A near-infrared fluorescent probe for imaging cysteine changes in Arabidopsis thaliana

In this work, a robust "turn-on" NIR fluorescent probe Cx-Cys was constructed for cysteine detection and imaging in Arabidopsis thaliana. Specifically, a 1,8-naphthalimide-based NIR fluorophore was used as the signaling group, while the acrylate group served as the recognition moiety for cysteine as well as the fluorescence quenching group. The probe shows a remarkable NIR response toward cysteine in the infrared region (718 nm), and a large Stokes shift (103 nm). Cx-Cys displayed high sensitivity and selectivity to cysteine with low detection limits of 73 nM over other amino acids and bio-thiols. Impressively, it was applied to obtain images of Arabidopsis thaliana and enabled visualization of cysteine content changes under external stimulations in root tips in vivo. Cx-Cys was also used to monitor the dynamic changes of the cysteine pool after incubation in cysteine solutions.