An activatable near-infrared fluorescent probe for tracking nitroxyl in vitro and in vivo

Nitroxyl (HNO) has been discovered to play a vital role in diverse physiological and pathological processes. In this work, we report a new reductant-resistant fluorescent probe (NHMC-P) for highly effective tracking of HNO in vitro and in vivo in the near-infrared regions. NHMC-P contains a nitrogen-hydroxylmerocyanine (NHMC) as the fluorophore, linked with a 2-(diphenylphosphino)benzoic acid through an ester bond as the recognition moiety. Upon reaction with HNO, the recognition moiety will be triggered to an aza-ylide, which then attacks the intramolecular ester carbonyl group to release the fluorophore NHMC and restore the fluorescence. NHMC-P exhibited ultra-sensitivity and high selectivity for HNO in the near-infrared region. Furthermore, ascribed to the excellent water-solubility, the probe was successfully employed to track HNO in living cancer cells and zebrafish models. Our work provides a potential tool for in vivo HNO tracking and is helpful for HNO-related pathological studies in living organisms.