Ni_1–xZn_xFe₂O₄@CoO (x = 0.25 and 0.50) Nanoparticles for Magnetic Resonance Imaging

Nanomagnets with regulated magnetic properties are incredibly advantageous in the framework of magnetic resonance imaging (MRI) for medical imaging. This work aims to achieve an improved MRI-contrast signal by considering variation in octahedral site substitution of Zn 2+ ions in nanoensembles of Ni 1– x Zn x Fe 2 O 4 @CoO ( x = 0.25 and 0.50) nanoparticles. We observe enhanced MRI-contrast efficiency in nanoensembles of Ni 0.75 Zn 0.25 Fe 2 O 4 @CoO with superior ground state magnetization of 210.6 μ B /cell and a higher asymmetric coercive field than that of Ni 0.5 Zn 0.5 Fe 2 O 4 @CoO. In addition, both systems show cell viability to a normal HEK cell line until 0.5 mM and no pro-tumorigenic activity until 1 mM. The ratio of transverse to longitudinal relaxivity ( r 2 / r 1 ) gives a value of 30 for Ni 0.75 Zn 0.25 Fe 2 O 4 @CoO and 19.5 for Ni 0.5 Zn 0.5 Fe 2 O 4 @CoO, resulting in promising candidates for MRI-transverse contrast agents with a small metal concentration up to 0.375 mM. A superior MRI-contrast signal is achieved in Ni 0.75 Zn 0.25 Fe 2 O 4 @CoO. As a result, we successfully achieve enhancement in MRI-contrast efficiency by considering manipulation in octahedral site substitution in cell-viable nanoensembles of Ni 1– x Zn x Fe 2 O 4 @CoO ( x = 0.25 and 0.50) and attaining the significant association of anisotropy field strength and easy axes alignment toward proton dephasing in the MRI-relaxivity mechanism.