acridinium esters: esters of acridine-9-carboxylic acid. They have a quaternary nitrogen centre and are derivatized at the 9 position to give a labile phenyl ester moiety. Acridinium esters such as 2′,6′-dimethyl-4′-[N-succinimidyloxy carbonyl]phenyl-10-methylacridinium- 9-carboxylate can be used as chemiluminescent labels for antibodies. Light emission is activated by adding hydrogen peroxide under alkaline conditions. In hybridization protection assays, single-stranded DNA probes labelled with acridinium esters are protected against rapid hydrolysis when hybridized with a target DNA molecule but not when they are in free solution.
