Acrolein-integrated ESIPT probe for NIR fluorescence detection of cysteine with ultrafast response and sub-nanomolar sensitivity

Cysteine (Cys) is an essential sulfur-containing amino acid in the human body and is involved in many important physiological processes. The reliable detection of Cys is of great significance for the precise diagnosis of diseases. Fluorescent probes are powerful tools for the detection of Cys. In the study, we designed and synthesized a series of Cys-recognizable fluorescent probes by employing different recognition groups and conjugated units. Our results demonstrated that the probe based on acrylate and acrolein emits almost no fluorescence in organic solvents, whereas it achieved a near-infrared fluorescence emission (652 nm) due to the excited-state intramolecular proton transfer (ESIPT) effect in the presence of Cys. Importantly, the probe exhibited high selectivity and fast response time (in 10 min). In particular, the limit of detection (LOD) is as low as 3.42 × 10^-4 µM. This probe has been successfully applied for the detection and imaging of Cys in biological cells.