In comparison to sensitive proteins such as enzymes, antibodies are highly stable proteins that retain activity in a wide range of biological conditions. As a result, storage is reasonably straightforward and should focus on two key considerations: 1) antibodies are sensitive to repeated freeze/thaw cycles and 2) excessive protein concentration dilution, particularly of purified antibody, can result in material losses and reductions in antibody stability.

Short-term Storage:
Unpurified serum that contains sodium azide can be stored at 4°C for 2-3 months at a time. Unpurified serum without azide, however, should be kept at -20°C in order to avoid bacterial growth. Purified antibodies, which contain azide by default, can also be stored at 4°C for 2-3 months at a time to allow for use without repeated freeze/thaw cycles.

Long-term Storage:
For long-term storage, we recommend storing serum vials and aliquots of purified antibody at -20°C. Storage at -80°C isn’t necessary.

Aliquoting Purified Antibody:
The purified antibody (which contains sodium azide) can be safely stored at 4°C for 2-3+ months at a time in order to avoid freeze/thaw cycles. For long term storage, however, we recommend aliquoting the purified antibody into several vials and storing these at -20°C. Each vial, which should contain enough purified antibody to cover use over a typical working period (2-3 months for example), can then be thawed a single time and stored at 4°C until depleted.

Antibody Concentration:
At low protein concentrations, antibody stability suffers and can lead to protein losses. Mechanically increasing antibody concentrations should also be avoided, since this will also typically cause protein losses. BSA can be added to purified antibody aliquots to increase concentration and improve stability (assuming that this doesn’t interfere with the assay system).

Freeze/Thaw Cycles:
Repeated freeze/thaw cycles represent a significant risk to antibody stability, especially with purified antibody (which is at a lower protein concentration in comparison to serum). In addition to following the guidelines above, we recommend the use of manual defrost freezers rather than frostless freezers.

Sodium Azide:
Sodium Azide is an antimicrobial agent that prevents the growth of bacteria in the serum or purified antibody. Azide is not added to the serum by default, but can be added upon request at no additional charge. Azide is added to all purified antibodies and columns by default in order to avoid contamination and to allow for storage at 4°C. It is important to note that sodium azide is not recommended for some applications. In particular, sodium azide blocks the cytochrome electron transport system, making it toxic to most organisms. Sodium azide can be dialyzed out of the serum if necessary.

Affinity Columns:
Affinity columns should be stored at 4°C and should not be frozen. Sodium Azide is added to these by default to avoid contamination and to allow for longer term storage at 4°C.

The addition of glycerol can help avoid freeze/thaw cycles while keeping antibodies or serum at -20°C. However, it is not necessary if the above guidelines and aliquot strategies are followed.

Next: Peptide Blocking Assay