A DNA swab is a cotton-tipped applicator used to gather cells from the inside of a person’s cheek. These buccal cells contain deoxyribonucleic acid (DNA), which is then used for various analyses. DNA swabs serve many purposes, including forensic investigations, paternity testing, ancestry research, and medical diagnostics. Maintaining the integrity and stability of the collected DNA is important for accurate and reliable test results.
Factors Influencing DNA Degradation
Several environmental and biological factors can cause DNA on a swab to degrade, making it difficult or impossible to analyze. High temperatures can directly damage DNA by breaking its chemical bonds. Even lower temperatures can cause significant damage, particularly in the presence of moisture.
Humidity and moisture accelerate DNA degradation by promoting the growth of microorganisms that produce enzymes. Additionally, exposure to light, especially ultraviolet (UV) radiation, directly harms DNA by altering its structure. Chemical contaminants, such as certain fixatives or combustion byproducts, can further compromise DNA integrity.
Maximizing DNA Preservation
Proper collection and storage methods are important for extending the viability of DNA on a swab. Before collection, it is often recommended to avoid eating, drinking, or smoking for at least 30 minutes to minimize contamination of the sample. Once the sample is collected, the swab should be air-dried promptly to remove moisture, which helps prevent microbial growth.
For packaging, breathable paper envelopes are recommended. Plastic bags should be avoided for long-term storage because they can trap moisture, creating an environment conducive to microbial growth and rapid DNA degradation.
Ideal storage temperatures also play a significant role. For short-term storage, keeping swabs dry and away from direct sunlight at room temperature is generally suitable. Refrigeration between 2°C and 8°C can extend DNA viability for over a year.
For long-term preservation, freezing at -20°C or -80°C is recommended, allowing for storage over many years. Some commercial collection kits include stabilizing buffer solutions that allow DNA to remain stable at room temperature for extended periods.
Practical Lifespans for DNA Swabs
The practical lifespan of DNA on a swab depends heavily on how it is collected and stored. For buccal swabs stored properly in a dry, cool, room-temperature environment, DNA can remain viable for up to 6 months without significant degradation. If refrigerated, the DNA from buccal swabs can last for over a year.
For very long-term storage, extracted DNA or samples stored under frozen conditions (e.g., -20°C or -80°C) can be preserved for many years, sometimes even decades.
Consumer DNA testing kits often include specialized buffer solutions that stabilize the DNA, allowing samples to remain viable at room temperature for up to 6 months. Some advanced preservation systems can maintain DNA stability for over two years at ambient temperatures, with some companies reporting stability for up to 15 years.
Extracted DNA stored by some laboratories can even last over 20 years in robotic freezers.
In forensic contexts, the viability of DNA on swabs is similar to general use, provided proper collection and storage protocols are followed. However, the lifespan of DNA from other forensic sample types, such as dried blood or hair with roots, can vary widely from weeks to years, or even centuries in the case of bone and teeth, depending on environmental conditions.
The ultimate goal in all these applications is to ensure that enough high-quality DNA can be extracted for accurate analysis. Improper storage, involving exposure to heat, moisture, or bacterial contamination, can cause DNA to degrade rapidly, often within days to weeks, compromising the usability of the sample.