The Use of Diamond Nucleic Acid Dye to Locate Both Finger Mark and Touch DNA on Non-Porous Items Obtained from Drug Seizures

Abstract

marks within forensic science can give two discriminatory pieces of evidence; touch DNA and finger mark ridge detail. Presently, these two pieces of evidence have not been able to be visualised together with one technique. Diamond™ Nucleic Acid Dye (DD) has been shown to be able to visualise touch DNA on a range of surfaces, however it has not been shown to be useful as a finger mark enhancement technique to the standard that Fingerprinting Officers could then use. DD has also been shown to inhibit amplification processes on plastic bags, which if improved would be crucial for DD use with illicit drug related seizures. Therefore, this study focussed on improving DD for the detection of touch DNA and finger mark ridge details, from latent finger marks deposited on plastic surfaces commonly associated with illicit drug seizures. A minimum fluorescent count from touch DNA was also investigated, to be able to prioritise the sampling of areas of touch DNA that will give a greater DNA profiling success. Finger marks were deposited on glass slides, plastic bags, and plastic containers where different solvents were used with DD to determine a better alternative for visualisation of touch DNA on these surfaces. Four solvents at various concentrations were used in this study: Ethanol, Triton X-100, Dimethylsulfoxide (DMSO) and 3M™ Novec™ 7100 Engineering Fluid (HFE 7100), with three different DD concentrations; 10x, 20x and 40x, together these combinations were called formulations. The formulations were then applied either with a spray device or with a pipette, and the fluorescence was visualised with both microscopy and forensic light sources. A manual fluorescence counting method was compared to a fluorescence counting method using a computer software called ImageJ. DNA profiling success of touch DNA samples was compared with standard and direct amplification methods using the Amp FLSTR™ Identifiler™ Plus PCR Amplification kit. A case study was used to look at how the chosen formulation would work with casework type samples, two participants were used for this, depositing finger marks on plastic bags and plastic containers. Lastly, finger mark ridge detail was determined by Fingerprint Officers in the New Zealand Police. This study showed that, on plastic surfaces the 90% HFE 7100/10% Ethanol 20x DD formulation has improved results when compared to the 75% Ethanol 20x DD formulation, as it can visualise both touch DNA and finger mark ridge detail, without inhibiting the amplification processes, improving DNA profiling success. DD has not been used before as a finger mark enhancement technique, but by improving the formulation it is now able to clearly identify ridge details, proving it could become a finger mark enhancement technique. To be able to validate and implement this technique within forensic casework would be hugely beneficial. Not only would you be able to accurately target areas of touch DNA and improve DNA profiling success, but finger marks can also be determined and either avoided, to allow Fingerprint Officers to use them for comparison, or sampled to reduce the possibility of mixed profiles.