Aqueous synthesis of magnetite nanoparticles for magnetic hyperthermia: Formation mechanism approach, high water-dispersity and stability

Superparamagnetic iron oxide nanoparticles (SPIONs) are interesting for biomedical applications in cancer treatment via magneto-hyperthermia. Its potential application contrasts with the challenges in producing systems with chemical and morphological uniformity and colloidal stability using simple, low-cost, and sustainable routes. Aqueous syntheses usually fail to control morphology and composition because SPIONs formation mechanisms are not fully understood. Here, we propose an aqueous route to synthesize SPIONs based on the controlled and stoichiometric reduction in situ of Fe3+ to Fe2+ ions in the presence of sulfite ions, followed by aging at 90 ∘C in an alkaline medium for 18 h. SPIONs with high water-stable and controlled characteristics in a sustainable, inexpensive, and scalable procedure were obtained. The nucleation, growth, and hydrolysis rates were adjusted by the excess of OH− ions, initial temperature, and iron precursor nature. The results are discussed concerning concepts of the classical and nonclassical nucleation theories, indicating an optimum pH of 9.5–10.5 for SPIONs formation. The SPIONs present an average size of 11 nm, narrow size distribution, and magnetite phase with about 34 mol% of maghemite due to structural defects. Nanoparticles are superparamagnetic, have a hydrodynamic diameter of 130 nm with a surface potential of ~ −40 mV (pH ≥ 7), and suitable magneto-hyperthermic properties fro cancer treatment. Specific Absorption Rate values were evaluated concerning the SPIONs physical-chemical properties, indicating a strong dependence on the average crystallite size and the magnetization at 250 Oe. Cell viability tests showed that SPIONs did not provide any significant change in cellular growth at used concentrations.