Preparation of ⁵⁹Fe-labelled magnetite nanoparticles with iron sulphates and by direct neutron activation

Magnetite nanoparticles (MNPs) are widely studied for scientific and industrial applications. Particular interest to them arises from biomedicine in which they are considered as a drug delivery platform. Usually MNPs are considered due to their superparamagnetic properties enabling their imaging with magnetic resonance (MRI). In some cases MRI is undesired, and the additional analytic signal for the same potential drug would be very useful. We propose labelling MNPs with ⁵⁹Fe that would allow their detection with γ-radiometry. First, extra pure ferric and ferrous sulphates were synthesized from carbonyl metal iron. Then, MNPs were synthesized from iron sulphates via modified Massart's sol-gel method. Sulphate-derived MNPs are superparamagnetic, cubic to spherical shaped, with the size of 11.5 nm. Radioactive [⁵⁹Fe]MNPs were synthesized from neutron-activated and [⁵⁹Fe]Fe-derived [⁵⁹Fe]ferric sulphate and obtained via neutron activation of non-labelled MNPs. Specific radioactivity of [⁵⁹Fe]Fe was 962 kBq/g, [⁵⁹Fe]Fe₂(SO₄)₃ - 278 kBq/g and [⁵⁹Fe]MNPs - 454 kBq/g after neutron activation. Specific radioactivity of [⁵⁹Fe]MNPs was 427 kBq/g (from [⁵⁹Fe]Fe₂(SO₄)₃ from [⁵⁹Fe]Fe), 634 kBq/g (from directly activated [⁵⁹Fe]Fe₂(SO₄)₃). The most convenient is synthesis from [⁵⁹Fe]Fe because of higher specific radioactivity and radionuclide purity. The calculated theoretical sensitivity of the method of detection of [⁵⁹Fe]MNPs is 1.11 ag.