fluorometry o-Phthalaldehyde fluorescent protein assay 2020-08-04T17:55:00Z MMO:0000730 OPA fluorescent protein assay When reacted with primary amines in the presence of mercaptoethanol, OPA (o-Phthalaldehyde) yields an intense blue-colored fluorescent product that has a maximum wavelength of excitation of 340 nm and emission at 455 nm. Wavelengths from 330-375 nm have been used for excitation and 436-490 nm for measuring emission. Protein concentrations as low as 50 ng/ml can be measured with an OPA assay. The inherent sensitivity and speed of OPA, along with its broad linear range, makes it a useful protein and peptide assay reagent. measurement_method_ontology slaulede