Preparation and Characterization of Coated ZnFe₂O₄Magnetic Nanoparticles for Potential Use as Magnetic Particle Imaging Tracers

Magnetic nanoparticles (MNPs) exhibit unique behaviors that make them appealing for a variety of clinical applications, including their use as tracer agents in magnetic particle imaging (MPI) and magnetic resonance imaging (MRI) systems, as heat generators in hyperthermia treatment, and in targeted drug delivery. We prepared maghemite cores (ZnFe₂O₄) by coprecipitation of Zn(II) and Fe(III) salts with ammonium hydroxide, followed by a mixture under N₂ gas. The cores were coated with coating agents: citric acid monohydrate (CA), l-ascorbic acid (AA), and l-(+)-tartaric acid (TA). State-of-the-art techniques characterized their structural and magnetic properties. XRD results showed that all the particles were consistent with the crystal structure of ZnFe₂O₄, and the average crystallite size ranged from 14 to 19 nm. The hydrodynamic diameters were found between 112 and 218 nm. Zeta potential values for negatively charged particles in the range of −29.7 to −60.3 mV provided good colloidal stabilization. FTIR analysis showed the existence of coating agents on the structures. SEM measurements confirmed the spherical geometry of all samples. All synthesized ZnFe₂O₄ nanoparticles showed a superparamagnetic behavior. The primary aim of this study was to investigate the potential ability of coated ZnFe₂O₄ nanoparticles to serve as molecular magnetic contrast agents in imaging studies for MPI systems. Consequently, the prepared samples were also tested with magnetic particle spectroscopy (MPS), and the results were compared with those of commercial reference tracers, Perimag and VivoTrax, which are used in MPI. The MPS results show that ZnFe₂O₄ samples yielded the best results, with the shortest effective relaxation time (2.09 μs for ZnFe₂O₄@CA and 2.85 μs for ZnFe₂O₄@AA) and an excellent spatial resolution (fwhm, 5.89 mT for ZnFe₂O₄@CA and 5.14 mT for ZnFe₂O₄@AA). The structural and magnetic characterizations of CA, AA, and TA-coated ZnFe₂O₄ nanoparticles indicate that they are suitable for biomedical applications and especially have great potential as tracer agents for MPI.