All freezers (-20C) we have are forest free. Is it safe to keep antibodies in those freezers? If safe, how many months?
Samples in a modern, properly operating frost-free freezer set at -20°C will not normally thaw during the defrost cycle. The defrost heater doesn't heat the storage chamber, it only heats the cooling coils to melt the ice that collects on them, and they are in a separate insulated compartment. This constant removal of moisture makes the cold air in the storage chamber extremely dry, so that any frost that forms when the freezer is opened simply evaporates. However, this also means that small-volume samples in simple snap-cap tubes can dry out over time.
In a frost-free freezer, the cooling elements are subjected to regular heating cycles to remove ice buildup. At least some of the contents will also thaw and freeze repeatedly. There's no universal answer for how many cycles or how much time must elapse before your experiments are affected. It will depend on the specific antibody and your freezer and where the antibody is within the freezer. To be safe, use a non-frost-free freezer and store antibodies in small aliquots to minimize freeze-thaw cycles.
I have stored aliquots of antibodies in cardboard boxes in our frost-free freezer for years that have continued to perform well. The one antibody that I recall "going bad" was an anti-GFP monoclonal from Covance Research Products. To be safe, I would use a Stratacooler or equivalent to keep your sensitive reagents at a constant temperature while the frost-free freezer cycles. We keep all our enzymes in such coolers.
I have not experienced any of our antibodies, tissue samples, or other proteins to be affected by frost free freezers because the freeze-thaw cycles in these type of freezers are very short bursts that do not necessarily drastically affect the overall temperature in the freezer, and therefore do not affect the contents. What destroys antibodies is the room temperature-very low temperature thaw like -20 to room temperature not a few degree change in temperature. When you use a freezer that is not freeze thaw and you need to defrost that freezer, you will have to take out your samples and expose them to drastic temperature changes--this is more detrimental to the integrity of the antibody or other proteins and tissues samples than a frost free freezer.
Zoraida, you bring up a good point. Slow temperature changes are the most detrimental to proteins, which is why we need practice rapid thawing and rapid freezing as well (using liquid nitrogen versus placing a purified protein aliquot in the freezer to slowly freeze).
Antibodies are very stable proteins. Freeze-thaw most likely is affecting the re-folding rather than degradation. the heating cycle is mostly near the walls.
Samples in a modern, properly operating frost-free freezer set at -20°C will not normally thaw during the defrost cycle. The defrost heater doesn't heat the storage chamber, it only heats the cooling coils to melt the ice that collects on them, and they are in a separate insulated compartment. This constant removal of moisture makes the cold air in the storage chamber extremely dry, so that any frost that forms when the freezer is opened simply evaporates. However, this also means that small-volume samples in simple snap-cap tubes can dry out over time.
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