A rhodamine-based fluorescent probe for Hg2+ and its application for biological visualization

A new visible light excitable fluorescent probe ( 1 ) is synthesized by appending a hydroxymethyl-pyridine to rhodamine B hydrazide. The probe displays very specific Hg 2+ -induced colour change and fluorescent enhancement in the aqueous systems. The “turn-on” response of fluorescence is based on a binding-induced ring-opening process from the spirolactam (nonfluorescent) to acyclic xanthene (fluorescent) in rhodamine B. The coordinating atoms O–N–N–O from the hydroxymethyl-pyridine and rhodamine B hydrazide play dominant role in the formation of a complex with 1:1 stoichiometry of Hg 2+ to 1 . It exhibits a linear response in the range of 0.1–5   μM with the limit of detection (LOD) of 15.7   nM (3 σ /slope), while the calculated value of the association constant of Hg 2+ / 1 is 0.70   ×   10 5   M −1 . Furthermore, confocal microscopy imaging experiment demonstrates the probe 1 can be applied as a fluorescent probe for visualization of Hg 2+ in living HeLa cells.