A novel rhodamine-based fluorescent probe for high selectively determining cysteine in lysosomes

An essential sulfhydryl amino acid in the human body is cysteine (Cys). Its abnormal level is related to coronary heart disease, hypertension, growth retardation, sleepiness, liver injury and AIDS. At present, although many cysteine fluorescent probes have been synthesized, there are relatively few fluorescent probes for sensing cysteine in lysosomes. Therefore, based on a rhodamine derivative, we constructed a fluorescent probe with high selectivity for detecting cysteine in lysosome. The probe chose acrylate as the recognition group and morpholine as the positioning group. The probe was in spirolactone state and displayed very weak fluorescence when cysteine was absent. After adding cysteine, the conjugated xanthene structure was formed through the conversion of the closed spirolactone structure and strong green fluorescence appeared. Compared with glutathione (GSH) and homocysteine (Hcy), the probe had better selectivity to Cys. When the Cys concentration was altered from 1.0 × 10−7 to 6.0 × 10−6 mol·L−1, there was a good linear relationship between fluorescence intensity of the probe and Cys concentration. The detection limit had been evaluated to be 7.5 × 10−9 mol·L−1 for Cys. The probe can work under a wide pH range, including pH under physiological conditions. The probe also has a good effect in non-cytotoxic confocal imaging of endogenous and exogenous cysteine in A549 cells. These findings showed that the fluorescent probe synthesized in this study could be a useful tool for the detection of endogenic and exogenic cysteine.