Structural, optical, and magnetic characterization of Cu–Zn–Ni spinel ferrite nanoparticles with antibacterial potential

One of the most pressing challenges in biomedical applications is the growing prevalence of bacteria that are resistant to multiple antibiotics. Metal-based nanoparticles are emerging as a promising strategy to address this problem, which is the focus of the present work. Cu_0.15Zn_0.2Ni_0.65Fe₂O₄ nano-ferrite was synthesized via the co-precipitation method. The chosen cation ratio preserves the spinel phase while Ni improves magnetic response, and Zn enhances magnetic softness and site stability. For comparison, single-cation ferrites NiFe₂O₄, ZnFe₂O₄, and CuFe₂O₄ were synthesized using the same procedure to enable a consistent evaluation of antibacterial activity. All ferrites were characterized using XRD and FTIR. Additional analyses including UV-Vis, SEM, EDX, XPS, TEM, VSM, and Atomic Absorption Spectroscopy (AAS) were performed for Cu_0.15Zn_0.2Ni_0.65Fe₂O₄ sample. XRD confirmed a cubic spinel phase for all ferrites. FTIR provided further evidence of cation redistribution of tetrahedral and octahedral sites. AAS verified the availability of Cu²⁺, Zn²⁺, and Ni²⁺ ions, supporting their contribution to antibacterial activity. VSM showed soft magnetic behavior with ~ 54.3 emu/g saturation magnetization. Antibacterial tests demonstrated that Cu_0.15Zn_0.2Ni_0.65Fe₂O₄ exhibits stronger inhibitory activity against S. aureus and E. coli at both low and high concentrations. At 500 μg/mL, the inhibition zone reached ~ 20 mm for S. aureus and ~ 17 mm for E. coli, The MIC values were found to be 40 μg/mL for S. aureus and 80 μg/mL for E. coli, indicating stronger sensitivity of Gram-positive bacteria. After establishing its individual performance, comparison has been obtained with single-cation ferrites. Across all trials, Cu_0.15Zn_0.2Ni_0.65Fe₂O₄ consistently produced larger inhibition zones, showing clear superiority. The superior antibacterial activity is attributed to the synergistic incorporation of Cu²⁺, Zn²⁺, and Ni²⁺ within a single spinel lattice, giving Cu_0.15Zn_0.2Ni_0.65Fe₂O₄ strong intrinsic antibacterial activity and improving performance over single-cation ferrites, confirming its novelty and potential for biomedical applications.