The SensoLyteŽ Biotin Quantitation Assay Kit provides a convenient assay for estimating the molar ratio of biotin to protein in biotin-protein conjugates or for quantifying biotin concentration in a solution. The assay is based on FRET principle. In the first step, avidin, Reagent A tagged with a quencher dye is briefly incubated with biotin samples/standards. In the second step, fluorescent biotin, Reagent B, is added to the assay mixture. The fluorescent signal is directly proportional to the amount of biotin in the sample and can be detected at Ex/Em=490/520 nm. The kit is best used to determine biotin concentration in the range from 2 to 20 picomoles. The kit also provides biotinylated IgG for use as a positive control and a protease for protein digestion to expose hidden biotin groups.