Farash K, Hanson E, Ballantyne J (2014) Enhanced Analysis of Single Human Bio-Particles Recovered by Simplified Micro-Manipulation from Forensic ‘Touch DNA’ Evidence. Journal of Visualized Experiments. e52612: 1-13. doi:10.3791/52612

DNA profiles can be obtained from ‘touch DNA’ evidence, which comprises microscopic traces of human biological material. Current methods for the recovery of trace DNA employ cotton swabs or adhesive tape to sample an area of interest. However, such a ‘blind-swabbing’ approach will co-sample cellular material from the different individuals, even if the individuals’ cells are located in geographically distinct locations on the item. Thus, some of the DNA mixtures encountered in touch DNA samples are artificially created by the swabbing itself. In some instances, a victim’s DNA may be found in significant excess thus masking any potential perpetrator’s DNA

In order to circumvent the challenges with standard recovery and analysis methods, the study developed a lower-cost, ‘smart analysis’ method that results in enhanced genetic analysis of touch DNA evidence. The team describes an optimized and efficient micro-manipulation recovery strategy for the collection of bio-particles present in touch DNA samples, as well as an enhanced amplification strategy involving a one-step 5 µl micro-volume lysis/STR amplification to permit the recovery of STR profiles from the bio-particle donor(s). The use of individual or few (i.e. “clumps”) of bio-particles results in the ability to obtain single source profiles.

These procedures represent alternative enhanced techniques for the isolation and analysis of single bio-particles from forensic touch DNA evidence. While not necessary in every forensic investigation, the method could be highly beneficial for the recovery of a single source perpetrator DNA profile in cases involving physical assault (e.g. strangulation) that may not be possible using standard analysis techniques. Additionally, the strategies developed here offer an opportunity to obtain genetic information at the single-cell level from a variety of other non-forensic trace biological material.

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