A fluorescent probe based on reversible Michael addition-elimination reaction for the cycle between cysteine and H 2 O 2 .

Cysteine oxidation by H2O2, generating either cysteine sulfenic acid (CSOH) or disulfide (CSSC), is involved in redox homeostasis and signaling. Compared with quantification of the cysteine content, monitoring the cysteine dynamics in real-time, in particular, takes on even greater importance. However, existing fluorescent probes suffer from low specificity or irreversible recognition mechanisms. In the present work, we have successfully developed a reversible fluorescent probe for the cycle between cysteine and H(2)O(2)based on the Michael addition-elimination reaction. This probe features a specific and quantitative response to cysteine. The reversible detection was realized repeatedly with the addition of cysteine and H(2)O(2)in order. We also demonstrated its usage for monitoring exogenous and endogenous cysteine in living cells. Eventually, this probe was capable of imaging cysteine dynamically in real-time.