IR 680 (IRDye® 680 equivalent) is a bright, water-soluble dye that is structurally very similar to the commonly used Cy®5.5 Dye. The water solubility, brightness, and self-quenching characteristics of this dye were significantly improved by the introduction of two additional sulfo groups. Far-red fluorescent IR 680 conjugates are spectrally similar to other 680 nm dyes that are used for flow cytometry, microscopy and other applications. Proteins can be labeled with IR 680 at high molar ratios without significant self - quenching, leading to brighter conjugates and more sensitive detection.
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 bonds.