Fast and sensitive near-infrared ratiometric fluorescent probe with a self-immolative spacer for imaging of endogenous alkaline phosphatase activity in cells and in vivo

Alkaline phosphatase (ALP), a vital hydrolase widely distributed in organisms, is regarded as a critical biomarker strongly associated with many physiological and pathological processes. Therefore, fast and efficient detection of ALP activity in vivo is of great value for clinical diagnosis. Herein, a novel near-infrared (NIR) ratiometric fluorescent probe (HP) was designed based on ESIPT for trapping ALP activity in cells and in vivo. Notably, incorporating a self-immolative spacer dramatically reduces the response time (8.5 min) of HP. Moreover, the probe exhibits excellent water solubility, large Stokes shift (147 nm), the ratiometric determination of ALP at 570 nm and 689 nm, low detection limit (3.98 U L−1). More importantly, the probe was also successfully applied to detect and monitor variations in endogenous ALP activity in zebrafish due to the drug (APAP) induced organ damages.