At the moment the biomedical applications of magnetic fluids are the subject of intensive
scientific interest. In the present work, magnetite nanoparticles (MNPs) were synthesized
and stabilized in aqueous medium with different carboxylic compounds (citric acid
(CA), polyacrylic acid (PAA), and sodium oleate (NaOA)), in order to prepare well
stabilized magnetic fluids (MFs). The magnetic nanoparticles can be used in the magnetic
resonance imaging (MRI) as contrast agents. Magnetic resonance relaxation measurements
of the above MFs were performed at different field strengths (i.e., 0.47, 1.5 and
9.4 T) to reveal the field strength dependence of their magnetic responses, and to
compare them with that of ferucarbotran, a well-known superparamagnetic contrast agent.
The measurements showed characteristic differences between the tested magnetic fluids
stabilized by carboxylic compounds and ferucarbotran. It is worthy of note that our
magnetic fluids have the highest r2 relaxivities at the field strength of 1.5 T, where
the most of the MRI works in worldwide.