Comparison of Three DNA Collection Methods on Nile Red Fluorescent Areas of a Porous Substrate

Abstract

The study to be presented utilized Nile Red dye to visualize hand-touched areas on white cotton while evaluating three DNA collection methods: traditional cutting, combination cutting, and M-Vac^® wet vacuum. Nile Red is a fluorescent dye known to bind to lipids that are likely deposited on substrates during the hand-touch process. Nile Red showed observable fluorescence in 50 of 60 test samples (examination of photographs using digital tools did indicate fluorescence in all 60 samples), clearly locating areas where biological material from human contact was deposited, maximizing the likelihood of obtaining touch DNA from these areas. The M-Vac wet vacuum and combination cutting methods had the highest percentage profiles obtained in the study. Sixteen of 20 samples collected with the combination cutting method and 15 for the M-Vac method resulted in full profiles compared with only 4 samples with the traditional cutting method. The M-Vac method produced the most nondonor alleles (94 alleles in 9 samples) followed by the combination method (12 alleles in 6 samples) and the traditional (9 alleles in 4 samples). Statistical analysis indicates that the M-Vac and the combination methods were not statistically different in DNA concentration, however, the DNA concentrations for both methods were statistically higher than the DNA concentrations obtained by the traditional method. This study shows that utilizing Nile Red as a detection method for areas containing trace DNA in conjunction with improved DNA collection methods is viable for DNA genotyping of trace DNA on cotton fabric. Crime laboratories can implement the combination sample collection method in lieu of traditional cutting methods without expansive changes in protocols or a large increase in laboratory expenditures.