Controlled intracellular self-assembly and disassembly of 19F nanoparticles for MR imaging of caspase 3/7 in zebrafish.

Compared to (1)H MRI, (19)F MRI provides higher selectivity but lower sensitivity. Therefore, the need to inject high doses of the (19)F probe to improve its sensitivity for in vivo diagnosis remains a challenge. A "smart" strategy is needed that could locally concentrate a low-dose (19)F probe while avoiding the fast transverse relaxation of the probes. Locally self-assembling and disassembling (19)F nanoparticles may be an optimal measure to achieve this goal. Herein, we report a dual-functional probe 1 for glutathione (GSH)-controlled self-assembly and subsequent caspase 3/7 (Casp3/7)-controlled disassembly of formed nanoparticles (i.e., 1-NPs). Consecutive assembly and disassembly of 1-NPs translate to "off" and "on" (19)F magnetic resonance (MR) signal states, respectively. Employing this smart strategy, we successfully used 1 for the consecutive detection of GSH and Casp3/7 activity in vitro and in cells and imaging Casp3/7 activity in cells and in zebrafish at low doses with a 14.1 T magnetic field.