การพัฒนาเทคนิคตรวจหาดีเอ็นเอที่เกิดจากการสัมผัสบนหลักฐานระเบิดแสวงเครื่องโดยใช้สารเรืองแสง

Abstract

Bombing cases are the second most frequent means of attack in the Southern Thailand’s insurgency. Improvised explosive devices or IEDs are made from household items, and the assembling process usually results in the deposition of touch DNA on the IEDs. However, STR typing from touch DNA mostly results in low success rates due to the low amount of DNA available and our inability to locate areas where they have been deposited. To solve this problem, six fluorescent DNA-binding dyes were evaluated at various concentrations to find the most efficient dye for touch DNA visualization that could also be used with direct PCR to increase success rates of STR typing from IED substrates. I found that SYBR® Green I at 0.9X and Diamond™ dye at 1.4X concentration were the two most efficient dyes. STR profiles from stained samples were investigated and indicated that DiamondTM dye inhibited PCR and resulted in fewer alleles when compared to SYBR® Green I; thus 0.9X of SYBR® Green I was chosen for further testing. The prepared SYBR® Green I dye was stable up to 24 h when stored in -20°C. Ten mock IEDs were constructed and investigated either using the developed method (visualization and direct PCR) in our laboratory or with the conventional method at a forensic police laboratory. The results showed that developed method produced significantly more alleles from the IED’s constructor (95% HDI: 0.7 to 10.0 alleles) and led to a decrease in non-donor’s allele. Moreover, the fluorescence level was directly correlated to the number of alleles obtained. The developed method has the potential to transform the way forensic scientists work with evidence potentially containing touch DNA.