Ultra-large Stokes-shifted NIR fluorescent probe for diagnosis of APAP-induced liver injury and its applications in food and bioimaging.

Cysteine (Cys), an essential biothiol in the human body, plays a significant role in physiological and pathological processes and is closely associated with various diseases. Therefore, the detection of Cys is very important for exploring the metabolic and physiological processes of Cys, which can be beneficial for early disease diagnosis and assessment of progression. In this study, we designed a fluorescent probe named PEN-Cys, which is a D1-π-A-π-D2-π-A-π-D1 system that specifically responds to Cys via an intramolecular charge transfer (ICT) pathway. The probe employs acrylate as the Cys recognition site and possesses a conjugated push-pull structure as well as aggregation-induced emission (AIE) properties. It exhibited excellent sensing performance: fast response (2 min), large Stokes shift (333 nm), low detection limit (0.91 nM), high selectivity/sensitivity for Cys, and linear response in 0-350.0 μM (R2 = 0.99389). Combined with fluorescence spectroscopy, DFT calculations, and confocal imaging, PEN-Cys successfully detected Cys in live RAW 264.7 cells and zebrafish (with low cytotoxicity), tracked Cys dynamics in APAP-induced liver injury mice, and achieved accurate Cys quantification in food samples (recovery 98.43-103.30 %, RSD ≤1.78 %). Moreover, when coupled with smartphone RGB analysis, PEN-Cys further enabled reliable instrument-free on-site Cys detection, with a strong linear correlation (R2 = 0.99602).