Hypochlorous acid (HOCl), as a highly potent oxidant, is well-known as a key "killer" for pathogens in the innate immune system. Recently, mounting evidence indicates that intracellular HOCl plays additional important roles in regulating inflammation and cellular apoptosis. However, the organelle(s) involved in the distribution of HOCl remain unknown, causing difficulty to fully exploit its biological functions in cellular signaling pathways and various diseases. One of the main reasons lies in the lack of effective chemical tools to directly detect HOCl at subcellular levels due to low concentration, strong oxidization, and short lifetime of HOCl. Herein, the first two-photon fluorescent HOCl probe (TP-HOCl 1) and its mitochondria- (MITO-TP) and lysosome- (LYSO-TP) targetable derivatives for imaging mitochondrial and lysosomal HOCl were reported. These probes exhibit fast response (within seconds), good selectivity, and high sensitivity (<20 nM) toward HOCl. In live cell experiments, both probes MITO-TP and LYSO-TP were successfully applied to detect intracellular HOCl in corresponding organelles. In particular, the two-photon imaging of MITO-TP and LYSO-TP in murine model shows that higher amount of HOCl can be detected in both lysosome and mitochondria of macrophage cells during inflammation condition. Thus, these probes could not only help clarify the distribution of subcellular HOCl, but also serve as excellent tools to exploit and elucidate functions of HOCl at subcellular levels.

Intracellular thermometry at the microscopic level is currently a hot topic. Herein we describe a small molecule fluorescent thermometer targeting mitochondria (Mito thermo yellow). Mito thermo yellow successfully demonstrates the ability to monitor the intracellular temperature gradient, generated by exogenous heating, in various cells.

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