Touch DNA, also known as trace DNA, is collected when cells are left behind on surfaces through contact. This can happen through:
- Touching: Simply touching an object can transfer skin cells.
- Holding: Gripping an object leaves behind more cells.
- Sneezing or Coughing: Droplets expelled during these actions can deposit DNA.
Touch DNA Collection Methods:
There are several methods used to collect touch DNA:
1. Swabs:
- Cotton swabs: These are the most common method. They are moistened with a sterile solution and rubbed over the surface to collect DNA.
- Nylon swabs: These are more effective at collecting DNA from porous surfaces like fabric.
2. Tape Lifting:
- Adhesive tape: This method is used to collect DNA from smooth surfaces like glass or plastic. A piece of tape is pressed onto the surface and then removed, taking with it any trace DNA.
3. Vacuuming:
- Vacuum cleaner: A specialized vacuum cleaner with a filter can collect DNA from large areas. This is often used in crime scenes.
4. Cutting:
- Scissors or a knife: This method is used to collect DNA from fabric or other materials that can be cut. The cut portion is then analyzed for DNA.
Considerations for Touch DNA Collection:
- Surface: The type of surface affects how much DNA is collected. Smooth surfaces like glass or plastic typically have less DNA than porous surfaces like fabric.
- Time: The amount of DNA present on a surface decreases over time as it degrades.
- Contamination: It is important to avoid contaminating the sample with DNA from other sources. This can be done by wearing gloves, using sterile equipment, and minimizing contact with the evidence.
Analyzing Touch DNA:
Once collected, touch DNA is analyzed in a laboratory using polymerase chain reaction (PCR). This process amplifies the DNA, making it possible to identify the individual who left the sample.
