Facile and Highly Selective Near-Infrared Emitting Fluorescent Indicator for Hypochlorous Acid Signaling and Bioimaging

A near-infrared emitting fluorescent chemodosimeter for hypochlorous acid (HOCl), PAM, was designed and synthesized by modifying on the sulfonate porphyrin chromophore with a diaminomaleonitrile substituent to form Schiff-base as the chemodosimetric recognition unit. PAM behaved as a sensitive fluorescence "off-on" reactor to HOCl with satisfying anti-interference capacity over other latent disturbing analytes. The drastic fluorescence enhancement originated from the HOCl-promoted intramolecular cyclization to rigidify the molecular structure to a substituted imidazole, which effectively inhibited the C--N isomerization. This chemical process is specific, expeditious and will not release extra compounds other than H2O. 1H NMR, FI-IR, HRMS, and spectral analysis confirmed the proposed mechanism. In addition to facilely synthesis, photo- and chemo-stable, PAM has outstanding features of fully water-soluble, low analytic limitation (6.3 nM), and positive linearity, which makes it practical to quantify HOCl in tap water and serum samples. Furthermore, PAM was efficiently leveraged for monitoring both exogenous and endogenous HOCl in living cells, as well as for differentiating between normal and cancer cells based on differences in basal HOCl levels. The versatility of this probe definitely provided a potential discovery tool for further elucidate the HOCl-associated neurological disorders.