Multifunctional Anisotropic Rod-Shaped CoFe2O4 Nanoparticles for Magnetic Resonance Imaging and Magnetomechanical Therapy

One-dimensional magnetic nanomaterials, such as nanorods,are oneof the most interesting but unexplored objects due to the complexityof their manufacture. In this work, we report on the template-assistedpreparation of rod-shaped cobalt ferrite (CoFe2O4) nanoparticles (NPs) using the akaganeite (& beta;-FeOOH) matrixand their application as multifunctional agents in biomedicine. Inthe beginning, rod-shaped & beta;-FeOOH NPs are prepared by a forcedhydrolysis technique. Then, amorphous Co(OH)(2) is depositedonto the surface of & beta;-FeOOH. Finally, a solid-state reactionresults in mesoporous rod-shaped (130 nm x 40 nm) CoFe2O4 NPs with a crystallite size of 7 nm. The proposed mechanismof synthesis involves the simultaneous transformation of & beta;-FeOOHand amorphous Co(OH)(2) in two corresponding oxides duringannealing, resulting in cation interdiffusion with the formation ofa CoFe2O4 phase, while the key role of the Co(OH)(2) shell in preserving the rod-shaped morphology of CoFe2O4 NPs is demonstrated. NPs exhibit a high coercivityof 73 kA m(-1) arising from their shape anisotropy,while their effective anisotropy constant of 1.1 x 10(5) J m(-3) is compared to bulk CoFe2O4. Despite the low value of saturation magnetization (13 Am-2 kg(-1)), NPs demonstrate dual-modalrelaxivity in MRI experiments with high values of r (1) = 2.3 s(-1) mM(-1) and r (2) = 228 s(-1) mM(-1). Finally, we show that the magnetomechanical stimulus from NPs leadsto the programmed death of breast cancer cells. Under the action ofa low-frequency magnetic field (31 Hz), such NPs mediate mechanicalvibrations, leading to cancer cell destruction even at a very lowconcentration of 6 & mu;g CoFe2O4 & BULL;mL(-1).