This Cyanine5 NHS ester, also known as Cy5 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 to be used in labeling reactions. 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.