Abstract
AbstractSuperparamagnetic nanoparticles, exposed to an external variable magnetic field, undergo rapid excitation/relaxation. So-called soft magnets, typically iron-based, rapidly and completely relax when the magnetic field returns to zero. Instead, cobalt-based (CoB) hard magnets retain residual magnetization, a characteristic related with the procedure for nanoparticles (NPs) production. Many researchers are still attracted by the potential of CoB NPs for theranostics as multifaced signal probes for imaging, microrobots, enhanced thermo/radiation therapy, and drug release. Since iron oxide NPs are the only magnetic NPs approved for human use, they are of reference for analyzing the potential of the disregarded CoB NPs.In vitroobserved toxicity of CoB NPs, largely attributable to cobalt ions and other chemical species released by dissolution, excluded them from further investigations in humans. Nevertheless, experimental evidences documenting thein vivotoxicity of engineered CoB NPs remain very few. The surface functionalization adds newer properties and could improve the biocompatibility of NPs, critical for the clinical exploitation. In our opinion, it would be worth to further exploit the potential of finely tunable properties of CoB NPs inin vivosystems in order to establish a systematic database of properties and effects suitable for human application.
Highlights
The discovery and exploitation of the superparamagnetism in nanoparticles began with the description of their ferrofluidic behavior [1] which opened the way to the development of nanomaterials with impressive chemical and physical oddities and exponential increase of research on their potential applications in biomedicine
Cobalt-based NPs, which behave as hard magnets, could be considered the possible counterpart of the soft magnets composed of iron oxide MNPs
The residual magnetization is higher in MNPs with a core of cobalt oxide or cobalt–ferrite, in comparison with zerovalent cobalt, while selected variants in the procedure for production, such as the temperature or the relative content of iron in cobalt–ferrite MNPs, can tune the saturation magnetization
Summary
The discovery and exploitation of the superparamagnetism in nanoparticles began with the description of their ferrofluidic behavior [1] which opened the way to the development of nanomaterials with impressive chemical and physical oddities and exponential increase of research on their potential applications in biomedicine. Application of an external magnetic field to such ferrofluidic materials leads to a very quick increase in magnetization, which is rapidly reduced (or abrogated) when the magnetic field is removed This behavior is revealed by superparamagnetic iron oxide (FeO)-based nanoprobes that, when excited, acquire a sharp appearance relative to the surrounding environment. For this reason, they attract the interest of researchers as negative contrast enhancing agents for Magnetic Resonance Imaging (MRI) [3,4]. These “soft materials” show low residual magnetism (Mr) (Figure 1), one main physical property for this type of medical application Since their early development occurred more than two decades ago, only one carbohydrate-coated iron-based nanoprobe has been approved by FDA for clinical use [5]. The method used to synthetize the CoB NPs determines their anisotropy degree and, thereof, the critical size, that greatly varies
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