Figure 2

Magnetism-engineered iron oxide (MEIO) nanoparticles and effects of their magnetic spin on MRI. a TEM images of MnFe₂O₄ (MnMEIO), Fe₃O₄ (MEIO), CoFe₂O₄ (CoMEIO), and NiFe₂O₄ (NiMEIO). All nanoparticles were synthesized to be ~12 nm with narrow size distributions (0 < ~8%). Scale bar, 50 nm. b Mass magnetization values of MFe₂O₄ nanoparticles. In face-centered cubic lattices of oxygen, the magnetic spins at On sites aligned in parallel with the direction of the external magnetic filed whereas those at Td sites aligned antiparallel. MnFe₂O₄ had the highest mass magnetization value, with a magnetic spin magnitude of 5 μg (e f) T2-weighted spin echo MR images, their color maps and relaxivity (R2) of a series of MEIO nanoparticles at 1.5 T. In f, the R2 of CLIO is also presented, for comparison. Consistent with the mass magnetion results, MnMEIO showed the strongest MR contrast effect (that is, darkest MR image, violet in color map) and had the highest R2 coefficient. Mass magnetization value, MR contrast and R2 coefficient gradually decreased as M2+ changed from Mn²⁺ to Fe²⁺, to Co²⁺ and to Ni²⁺[31]