The Effect of Silica Shell Thickness on Magnetic and Proton Relaxometric Properties: Fe3O4@mSiO2 Nanoparticles

Here, we report the effect of silica shell thickness on proton relaxivities (r(2) and r(1)) and magnetic properties. Starting from hydrophobic 7 nm of Fe3O4, we have coated Fe3O4 with cetyltrimethylammonium bromide (CTAB) for phase transformation from hydrophobic to hydrophilic. Core-shell structure Fe3O4@mSiO(2) with different silica shell thickness have been obtained. The obtained Fe3O4@mSiO(2) have been characterized by TEM, Fourier Transform Infrared (FTIR), Superconducting Quantum Interference Device (SQUID), and the proton relaxivities of the nanoparticles (NPs) have been determined. The presence of silica did alter the relaxivity with slightly increased the r(2), and dramatically decreased the r(1) of Fe3O4@mSiO(2). We find that the r(2) and r(1) relaxivity decreased with the increase of silica shell thickness. Moreover, the high r(2)/r(1) ratio shows that Fe3O4@mSiO(2) may serve as T-2 contrast agents in magnetic resonance imaging (MRI).