The protein or peptide is known as the "building blocks of life" and is one of the most important macromolecules in life science. Protein determination is a very common practice. Simple, direct and automation-ready procedures for measuring protein or peptide concentration are very desirable. The protein assay kit is based on an improved ophthalaldehyde method. This reagent reacts with primary amines in protein or peptide and forms a blue fluorescent product, allowing detection of nanograms of proteins. The fluorescence intensity (lex/em = 360/450nm) is proportional to the protein concentration in the sample.