A sensitive ratiometric fluorescence probe for chymotrypsin activity and inhibitor screening

Chymotrypsin (CHT) is involved in a series of physiological processes and disorders and it is known as a biomarker of pancreatic function. Thus, a sensitive and selective method for evaluating the relative CHT levels in different live cells is urgently needed to better understand the function of CHT. Herein, a ratiometric fluorescence probe (NI) with strong intramolecular charge transfer (ICT) has been rationally designed. The probe is constructed by incorporating a recognition group of 4-bromobutyryl into the fluorescent skeleton of 1,8-naphthalimide. The presence of CHT cleaves the 4-bromobutyryl group from naphthalimide and remarkably alters the probe's photophysical properties with a large Stokes shift, thus achieving ratiometric detection of CHT. With a detection limit of 8.4 ng/mL, NI shows high binding affinity and comparable catalytical efficiency against CHT and was successfully applied for the inhibitor characterization. The results also demonstrate that the designing strategy in the text provides a more promising application prospect for screening others CHT inhibitors.