Polyethyleneimine-mediated synthesis of superparamagnetic iron oxide nanoparticles with enhanced sensitivity in T₂ magnetic resonance imaging

The development of iron oxide nanoparticles (IONPs) with enhanced r₂ relaxivity is important for achieving greater sensitivity in in vivo magnetic resonance (MR) imaging. In this study, it was considered that polyethyleneimine (PEI) could play a role in varying the particle and cluster sizes in IONP synthesis, leading to different r₂ relaxivities. To demonstrate this, superparamagnetic IONPs were synthesised in the presence of NH₄OH and PEI using a co-precipitation method. PEI acted as an active stabiliser during IONP synthesis, and therefore the particle size, hydrodynamic cluster size, coating layer thickness, saturation magnetisation, and r₂ relaxivity were all strongly influenced by the PEI concentration. Monodispersed IONPs with a mean hydrodynamic cluster size of 14.4nm were synthesised at a PEI concentration of 0.05wt% and in this case, the r₂ relaxivity was increased up to 227.6mM^-1s^-1. This confirmed the viability of PEI-mediated synthesis as a means of controlling the particle/cluster size and enhancing the r₂ relaxivity. The PEI-IONPs exhibited no significant cytotoxicity up to 132ppm. Rapid and strong uptake of PEI-IONPs was detected in rat liver by in vivo MR imaging. The superparamagnetic PEI-IONPs prepared in this study are considered to be sufficiently sensitive for use as MR imaging contrast agents, which can be used as parent particles for further functional modification.