Effect of surfactant functionalization on Fe₃O₄ aqueous ferrofluid stability and magnetic hyperthermia performance

Developing stable water-based ferrofluids with efficient magnetic heating remains a key challenge for biomedical hyperthermia. In this work, we functionalize Fe₃O₄ nanoparticles with surfactants of different chemical nature namely ethylenediaminetetraacetic acid (EDTA), ethanolamine and betaine and examine the role of surface chemistry on colloidal stability and heating performance in aqueous media. HRTEM study on these samples reveals particle sizes of ~10-13 nm, indicating monocrystalline nanoparticles with a surface coating. We confirm the successful functionalization with different functional groups such as carboxylate, amine and zwitterionic groups by FTIR, TGA, and XPS analysis. Zeta potential values ranging from -22.5 to -46.2 mV indicate negatively charged surfaces governed by Fe-O -groups and surfactant functionalities which ensures electrostatic stabilization in water. VSM measurements confirm superparamagnetic behavior with saturation magnetization of 55-63 emu g⁻¹ indicating that the magnetic core structure is preserved. Among the studied systems, EDTA-functionalized Fe₃O₄ exhibits exceptional long-term stability, retaining its ferrofluid state without sedimentation for over one year. This stable dispersion correlates with superior magnetic heating performance, achieving the highest SAR (~245 W g⁻¹ at 0.5 mg mL⁻¹). These results demonstrate that surface functionalization plays a critical role in stabilizing aqueous ferrofluids, enhance hyperthermia efficiency and provide a practical basis for designing biocompatible magnetic nanofluids.