Polyethyleneimine-modified iron oxide nanoparticles: their synthesis and state in water and in solutions of ligands

Water-soluble iron oxide nanoparticles (IONPs) are synthesized from oleate-stabilized particles (IONPs-OA) by replacing oleate moieties with 3,4-dihydroxybenzoic acid (3,4-DHB) and polyethyleneimine (PEI). Investigation of the obtained composite nanoparticles by TEM, SEM, and AFM methods demonstrated that the parent IONPs-OA particles have a narrow size distribution and that the size of the magnetite core (4.3 nm) was retained in the polyethyleneimine modified IONPs-PEI nanoparticles (4.5 nm). IONPs-PEI exist in the form of separate nanoparticles distributed in the bulk polymer matrix as well as elongated chains (up to 20 nm in length) consisting of 3–6 nanoparticles, and mostly in the form of large clusters (~ 150 nm). The NMR relaxometric properties of IONPs-PEI in the water at various pHs are determined. Relaxivity of such modified nanoparticles remains constant over a wide pH range (3–9) and decreases only in strongly alkaline solutions due to the destruction processes. In the presence of physiological amounts of NaCl (0.15 M), the relaxivity of IONPs-PEI solutions is reduced by 37%. The effect of the addition of various iron(III) chelators is analyzed. Tiron (disodium 4,5-dihydroxy-1,3-benzenedisulfonate) is the only ligand which destroys the polymer-bound IONP system in solution, dissolving the iron oxide core, while other ligands (3,4-DHB, 2,4-DHB, citric acid) do not reduce the relaxation of the composite aqueous solution. The developed polyethyleneimine-modified iron oxide nanoparticles can be regarded as a promising model of a contrast agent for magnetic resonance imaging (MRI).