A common way to synthesize an NHS-activated acid is to mix NHS with the desired carboxylic acid and a small amount of an organic base in an
anhydrous solvent. A
coupling reagent such as
dicyclohexylcarbodiimide (DCC) or
1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) is then added to form a highly reactive activated acid intermediate. NHS reacts to create a less labile activated acid. The group is usually written as SuO- or -OSu in chemical notation. Such an ester with acid and NHS, sometimes called succinate ester, is stable enough to be purified and stored at low temperatures in the absence of water and, as such, is commercially available. NHS esters are commonly used for
protein modification (e.g. an NHS ester of
fluorescein is commercially available, and can be added to a protein to obtain a fluorescently labeled protein in a straightforward reaction and purification step). NHS can be used with EDC to immobilize
enzymes for
biosensor applications. ==Alternatives==