Magnetic and pH-sensitive nanoparticles for antitumor drug delivery

A dually responsive nanocarrier with multilayer core–shell architecture was prepared based on Fe3O4@SiO2 nanoparticles coated with mPEG-poly(l-Asparagine). Imidazole groups (pKa ∼ 6.0) were tethered to the side chains of poly(l-Asparagine) segments by aminolysis. These nanoparticles were expected to be sensitive to both magnetic field and pH environment. The obtained materials were characterized with FTIR, dynamic light scattering, ζ-potential, TEM, TGA and hysteresis loop analysis. It was found that this Fe3O4@SiO2–polymer complex can form nano-scale core–shell–corona trilayer particles (∼250 nm) in aqueous solution. The Fe3O4@SiO2, poly(l-Asparagine) and mPEG segments serve as a super-paramagnetic core, a pH-sensitive shell, and a hydrophilic corona, respectively. An antitumor agent, doxorubicin (DOX), was successfully loaded into the nanocarrier via combined actions of hydrophobic interaction and hydrogen bonding. The drug release profiles displayed a pH-dependent behavior. DOX release rate increased significantly as the ambient pH dropped from the physiological pH (7.4) to acidic (5.5). This is most likely due to protonation and a change in hydrophilicity of the imidazole groups in the poly(l-Asparagine) segments. This new approach may serve as a promising platform to formulate magnetic targeted drug delivery systems.