A comparative study of the performance of zinc-doped iron oxide nanoparticles with different capping agents as a potential tracer in magnetic particle imaging

Magnetic nanoparticles have attracted significant attention in medical applications because of their enhanced biocompatibility and multifunctional properties. They support advanced drug delivery, nanotheranostics, and in vivo imaging. This study examines how different capping agents, including ascorbic acid (AA), tartaric acid (TA), lauric acid (LA), and malic acid (MA), influence the structure and magnetic performance of zinc-doped (Zn_0.75Fe_2.25O₄) nanoparticles, aiming to identify effective tracers for Magnetic Particle Imaging (MPI). All samples exhibited superparamagnetism with M_s = 40–52 emu/g (300 K) and high colloidal stability (zeta potential − 26.9 to − 52.8 mV). The MA-coated sample delivered the strongest MPS response with the highest 5th/3rd harmonic ratio (0.49) and the narrowest PSF FWHM (8.16 mT), compared to AA- (0.31; 10.89 mT), TA- (0.40; 9.57 mT), and LA-(0.29; 8.38 mT) coated samples. This study demonstrates that controlled Zn²⁺ doping combined with tailored surface chemistry via specific organic coatings can effectively tune the structural and magnetic properties of ferrite nanoparticles toward high-resolution MPI performance, indicating that appropriately capped Zn-ferrite nanoparticles are promising candidate tracers. However, in vivo and in vitro validation and benchmarking against established agents are still required.