Patent ID: 8524195

Claim:
A method for preparing iron oxide nano contrast agents, comprising the steps of: coating surfaces of hydrophobic FeO nanoparticles with a coating material selected from the group consisting of polyethylene glycol-phospholipid conjugate, dextran, chitosan, dimercaptosuccinic acid and mixtures thereof in an organic solvent to form hydrophilic FeO nanoparticles having hydrophilic surfaces and dispersibility in water; dispersing the hydrophilic FeO nanoparticles in water to oxidize FeO; and exposing the oxidized hydrophilic FeO nanoparticles to an acidic buffer solution to dissolve and remove interior unoxidized FeO portions, and thereby to form Fe 3 O 4 nanoparticles having an interior space, wherein the pH of the acidic buffer solution is 2 to 5.