Magnetic resonance imaging (MRI) is a constantly evolving radiological tool that has already traveled far beyond its conception in the early 1973 when Lauterbur and Mansfield produced the first MR images. Advancement in the molecular biology of cancer offers the promise of molecular and cellular imaging by using exogenous or endogenous markers. Herein, we demonstrate T1 and T2 MRI contrast agent for enzyme profiling and enhancing the specificity of superparamagnetic iron oxide (SPIO) nanoparticles (NPs) via engineered polyethylene glycol (PEG) respectively.

　　β-Glucuronidase is a key lysosomal enzyme and is often overexpressed in necrotic tumor masses. A pro receptor-induced magnetization enhancement (pro-RIME) MRI contrast agent ([Gd(DOTA-FPβGu)]) was develop for molecular imaging of β-glucuronidase activity in tumor tissues. In vitro and in vivo MR images obtained in the presence of ([Gd(DOTA-FPβGu)]) demonstrated appreciable differences in signal enhancement in the cell lines and tumor xenografts in accordance to their expression levels of β-glucuronidase.

　　Superparamagnetic nanoparticles (NPs) is in nascent stage and hold great potential as contrast agents for MRI applications. A facile strategy is proposed to enhance the specificity of SPIO NPs via passively masking charge. To demonstrate the approach we develop MnMEIO-silane-NH2-(Erb)-mPEG NPs. The data obtained indicate that masking surface charges on contrast agents is a useful strategy to improve imaging efficacy.