ACS Nano http://doi.org/ssj (2014)

Ferromagnetic materials produce heat when exposed to a high-frequency alternating magnetic field — a consequence of their intrinsic hysteresis loop. Such 'magnetic heating' could be exploited in hyperthermia therapy for cancer treatment at the single-cell level: a magnetic nanoparticle could act as a 'heater' for a nearby target cell.

Detailed understanding of the local-heating process near a ferromagnetic nanoparticle is essential for any such biomedical application, and Juyao Dong and Jeffrey Zink have taken an important step forward by synthesizing dual-core nanoparticles, containing both a heater and a thermometer, and performing a comprehensive study of the particles' heat production.

The authors embedded mesoporous silica nanoparticles with iron-based nanocrystals (Fe3O4) and nanorods of a particular up-conversion compound (NaYF4:Yb3+, Er3+). The latter's up-conversion emission spectrum has two luminescence bands and the intensity ratio of the bands is temperature-dependent — a feature that provides a temperature probe. By monitoring the temperature evolution under various experimental conditions, Dong and Zink found that the temperature increase is proportional to the field induction power and linearly dependant on exposure time, and that it takes a few seconds to cool back down to ambient temperature.