Phosphoprotein staining for sodium dodecyl sulfate–polyacrylamide gel electrophoresis using fluorescent reagent morin hydrate

A fluorescence-based stain with 3,5,7,2′,4′-pentahydroxyflavone (morin hydrate, MH) was designed to stain phosphoproteins in one-dimensional sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). Al3+ was applied as a “fixed bridge,” providing an efficient energy transfer channel between phosphoprotein and MH, to produce a strong fluorescent complex for the determination of phosphoprotein. As little as 62.5 ng of α-casein (7 or 8 phosphates) and β-casein (5 phosphates), 125 ng of ovalbumin (2 phosphates), and κ-casein (1 phosphate) could be visualized with a wide linear dynamic range. In comparison with conventional methods, MH stain is a time-saving method that takes just 90 min. It also has good compatibility with routine protein stainings such as Coomassie Brilliant Blue R (CBBR) and SYPRO Ruby for total protein analysis.