The integrity of deoxyribonucleic acid (DNA) is dependent on proper handling and storage, a process known as DNA banking. This practice involves maintaining genetic material in a state that prevents chemical and physical degradation over time. Improper storage can render the sample unusable for future analysis, regardless of its original quality. Effective storage protocols ensure that the genetic blueprint remains accurate and accessible for decades.
The Purpose of Preserving Genetic Material
The decision to preserve genetic material is often driven by the need for future analysis in various fields. For the public, one common application is genealogical research, where stored DNA allows individuals to trace family lineage and ancestral origins by comparing genetic markers across generations. Forensic science relies heavily on banked DNA to identify individuals or link suspects to crime scenes, often utilizing specialized databases to match profiles. Furthermore, preserved samples are increasingly used in medical diagnostics to study inherited conditions and predict disease susceptibility. Analyzing stored DNA provides insights into genetic disorders, paving the way for personalized treatments and understanding health risks for future generations.
Preparing Samples for Long-Term Preservation
The actions taken before a sample reaches its final storage environment significantly influence its longevity. When preparing whole samples, such as buccal swabs or dried blood spots, the focus is on immediate stabilization to protect the nucleic acids. A common technique involves placing the sample directly onto specialized filter paper, like FTA cards, which contain chemicals that immediately lyse the cells and denature proteins. This chemical treatment binds the DNA to the card matrix while inactivating potential degradation agents like nucleases, allowing the whole sample to be stored at room temperature.
For purified DNA extracted from biological material, preparation shifts to resuspending the molecule in a protective solution. A standard choice is Tris-EDTA (TE) buffer, where the EDTA component acts as a chelating agent to bind metal ions that could otherwise catalyze damaging chemical reactions. Storing DNA as a completely dried pellet, often achieved through lyophilization or air-drying, offers an alternative to remove water, which is a key driver of DNA breakdown.
Common Storage Methods and Environments
The physical conditions of the storage environment are the primary determinant of a sample’s long-term viability. For short-term use, purified DNA resuspended in TE buffer is often kept refrigerated at $4\,^\circ\text{C}$ for several months, or frozen at $-20\,^\circ\text{C}$ for storage lasting a year or more. Maintaining a consistent, low temperature significantly slows the rate of damaging chemical reactions.
Long-term preservation, particularly in laboratory settings like biobanks, relies on ultra-low temperature (ULT) freezers set at or below $-80\,^\circ\text{C}$, which is considered the gold standard for freezing DNA. Storing samples at this temperature prevents the degradation of nucleic acids for decades by halting virtually all enzymatic and chemical activity. To prevent damage from repeated temperature fluctuations, samples intended for frequent use are often divided into smaller portions, known as aliquots, so that only the necessary amount is thawed at any one time.
An alternative involves storing the DNA in a dry state at room temperature, a method increasingly used for consumer-level kits and specialized lab archives. This dry storage method, often involving a stabilization matrix like the FTA card, eliminates the need for expensive freezers and constant power supply. Whether stored dry or frozen, the samples must be kept in sterile, airtight containers to prevent contamination and minimize exposure to moisture and light, especially UV radiation.
Understanding DNA Degradation and Shelf Life
DNA molecules are susceptible to various forms of damage that ultimately determine the sample’s shelf life. The most significant factor causing breakdown is hydrolysis, a chemical reaction where water molecules attack and cleave the phosphodiester bonds that form the backbone of the DNA strand. This reaction is accelerated by heat and moisture, which is why dry storage methods or low-temperature freezing are employed to mitigate water’s damaging effects.
Another major threat is oxidation, which occurs when reactive oxygen species attack the nitrogenous bases of the DNA, particularly guanine. This damage can lead to base loss and strand breaks, compromising the genetic code’s integrity. Heat exposure also increases the rate of depurination, further weakening the molecule.
The shelf life of a sample is drastically affected by the storage method chosen. DNA stored in an aqueous solution at room temperature may only remain viable for several months, whereas storage in TE buffer at $4\,^\circ\text{C}$ extends this to about a year. Conversely, storing purified DNA at $-80\,^\circ\text{C}$ can preserve the material for decades, while stabilized, dried DNA stored at room temperature maintains integrity for at least several years, offering a practical alternative for long-term archiving.