Insight into the Internal Structure of High-Performance Multicore Magnetic Nanoparticles Used in Cancer Thermotherapy
Résumé
Multicore magnetic nanoparticles (MNPs), comprising iron oxide cores embedded in a sugar or starch
matrix, are a class of nanomaterials with promising magnetic heating properties. Their internal structure,
and particularly the strength of the internal core-core magnetic interactions, are believed to determine
the functional properties, but there have been few detailed studies on this to date. We report here on an
inter-laboratory and multi-modality transmission electron microscopy (TEM) and magnetic study of a
high-performance MNP material (supplied by Resonant Circuits Limited, RCL) that is currently being
used in a clinical study for the treatment of pancreatic cancer. TEM data were collected under a variety
of conditions: conventional; high-resolution; scanning; cryogenic; and, for the first time, liquid-phase.
All the imaging modes showed mostly irregular dextran lamellae of lateral dimensions 30-90 nm, plus
ca. 15% n/n of what appeared to be 30-60 nm long “nanorods”, and a multitude of well-dispersed
ca. 3.7 nm diameter iron oxide cores. Cryogenic electron tomography indicated that the nanorods were
edge-on lamellae, but in dried samples, tomography showed rod- or lath-shaped forms, possibly
resulting from the collapse of lamellae during drying. HRTEM showed the dextran to be crystallized in
the low-temperature hydrated dextran polymorph. Magnetic remanence Henkel-plot analysis indicated
a weak core-core interaction field of ca. 4.8 kA/m. Theoretical estimates using a point-dipole model
associated this field with a core-to-core separation distance of ca. 5 nm, which tallies well with the
ca. 4-6 nm range of separation distances observed in liquid-cell TEM data. On this basis we identify the
structure-function link in the RCL nanoparticles to be the unusually well-dispersed multicore structure
that leads to their strong heating capability. This insight provides an important design characteristic for
the future development of bespoke nanomaterials for this significant clinical application
Domaines
ChimieOrigine | Fichiers produits par l'(les) auteur(s) |
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