Combined immunostaining and Coomassie Brilliant Blue staining of polyvinylidene difluoride membranes without organic solvent.

A method for staining proteins on polyvinylidene difluoride membranes without using organic solvent is described. The method uses preblocking of the membrane with either Tween 20 or polyethylene glycol followed by staining with 0.01% Coomassie Brilliant Blue. No destaining of the membrane is needed afterwards. Preblocking with polyethylene glycol is compatible with microsequencing while Tween 20 leads to very low initial yields. Preblocking with Tween 20 has the additional advantage of allowing immunostaining followed by Coomassie Brilliant Blue staining for total protein on the same membrane.