FIG1. (a–e) SEM photos of our vortex microparticles (Ø1.4µm thickness t=100 nm); (f-g) Optical microscopy of these particles in solution (f) Particles chains formation in μ0H ~ 4 mT due to their magnetostatic interaction once polarized by the applied field. (c) Dispersion in H ~ 0 after having switched-off the field.
Magnetic nanoparticles are more and more used for various biotechnological applications, due to their capability to exert actuation on biological species thanks to magnetic fields applied remotely. A condition for their use in biotechnology is the ability to avoid their agglomeration when dispersed in solution, as micromagnets which tend to attract each others. Furthermore, for actuation purposes, the forces or the torques that these particles can exert on biological species should be as large as possible in easily accessible magnetic fields (typically less than 0.1Tesla). In the present study, the actuation and dispersion capabilities have been evaluated and compared for two types of innovative magnetic nanoparticles, both prepared by top-down approaches. One type is made of a single magnetic layer and has a magnetic vortex configuration whereas the second one has a multilayered structure called synthetic antiferromagnet (SAF) which consists of two magnetic layers whose magnetizations are coupled antiparallel to each other but can be easily polarized by an applied field. These two types of particles have superparamagnetic like behaviour i.e. a zero net magnetization at zero field avoiding their agglomeration but a large susceptibility allowing them to get polarized in moderate magnetic fields (Fig.1).
FIG2. Comparison of torques generated by vortex and SAF particles versus their thickness in a field μ0H =10 mT applied at μ = 45° to the particle plane.
In addition, since they are not spherical in contrast to conventional magnetic particles prepared by chemical routes, they can easily get reoriented under a rotating magnetic field thus creating large torques on biological species. Our comparative study has shown that both types of particles have their own advantages. The vortex particles are easier to prepare including in iron oxide to be biocompatible. They never agglomerate when dispersed in solution but the mechanical torque that they can create under magnetic field is weaker than for their SAF counterparts (Fig.2). In contrast, the SAF particles are more difficult to prepare and to make biocompatible and their susceptibility has to be adjusted to avoid agglomeration. However, the torque that they can exert on biological species could be larger than for vortex particles.
The efficiency of these magnetic torques allows foreseeing new biomedical applications of these particles, in particular the possibility to trigger the spontaneous death of cancer cells by the vibration of such particles properly functionalized to get attached to the cells membrane.
Acknowledgement: This work was partically supported by Agence Nationale de la Recherche via the P2N grant Nanoshark reference ANR-11-NANO-001 and funding for this project was partially provided by a grant CIBLE 2012 from La Région Rhône-Alpes.
Publi : Comparison of dispersion and actuation properties of vortex and synthetic antiferromagnetic particles for biotechnological applications, S. Leulmi, H. Joisten, T. Dietsch, C. Iss, M. Morcrette, S. Auffret, P. Sabon and B. Dieny, Appl. Phys. Lett. 103, 132412 (2013)
Last update : 11/26 2013 (902)