Development of a series of catechol-containing xanthene fluorophores and their application to detect S-adenosylmethionine (SAM) utilizing catechol-O-methyltransferase (COMT) activities.

S-Adenosylmethionine (SAM) is a vital methyl donor regulating epigenetic processes, but its instability necessitates rapid quantification methods. Here, we report a series of catechol-containing xanthene fluorophores designed as direct substrates for catechol-O-methyltransferase (COMT) to achieve one-step fluorogenic SAM detection. We found that, by leveraging metal-ion coordination, the formation of non-fluorescent catechol dianions at physiological pH becomes possible, and robust fluorescence activation was observed via methylation of the probes upon consuming SAM, enabling precise quantification.