Construction of small-sized superparamagnetic Janus nanoparticles and their application in cancer combined chemotherapy and magnetic hyperthermia.

Novel Janus nanoparticles (J-NPs) are developed by using single iron oxide (Fe3O4) nanoparticles as the core and hydrophobic/hydrophilic polymeric brushes as the cloak. Because of the superparamagnetism and asymmetric functionality of J-NPs, they are used as drug carriers and therapeutic agents for cancer chemotherapy and magnetic hyperthermia with a magnetic resonance imaging (MRI) guide. The asymmetric functionality is constituted of hydrophobic polymethyl methacrylate (PMMA) brushes and hydrophilic polyacrylic acid (PAA) brushes, which are 'grafting to' or 'grafting from' Fe3O4 nanoparticles via activators regenerated by electron transfer atom transfer radical polymerization. The terminal chains of PMMA and PAA brushes are coordinated with Fe3O4 nanoparticles, so PMMA/Fe3O4/PAA J-NPs possess structural stability in solvents. Because of the brush-structure, PMMA/Fe3O4/PAA J-NPs show high encapsulation efficiency (89.75 +/- 2.35%) and loading capacity (8.95 +/- 0.26%). Under the alternating magnetic field (AMF), drug-loaded J-NPs achieve the highest cell proliferation-inhibition ratio in the cell proliferation test in vitro and the tumor growth inhibition test in vivo compared to single chemotherapy or magnetic hyperthermia. Meanwhile, J-NPs show good T-2 imaging.