Rational Design and Bioimaging Applications of Highly Specific "Turn-On" Fluorescent Probe for Hypochlorite

Hypochlorite (OCl^-), an essential part of reactive oxygen species (ROS), plays a crucial role in cellular redox balance. OCl^- has been shown to be implicated in many physiological and pathological processes, including liver injury and cancer. Exploitation of fluorescent probes for the OCl^- helps to reveal its function in the genesis and progression of the aforementioned diseases. Here we propose an easy-to-fabricate coumarin-based fluorescent probe incorporated with an aryl dihydrazide linker for highly specific detection and biological imaging of OCl^- in living cells and tissues. The p-nitrophenyl-modified dihydrazide-linked coumarin derivative (Cou-dhz-Ph-NO₂) was screened from a series of candidate molecules and served as a "turn-on" probe with a low background fluorescence interference due to the nitro-group-based quenching on the coumarin fluorescence. The Cou-dhz-Ph-NO₂ probe showed high selectivity and fast response with excellent linear relationship for detection of OCl^-. A specific OCl^--responsive mechanism that the dihydrazide linker could be oxidatively cleaved by OCl^- was deduced. The exogenous OCl^- and endogenous OCl^- were successfully visualized using the Cou-dhz-Ph-NO₂ probe in living cells, such as MDA-MB-231 cells, RAW 264.7 cells and neutrophils, and the pathologic tissues, including the tumor tissue and the acutely injured liver tissue. This study paves the way for utilizing the aryl dihydrazide linker as OCl^--responsive module, which can aid the evolution of increasingly specific probes for detection of OCl^- and diagnosis of OCl^--coupled diseases.