Aided by contrast agents, magnetic resonance imaging (MRI) is becoming one of the most powerful diagnosis tools for biomedical imaging.Recently, magnetic nanoparticles as MRI contrast agent have received enormous attention due to its high efficiency and suitable circulation time.Typically Gd-containing Nips as T1-weighted contrast agent.Those biocompatible nanoparticles should be stable under physiological condition, resistant to RES uptake, long circulation time, and clearance from the body.