Evaluation of a Cotton-Mouton Relaxometer for the Characterization of Superparamagnetic Iron Oxide Nanoparticles

When using superparamagnetic iron oxide nanoparticles (SPIONs) as contrast agents or tracers in biomedical applications, knowledge of the hydrodynamic diameter is crucial. The hydrodynamic diameter influences the circulation time of the particles in the blood cycle as well as the accessibility of the target structure. Common methods to determine the hydrodynamic diameter include magnetorelaxometry (MRX) or photon cross-correlation spectroscopy (PCCS). In this work, a combination of the Cotton-Mouton effect and the Brownian relaxation is used. It promises a fast and straightforward determination of the hydrodynamic diameter of SPIONs. Earlier publications already showed that the determination of the hydrodynamic diameter of SPIONs using a Cotton-Mouton relaxometer is possible. Subsequent, this work addresses the thorough investigation of the reliability of the setup. Studies show that sample temperature affects measurement results. Therefore, a calibration and temperature stabilization of the setup is mandatory. Additionally, the effect of other critical parameters as, for instance, the viscosity (which varies with temperature) or ambient light should be taken into consideration.