Friday, July 17, 2020

New modified fingerprint chemical that fluoresces touch DNA on clothing

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Michael Whyte
Crime Scene Officer and Fingerprint Expert with over 12 years experience in Crime Scene Investigation and Latent Print Analysis. The opinions or assertions contained on this site are the private views of the author and are not to be construed as those of any professional organisation or policing body.
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In sexual assault and burglary investigations, the recovery of DNA from items that have been handled by the suspect is very important. This is called touch DNA analysis and is a key technique in forensic investigations.

When examining clothing for touch DNA, traditionally the Forensic Investigator has relied upon CCTV footage or witness/victim testimony in order to target the correct area for sampling. This can often be a difficult and time consuming process and there’s no guarantee the examiner is targeting the correct area that will yield a DNA profile. It’s only after the sample is analysed that this confirmation is provided and if unsuccessful, the Forensic Investigator can target a different area.

What if there was a way to visualise exactly where the touch DNA is located on the clothing… What if it glowed under a florescent light source that it made it ideal to be photographed and recorded correctly. Well that’s exactly what these Japanese researchers reported on in their study published in Forensic Science International: Genetics.

The researchers developed a modified formulation of a fingerprint development chemical known as DMAC (p-dimethylaminocinnamaldehyde). The conventional DMAC method mainly develops fingerprints deposited on paper, thermal paper, and bills by heating with DMAC in a fume hood or placing the forensic sample between two sheets of copy paper that have been soaked in DMAC. To date, no method has been developed for spraying DMAC on clothing directly to visualise touch DNA from finger or palm prints that may have had contact with it. 

In the study, the researchers sprayed the modified DMAC solution onto clothing and left for 2 hours before visualising it under irradiation with a blue LED light (452nm). Not only were they able to visualise the touch DNA from where the finger and palm prints made contact with the shirt but they were also successful in obtaining DNA profiles from the target areas.

A latent finger and palm print was deposited on a T-shirt (100% polyester) for 10 s. The print was developed by spraying with DMAC solution and then visualized 2 h later with a 550-nm longpass camera filter under irradiation with a blue LED (452 nm).

The researchers concluded that that use of the DMAC solution and irradiation with a blue LED did not adversely affect the DNA extraction, quantification, or amplification processes for STR analysis.

The researchers want to investigate a larger variety of types of clothes and biological samples in future. However, their study shows that DMAC treatment of touch DNA on materials is useful for forensic investigations.

For more information about the research, in particular the formulation of the modified DMAC reagent;

Read the Paper Here

Development of a modified p-dimethylaminocinnamaldehyde solution for touch DNA analysis and its application to STR analysis, Forensic Science International: Genetics, https://doi.org/10.1016/j.fsigen.2018.10.007

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