Ultrasmall Manganese Ferrites as Multimodal Bioimaging Agents and Fenton/Haber-Weiss Catalysts

Ultrasmall manganese ferrite nanoparticles display interesting features in bioimaging and Fenton nanocatalysis. However, little is known about how to optimize these nanoparticles to achieve simultaneously the highest efficiency in both types of applications. Herein, we present a cost-efficient synthetic microwave method that enables manganese ferrite nanoparticles to be produced with excellent control in size, chemical composition and colloidal stability. We show how the reaction’s pH has a substantial impact on the Mn incorporation into the nanoparticles and the level of Mn doping can be finely tailored to a wide range (Mn_xFe_3-xO₄, 0.1 ≤ x ≤ 2.4). The magnetic relaxivities (1.6 ≤ r₁ ≤ 10.6 mM^-1s^-1 and (7.5 ≤ r₂ ≤ 29.9 mM^-1s^-1) and Fenton/Haber-Weiss catalytic properties measured for the differently doped nanoparticles show a strong dependence on the Mn content and, interestingly, on the synthetic reaction’s pH. Positive contrast in magnetic resonance imaging is favored by low Mn contents, while dual mode magnetic resonance imaging contrast and catalytic activity increases in nanoparticles with a high degree of Mn doping. We show that this is valid in solution, in a murine model and intracellularly respectively. Besides, this synthetic protocol allows core-radiolabeling for high-sensitive molecular imaging while maintaining relaxometric and catalytic properties. All of these results show the robust characteristics of these multifunctional manganese ferrite nanoparticles as theranostic agents.