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.