b>Results</b>: The formed nanoparticles' dispersion (IONPs-GTw80) had a particle size of 9.7 ± 2.1 nm, a polydispersity index of 0.111 ± 0.02, and a zeta potential of -11.4 ± 2.4 mV. MIC of IONPs-GTw80 values against <i>S. aureus</i> and <i>E. coli</i> were reduced by more than ten-fold compared to IONPs-G. MBC was twice MIC, confirming the bactericidal activity of IONPs-GTw80. In vivo studies of IONPs-GTw80 confirmed their biocompatibility with intact/abraded skin and eyes; this was further confirmed by histopathological and biochemical analyses. <b>Conclusions</b>: IONPs-GTw80 might be recommended as a disinfectant in healthcare settings or a topical antimicrobial agent for treatment of infected wounds. Nevertheless, further studies are required for their clinical translation.