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Executive summary

The last five years have witnessed an exponential growth in activities associated with the potential use of magnetic nanoparticles in biomedical applications. In our previous review published in 2003, we described state-of-the-art synthetic routes for the preparation of magnetic nanoparticles for biomedical applications and the importance of having well-defined synthetic routes to produce materials not only with similar physical features but also with similar crystallochemical characteristics. Following the same principles, this short review intends to summarize some of the progress achieved in the development of synthetic strategies for the controlled production of magnetic nanoparticles during the period 2003–2008.

Synthetic routes to producing ferrites

The first section of this review describes synthetic routes to produce ferrites with different sizes and shapes, which are the most suitable materials for biomedical applications. It is well known that size and composition influence the bio-application of magnetic nanoparticles. Thus, for applications in angiography and tumour permeability, ultra-small superparamagnetic iron oxide particles (USPIO) are preferred. However, for liver imaging, superparamagnetic particles (SPIO) with intense macrophage uptake are preferred. For hyperthermia treatment, particles with sizes around the monodomain–multidomain transition, i.e. particles below 50 nm in diameter, have been found to produce the maximum specific absorption rate (SAR). It has been reported that the SAR of 35 nm magnetite particles is twice that of 10nbsp;nm particles.

Specifically, the first section of this review describes synthetic routes producing equiaxial magnetic iron oxide particles below 10 nm (USPIO) which exhibit superparamagnetism combined with surface effects; those between 10 and 30 nm (SPIO) which exhibit superparamagnetic effects and some blocking; above 30 nm which are at the monodomain–multidomain boundary and also methods that produce anisometric nanoparticles. It should also be noted that due to high crystallinity and low size dispersion many of the examples described for the production of the iron oxide ferrites make use of high boiling point organic solvents. For these materials further surface modification is required to yield hydrophilic particles. Some of the strategies followed to achieve this are described and are summarized in the article.

Alternative materials

Next, we describe synthetic methods dealing with cobalt ferrite, manganese ferrite, metals and alloys such as Fe and FePt, and manganites, which are alternative magnetic nanoparticles proposed for biomedical applications. Finally, the future of magnetic nanoparticles in biomedicine lies in their combination with other materials that can impart multifunctionality to the system. Thus, the final section of this review deals with multicomponent colloidal systems.

>> Full article (free to read until Nov 2010)

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60 second interview with the lead author

Puerto Morales from the Instituto de Ciencia de Materiales de Madrid, Spain, shares her thoughts on the next big breakthrough in nanomedicine (PDF download).

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Comment: tailor-made magnetic nanoparticles are key to unlocking the full range of biomedical opportunities

Kevin O’Grady from the University of York, UK, puts the technology in perspective by explaining how advances in chemistry and a better understanding of the underlying physics of magnetic nanoparticles have led to a boom in clinical applications.

Keywords: magnetic nanoparticles, drug delivery, MRI, cancer therapy

Reference

Progress in the preparation of magnetic nanoparticles for applications in biomedicine, A G Roca, R Costo, A F Rebolledo, S Veintemillas-Verdaguer, P Tartaj, T González-Carreño, M P Morales and C J Serna, 2009, J. Phys. D: Appl. Phys. 42 224002

Want to know more about the functionalization and application of magnetic nanoparticles in biomedicine? Then check out the J. Phys. D: Appl. Phys. cluster review.