A fluorogenic probe for SNAP-tag protein based on ESPT ratiometric signals

Protein self-labeling tags achieve selective fusion and labeling of target proteins through genetic coding technology, but require exogenous fluorescent probes with fluorogenicity for protein tag binding to have the performance of wash-free fluorescence imaging in live cells. In this paper, we reported a fluorogenic probe 1 capable of ratiometric fluorescence recognition of SNAP-tag proteins. In this probe, the O6-benzylguanine derivative of 3‑hydroxy-1,8-naphthalimide underwent a selective covalent linkage reaction with SNAP-tag protein. The hydroxyl group on the naphthalimide fluorophore formed a hydrogen bond with the functional group near the protein cavity. The excited state proton transfer occurred after illumination, to obtain the ratio fluorescence signal from blue emission to red emission, realizing the wash-free fluorescence imaging of the target proteins.