Novel near-infrared fluorescent probe with large stokes shift for detection of cysteine in food sample and living cells

Cysteine (Cys) plays a pivotal role in numerous physiological processes and holds significant importance in food analysis. In this study, we designed a novel near-infrared (NIR) fluorescent probe TF for specifically detecting Cys, derived from benzo[e]indole-conjugated tetrahydro-acridine salt. Leveraging the electron-withdrawing properties of the 3,5-bis(trifluoromethyl)benzenethiol group, the probe exhibits a distinctive colorimetric response and a notable enhancement in NIR emission, featuring a substantial Stokes shift of 135 nm, facilitating precise Cys detection. The detection mechanism was elucidated through comprehensive analyses including NMR, MS spectral, and quantum theory calculations. Moreover, the probe demonstrates exceptional attributes such as rapid response (8 min), exceptional selectivity, and sensitivity (with a detection limit as low as 74 nM). The probe's NIR fluorescent response, coupled with its large Stokes shift, enables accurate quantification of Cys in real food samples and facilitates imaging for monitoring both exogenous and endogenous Cys levels in living cells.