It was shown that the encapsulation of SPIO-based contrast agents in the red blood cells (RBCs) increases the circulation time in blood of these nanomaterials. Not all iron oxide particles are eligible for the entrapment into RBCs, depending on several factors and synthesis protocol. We have recently identified some type of nanoparticles that can be loaded with our method into RBCs to produce biocompatible SPIO-RBCs carriers that could be used as new intravascular tracers for biomedical applications, such as Magnetic Particle Imaging (MPI). Here, we report the first in vitro results obtained by using the Synomag®-D-PEG-OMe nanoparticles with both human and murine RBCs. MPS analysis showed that human Synomag®-D-PEG-OMe-loaded RBCs produced a signal that is weaker respect to the remarkable signal obtained with ferucarbotran loaded-RBCs prepared at the same condition, but it is to be noted that the encapsulation efficiency of Synomag®-D-PEG-OMe into cells is lower compared to ferucarbotran nanoparticles.