Detection of latent DNA in fingermarks using Diamond™ Nucleic Acid Dye

Abstract

Fingermark deposits on surfaces can be critical pieces of evidence in an investigation and may also contain latent DNA, often invisible to the naked eye. The purpose of this research was to investigate the use of Diamond™ Nucleic Acid Dye (DD) as a latent DNA screening tool for fingermarks on touched items relevant to a casework setting. This research explored different DD application methods on nonporous surfaces and investigated the ability to produce a DNA profile from these. An automated counting method was also assessed. Fingermarks were deposited onto five surfaces, aluminium drinking cans, nitrile gloves, plastic snap-lock bags, and glass slides held vertically or horizontally. DD was applied to 200 fingermark deposits in four different ways (laboratory pipette, plastic pasture pipette, atomizer spray and glass spray bottle) and the most practical application technique was selected. In subsequent experiments, the glass spray bottle was used to apply DD to 100 fingermarks supplied by two participants. In addition the webbings and palms of all the gloves were stained with DD and examined, this was an additional 104 areas. Fluorescence was observed by microscopy and counted with a manual and an automatic method. A selection of fingermark deposits from participants were selected and subjected to DNA profiling. Standard PCR and direct PCR procedures were compared using the AmpFLSTR™ Identifiler™ Plus PCR Amplification kit. The results show that all application techniques were comparable. There was variability in the fluorescence seen, likely due to the different amounts of cellular material deposited and retained on each item. Practically, spray applications were suitable for large and vertical items while a pipetting application was more suitable for small horizontal surfaces. Full volume, direct amplification performed the best and the success of DNA profiling largely depended on the fluorescent counts obtained with the most success in fluorescent counts over 500. Plastic snap-lock bags were not successful. There were no statistically significant differences of the fluorescent counts when using the manual counting method compared to the ImageJ automated counting method and the later was more suitable for images with a higher level of fluorescence observed. These results show immense potential for DD to be integrated into casework as a latent DNA screening tool. Further research into this method would be of value.