Magnetic fluids: Biomedical applications and magnetic fractionation

In addition to engineering applications, magnetic fluids containing magnetic nanoparticles are being increasingly applied to biomedical purposes. Besides the well established use of magnetic particles for biological separation or as contrast agents for magnetic resonance imaging, magnetic particles are also being tested for the inductive heat treatment of tumors or as markers for the quantification of biologically active substances. The properties of magnetic nanoparticles usually exhibit a broad distribution, so in many cases upon application only a small fraction of the particles contribute fully to the desired magnetic effect. Therefore, magnetic fluids have to be optimized by fractionation techniques. This is preferentially achieved by methods that separate magnetic nanoparticles in accordance with their magnetic properties. Hence, a magnetic technique has been developed for the fractionation of magnetic fluids. Two different magnetic fluids were fractionated by this method. The fractions obtained and the original samples were characterized with respect to their magnetic properties as well as their particle sizes. They were investigated not only in terms of their magnetization curves but also in respect to biomedical applications. The magnetic fractions show clearly improved magnetic properties compared to the original samples and are therefore especially suited for distinct applications. Furthermore, the results indicate that the magnetic method fractionates the particles in accordance with their magnetic moment and has a good reproducibility.