Coumarinocoumarin-Based Two-Photon Fluorescent Cysteine Biosensor for Targeting Lysosome

Coumarinocoumarin, one of the coumarin derivatives, is easy to synthesize and has rich modification sites. The large conjugate plane of coumarinocoumarin gives it a more excellent optical property than conventional coumarin, for example, the two-photon fluorescence property. So, the coumarinocoumarin-based probe (CCy) has been designed and synthesized, which is the first lysosomal targeting fluorescent biosensor for cysteine. This probe was prepared by a three-step procedure as a latent fluorescence probe to achieve high sensitivity and fluorescence turn-on response toward cysteine (Cys) over homocysteine (Hcy), glutathione (GSH), and other various natural amino acids under physiological conditions. Upon addition of Cys to the solution of CCy, remarkable enhancement on 520 nm of fluorescence spectra can be monitored. This probe was then successfully used for fluorescence imaging of Cys in mice organ tissues and HeLa cells, and quantitative determination has been achieved within a certain range, which proved the permeability of CCy. The concentration of Cys in animal serum was measured and the viability exceeded 80%, indicating that CCy can be a biocompatible and rapid probe for Cys in vivo. Simultaneously, its ability to detect Cys in lysosome has been validated by its lysosomal targeting.