The D-amino acid oxidase (DAO) assays are fluorescence-based assays, in which the hydrogen peroxide (H2O2) generated from the reaction of D-serine with DAO and Flavine Adenine Dinucleotide (FAD), is linked to oxidation of Amplex Red in the presence of horseradish peroxidase (HRP). The Amplex Red reagent reacts with H2O2 in a 1:1 stoichiometry to produce the red-fluorescent oxidation product, resorufin, which is measured fluorometrically.