From dopant synthesis to antimicrobial activity: understanding structure–activity relationships in ferrite nanoparticles

This paper presents a comprehensive study on the synthesis and characterization of ferrite nanoparticles doped with barium (Ba), calcium (Ca), cadmium (Cd), chromium (Cr), gallium (Ga), lanthanum (La), neodymium (Nd), praseodymium (Pr), samarium (Sm), and zinc (Zn). The nanoparticles were prepared through a thermal decomposition of acetylacetonate salts synthesis method, allowing for precise doping with the selected elements. Transmission electron microscopy revealed uniform morphology and particle sizes ranging from 8 ± 2 to 13 ± 2 nm, with Zn-doped nanoparticles forming larger cauliflower-like aggregates. The specific surface area, determined by nitrogen adsorption using the Brunauer-Emmett-Teller (BET) method, ranged from 2 to 16 m²/g depending on the dopant. XRD confirmed the formation of spinel structures with minor secondary phases in Ba and Cd-doped samples. Fluorescence spectroscopy demonstrated intense emission bands (420–540 nm) in Ca-, Sm-, and Zn-doped samples, linked to structural defects. The Minimum Inhibitory Concentration (MIC) values indicated that the nanoparticles demonstrated moderate activity against Gram-positive and Gram-negative bacteria (MIC varied from 31.25 to 205  μg/ml) and the pathogenic fungus Candida krusei (MIC varied from 62.5 to 125  μg/ml). The findings demonstrate that precise doping can synergistically enhance magnetic, optical, and antimicrobial features, enabling targeted design of ferrite-based nanomaterials for multifunctional applications.