Quantification of proteins in the low nanogram range by staining with the colloidal gold stain AuroDye

A simple assay for proteins in the low nanogram range is described. Proteins are bound to nitrocellulose paper in a band, stained with the commercially available colloidal gold stain AuroDye (a registered trademark of Jansen Life Sciences Products), and quantified by scanning densitometry: 1.25 to 20 ng of protein can be consistently measured. Variation in the staining intensity of different proteins is discussed. DNA, RNA, polyvinylpyrrolidone, Ficoll, and 6 M urea do not affect the assays, and samples from cellular material in a simple lysis buffer containing 0.1% of sodium dodecyl sulfate can be assayed.