4',5'-Bis(1,3,2-dithiarsolan-2-yl)-3',6'-dihydroxy-3-oxospiro[isobenzofuran-1(3H),9'-[9H]xanthene]-6-carboxylic Acid, is used as a probe able to bind efficiently and selectively to Cys-tagged proteins. The interaction with the protein is detected by an increase of the fluorescence emission of CrAsH.
