This Cyanine5 NHS ester is a reactive dye for the labeling of amino-groups in peptides, proteins, and oligonucleotides. This dye requires a small amount of organic co-solvent (such as DMF or DMSO) to be used in labeling reactions (please see our recommended protocol for more details). This reagent is ideal for very cost-efficient labeling of soluble proteins as well as all kinds of peptides and oligonucleotides. This reagent also works well in organic solvents for small molecule labeling. For more sophisticated targets such as easily degradable proteins, when the use of DMF or DMSO is undesirable, consider using water-soluble sulfo-Cyanine 5 NHS ester which does not require any co-solvent, and features very similar fluorescent properties.