Intracellular self-assembly of Ru(bpy)₃²⁺ nanoparticles enables persistent phosphorescence imaging of tumors

Nanoprobes are advantageous over small molecular probes in sensitivity but most luminescence molecules used to construct nanoprobes often suffer from an aggregation-caused quenching effect. Herein, we rationally designed a small molecular probe Cys(StBu)-Lys(Ru(bpy)32+)-CBT (1) which "smartly" self-assembled into nanoparticles 1-NPs inside cells with non-quenched, persistent phosphorescence. Employing this property, we successfully applied 1 for long-term sensing of biothiol activity in living HepG2 cells and tumors. We envision that, by modifying the amino group with an enzyme substrate, our probe 1 could be further developed for sensing intracellular enzyme activity with non-quenched, persistent phosphorescence.