Collection method of touch DNA from Fabric and it’s Effect

What is Touch DNA?

Touch DNA is the DNA transferred from the suspect as a result of contact. Touch DNA, also known as Contact Trace DNA, is extracted from epithelial cells of the skin and transferred to surfaces when a person comes into contact with any surface. Traces of DNA carried from the perpetrator via interaction with evidence found at the crime scene can assist in the investigation in such circumstances.

How to Collect Touch DNA?

Touch DNA can be collected from a variety of surfaces, such as tools, door handles, and clothing, but it is more difficult to collect than other biological samples because the surface type, environmental factors, collection methods, collection techniques, and extraction kits can all affect the amount of Touch DNA collected. Cotton swabs, nylon swabs, and tapes are commonly used to collect touch DNA, and previous research has shown that different types of surfaces require different collection methods.

Salem K Alketbi conducted the study “The Impact of Collection Method on Touch DNA Collected from Fabric.” This study evaluated the effect of collecting method and extraction type on Touch DNA obtained from cloth.

There were three methods of data collection used: 

  • Copan cotton swab (150C) (CS),
  • Copan nylon flocked swab (4N6FLOQSwabs®) (NS), and,
  • Scene Safe Fast™ minitape (K545) (MT).

The Quantifiler® Trio DNA Quantification Kit, Quant Studio 5 Real-Time PCR (qPCR), and HID Real-Time PCR analysis software v1.3 were used to quantify the extracted samples (Thermo Fisher Scientific). The samples were amplification for 30 cycles using an ABI GeneAmp® 9700 PCR Results and Discussion System (Life Technologies, Foster City, CA) using the Global FilerTM PCR amplification Kit. On an ABI 3500 Genetic Analyzer (Life Technologies), amplified products were size-separated and identified using 1l PCR product, 9.6l Hi-DiTM formamide, and 0.4 GenescanTM 600 LIZ® Size Standard v2.0 (Thermo Fisher Scientific). Factorial analysis of variance (ANOVA) and Microsoft Excel were used in the statistical analysis.

After evaluating all three procedures, Scene Safe FastTM minitape (K545) excelled Copan cotton swab (150C) and Copan nylon flocked swab (4N6FLOQSwabs®) in recovering contact DNA from fabric.

 The type of collecting method used can affect the recovery of Trace DNA from clothing, with tape, such as minitape, being more suitable for obtaining DNA from porous surfaces like fabric.

Key Points

  • Touch DNA only requires seven or eight cells from the outermost layer of our skin.
  • PCR (Polymerase Chain Reaction) used to make lots of copies of the genes.
  • Genetic Profiles generated form fingermarks were first described in 1997 by RAH Van Oorschot et al.
  • Most common collection method of Touch DNA is ‘Swab Technique’.

Reference:

Salem K A. The Impact of Collection Method on Touch DNA Collected from Fabric. J Forensic Sci & Criminal Inves. 2022; 15(5): 555922. DOI: 10.19080/JFSCI.2022.15.555923

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