Integrative Modulation of Magnetic Resonance Transverse and Longitudinal Relaxivity in a Cell-Viable Bimagnetic Ensemble, γ-Fe 2 O 3 @ZnFe 2 O 4 .

The potential application of magnetic nanosystems as magnetic resonance imaging (MRI) contrast agents has been thoroughly investigated. This work seeks to attain robust MRI-contrast efficiency by designing an interacting landscape of a bimagnetic ensemble of zinc ferrite nanorods and maghemite nanoparticles, γ-Fe 2 O 3 @ZnFe 2 O 4 . Because of competing spin clusters and structural anisotropy triggered by isotropic γ-Fe 2 O 3 and anisotropic ZnFe 2 O 4 , γ-Fe 2 O 3 @ZnFe 2 O 4 undergoes the evolution of cluster spin-glass state as evident from the critical slowing down law. Such interacting γ-Fe 2 O 3 @ZnFe 2 O 4 with spin flipping of 1.2 × 10 -8 s and energy barrier of 8.2 × 10 -14 erg reflects enhanced MRI-contrast signal. Additionally, γ-Fe 2 O 3 @ZnFe 2 O 4 is cell-viable to noncancerous HEK 293 cell-line and shows no pro-tumorigenic activity as observed in MDA-MB-231, an extremely aggressive triple-negative breast cancer cell line. As a result, γ-Fe 2 O 3 @ZnFe 2 O 4 is a feasible option for an MRI-contrast agent having longitudinal relaxivity, r 1 , of 0.46 s -1 mM -1 and transverse relaxivity, r 2 , of 15.94 s -1 mM -1 , together with r 2 /r 1 of 34.65 at 1.41 T up to a modest metal concentration of 0.1 mM. Hence, this study addresses an interacting isotropic/anisotropic framework with faster water proton decay in MR-relaxivity resulting in phantom signal amplification.