In the presence of an oscillating magnetic field (OMF), a superparamagnetic iron oxide nanoparticle (SPION) generate heats. Understanding the local heating mechanism of a SPION in a nanoparticle will advance the design of hyperthermia-based nanotheranostics and OMF-stimulated drug delivery in biomedical applications. The heating process of single-domain SPION can be caused by two basic relaxation mechanisms, Néel relaxation (internal rotation of the magnetic dipole moment) and Brownian relaxation (rotation of the particle as a whole). The latter is investigated using fluorescence depolarization based on detecting the mobility-dependent degree of polarization P=(I∥-I⊥)/(I∥+I⊥) of two luminescence emission bands at different wavelengths corresponded to the europium-doped fluorescent SPION core and the silica-based intrinsically emitting shell of the novel synthesized core-shell MSN. The fluorescence depolarization experiments were carried out with the free and the silica-encapsulated SPION in different experimental conditions, including the OMF induction power, the solvent viscosity, and the bulk temperature. No OMF-induced rotational motion of the core-shell nanoparticles was observed, indicating that the interior heating of the nanoparticles was not dominated by Brownian relaxation but by Néel relaxation. The unique dual-fluorescence approach can also be employed to analyze relative core-shell motions of various kinds of nanoparticles used in drug delivery systems.

Probing the interior nanoscale heating mechanism of a magnetic core in mesoporous silica drug-delivery nanoparticles using fluorescence depolarization

2019 Fall National Meeting

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