Abstract
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.