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Sulfhydryl-containing proteins play critical roles in various physiological and biological processes, and the activities of those proteins have been reported to be susceptible to thiol oxidation. Therefore, the development of protein thiol target fluorescent probe is highly desirable. In the present work, a biotinylated coumarin fluorescence "off-on" probe SQ for selectively detecting protein thiols in biotin receptor-positive cancer cells was designed with a 2,4-dinitrobenzenesulfony as the thiol receptor. The probe exhibited dramatic fluorescence responses toward sulfhydryl-containing proteins (ovalbumin (OVA), bovine serum albumin (BSA)): up to 170-fold fluorescence enhancement with 70 nm blue-shift was observed with the addition of OVA. However, low molecular weight thiols (Cys, glutathione (GSH), Hey) caused negligible fluorescence changes of SQ In addition, biotin receptor-positive Hela cells displayed strong red and green fluorescence after incubation of SQfor 1 h; neither red nor green fluorescence signal could be visualized in biotin-negative normal lung Wi38 cells. These results imply that the probe has potential application in fluorescent imaging protein thiols on the surface of Hela cells. [ABSTRACT FROM AUTHOR]