Size-controlled preparation of magnetic iron oxide nanocrystals within hyperbranched polymers and their magnetofection in vitro

A new strategy for the size-controlled preparation of magnetic iron oxide nanocrystals (NCs) within hyperbranched poly(ethylenimine)s (HPEIs) has been described. HPEI was not only utilized as the nanoreactors and stabilizers to prepare size-controlled magnetic NCs, but also skillfully used as a base supplier to avoid introducing alkali hydroxide or ammonia. By changing the weight ratio of FeSO4 center dot 7H(2)O to HPEI, magnetic iron oxide NCs with various sizes were obtained. Owing to the efficient gene transfection properties of HPEI, the resulting iron oxide/HPEI nanocomposites were used as magnetic nonviral gene vectors for magnetofection and showed to be good gene vectors. It was found that the size of magnetic iron oxide had a significant effect on the magnetofection properties while a pure HPEI transfection enhancer was not introduced. When the mean size of magnetic iron oxide increased, the transfection efficiency was enhanced. With the addition of a pure HPEI transfection enhancer, the size of magnetic iron oxide showed a slight impact on the magnetofection properties. The luciferase expression levels mediated by iron oxide/HPEI nanocomposites with various iron oxide sizes in COS-7 cells under a magnetic gradient field were all more than 115 fold of that of standard HPEI transfection.