Effect of core–shell nanoparticle geometry on the enhancement of the proton relaxivity value in a nuclear magnetic resonance experiment

Abstract

This work illustrates the effect of core–shell nanoparticle geometry on the enhancement of the proton relaxivity value in a nuclear magnetic resonance experiment. Chemically synthesized CoFe₂O₄–MnFe₂O₄ core–shell nanoparticles were chosen as a candidate material. A two step methodology was used to synthesize the core–shell nanoparticles. In the first step, CoFe₂O₄ seed nanoparticles were synthesized and in the second step a MnFe₂O₄ phase was grown over seed CoFe₂O₄ nanoparticles to form the core–shell geometry. Characterization of the as-synthesized nanoparticles by diffraction methods, electron microscopy and X-ray photoelectron spectroscopy confirmed the formation of uniform core–shell nanoparticles. Magnetic measurement revealed the superparamagnetic nature of the as-synthesized core–shell nanoparticles. The transverse proton relaxivity values obtained by the nuclear magnetic resonance experiment conducted at room temperature using a field of 9.4 T in the presence of single phase CoFe₂O₄, MnFe₂O₄ and CoFe₂O₄–MnFe₂O₄ core–shell nanoparticles were 60.9 mM⁻¹ s⁻¹, 83.2 mM⁻¹ s⁻¹ and 194.8 mM⁻¹ s⁻¹ respectively. This result clearly illustrated that a greater magnetic inhomogeneity induced in the medium surrounding the core–shell nanoparticles containing two different magnetic phases yields the highest value for the transverse proton relaxivity.