For a different medical applications nanoparticles (NPs) with well-defined magnetic properties have to be used. Coating ligand can change the magnetic moment on the surface of nanostructures and therefore the magnetic behavior of the system. Here we investigated magnetic NPs in a size of 13 nm conjugated with four different kind of surfactants. The surface anisotropy and the magnetic moment of the system was changed due to the present of the surfactant on the surface of iron oxide NPs.

Magnetic properties of colloidal nanoparticles (NPs) depend on various parameters, such as size, size distribution, interparticle distance, shape, condition of synthesis and stabilizing surfactants. Nowadays, those magnetic nanoparticles (MNPs) are preferably produced in hydrophobic organic solvents, while biomedical applications need hydrophilic properties. Thus, a major challenge is the hydrophilization of the particles, while avoiding destabilization and aggregation. Here we present magnetic characteristics of noninteracting, highly crystalline iron oxide NPs in physiological solutions that are coated with modified polyacrylic acid. The magnetic analysis comprised both static and dynamic magnetic behaviour of 4 nm NPs. The NPs have been further characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX).