Asymmetric flow field-flow fractionation of superferrimagnetic iron oxide multicore nanoparticles

Magnetic nanoparticles are very useful for various medical applications whereas each application requires particles with specific magnetic properties. In this contribution we describe the modification of the magnetic properties of magnetic multicore nanoparticles (MCNP) by size dependent fractionation. This classification was carried out by means of asymmetric flow field-flow fractionation (AF4). A clear increase of the particle size with increasing elution time was confirmed by multi-angle laser light scattering coupled to the AF4 system, dynamic light scattering, and Brownian diameters determined by magnetorelaxometry. By this way 16 fractions of particles with different hydrodynamic diameters in the range between about 100 and 500 nm were obtained. A high reproducibility of the method was confirmed by the comparison of the mean diameters of fractions of several fractionation runs under identical conditions. The hysteresis curves were measured by vibrating sample magnetometry. Starting from a coercivity of 1.41 kA/m for the original MCNP the coercivity of the particles in the different fractions varies from 0.41 to 3.83 kA/m. In our contribution it is shown for the first time that fractions obtained from a broad size distributed MCNP fluid classified by AF4 show a strong correlation between hydrodynamic diameter and magnetic properties. Thus we state that AF4 is a suitable technology for reproducible size-dependent classification of magnetic multicore nanoparticles suspended as ferrofluids.