Recently, the potential of red blood cells (RBCs) loaded with superparamagnetic iron oxide (SPIO)-based nanoparticles as new blood-pool tracer material for the Magnetic Particle Imaging (MPI) has been investigated. It was shown that the encapsulation of SPIO-based contrast agents in the RBCs increase the circulation time in blood of these nanomaterials. However, not all iron oxide nanoparticles are eligible to the encapsulation into RBCs, depending on several factors such as dispersant agent nature, nanoparticle size and synthesis protocol. Therefore, we have recently started a program to identify those nanoparticles that can be potentially loaded with our method into RBCs. The goal is to produce biocompatible SPIO-RBCs carriers that can be used as new intravascular magnetic susceptible agents in biomedical applications, such as MRI and MPI. Here, we report the in vitro results obtained by using the Synomag®-D-PEG-OMe nanoparticle suspension (micromod Partikeltechnologie GmbH) with both human and murine red blood cells. MPS analysis showed that human Synomag®-D-PEG-OMe-loaded RBCs produced a signal that is weaker respect to the remarkable signal of 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.