The SDP (sulfodicholorphenol) ester is currently the most hydrolytically stable amine-reactive moiety available from Invitrogen. Conjugates produced with the Alexa Fluor™ 488 5-SDP ester produce the same strong amide bond between the dye and the compound of interest as succinimidyl (SE or NHS) and tetrafluorophenyl (TFP) esters, but with the improved stability in water and buffers, the SDP ester can potentially offer increased control and consistency in these reactions compared to the NHS and TFP esters.