HABA is a dye with absorbance and avidin-binding properties that help enable the quantitation of biotin in a sample. When HABA is bound to avidin, the complex absorbs light at 500 nm (e = 34,000/M cm). When a biotin-containing sample is added, the biotin binds strongly to avidin and displaces the weakly bound HABA resulting in a decrease in absorbance relative to the amount of HABA displaced.