Sample Integrity: The Key to Success
Nucleic acids are the backbone of molecular biology research. As such, preservation of their integrity and purity is fundamental for genomic research. Low quality samples can lead to inconsistent results, inaccurate data, and incorrect concentration measurements.
DNA and RNA, however, are prone to degradation particularly when stored incorrectly. They are especially sensitive to depurination, deamination, depyrimidination, hydrolytic cleavage, nuclease contamination, and oxidation. Incorrect temperatures, contamination from nearby samples, and freeze-thawing can all have detrimental effects on nucleic acid samples.
While labs may sometimes encounter difficulties in correctly storing DNA and RNA due to cost limitations, lab space restrictions, or lack of appropriate pre- and post-extraction storage consumables knowledge, a host of solutions are available to accommodate any budget or laboratory space, as will be discussed.
Off to a Good Start: Handling Raw Materials
Downstream molecular results are only as good as the nucleic acids that were used to generate them; optimal results rely on good sample collection, preservation, and storage. This is especially pertinent when nucleic acid collection sites are in remote locations.
Raw materials including polymerases, primers, nucleotides, and buffers can fall victim to damage or degradation when handled incorrectly. In fact, nucleic acid synthesis materials are prone to many of the same problems as the DNA/RNA product itself, including freeze-thaw effects, deterioration, and contamination.
The correct storage consumables and devices are indispensable when handling raw materials used in DNA or RNA synthesis. Samples should be aliquoted into smaller quantities where appropriate, and stored in consumables engineered to mitigate risk and preserve integrity.
From Collection to Storage: Quality, Traceability, and Automation
The quality of collection and storage containers when working with DNA, RNA, and raw materials is an area of consideration that should not be overlooked. It is recommended to use sample storage consumables that are free from common contaminants such as DNAse and RNAse. Keep in mind that every consumable used in an experiment should meet the same high standards including pipette tips. Nuclease-free products are particularly relevant when working with forensic samples, which must be certified forensic DNA grade, i.e., free of human DNA, DNase, and RNase.
When selecting sample storage consumables, an important feature to look for is the incorporation of 2D barcodes that facilitate full traceability for accurate tracking throughout sample processing. Automation-friendly 2D barcodes help to streamline the transport of samples to different sites. Furthermore, 2D barcodes enable the ability to interface with laboratory information management systems (LIMS) to provide audit trails of sample history as well as quell security concerns by simplifying dual identification.
Sample sharing and sample standardization drive the need for dual barcode identification. In addition to 2D barcodes, human-readable “1D barcodes” are a useful feature of any storage consumable; they provide an additional layer of security in terms of sample identification and simplify sharing with remote sites that may not have 2D barcode capability.
Container size and type are other factors to consider, to ensure compatibility with downstream processing, to preserve sample integrity, and to maximize space. Choosing storage devices that prevent sample-to-tube adhesion is also a good tactic.
In general, the lower the temperature, the greater the stability of nucleic acids. This is especially true for highly dilute samples (Smith and Morin, 2006).
For long-term storage of nucleic acids (months to years), it’s common practice to store nucleic acid samples in freezers at -20 °C or -80 °C, or cryo-preserved in liquid nitrogen (-196 °C), all of which are reliable solutions that come in a range of formats for any laboratory space.
When storing nucleic acids long-term in liquid nitrogen, it is common to precipitate the sample in ethanol beforehand. When storing nucleic acids at -20 °C or -80 °C, Tris-EDTA is typically added to the samples. These measures help to prevent chemical and enzymatic degradation.
For short-term storage (days to weeks), nucleic acids are generally stored in a Tris-EDTA at +4 °C. It’s important to keep in mind that Tris and other additives can cause problems downstream, such as inhibition of certain PCR reactions. However, by following buffer recommendations from the supplier, these issues can be avoided. Advantages to storing nucleic acid samples at +4 °C in the short term include avoidance of repeat freeze-thawing, and energy cost savings.
Storage temperature is recognized as being critical to long-term DNA stability (Ivanova and Kuzmina, 2013). And because genomic samples increasingly need to be stored in great numbers for large-scale genetic studies and for medical, clinical, pharmaceutical, and forensic applications, it’s more important than ever before to choose the correct storage strategy to prevent nucleic acid deterioration.
Cold Storage Necessities
Refrigerator, freezer, and cryopreservation system design is fundamental to storing nucleic acids. Today there are many options available to suit any budget, need, or space.
Laboratory-grade refrigerators and freezers offer key benefits over domestic or retail models, including microprocessor-controlled setpoints and electrical output signals. Significant features to look for in a freezer or refrigerator for nucleic acid samples include the ability to hold a uniform temperature, and the presence of temperature monitors and alarms in case of power outages.
They are available in several formats allowing multiple freezing profiles, remote temperature control, and protection from heating or temperature fluctuation. Frost-free freezers help to protect nucleic acids from water contamination and are capable of holding various types of vials, tubes, and racks.
Cryogenic storage solutions include liquid nitrogen dewars and canisters. These are also available in several set-ups to allow various types of nucleic acid sample container to be frozen at liquid nitrogen temperature (-196 °C). A good dewar or canister will allow multiple boxes to be stored and organized in an accessible manner, and include features to minimize liquid nitrogen evaporation. Storing at liquid nitrogen temperatures ensures that samples remain at cryogenic conditions even in the event of a power failure. When working with liquid nitrogen, remember to always use appropriate accessories and PPE.
Biobanking: A Critical Piece of the Puzzle
Biobanks are integral components of modern genomic research, combining sample storage with data and automation. Data from biobanks enables new therapies to be developed through collaborations between medical professionals and researchers worldwide, which is especially relevant for today’s evolving personalized medicine research.
Pay-per-sample or -service biobank models are becoming increasingly popular, elevating the role of biobanks in today’s research. These models allow sample sharing between labs, and enhances confidence in data owing to the associated background and historical information linked to any biobanked sample, whether stored in a local biorepository or a remote location.
Biobanks are ideal for long- and short-term storage of DNA, RNA, DNA libraries, and oligonucleotide stocks. They permit appropriate, secure storage, allowing researchers to easily access biobank data for genomic research or other studies. Modern pay-per-service models are revolutionizing the sharing of genetic materials by providing easy access to samples and data from anywhere in the world, which is helping to further genomic research.
For research groups that do not have the resources to maintain an automated biobank, remote biobank storage is essential to successful research. For labs in this position, sample storage consumable features to look for to ensure smooth biobanking integration include tubes that feature 2D barcodes, and common format labware for compatibility with downstream processing.
Nucleic acids are pivotal to a myriad of downstream applications, so choosing suitable storage consumables and devices is no small task. A high-quality storage tube or container will allow for fast freezing, prevent sample loss upon opening, resist physical damage, be compatible with common buffers, and be free of nucleases, DNA / RNA-binding agents and other denaturing materials. Appropriate sample storage devices will prevent freeze-thaw effects and contamination, as well as have superior features to ensure appropriate, safe storage. The correct consumable-equipment combination enables seamless labeling, automation, and organization of hundreds or thousands of samples. Thermo Fisher Scientific has a vast range of flexible solutions to help you make the right choice, no matter your space or budget.
S. Smith and P.A. Morin, “Optimal storage conditions for highly dilute samples: a role for trehalose as a preserving agent,” J Forensic Sci 50(5):1101-1108, 2005.
N.V. Ivanova and M.L. Kuzmina, “Protocols for dry DNA storage and shipment at room temperature,” Mol Ecol Resour 13(5):890-898, 2013.
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