Nanomolar Detection of HS in an Aqueous Medium: Application in Endogenous and Exogenous Imaging of HeLa Cells and Zebrafish.

The homeostasis of short-lived reactive species such as hydrogen sulfide/hypochlorous acid (HS/HOCl) in biological systems is essential for maintaining intercellular balance. An unchecked increase in biological HS concentrations impedes homeostasis. In this report, we present a molecular probe pyrene-based sulfonyl hydrazone derived from pyrene for the selective detection of HS endogenously as well as exogenously through a "turn-off" response in water. The structure of the receptor is confirmed by Fourier-transform infrared spectroscopy, H and C nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction studies. The receptor shows excellent green emission in both the aqueous phase and solid state. Quenching of green emission of the receptor is observed only when HS is present in water with a detection limit of 18 nM. Other competing anions and cations do not have any influence on the receptor's optical properties. The efficiency of HS detection is not negatively impacted by other reactive sulfur species too. The sensing mechanism of HS follows a chemodosimetric reductive elimination of sulfur dioxide, which is supported by product isolation. The receptor is found to be biocompatible, as evident by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and its utility is extended to endogenous and exogenous fluorescence imaging of HeLa cells and zebrafish.