Core/shell nanoparticles offer an additional degree of flexibility to nanoparticle-based applications. Comprised of an inorganic core and one or more shell layers, such particles enable a wider range of physical properties than would be possible for each of the component materials taken separately. In the case of bi-magnetic core/shell nanoparticles, the constituent materials exhibit distinct magnetic properties, yielding an extra layer of customization to the particle, based on the exchange interaction between the components.
The synthesis and subsequent utility of these nanoparticles represent a growing area of academic research. A review article published recently in “Physics Reports” presents an overview of the current state of the field, including approaches to synthesis, characterization, and potential applications.
Synthesis approaches and subsequent characterization of nanoparticles
The main approaches to synthesizing core/shell nanoparticles employ either chemical or physical methods. Physical approaches, such as radiolysis and radioactive gas condensation, can be found in the literature, but are not as widely employed as chemical techniques. Chemical synthesis is more common and has been given wider attention.
One of the simplest chemical approaches is surface treatment of a particle, e.g., oxidation or reduction, to give rise to a layer with altered physiochemical properties. There are drawbacks to this approach that has limited its utility despite its simplicity. The drawbacks stem from the fact that the outer layer is derived from the core, thus limiting the core/shell phase options, the structural quality of the shell, and the ability to control the size of each component.
Alternatively, the seeded-growth approach entails deposition of the shell onto the nanoparticle core. This method is not as simple, but enables the synthesis of nanoparticles composed of different core and shell materials. Additionally, it allows a greater degree of control over the size and morphology of the components.
Subsequent characterization of the synthesized particle is important. Attributes such as size and shell thickness are relevant to the resulting particle’s magnetic properties. Techniques such as X-ray diffraction, neutron diffraction, and transmission electron microscopy are commonly utilized to investigate morphology and structure.
Current and potential applications
Patents utilizing the concept of core/shell nanoparticles date as far back as 1964. Currently, bi-magnetic core/shell nanoparticles are employed in a number of applications, including recording media and microwave absorption. Or particular note is the increasing utility of the particles in permanent magnets, where they provide a number of advantages over conventional materials.
The use of bi-magnetic core/shell nanoparticles in the biomedical field has been focused in three particular areas, as evidenced by patent applications. These are hyperthermia, magnetic resonance imaging, and cell manipulation. Additional applications have been proposed, but research in these areas remains preliminary.
An in-depth analysis of the approaches to synthesis, characterization, and applications of core/shell nanoparticles be found in the review article titled “Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles” in the October issue of “Physics Reports”.
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