How size and composition of cobalt doped iron oxide nanoparticle tracers enhance magnetic particle imaging performance

Magnetic particle imaging (MPI) is a promising diagnostic imaging technique that enables direct and precise tracking of magnetic tracers. The optimization of iron oxide-based nanoparticle tracers is of utmost importance in MPI for attaining high sensitivity and good spatial resolution. Currently, the state-of-the-art MPI tracers utilize undoped, magnetite iron oxide nanoparticles (NPs). In this study, we present the first comprehensive analysis of how doping with cobalt influences the MPI performance of iron oxide-based NPs. We observed a 1.4-1.7-fold and 1.2-1.3-fold enhancement in the saturation magnetization (M_sat) value by doping Co into 9 and 20 nm magnetite NPs, respectively. The amplification in the maximum point spread function (PSF) signal showed a significant increase, ranging from 1.6 to 1.8 times higher for both 9 and 20 nm NPs when subjected to doping with 12 at. % Co. Importantly, in NPs with a higher degree of doping of 22 at. % Co, the augmentation in maximum PSF signal was even more remarkable, achieving a 2-fold increase when compared to undoped magnetite NPs. By introducing Co doping, we show that tracers can be created that have excellent MPI performance while achieving a smaller size, making them highly suitable for a wide range of in vivo applications.