Fluorescein aldehyde with disulfide functionality as a fluorescence turn-on probe for cysteine and homocysteine in HEPES buffer

We developed a fluorescein aldehyde probe with disulfide functionality for the fluorescence detection of biologically important thiols. The probe displayed highly selective responses to cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) due to the rapid ring formation reaction of Cys and Hcy with the aldehyde group of the probe and the concomitant cleavage of the disulfide group followed by subsequent intramolecular cyclization. The fluorescent probe also exhibited a highly sensitive fluorescence turn-on response to Hcy with a detection limit of 2.4 μM Hcy in HEPES buffer.