Copper iodide staining of protein blots on nitrocellulose membranes

Copper iodide staining which can detect protein levels as low as 100-150 pg/mm2 on nitrocellulose membranes is described. The staining is quantitative as measured by densitometry. Staining is complete within 5 min and may be removed by washing the membrane for 15 min without loss of immunoreactivity. The stain utilizes a reddish-brown precipitate of copper iodide in highly alkaline conditions. Because of its high sensitivity, convenience, and low cost, this stain may be more practical than amido black or gold- and silver-based stains for most laboratory purposes.