Zheng_2026_J.Photochem.Photobiol.B_277_113392

Carboxylesterases play critical roles in drug metabolism and detoxification, and there is an urgent need for tools capable monitoring of CES activity in pathological states. Herein, we developed N-OAC, a novel fluorescent probe based on ICT mechanism, for the highly selective and sensitive detection of CES. Upon CES activation, N-OAC exhibited a significant fluorescence enhancement at 585 nm with a large 145 nm Stokes shift, achieving ultrasensitive detection limit of 3.42 x 10(-4) U/mL and excellent linearity (R(2) = 0.9986). HRMS and DFT studies collectively confirmed the proposed mechanism wherein CES hydrolyzes the acetoxy group, thereby re-establishing the ICT pathway and leading to fluorescence recovery. N-OAC demonstrated exceptional selectivity over biological interferents and was successfully applied to monitor CES fluctuations in HepG2 cells under DILI and organophosphorus pesticide exposure. Notably, N-OAC visualized CES upregulation by NAC in APAP-injured liver tissues, offering a promising tool for assessing DILI severity and therapeutic efficacy.