Self-assembling nanoprobes that display off/on 19F nuclear magnetic resonance signals for protein detection and imaging

Magnetic resonance imaging (MRI) is one of the most promising techniques for the non-invasive visualization of biomarkers and biologically relevant species, both in vivo and ex vivo. Although H-1 MRI with paramagnetic contrast agents, such as Gd3+ complexes and iron oxide, is widely used, it often suffers from low contrast because of the large background signals caused by the abundant distribution of protons in biological samples. Here we report the use of supramolecular organic nanoparticles to detect specific proteins by F-19-based MRI in an off/on mode. In NMR spectroscopy these designed probes are silent when aggregated, but in the presence of a target protein they disassemble to produce a sharp signal. This 'turn-on' response allowed us to visualize clearly the protein within live cells by F-19 MRI and construct an in-cell inhibitor assay. This recognition-driven disassembly of nanoprobes for a turn-on F-19 signal is unprecedented and may extend the use of F-19 MRI for specific protein imaging.