Polyol process to produce multicore magnetic iron oxide nanoparticles

Abstract

Magnetic nanoparticles present a great potential for the development of biomedical applications, ranging from the already in use contrast agents for Magnetic Resonance Imaging (MRI) to the drug delivery carriers or heating tools for improved cancer treatment through magnetic hyperthermia. Several synthesis methods to obtain magnetic nanoparticles suitable for biomedical applications are extendedly used, such as iron salts coprecipitation in water or the decomposition of organometallic compounds in organic media. A not so frequently used synthesis approach, based on a polyol process, is gaining interest in the past years given its potential to produce well-controlled hydrophilic multicore structures in one step. The assembly of crystallites to more complex structures can give rise to interesting collective magnetic properties considerably different from their equivalent single-core nanoparticles or bulk materials. Through the versatile polyol mediated synthesis, we have assembled magnetite nanocrystals into complex secondary structures [1]. In the present work, single-core and multi-core nanoparticles, namely nanoflowers and hollow spheres have been synthesized (Figure 1). We demonstrate that the precipitator concentration plays a crucial role in the structure adopted (single-core, nanoflowers or hollow spheres). In addition, while the particle size in the nanoflowers is maintained unchanged, by modification of the recrystallization time, nanoflowers with different core size have been produced. All samples regardless of their structures show ferrimagnetic behaviour at low temperature but samples with crystal sizes bellow 20 nm display superparamagnetic behaviour at room temperature. The magnetic properties of the nanostructures reflect not only the core size, that justifies the nearly bulk saturation magnetisation values, but also the collective behaviour in the case of the flower-like particles leading to a susceptibility enhancement.