Field-dependent motion of bio-functionalized magnetic nanoparticle clusters under a rotating magnetic field

A better understanding of the behavior of biofunctionalized, magnetic nanoparticle clusters under rotating magnetic fields in an aqueous solution can help to facilitate the use of such nanoparticles in biomedical applications. In our previous study, two modes of motion, rotation and oscillation, were observed when biofunctionalized magnetic nanoparticle clusters in an aqueous solution were subjected to a rotating magnetic field, and a critical cluster size was defined to distinguish the motion. In this paper, we further investigated this behavior as the magnetic field was varied. The results showed that as the frequency of the magnetic field increased and the field strength was held constant, the critical cluster size decreased. On the other hand, as the field strength increased and the field frequency was held constant, the critical cluster size increased. Accordingly, a field-dependent phase diagram was constructed to evaluate the efficacy of altering the cluster motion type by changing field conditions such as the frequency or amplitude for different cluster sizes. Moreover, it was found that the phase lags of clusters exhibiting rotational motion increased and the amplitudes of clusters exhibiting oscillational motion decreased as either the field frequency increased or the field strength decreased.