A red-emitting ratiometric fluorescent probe with large Stokes shift and emission peak shift for imaging hypochlorous acid in living cells and zebrafish

Abstract

Hypochlorous acid (HClO) with strong oxidizing property holds an essential role in the resistance against offensive microorganisms in the inherent immune system of living organism. However, an excess of HClO can bring about oxidative stress and cellular damage, which are associated with many diseases. Herein, a novel nopinone-based ratiometric fluorescent probe BIDID (2-(4-(5,5-dimethyl-4,5,6,7-tetr-ahydro-1H-4,6-methanobenzo[d]imidazole-2-yl)benzylidene)-1H-indene-1,3(2H)-dione) was rationally devised to track exogenous and endogenously generated HClO in vitro and vivo. BIDID itself featured an extremely large Stokes shift (241 nm) and exhibited a bright red emission at 641 nm. Upon treating with HClO, the CC bond of BIDID was exclusively broken, thereby resulting in the generation of compound BID (4-(5,5-dimethyl-4,5,6,7-tetrahydro-1H-4,6-methanobenzo[d]imidazole-2-yl)benzalde-hyde) with a remarkably hypochromatic-shifted emission at 501 nm. As expected, this probe was highly responsive to HClO with good selectivity, superior sensitivity, low limit of detection (13.2 nM), rapid response (within 0.5 min), and wide pH range (6–12). What's more, BIDID was applicable for validation of HClO on solid platform and in real water samples. Additionally, the confocal fluorescent images of HClO in vitro and in vivo demonstrated that BIDID can function as a reliable tool for studying HClO-related physiological and pathological processes.