Intra- and interparticle magnetism of cobalt-doped iron-oxide nanoparticles encapsulated in a synthetic ferritin cage

Abstract

We present an in-depth examination of the composition and magnetism of cobalt (Co 2+ )-doped iron-oxide nanoparticles encapsulated in Pyrococcus furiosus ferritin shells. We show that the Co 2+ dopant ions were incorporated into the γ-Fe2O3/Fe3O4 core, with small paramagnetic-like clusters likely residing on the surface of the nanoparticle that were observed for all cobalt-doped samples. In addition, element-specific characterization using Mössbauer spectroscopy and polarized x-ray absorption indicated that Co 2+ was incorporated exclusively into the octahedral B-sites of the spinel-oxide nanoparticle. Comparable superparamagnetic blocking temperatures, coercivities, and effective anisotropies were obtained for 7, 10 and 12% cobalt-doped nanoparticles, and were only slightly reduced for 3% cobalt, indicating a strong effect of cobalt incorporation, with a lesser effect of cobalt content. Due to the regular particle size and separation that result from the use of the ferritin cage, a comparison of the effects of interparticle interactions on the disordered assembly of nanoparticles was also obtained that indicated significantly different behaviours between un-doped and cobalt-doped nanoparticles.

Magnetic Nanoprobes for Spatio-Mechanical Manipulation in Single Cells

“…Figure 2 c,d shows zero-field-cooling/field-warming (ZFC/FW) experiments. MFt exhibited a broad maximum centered at 86 K, which indicates the effective blocking temperature T B , and an irreversibility point at about 150 K. The MFt ZFC/FW maximum at 86 K found in this work is significantly larger than the T B reported in [ 44 ] ( T B = 40 K) and in [ 45 ] ( T B = 13 K). This shift in T B may have resulted from reduced distances and dipole–dipole interactions between cores in the powdered samples after the drying process.…”

Magnetic Nanoprobes for Spatio-Mechanical Manipulation in Single Cells

“…Figure 2(c)-(d) shows zero-field-cooling/field-warming (ZFC/FW) experiments. MFt exhibits a broad maximum centered at 86 K, which indicates the effective blocking temperature TB, and an irreversibility point at about 150 K. The MFt ZFC/FW maximum at 86 K found in this work is significantly larger than the TB reported in [40] (TB = 40 K) and in [41] (TB = 13 K). This shift in TB may result from reduced distances and dipole-dipole interactions between cores in the powdered samples after the drying process.…”

Magnetic control of cellular processes using biofunctional nanoparticles

“…A solution might reside in the use of genetically-encoded MNPs, in the form, for instance, of natural ferritin cage proteins 67 – 71 , 79 or viral capsids. 39 , 57 , 72 Yet, a difficulty with endogenous ferritin is that they store iron as ferrihydrite, which has reduced magnetic properties compared to iron oxides.…”