Porous Fe₃O₄-SiO₂ core-shell nanorods as high-performance MRI contrast agent and drug delivery vehicle

A high-performance MRI contrast agent and a drug nanocarrier have been realized in porous Fe₃O₄@SiO₂ nanorods (NRs). The Fe₃O₄@SiO₂ NRs of length ~520 nm and diameter ~180 nm are synthesized by annealing FeOOH@SiO₂ nanorods at a temperature of 300 ℃ under continuous flow of forming gas. The magnetic measurement confirms that the Fe₃O₄@SiO₂ NRs is ferrimagnetic in nature with magnetization of 20 emu/g and coercivity H_C ~450 Oe. The aqueous suspension of the NRs is stable over a time frame of one month and exhibits a high R₂ relaxivity value of 192 mM⁻¹ s⁻¹. The R₂ darkening effect is also observed in HeLa cells incubated with NRs in comparison to untreated control cells. The porous Fe₃O₄@SiO₂ NRs further work as an excellent carrier for doxorubicin (DOX) drug with loading efficiency of 65%. The drug release study shows a pH-dependent behavior and is higher in acidic pH (4.3) as compared to the physiological pH (7.4). After 72 h, the cumulative DOX release is found to be ~58% at pH 4.3 and ~17% at pH 7.4. The induction heating studies of the NRs exhibit a sharp increasing trend of SAR value with the increase of magnetic field. - Highlights: • Porous Fe₃O₄@SiO₂ NRs shows enhanced MRI contrast agent and drug carrier properties. • The stable aqueous dispersion of NRs exhibits a high R₂ relaxivity of 192 mM⁻¹ s⁻¹. • The porous NRs also work as a nanocarrier for DOX with a loading efficiency of 65%. • The drug release study shows a pH-dependent behavior and is higher in acidic pH (4.3).