Hola ! 

Kept it at -80 ºC in 5% skin milk for several months, it works. You can do some low-volume aliquots in order to avoid freeze and unfreeze many times.

Hi there,

Diluted primary antibody may be kept several days at 4°C in the presence of 0.02% NaN3 to avoid microbial growth in the skimmed milk.

Thank you!

Hola ! 

Kept it at -80 ºC in 5% skin milk for several months, it works. You can do some low-volume aliquots in order to avoid freeze and unfreeze many times.

Agree with Daniel, regarding storing in small(single use aliquots). 5% non fat skim milk in PBS + Tween 20 (0.5%). azide can interfere with assay activity and isn't really necessary if you store at -80

Well if the purpose is to probe more than two membranes within the same week then storage at 4°C is better. If the purpose is to save a diluted antibody used once for the next probing which is not planned in the same week then freezing is better. About azide if the primary antibody is not conjugated to any enzymatic activity then it's not a problem as it will be washed away prior the application of the secondary antibody bearing the conjugated activity.

For more info, you may read the following:

http://www.biocompare.com/Bench-Tips/135857-Western-Blot-Antibodies-Ready-Set-Reuse/

Thanks, I´m planning to run the experiments in the same week, so I guess storage at 4ºC should work.

I have used dilutions with 3% BSA or 5% milk for first antibody, without azide. This dilution as Daniel Gutierrez wrote, can be kept at-80 but I have it stored at -20 several times in order to recycle the antibody,( for example 6 times), and it works well. An important thing is, sometimes or the companies suggest don´t use milk  solutions when you are going to use Protein Streptactin-HRP for the development step, because milk has high biotin and the signal decrease. I have not sure about this last, because I prefer use 3% BSA. 

I have good experience with R&D Systems and Sigma antibodies, I have not used those from Santa Cruz

I have diluted the primary antibody in PBS in blocking solution (5% milk +0.1% tween 20 in 1x PBS) or in 0.1% TTBS