Core@shell Fe@FexOy nanoparticles (NPs)
have the potential to be promising tools for many applications,
thanks to their combination of an iron core, with a high
magnetic moment and an iron oxide shell which could protect
the core from oxidation. However, the deterioration of NPs
structure can lead to the shrinking of the core and the
hollowing of the structure, diminishing the magnetic properties. The ability to retain the iron core under biomedically
compatible conditions is desirable for many applications. In
this paper, we have developed a synthetic method to produce
core@shell α-Fe@FexOy NPs with tunable sizes and evaluated
the retention of the stable magnetic α-Fe core upon exposure
to air and after ligand exchange and its resulting effect on the magnetic hyperthermia. In particular, using a continuous injection
of the precursor, we were able to finely tune the final size of the core@shell NPs producing four samples with average sizes of
12, 15, 18, and 20 nm. The structural properties of the particles were studied, and while the size increases, the chemical stability
of the iron core is enhanced, and the magnetic properties improved accordingly. Particles larger than 20 nm were shown to be
prone to aggregation, resulting in an abrupt increase of the particle size distribution. Two samples with high magnetization
saturation value and low polydispersity, 15 and 18 nm, were transferred in water using a dopamine-functionalized
poly(isobutylene-alt-maleic anhydride) polymer, resulting in colloidal stability over a wide range of pH and ionic strength
comparable to physiological conditions. We found that the 18 nm particles retain their chemical properties over 2 months, with
less oxidation of the Fe core; this results in a specific absorption rate (SAR) value of 660 W g−1 and intrinsic loss power (ILP) of
3.6 nHm2 kg−1
, while the 15 nm NPs resulted in the reduction of their properties due to oxidation of the core
