A novel ratiometric pH-responsive fluorescent probe based on FRET-ICT mechanism for lysosome targeting and in vivo imaging of colorectal cancer

Intracellular pH dynamics significantly influences a wide array of cellular processes, including cell proliferation, apoptosis and endocytosis and enzyme activity. To monitor real-time change of intracellular pH values, we developed a novel ratiometric pH-responsive fluorescent probe, TPSP, based on Förster resonance energy transfer (FRET) and intramolecular charge transfer (ICT) mechanism. Extracellular evaluations demonstrated a good linear correlation (R 2 = 0.9935) between the fluorescence ratio of TPSP and pH values ranging from 4.0 to 5.0 (pK a =4.64). Given the remarkable acidic microenvironment (pH 3.8–4.7) in tumor cell lysosomes, we performed further biological experiments, which validated precise localization of lysosomes in colorectal cancer (CRC) cells and specific in vivo imaging of CRC tumors in mouse models. These findings preliminarily suggest that TPSP could serves as a promising molecular tool for pH dynamics monitoring, lysosomal function assessment and intraoperative navigation. • Sensitive pH-response based on ratiometric sensing strategy. • Reversible response and anti-interference characteristic. • Specific lysosomal targeting capability. • Precise delineation of colorectal tumor due to its acidic microenvironments.