Fluorinated hydrogel nanoparticles with regulable fluorine contents and T 2 relaxation times as 19 F MRI contrast agents.

Medical imaging contrast agents that are able to provide detailed biological information have attracted increasing attention. Among the new emerging imaging contrast agents, 19 F magnetic resonance imaging contrast agents ( 19 F MRI CAs) are extremely promising for their weak background disturbing signal from the body. However, to prepare 19 F MRI CAs with a long T 2 relaxation time and excellent biocompatibility in a simple and highly effective strategy is still a challenge. Herein, we report a new type of 19 F MRI hydrogel nanocontrast agents ( 19 F MRI HNCAs) synthesized by a surfactant-free emulsion polymerization with commercial fluorinated monomers. The T 2 relaxation time of 19 F MRI HNCA-1 was found to be 25-40 ms, guaranteeing its good imaging ability in vitro . In addition, according to an investigation into the relationship between the fluorine content and 19 F MRI signal intensity, the 19 F MRI signal intensity was not only determined by the fluorine content in 19 F MRI HNCAs but also by the hydration microenvironment around the fluorine atoms. Moreover, 19 F MRI HNCAs demonstrated excellent biocompatibility and imaging capability inside cells. The primary exploration demonstrated that 19 F MRI HNCAs as a new type of 19 F MRI contrast agent hold potential for imaging lesion sites and tracking cells in vivo by 19 F MRI technology.