Arylamino-substituted Rhodamine as a Fluorogenic Molecular Rotor for the Wash-free Imaging of Non-catalytic Proteins in Live Cells

Fluorescent probes are valuable tools to visualize non-catalytic proteins in live cells. Currently, the majority of imaging reagents for non-catalytic proteins are based on “always-on” fluorophores and the use of these reagents usually necessitate a wash step to remove unbounded fluorophores before microscope imaging. Herein, we report the use of arylamino-substituted rhodamine as an activatable fluorophore for the imaging of non-catalytic protein in live cells. We have shown the induction of an arylamino to structurally rigid rhodamine could significantly reduce the fluorescent emission in aqueous medium but the ligand-directed binding of this molecule to protein receptor could effective restrict its intramolecular motion and thus lead to enhancement in fluorescence intensity at 590 nm over 30-fold. With fluorescent probes based on this fluorophore, we could visualize integrin α_vβ₃ and azido-functionalized glycans in living cells with high contrast in a wash-free manner.