Key Considerations for Reliable Biological Sample Storage
Making sure samples are stored in optimal, consistent environmental conditions is essential to maintaining their integrity, and ultimately achieving accurate, reproducible study results.
But ensuring suitable biological sample storage conditions isn’t always straightforward. Optimal storage environments can vary significantly depending on the sample type, preservation method, and storage duration.
Here, we outline some consequences of improper sample storage, as well as key considerations and best practices for making sure your precious samples stay protected.
Consequences of inadequate biological sample storage
Improperly stored biological samples introduce several risks:1
- Inaccurate or unreliable data: even small temperature deviations can compromise sample quality, impacting the reliability and reproducibility of study results
- Unexpected delays and increased costs: if sample quality degrades such that samples are unusable, the samples will need to be replaced, which can prolong study timelines and increase costs. Some samples, such as rare patient biopsies, may be irreplaceable, so their loss could halt a project altogether.
- Regulatory non-compliance: inadequate storage conditions can put you in violation of regulatory guidelines, which can have legal consequences
In short, ensuring that samples are stored under optimal conditions isn’t just a best practice — it's a necessity.
Which biological samples can be stored where?
Choosing the right storage temperature is fundamental to sample protection. But different types of biological materials have different requirements. Understanding these requirements, and storing your samples accordingly, helps ensure your samples remain viable for their intended use
Room temperature (15°C to 27°C)
Room temperature storage is suitable for samples preserved in protective solutions such as paraffin or formalin. Thanks to advancements in chemical stabilization, some DNA and RNA samples can also be stored at room temperature2 — an option that offers both energy and cost savings relative to cold storage.
Refrigerator (2°C to 8°C)
This temperature range is ideal for the short-term storage of biological reagents, buffers, and freshly collected tissue or blood samples that may need to be accessed frequently.
Freezer (-20°C)
General guidance for handling samples stored in freezers:
Proper sample handling is essential when working with materials stored at freezer temperatures. Rapid thawing can cause damage to samples, so when removing them from the freezer, it is best to place them on ice to slow down the thawing process. Undergoing frequent freeze/thaw cycles also risks degrading sample integrity. Storing samples in smaller aliquots where possible and only defrosting what you need can help keep samples protected from freezer/thaw damage.
A standard freezer is appropriate for storing samples and reagents that are unstable at higher temperatures (but that don’t require ultra-low conditions) and are used routinely. DNA and RNA can also be stored in a freezer short-term, if they are preserved in appropriate stabilizing solutions.
Since freezing happens relatively slowly at -20°C, there is an increased risk of ice crystal formation in standard freezers, which can damage samples. To minimize this risk, use smaller aliquots or pre-cool sample containers before placing them in the freezer.
Ultra-low temperature (ULT) Freezer (-80°C)
ULT freezers are ideal for long-term storage of biological samples like tissues and cells. As such, ULT freezers are especially useful for storing samples for retrospective studies, which may need to be examined months or years after collection.
Cryogenic storage (-150°C or lower)
Cryogenic temperatures effectively suspend all biological activity, making them the optimal environment for long-term sample storage of more complex tissues, such as stem cells, embryos, and bone marrow.
Cryogenic storage solutions come in two main types: liquid nitrogen (LN
2) and mechanical. Generally, mechanical freezers are preferred as they have lower costs, are better for the environment, minimize risks of cross contamination, and are safer, but, if you require rapid sample cooling, LN
2 freezers may be preferable. For more information on LN
2 vs. mechanical freezers, read our
recent whitepaper on the topic.
Maintaining consistent biological sample storage temperatures
No matter what temperature range you';re storing your samples at, consistency is key. Even brief fluctuations in temperature can cause damage to some biological samples, potentially impacting study results.
Room temperature
While the acceptable temperature ranges here may be broader than those in cold storage, it’s still important to ensure that conditions remain stable. Samples should be housed in a climate-controlled room to avoid any major fluctuations in temperature caused by seasonal changes or air conditioning cycles, for instance.
Cold storage
Samples that are stored in cold storage, especially in ULT and cryogenic freezers, are inherently more sensitive. Even slight deviations in temperature can risk compromising their integrity which can, in turn, impact the accuracy of study results.
To help maintain consistent temperatures, look for a cold storage unit with the following characteristics:
- Door alarms to alert users when the door has been open for too long, helping prevent unnecessary temperature excursions
- Back-up power systems to ensure that, in the event of a power outage, the unit can remain functional until power is restored
- Dual compressors so that if one compressor fails, the other can continue to keep the unit running until it can be repaired, avoiding sample losses
- Dependable temperature uniformity and recovery to reliably maintain uniform temperatures throughout the chamber, and allow for a quick return to the set temperature following door openings
Evaluating these metrics before purchasing a new unit is essential for reliable preservation of biological samples. You can find out more on assessing cold storage metrics
in our Decoding the Data eBook.
Regulatory considerations for traditional vaccine storage
For traditional vaccines, maintaining consistent storage conditions is not only essential for vaccine integrity, but is also a regulatory requirement.
The Centers for Disease Control and Prevention (CDC) makes several important recommendations to ensure cold storage chains are maintained, and vaccines are protected:3
- Use purpose-built pharmaceutical-grade units: these units are specifically designed for the storage of biologics (including vaccines), offering more precise temperature control and more reliable temperature uniformity and recovery
- Ensure there is enough space in the unit: the cold storage unit should be able to accommodate your maximum inventory without overcrowding. Overcrowding can restrict airflow, resulting in uneven temperatures and an increased risk of vaccine degradation
- Equip each unit with a temperature monitoring device (TMD): the CDC specifically recommends using a digital data logger (DDL), which provides the most detailed temperature information, including information on how long a unit has been operating outside the recommended temperature range
- Maintain units regularly: routine maintenance helps to ensure your equipment is functioning efficiently and can prevent issues such as temperature fluctuations caused by aging components or failing seals
Ensuring long-term sample integrity
Effective biological sample storage is all about understanding the specific conditions your samples need and maintaining those conditions consistently. Finding a sample storage solution that offers reliable, consistent protection is essential for preserving sample integrity and, ultimately, achieving reliable study results.
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