ETT activator is an activator solution containing 5-(Ethylthio)-1H-tetrazole – a powerful activator – in acetonitrile. It is mixed with phosphoramidite during the extension step in which it reacts with the amidite group to form a highly reactive intermediate. The intermediate then forms an internucleotide bond with the detritylated 5′hydroxyl group of the growing oligonucleotide chain.

ETT activator has been used in the fast and low-cost synthesis of photolithographic DNA microarrays.