The AttoPhos Substrate (2´-[2-benzothiazoyl]-6´-hydroxybenzothiazole phosphate [BBTP]) is cleaved by alkaline phosphatase (AP) to produce inorganic phosphate (Pi) and the alcohol, 2´-[2- benzothiazoyl]-6´- hydroxybenzothiazole (BBT). This enzyme-catalyzed conversion of AttoPhos Substrate to BBT is accompanied by an enhancement in fluorescence properties that include increased quantum efficiency plus fluorescence excitation and emission maxima that are red-shifted further into the visible region.