Rational Design of a Ratiometric Fluorescent Probe Based on Arene-Metal-Ion Contact for Endogenous Hydrogen Sulfide Detection in Living Cells.

We report the design and development of a fluorescent Cd(II) ion complex that is capable of the ratiometric detection of H2 S in living cells. This probe exploits the metal-ion-induced emission red shift resulting from direct contact between the aromatic ring of a fluorophore and a metal ion (i.e., arene-metal-ion or "AM" contact). The Cd(II) complex displays a large emission blue shift upon interaction with H2 S as the Cd(II) -free ligand is released by the formation of cadmium sulfide. Screening of potential ligands and fluorophores led to the discovery of a pyronine-type probe, 6⋅Cd(II) , that generated a sensitive and rapid ratio value change upon interaction with H2 S, without interference from the glutathione that is abundant in the cell. The membrane-impermeable 6⋅Cd(II) was successfully translocated into live cells by using an oligo-arginine peptide and pyrenebutylate as carriers. As such, 6⋅Cd(II) was successfully applied to the ratiometric detection of both exogenous and endogenous H2 S produced by the enzymes in living cells, thus demonstrating the utility of 6⋅Cd(II) in biological fluorescence analysis.