IR 650 Maleimide (IRDye® 650 Maleimide analog) is a water-soluble, bright, far-red-fluorescent dye and is spectrally similar to other 650 dyes that are used for flow cytometry, microscopy and other applications. IR 650 conjugates ideally suited for the 633 nm or 647 nm laser lines. A significant advantage to using long wavelength dyes such as Cy5® Dye or Alexa Fluor® 647 dye over other fluorophores is the low autofluorescence of biological specimens in this region of the spectrum.
Maleimide is the most popular sulfhydryl-reactive reactive group for conjugating the dye to a thiol group on a protein, oligonucleotide thiophosphate, or low molecular weight ligand. The maleimide group specifically and efficiently reacts with reduced thiols (sulfhydryl groups, –SH) at pH 6.5 to 7.5 to form stable thioether bond. The resulting conjugates exhibit brighter fluorescence and greater photostability than the conjugates of many other spectrally similar fluorophores.