Paramagnetic Mn 8 Fe 4 - co -Polystyrene Nanobeads as a Potential T 1 -T 2 Multimodal Magnetic Resonance Imaging Contrast Agent with In Vivo Studies.

In developing a cluster-nanocarrier design, as a magnetic resonance imaging contrast agent, we have investigated the enhanced relaxivity of a manganese and iron-oxo cluster grafted within a porous polystyrene nanobead with increased relaxivity due to a higher surface area. The synthesis of the cluster-nanocarrier for the cluster Mn ₈ Fe ₄ O ₁₂ (O ₂ CC ₆ H ₄ CH═CH ₂ ) ₁₆ (H ₂ O) ₄ , cross-linked with polystyrene (the nanocarrier), under miniemulsion conditions is described. By including a branched hydrophobe, iso -octane, the resulting nanobeads are porous and ∼70 nm in diameter. The increased surface area of the nanobeads compared to nonporous nanobeads leads to an enhancement in relaxivity; r ₁ increases from 3.8 to 5.2 ± 0.1 mM ^-1 s ^-1 , and r ₂ increases from 11.9 to 50.1 ± 4.8 mM ^-1 s ^-1 , at 9.4 teslas, strengthening the potential for T ₁ and T ₂ imaging. Several metrics were used to assess stability, and the porosity produced no reduction in metal stability. Synchrotron X-ray fluorescence microscopy was used to demonstrate that the nanobeads remain intact in vivo . In depth, physicochemical characteristics were determined, including extensive pharmacokinetics, in vivo imaging, and systemic biodistribution analysis.