A near-infrared ratiometric fluorescent probe for rapid and highly sensitive imaging of endogenous hydrogen sulfide in living cells

Abstract

We describe the design and synthesis of a cyanine-based near-infrared ratiometric fluorescent probe, HS–Cy, for H₂S detection, which features rapid response, high sensitivity, and mitochondria targeting. After a rapid quenching at 780 nm by initial nucleophilic addition on the aldehyde group, HS–Cy experienced a polymethine π-electron conjugation modulation triggered by a second nucleophilic addition on the ester, releasing the cyanine fluorophore which underwent tautomerism from enol form to ketone form. Therefore, gradual emergence of a new peak at 625 nm was observed, constructing a ratiometric signal for H₂S with a detection limit of 5.0–10 nM, which is the most sensitive among the reported H₂S-sensing fluorescent probes. HS–Cy was proven to selectively locate into mitochondria with faster trapping kinetics towards H₂S. Based on this, the endogenously generated H₂S in human A549 cells was ratiometrically detected and imaged by HS–Cy.