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 14.4 nm were synthesised at a PEI concentration of 0.05 wt% and in this case, the r2 relaxivity was increased up to 227.6 mM−1 s−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 132 ppm. 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.