A Water‐Soluble, Two‐Photon Probe for Imaging Endogenous Hypochlorous Acid in Live Tissue

Abstract Detection of hypochlorous acid (HClO) in the living system may help to uncover its essential biological functions. However, current imaging agents suffer from poor water solubility that limit their live‐tissue applications. Here, a water‐soluble probe ( NNH ) is devised through innovative hydrazone modification of 1,8‐naphthalimide at 3′ position. NNH was successfully applied to tracking endogenous HClO in both cultured macrophages and a liver injury model in mice. NNH demonstrated remarkably increased water solubility and multiple desirable features including two‐photon absorbance, anti‐bleaching capability, rapid cellular uptake, and low cytotoxicity. NNH is the first hydrazone‐based probe for real‐time imaging of HClO in live tissue.