You can preserve DNA at home by storing it in alcohol within a tightly sealed container.
Preserving DNA at home, usually after extracting it from a sample like saliva, requires a method that inhibits degradation and contamination. The most common and straightforward method involves using alcohol. Here's a breakdown:
Best Method: Alcohol Precipitation and Storage
Why Alcohol Works
- Dehydration: Alcohol dehydrates the DNA, making it less susceptible to enzymatic degradation.
- Precipitation: DNA is not soluble in alcohol, causing it to precipitate out of solution, making it easier to handle and store.
- Inhibition of Enzymes: Alcohol inhibits the activity of enzymes like DNases that can break down DNA.
Steps for Preservation
- Extraction: First, you need to extract the DNA. This is typically done using a DNA extraction kit readily available online or from scientific supply stores. You can also use simpler methods involving household items like salt, dish soap, and rubbing alcohol, but the purity will be lower.
- Alcohol Precipitation: Add cold (ideally frozen) 70-95% isopropyl alcohol (rubbing alcohol) or ethanol to the DNA solution. The ratio of alcohol to DNA solution is usually around 2:1 or 3:1.
- Incubation: Gently mix the solution and let it sit (incubate) at a cold temperature (like -20°C or in a freezer) for at least 30 minutes, or preferably overnight. This allows the DNA to fully precipitate. You should start to see a cloudy, white precipitate forming.
- Pelleting: Carefully centrifuge the tube at a low speed to pellet the DNA. If you don't have a centrifuge, let the DNA settle to the bottom of the tube naturally (this will take much longer).
- Washing (Optional): Carefully remove the supernatant (the liquid above the pellet) without disturbing the pellet. Wash the pellet with cold 70% ethanol to remove any remaining salts or contaminants. Centrifuge again briefly, then remove the ethanol.
- Drying: Allow the DNA pellet to air dry completely. This can take 30 minutes to a few hours. Crucially, do not over-dry, as this can make the DNA difficult to re-dissolve.
- Storage: Once dry, re-suspend the DNA in a suitable buffer, such as TE buffer (Tris-EDTA), or sterile distilled water. You can also store the DNA directly in 70% ethanol. Store in a tightly sealed, sterile container. For long-term storage, keep the sample in a freezer (-20°C or -80°C).
Important Considerations:
- Sterility: Use sterile containers and solutions to prevent contamination.
- Temperature: Keep the DNA cold during the precipitation and storage process.
- Agitation: Avoid vigorous shaking or mixing, as this can shear the DNA, breaking it into smaller, less useful fragments. This is especially important for high molecular weight DNA applications.
- Container: Use a tightly sealed container to prevent evaporation and contamination. Glass or polypropylene tubes are suitable.
Avoiding Degradation
DNA degradation can occur through several pathways:
- Enzymatic Degradation: DNases (enzymes that degrade DNA) are ubiquitous. Using sterile techniques and storing DNA in alcohol helps to inhibit DNase activity.
- Hydrolytic Degradation: Water can also contribute to DNA degradation over time. Storing DNA in a dehydrated state (alcohol) minimizes this.
- Oxidative Damage: Exposure to oxygen and free radicals can damage DNA. While not typically a major concern for short-term storage, antioxidants in the storage buffer can help prevent this for long-term archiving.
Storage Duration
When stored properly using the alcohol precipitation method described above, DNA can last for several years. Freezing (-20°C or -80°C) provides the best long-term storage conditions.
