A novel near-infrared fluorescent probe for detecting intracellular alkaline phosphatase and imaging of living cells

Development of novel near-infrared (NIR) fluorescent probes for the monitoring of active substances in living organism is desirable in biological studies. Herein, we designed a novel NIR MTR fluorophore which has a longer emission wavelength, greater Stokes shift and higher quantum yield than the classic hemicyanine NIR fluorophore. The synthesized MTR-derived NIR probe (MTR-P) is highly selective and sensitive to alkaline phosphatase (ALP) activity. In the presence of ALP, MTR-P exhibited increased fluorescence signal by up to 56 fold at 723 nm, and it was determined to be 0.042 U L-1. In addition, the mechanism of the MTR-P probe was further examined by HPLC, mass spectrometry and DFT/TDDFT calculations. The NIR probe MTR-P was successfully applied to measure the levels of alkaline phosphatase in different types of cells by fluorescence imaging.