A dual-emission two-photon fluorescent probe for specific-cysteine imaging in lysosomes and in vivo

Cysteine (Cys) can effectively maintain lysosomes under a highly reductive environment. However, fluorescent probes for specific detection of lysosomal Cys over other biothiols are rare. Probe Lyso-DCHO utilizing a carbazole-based two-dimensional intramolecular charge transfer (ICT) system was designed to detect Cys with a ratiometric signal (119 nm emission shift). The sensing mechanism was fully supported by H-1-NMR titration, ESI-MS and DFT calculations. Lyso-DCHO can be well localized in lysosomes along with good biocompatibility. Furthermore, Lyso-DCHO achieved a dual-channel fluorescence response toward Cys in lysosomes and zebrafishes with high selectivity under the two-photon (TP) excitation.