Controllable synthesis, magnetic and biocompatible properties of Fe3O4 and α-Fe2O3 nanocrystals

► Iron oxide NCs with a series of well-controlled morphologies (octahedron, rod, wire, cube, and plate) and compositions (Fe3O4 and α-Fe2O3) were synthesized via a facile hydrothermal method. ► The mechanism of the morphological and compositional control process is directly related to precursor thermolysis kinetics and surfactants. ► These iron oxide NCs exhibited excellent magnetic response and good biocompatibility, which should have great applications in the cell separation and biodetection.