Fig. 1. Characterization of nanoparticles. (a) TEM image of Fe₃O₄ nanoparticles; (b) TEM image of Fe₃O₄@Gd nanoparticles; (c) EDX mapping images of one nanoparticle; (d) the magnetic hysteresis loops of Fe₃O₄ and Fe₃O₄@Gd nanoparticles at room temperature; (e) size distribution of Fe₃O₄@Gd nanoparticles; (f) zeta potential of Fe₃O₄@Gd nanoparticles; (g) IR spectra of Fe₃O₄@DTPA nanoparticles, Fe₃O₄ nanoparticles and DTPA.