Double-blotting: a solution to the problem of nonspecific binding of secondary antibodies in immunoblotting procedures.

"Double-blotting" (DB) has been developed to overcome the problem of nonspecific binding of secondary antibodies in immunoblotting (IB). After it has been probed by the primary antibody, the membrane with the blotted proteins is assembled with a second blank membrane and submitted to a second blotting under acidic conditions. The primary antibody molecules are thus desorbed from their corresponding antigen and transferred onto the second membrane, whereas the antigen and the interfering proteins remain bound to the first one. The second membrane can then be probed by the secondary antibodies without the risk of nonspecific binding. This method has been developed for the study of erythropoietin (EPO) in concentrated urine since a strong nonspecific binding of biotinylated secondary antibodies to some urinary proteins is observed using classical IB protocols. However, its concept makes it usable in other applications that come up against this kind of problem.