Optimization of Solvothermal Parameters for Tailoring Magnetic Nanosphere Size and their Influence on Antibacterial Efficacy

Abstract

The increasing prevalence of multidrug-resistant bacteria has intensified the global search for novel nanomaterials capable of enhancing existing antimicrobial strategies. In this study, magnetite (Fe₃O₄) nanospheres were synthesized via a systematically optimized solvothermal route, where the reaction parameters, including the temperature, precursor ratio, and time, were fine-tuned to control the crystallinity, surface morphology, and particle size distribution. Scanning electron microscopy confirmed that varying the solvothermal conditions modulated the nanosphere diameter from 25 to 70 nm, whereas X-ray diffraction revealed size-dependent crystallinity transitions characteristic of the cubic spinel Fe₃O₄ phase. Fourier transform infrared spectroscopy revealed Fe-O lattice vibrations at ~580 cm⁻¹, verifying structural integrity and purity. Beyond morphological optimization, the mechanistic pathways underlying antibacterial synergy have been elucidated. The Fe₃O₄ nanospheres generated reactive oxygen species (ROS) through Fenton-like redox cycling of Fe²⁺/Fe³⁺, triggering lipid peroxidation, membrane rupture, and protein oxidation. Magnetic field–induced aggregation further facilitated localized membrane stress, enhancing antibiotic permeation and bactericidal efficacy. Comparative antibacterial assays against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa demonstrated a pronounced, dose-dependent inhibition profile, with optimized Fe₃O₄ formulations resulting in zone diameters that were up to 40% greater than those of unoptimized samples. The integrated analysis of synthesis optimization, mechanistic pathways, and antibacterial spectra established Fe₃O₄ magnetic nanospheres as multifunctional antimicrobial agents with tunable physicochemical properties and synergistic therapeutic potential. These findings provide a rational framework for engineering magnetically responsive nanomaterials to counteract microbial resistance and improve antibiotic efficacy in biomedical applications.

Keywords: Fe₃O₄ nanospheres, solvothermal optimization, antibacterial mechanism, reactive oxygen species, multidrug resistance, nanotechnology synergy.