Iron-doped calcium phytate nanoparticles as a bio-responsive contrast agent in 1 H/ 31 P magnetic resonance imaging

We present the MR properties of a novel bio-responsive phosphorus probe doped with iron for dual proton and phosphorus magnetic resonance imaging ( 1 H/ 31 P-MRI), which provide simultaneously complementary information. The probes consist of non-toxic biodegradable calcium phytate (CaIP 6 ) nanoparticles doped with different amounts of cleavable paramagnetic Fe 3+ ions. Phosphorus atoms in the phytate structure delivered an efficient 31 P-MR signal, with iron ions altering MR contrast for both 1 H and 31 P-MR. The coordinated paramagnetic Fe 3+ ions broadened the 31 P-MR signal spectral line due to the short T 2 relaxation time, resulting in more hypointense signal. However, when Fe 3+ was decomplexed from the probe, relaxation times were prolonged. As a result of iron release, intensity of 1 H-MR, as well as the 31 P-MR signal increase. These 1 H and 31 P-MR dual signals triggered by iron decomplexation may have been attributable to biochemical changes in the environment with strong iron chelators, such as bacterial siderophore (deferoxamine). Analysing MR signal alternations as a proof-of-principle on a phantom at a 4.7 T magnetic field, we found that iron presence influenced 1 H and 31 P signals and signal recovery via iron chelation using deferoxamine.