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Samples storage conditions
The correct storage conditions of samples for biological, medical and scientific research are incredibly important due to the precious nature of the samples. Sample types have their own individual characteristics, and therefore each sample will require its own storage method to avoid degradation. It is critical to know which temperature is ideal based on the duration that the sample needs to be stored for and kind of sample material being stored. There are a few different options for preservation temperature, samples can be kept at either: +20°C (ambient temperature), at +4°C (in the refrigerator), -20°C (in the freezer), at -80°C (in the ULT freezer) or in a liquid nitrogen cryogenic tank or freezer (for -150°C and lower). For long term storage you would typically use an cryogenic or ULT freezer, the other options are mostly used for shorter term storage. Below is a breakdown of in which situations you may store samples at each temperature (this is just a basic guideline, as mentioned previously, each sample material will have specific conditions that need to be met).
Ambient sample storage
Ambient temperatures are only suitable if the sample material is preserved in a protective solution, for example hair or blood on filter paper. For longer term preservation it is usually recommended to store them in a freezer to preserve the quality of the sample. However, room temperature sample storage (RTSS) is on the rise where it is possible to do so. This method enables safe storage of biological material at room temperature. Where it is possible it can be highly beneficial, as it eliminates the need for cold storage and cold shipping, providing a cost-effective alternative. Newly developed chemical stabilizers allow materials such as purified DNA and RNA to be stored at room temperature. Formalin-fixed paraffin-embedded tissue can also be stored at ambient if the samples will only be used for histology in the future. Some proteins and antibodies might also be damaged by freezing and thawing.
Refrigerated sample storage
Samples that are recommended to be stored in a refrigerator (at a minimum) for short-term storage are items like fresh tissue, organs, DNA, RNA and other active proteins. Fresh biofluids can also be stored in the refrigerator for short term preservation but if the samples are required in a component study later on it is advised to keep them in the freezer, even for short-term storage. Most of these sample types should be stored in an ultra-low freezer or cryogenic tank/ freezer for longer term storage.
Freezer sample storage
The freezer can be used for the short-term storage, for example with some cells, but if they need to be kept functional, they should always be kept at cryogenic temperatures. Sample types such as tissue, organs, blood, hair, or nails that can be stored for short-term in either ambient temperature or in the refrigerator should be kept in a freezer when storing them for longer term. Even for short-term storage, some samples should always be kept in a frozen environment. Materials such as bacteria, nucleic acids, steroid hormones or biofluids that are intended for component studies.
Cryogenic sample storage
Finding the ideal storage temperature is more complex for some materials such as bone marrow, stem cells, sperm, etc. If the cellular structure of a sample needs to remain untarnished, a specific protocol to optimise preservation will likely need to be designed. For mammals, fish, and plants, this usually involves temperatures of -130°C and colder. The reason -130°C is because it is the glass transition point of water and most biological activity is halted at these temperatures, meaning samples can be preserved for many years if needed without being affected very much. Cryogenic tanks are typically used for this, however Withnell Sensors partner Angelantoni with the patented and revolutionary SmartFreezer, the first and only fully automated liquid nitrogen cryofreezer.
Costs and solutions
Ultra-low temperature (ULT) and cryogenic freezers are essential storage devices for biological samples forming a vital part of many biobanks, clinics, and laboratories all around the world. However, the cost to purchase is quite high due to their specialist engineering and ULT freezers also consume a huge amount of energy. A lot of freezers can be poor for the environment too so choosing one that uses an eco-friendly refrigerant with a low GWP (global warming potential) is important.
For example, for one of the most common types of sample storage freezer, the upright -80 freezer, a constant power supply is required to maintain the low temperatures. It has been said that the average ULT freezer consumes roughly 20kWh per day- the same amount of energy as a single-family home. With the price of electricity currently standing at £0.28 per kWh that is £5.60 per day and £2044 for the year.
Solutions to this are energy efficient freezers like the NEXUS green line. These ULT freezers can generate significant reductions in consumption (up to 30%). They also use eco-friendly refrigerants with a much lower GWP to lower the environmental impact.
Another option would be off site storage. Not only does mean you don’t need to purchase a freezer, maintenance and running costs are eradicated and the cost of a monitoring system and its calibration aren’t necessary. Staffing for the freezer is no longer required, allowing employees to focus on more important work than checking on samples in storage. This also allows you to free up space in house and provides risk mitigation for your precious samples.
