Ratiometric Detection of Mitochondrial Thiol with a Two-Photon Active AIEgen

In clinical studies, thiol measurement in the whole blood is of diagnostic and prognostic significance. In addition, the detection of mitochondrial thiol is very important for investigating cellular functions or dysfunctions. Here, a ratiometric aggregation-induced emission luminogen (AIEgen) called TPE-PBP for thiol detection was developed by introducing a <i>para</i>-dinitrophenoxy benzylpyridinium moiety to tetraphenylethylene. TPE-PBP exhibits excellent biocompatibility, high photostability, and large two-photon absorption cross-section. TPE-PBP emits red fluorescence in PBS buffer without thiol. Upon addition of thiol, there is a gradual blue shift of TPE-PBP's emission with ratiometric fluorescent response because of cleavage of the dinitrophenyl ether bond by thiol followed by the self-immolation of the <i>para</i>-hydroxybenzyl moiety to produce a less conjugated AIEgen. The <i>in vitro</i> quantification of thiol is enabled by the linear ratiometric fluorescence response with a very low limit of detection. Considering the high sensitivity and good selectivity toward thiol detection, TPE-PBP was also utilized to detect thiol in the blood. Furthermore, mitochondrial thiols <i>in vitro</i>, <i>ex vivo</i>, and <i>in vivo</i> were quantitatively mapped by TPE-PBP using fluorescence microscopy under one- and two-photon conditions.