A turn-on NIR probe with rotational-release mechanism for HOCl imaging in CIRI

Cerebral ischemia-reperfusion injury (CIRI) remains a major therapeutic challenge, with mitochondrial dysfunction and hypochlorous acid (HOCl) overproduction playing key roles in its progression. Real-time monitoring of HOCl fluctuations is helpful for understanding its pathological involvement. Conventional HOCl fluorescent probes based on CC bond cleavage often suffer from decreased near-infrared emission upon reaction and small Stokes shifts, which may limit their biological imaging performance. Therefore, the development of a sensitive NIR probe with a large Stokes shift for effective HOCl imaging in living systems is of considerable interest.

We developed XZTU.BBT, a D-π-π'-A molecular rotor probe that responds to HOCl via a rotational-release mechanism. In the native state, rotation around the C2-C3 single bond facilitates non-radiative decay, keeping the probe in an off state. HOCl-triggered oxidative cleavage of the C1C2 bond releases the rotatable acceptor, restoring NIR fluorescence at 698 nm with a large Stokes shift of 196 nm. The probe exhibits a rapid response (<5 s), good sensitivity (LOD = 2.3 nM), and acceptable selectivity toward HOCl. It was successfully applied to image HOCl fluctuations in oxygen-glucose deprivation/reperfusion (OGD/R) cell models and in a mouse model of ischemic stroke (MCAO). Furthermore, the probe was used to evaluate the antioxidant effects of phelligridimer A (PA), suggesting its potential utility in screening neuroprotective agents.

This work presents a molecular rotor probe with a rotational-release mechanism for HOCl sensing. Unlike conventional CC cleavage probes showing spectral blue-shift, XZTU.BBT maintains NIR emission with a large Stokes shift, offering a potential tool for HOCl biology and antioxidant evaluation in CIRI.