A peptide-based fluorescent sensor for selective imaging of glutathione in living cells and zebrafish

Monitoring and imaging glutathione (GSH) in living systems is an essential tool to determine the key roles of GSH in biological pathways, but most fluorescent sensors can only be used in vitro because of their potential biotoxicity. Here, a peptide-based fluorescent sensor, FP, has been successfully designed and synthesized based on the biocompatibility of the peptide backbone and low toxicity. The design strategy of FP contains a specific spatial structure of the peptide sequence which selectively binds to Cu²⁺, triggering fluorescence quenching. Interestingly, the fluorescence of FP can be fully restored by GSH, due to the strong binding between Cu²⁺ and the GSH sulfhydryl groups. Finally, the sensor is highly sensitive and selective for imaging GSH both in vitro and in vivo with low toxicity. Thus, FP with its strong "on-off-on" fluorescence changes is a powerful way to image GSH both in cells and zebrafish larvae to study the GSH pathway.