Ultra-fast method to synthesize mesoporous magnetite nanoclusters as highly sensitive magnetic resonance probe

► A rapid and economical method to synthesize magnetite (Fe3O4) nanoclusters. ► The diameter of magnetite nanoclusters can be controlled between 75 and 115 nm. ► The magnetite nanoclusters show very high magnetic resonance contrast properties. ► Cytotoxicity study confirms the magnetite nanoclusters are nontoxic. ► Magnetite nanoclusters are in reticuloendothelial system post i.v. administration in vivo.