A ratiometric two-photon fluorescence probe for monitoring mitochondrial HOCl produced during the traumatic brain injury process

Mitochondrial hypochlorous acid (HOCl) is closely related to the redox balance in mitochondria. Abnormal HOCl levels in mitochondria can induce mitochondrial inactivation and further cause cell apoptosis. Consequently, developing a reliable method for detecting HOCl in mitochondria is essential. A mitochondria-targeting two-photon fluorescence probe (Mito-P-OCl) with zero cross-talk ratiometric emission was synthesized and applied to study the traumatic brain injury process in mice. The probe gives a considerable variation (up to 58.5-fold) in its fluorescence intensity ratio (I595/I453) upon reacting with HOCl for 150 s. Mito-P-OCl exhibited excellent properties such as fast response, high sensitivity with a low detection limit of 55.4 nM, high selectivity and deep tissue penetration (270 μm). Moreover, the probe possesses the capability of monitoring endogenous HOCl in living cells and tissues using dual-emission channels and two-photon microscopy.