Our lab has encountered a very strange problem recently with western blots. A few of us have successfully blotted for our protein of interest, only to produce blank films on the subsequent blot. For example, I recently blotted for my protein of interest, but wasn't satisfied with the way the blot turned out and didn't have time to deal with it that day. I put the membrane back in the same antibody prep overnight and tried to develop it the following day. My film was blank even after I left it down for over an hour. This also frequently occurs when blotting for loading proteins after successfully blotting for the protein of interesting. In most cases, the membrane has not been stripped, and in all cases, the marker is still visible on the membrane. We use PVDF (soaked in methanol and the transfer buffer prior to the transfer). This issue seems to occur regardless of the target protein (tags on overexpressed proteins, endogenous tricky proteins, loading controls). Is it possible for protein to diffuse off of PVDF? None of us can think of a reasonable explanation, and are pretty frustrated at this point. Any ideas are appreciated!