RST department colloquium, 11.05.15
Title: Functional magnetic nanostructures for tunable RF and biomedical applications
Speaker: Dr. Hari Srikanth (University of South-Florida, Tampa )
Author: Edgar Schönfeld
Hari Srikanth is a phycisist and works with magnetic nanoparticles. In his presentation he gave an overview over biomedical applications of magnetic nanostructures, of which some are also a subject of research in his own research group. Magnetic nanoparticles are easy to synthesize and can be manipulated non-invasively by an external magnetic field once they are within the human body. Those applications can be found in diagnosis and treatment, and encompass target drug delivery, cell sorting, MRI image enhancers, biosensors and more.
A research subject of Hari’s lab is magnetic hyperthermia treatment for cancer, which is a promising alternative to normal hyperthermia treatment or radio therapy. The idea is that magnetic particles find tumor cells and exclusively localize there. This can be achieved with an antibody tag for example. Subsequently a fluctuating external EM field is applied with frequencies around 100 kHZ.The electron magnetic moments of the nanoparticles have to realign continuously and thereby dissipate energy as heat. Raising the temperature to 42° C is often enough to kill cancer cells. The faster this heating occurs the better. An important property of such a particle is the heating efficiency that is expressed as the SAR-value (Specific Absorption Rate), as a higher SAR allows for lower radiation energies. The same is true for a higher particle density in the tissue. This is important because not heating the surrounding tissue is a big challenge and is observed in the currently running human phase 1 trials with Fe2O3 particles (Iron(III)-Oxide, the only licensed particle at the moment). A body region consisting of a complex interplay of different tissues, especially bone, has different refractive indices. This can result in local hot spots. For example, brain tumors can be treated with more power than prostate tumors . The current main challenge is to engineer particles with a higher SAR value. The SAR depends on particle size R, magnetization saturation Ms and the anisotropy constant K. The objective is to fine-tune R, Ms and K. For Fe2O3 it can be shown that the peak SAR lies at a diameter of ca 17 nm. Ms depend on the material, while K also depends on the shape. Promising new techniques include for instance core-shell nanoparticles. As an example, Hari presented a particle the has an inner FeCo core and an outer Iron-Oxide shell. Ligands but also drugs can be attached to the outside. The Iron-Cobalt that is used has a 4 times higher Ms than the Fe2O3 particles. A technique from Hari’s own lab are Iron-Oxide hollow nano spheres. However, new experiments with shapes revealed that cubes have a higher SAR than spheres, and octopods have an even higher SAR than that. Then again, Fe-Co nanowires take the SAR to incredible dimensions. All in all, these advances seem very promising to me and I am sure it will cause a lot of improvement in cancer treatments.
For more theoretical insight into magnetic nanoparticles for hyperthermia (easy to understand and many coloured graphs):
1) C. Binns, “Magnetic Nanoparticle Hyperthermia Treatment of Tumours,”Berlin, Springer-Verlag, 197-215(2013)