Elongated magnetic nanoparticles with high-aspect ratio: a nuclear relaxation and specific absorption rate investigation

Abstract

High aspect-ratio elongated nanoparticles with suitable porosity present partially controlled chemico-physical properties to obtain good heating/contrast efficiency for biomedical applications.

How size, shape and assembly of magnetic nanoparticles give rise to different hyperthermia scenarios

“…In the case of nanoflowers, the reported SAR values are around 500 W g Fe −1 (H × f = 4.40 × 10 9 A m −1 s −1 ) for a size of 24 nm; 50 and for spindles, the reported SAR values are around 400 W g Fe −1 (H × f = 4.80 × 10 9 A m −1 s −1 ) for the dimensions of 87 × 16 nm. 9 This work opens the possibility of further enhance those values, even in viscous media, through the sample's preassembly forming nano-size chains (in the case of the flowers and the spindles chains, respectively, when oriented parallel or perpendicular with respect to the applied AMF). In addition, this work successfully achieves heating rates exceeding those using non-spherical Fe 3 O 4 /γ-Fe 2 O 3 nanoparticles prepared by aqueous chemistry in highly viscous media.…”

“…5 Among MNPs, those presenting anisometric shape have raised great interest in the field of MHT due to their additional shape anisotropy, which has accounted for increased heat performances. In the past years, there has been hectic research on the heat released by anisometric nanoparticles, including nanocubes, 6 nano-octopods, 7 nanoflowers, 8 elongated nanoparticles 9,10 and nanodisks 11 and, in some cases, their corresponding heat release mechanisms. As an example, Cabrera et al reported a large decrease (80% drop) in the SAR of 21 nm magnetite cubes (this size lies in superparamagnetic-ferromagnetic regime) in viscous media (∼100 mPa s), which was attributed to the Brownian relaxation suppression.…”

“…With respect to the synthesis of MNPs, the enormous progress that has been done in the chemical synthesis of nanostructures, allows nanotechnologists to prepare MNPs with well-controlled composition and morphology. 2 We have selected hydrothermal and solvothermal routes, previously reported by some of us, for the preparation of the following anisometric Fe 3 O 4 /γ-Fe 2 O 3 MNPs: polyhedral/cubic, 17 elongated, 9 disk-shaped 18 and ensembles consisting of smaller cores (nanoflowers). 19 Hydrothermal and solvothermal routes are more environmentally friendly, reproducible and scalable because of the use of non-toxic solvents and milder reaction conditions, overcoming some of the major concerns of the current MNPs synthetic approaches.…”

Shape Anisotropic Iron Oxide-Based Magnetic Nanoparticles: Synthesis and Biomedical Applications

“…Elongated magnetic nanoparticles, mainly nanorods, have been of interest in various industrial [61,62], and biomedical applications [63][64][65]. Classification is based on the external energy required for inversion of the magnetization [61].…”

“…Here, tumor growth was suppressed, and in vivo localization and visualization of the tumor was possible due to the darkening effect promoted by the nanorods in T 2 -weighted MR images. More recently, elongated magnetite nanoparticles were synthesized by an environmentally friendly hydrothermal method, and it was demonstrated that the presence of larger pores resulted in the highest M S value (97 emu g −1 ) and transversal relaxivity (r 2 = 343 s −1 mM −1 ) [63]. It is worth to note that the abovementioned iron oxide nanoparticles have higher transversal relaxivity values than the ones obtained for clinically approved T 2 contrast agents, such as Ferumoxide (Endorem ® or Feridex ® ) and Ferrixan (Resovist ® ) with r 2 values of~98 s −1 mM −1 [181] and~150 s −1 mM −1 [182], respectively.…”