An Excited‐State Intramolecular Proton Transfer Mechanism‐Based Reactive Probe for Ratiometric Fluorescence Detection of Epinephrine in Live Cells

Epinephrine (EPI), also known as adrenaline, is involved in various physiological processes of the sympathetic nervous system and may be linked to the progression of different serious diseases, including cancers, Alzheimer's, and Parkinson's diseases etc. There is an urgency in developing a fluorescence probe for the detection of EPI. An excited-state intramolecular proton transfer mechanism (ESIPT)-based reactive probe HBT-EPI has been successfully developed for ratiometric fluorescent detection of EPI in physiological conditions. EPI undergoes a cascade of nucleophilic attack at the carbonothioate site of the probe using the secondary amine and β-hydroxyl group to release the ESIPT-active 2-(2'-hydroxyphenyl) benzothiazole (HBT) fluorophore. Thus, a ratiometric fluorescence response is obtained. The probe is highly selective for EPI detection compared to other catecholamine-based neurotransmitters. A minimum of 1 µM of EPI can be easily detected using this probe. HBT-EPI has been successfully demonstrated for ratiometric fluorescence detection of EPI in live cells via confocal imaging.