The oriented attachment of magnetic nanoparticles is recognized as an important pathway in the magnetic-hyperthermia cancer treatment roadmap, thus, understanding the physical origin of their enhanced heating properties is a crucial task for the development of optimized application schemes. Here, we present a detailed theoretical analysis of the hysteresis losses in dipolar-coupled magnetic nanoparticle assemblies as a function of both the geometry and length of the array, and of the orientation of the particles' magnetic anisotropy. Our results suggest that the chain-like arrangement biomimicking magnetotactic bacteria has the superior heating performance, increasing more than 5 times in comparison with the randomly distributed system when aligned with the magnetic field. The size of the chains and the anisotropy of the particles can be correlated with the applied magnetic field in order to have optimum conditions for heat dissipation. Our experimental calorimetrical measurements performed in aqueous and agar gel suspensions of 44 nm magnetite nanoparticles at different densities, and oriented in a magnetic field, unambiguously demonstrate the important role of chain alignment on the heating efficiency. In low agar viscosity, similar to those of common biological media, the initial orientation of the chains plays a minor role in the enhanced heating capacity while at high agar viscosity, chains aligned along the applied magnetic field show the maximum heating. This knowledge opens new perspectives for improved handling of magnetic hyperthermia agents, an alternative to conventional cancer therapies. © 2014 American Chemical Society.

C.M.B. was supported by the Spanish Government under the ’Ramón y Cajal’ Fellowship program. K.S. thanks the Action “Supporting Postdoctoral Researchers” of Operational Program “Education and Lifelong Learning”, co-financed by the European Social Fund (ESF) and the Greek State (GSRT). The work of D.S. and O.C.-F. has been supported by the EU project NNP3-SL-2012-281043 (FEMTOSPIN) and the Spanish Ministry of Science and Innovation under the Grant FIS2010-20979-C02-02. M.P.M.’s work was partially supported by grants from the Spanish Ministry of Economy and Competitiveness (MAT2011-23641) and the European Union (EU-FP7 MULTIFUN project, ref. 246479). D.B. acknowledges the Spanish Ministry of Economy and Competitiveness for project MAT2009-08165.

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