Conversion of ferritin ferrihydrite core to magnetite by gold ions binding and the derived nanoparticle formation

Inspired by the multi-functionalities of vegetal extracts, we first focused on developing a new gold nanoparticle (AuNP) synthesis method using tomato extract ( Solanum lycopersicum Mill, Carmen variety) under conditions in which proteins could be preserved and unexpected additional synthesis of superparamagnetic magnetite occurred. The AuNPs and magnetite were characterized by UV–visible spectroscopy, dynamic light scattering, superconducting quantum interference device, high-resolution transmission microscopy and energy-dispersive X-ray spectroscopy. Based on the literature, the ferrihydrite core of holoferritin was postulated to be the magnetite precursor. Consistently, the tomato genome encodes a protein homologous to ferritin and an identical result was obtained with purified horse spleen ferritin (HSF). The electron paramagnetic resonance spectrum of the lyophilized tomato pulp extract at 298 K featured HSF signal with (g 0 = 2.070). This signal is absent in another tomato variety ( Solanum lycopersicum , cherry variety), as well as in the boiled Carmen tomato extract, which produced only AuNPs after stirring with HAuCl 4 . The synthesis of magnetite in an air atmosphere is feasible only using holoferritin because the synthesis by loading apoferritin with iron salt requires an inert atmosphere and controlled stoichiometry. In addition, AuNPs produced by this method exhibited potential for use in photodynamic therapy.