Combining magnetic field/temperature dual stimuli to significantly enhance gene transfection of nonviral vectors.

Monodisperse magnetic nanoparticles (MNPs) were prepared through an organic phase process, and the obtained MNPs were capped with poly[2-(2-methoxyethoxy)ethyl methacrylate]-b-poly[2-(dimethylamino)ethyl methacrylate] synthesized by surface-initiated atom transfer radical polymerization (ATRP). The MNPs-polymer brushes exhibited both superparamagnetic and thermoresponsive behaviors, and could condense plasmid DNA into nanocomplexes with a size of 100-120 nm at appropriate complexing ratios. Enhanced gene expression in COS-7 cells and HepG-2 cells was achieved under a magnetic field and variable temperature conditions due to magnetic force-facilitated internalization of nanocomplexes, and temporary cooling-triggered intracellular gene unpacking. Amazingly, combining magnetic field and temperature dual stimuli contributed to a 50-100- and 25-45-fold increase of the transfection efficiency in HepG-2 cells compared to conventional protocol and PEI25k, respectively.