A mitochondria-targeted ratiometric two-photon fluorescent probe for detecting intracellular cysteine and homocysteine.

A novel mitochondria-targeted ratiometric two-photon fluorescent probe (Mito-MQ) for detecting intracellular cysteine (Cys) and homocysteine (Hcy) has been designed. Mito-MQ showed the ratiometric fluorescent detection signal (the green-to-blue emissionfrom 517nm to 460nm) to cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH), along with the fast response rate (10min). The detection mechanism was illustrated by 1 H NMR, ESI-MS and theoretical calculation. The co-localization coefficient of 0.87 between Mito-MQ and MitoTracker Red revealed that the probe was predominantly present in mitochondria, therefore, Mito-MQ was successfully applied to detect mitochondrial oxidative stress by detecting the change of Cys/Hcy. Moreover, imaging in fresh tissue slices indicated that Mito-MQ could work in deep tissue (ca. 130µm) under two-photon excitation. Furthermore, the measurement of Cys/Hcy detection in zebrafish showed that probe can be used in determination of biothiols in vivo.