Fluorescent probes that distinguish proteins with single or two close mercapto groups

Two water soluble fluorescent probes with quaternary ammonium salts as solubilization groups were designed and synthesized to detect proteins with close mercapto groups. The unique structure of V-shape oligo(o-phenylene-ethynylene) backbone connecting two maleimide groups as mercapto group recognition sites enables the probes to distinguish a single mercapto group from two close mercapto groups in proteins. The probe had no fluorescence response to proteins with only one mercapto group, but had strong fluorescence response to proteins with mercapto group combination at the concentration of 10−6 mol/L. The probe worked under a wide range of pH, from 4 to 8. This work also demonstrates the concept of functional group combination detection.