When designing a new protocol for biosample storage, a fundamental point to consider is the temperature at which the collection will be maintained. Optimal storage temperatures depend on a variety of factors, such as sample type, container design, expected storage time and planned future assays, and essentially, biobank storage temperature options fall into five main categories:
- room temperature (+20°C),
- refrigeration (+4°C),
- frozen (-20°C),
- ultra-low (-80°C) and
- cryogenic (-196°C).
Given that samples stored at lower temperatures are typically better preserved, it may come as somewhat of a surprise that some biosamples are best stored at temperatures above the freezing point of water. What’s more, freezing is sometimes unnecessary –and could even be detrimental for certain samples.
To illustrate my point, here’s a short list of sample types that can be stored at temperatures above the freezing point of water:
- Purified DNA and RNA. Thanks to newly-developed chemical stabilizers (PDF), purified DNA and RNA can both be stored at room temperature. Studies have shown genetic material can be stored for years this way without any loss in quality.
- Formalin-fixed paraffin-embedded (FFPE) tissue. Formalin-fixed paraffin-embedded (FFPE) tissue can also be stored above freezing. If the samples will only be used for histology in the future, they can be stored indefinitely at room temperature. However, if you intend to extract DNA or RNA from the samples, it’s much better to store them at 4°C.
- Proteins prone to denaturation. Some biosamples, such as certain proteins and antibodies, might be damaged (denatured) by freezing –particularly if they undergo several freezing and thawing cycles. Samples at risk of denaturation should be maintained under refrigeration, but it’s important to know how long they can remain active under those conditions. The same rules apply to biological samples that will be used for protein or antibody studies; if freezing the whole sample damages the protein or antibody under investigation, you’ll need to determine an alternative storage method.
Before trying a new storage protocol on irreplaceable biosamples, conduct a small pilot study to ensure samples won’t be harmed. Stanford University used a small-scale study (PDF) in 2009 to determine if biosamples could be moved out of freezers and into room temperature storage. The result: no loss in sample quality and a possible $1.2 to 1.4 million savings in yearly electrical bills. (Higher storage temperatures also eliminate the need for bulky freezers, saving space and possibly other resources, as well.)