A biodegradable tumor targeting nano-probe based on poly（ε-caprolactone）-b-poly（ethylene glycol） block copolymer （PCL-b-PEG）micelle functionalized with a magnetic resonance imaging （MRI） contrast agent diethylenetriaminepentaacetic acid-gadolinium （DTPA-Gd＋） on the shell and a near-infrared （NIR） dye in the core for magnetic resonance and optical dual-modality imaging was prepared. The longitudinal relaxivity （rl） of the PCL-b-PEG- DTPA-Gd3＋ micelle was 13.4 （mmol/L）^-1s^-1, three folds of that of DTPA-Gd3＋, and higher than that of many polymeric contrast agents with similar structures. The in vivo optical imaging of a nude mouse bearing xenografied breast tumor showed that the dual-modality micelle preferentially accumulated in the tumor via the folic acid-mediated active targeting and the passive accumulation by the enhanced permeability and retention （EPR） effect. The results indicated that the dualmodality micelle is a promising nano-probe for cancer detection and diagnosis.
