Bromobimane (Monobromobimane) is a non-fluorescent substance, but reacts with thiols to produce a fluorescent product.Bromobimane is used as a probe, often in clinical medicine, to test for sulfide levels in blood.

Bromobimanes in solution (aqueous or organic solvents of medium polarity) react with small thiols, and with reactive protein thiol groups (e.g., hemoglobin). The reactions of bromobimanes with thiols are second-order and dependent on pH, the active nucleophile being the thiolate anion. The reaction of bromobimane with a thiolate converts the nonfluorescent agent into water-soluble fluorescent products [1]. The highly selective, rapid reactivity of bromobimanes toward thiols, the stability and fluorescence yield of the thiol derivatives, the ease of separation of the derivatives by reversed-phase HPLC, and the availability of both cell-penetrating and nonpenetrating forms, make the use bromobimanes an extremely powerful approach to the analysis of low molecular weight biothiols [2].