การตรวจพิสูจน์ดีเอ็นเอจากวัตถุพยานทางชีวภาพที่ผ่านการทดสอบเบื้องต้น (Presumptive test) โดยวิธีไดเร็คพีซีอาร์ (Direct PCR)

Abstract

Biological evidence is important for forensic investigation. In some cases, only small amounts can be found and they can be heavily degraded due to the environmental factors at the crime scene. As such, the DNA purified from the extraction process may not be enough for STR typing. The problem is worsened when part of a sample has to be spared for presumptive testing. Therefore, the aims of this research are to apply direct STR typing to both presumptive tested and non-presumptive tested biological samples on filter papers and also to study associated factors that influence the process. The results showed that the developed direct PCR technique was able to achieved a high rate of successful DNA amplification (full DNA profiles). Non- presumptive tested samples gave 95.6% first pass success rates (N = 90). Furthermore, the kind of presumptive test kit had an effect on the success rates of STR typing as follows, Luminol (88% of samples gave full DNA profiles), Hemastix (78%), Leucomalachite green, and Kastle-Meyer (50%). Semen presumptive test (acid phosphatase) and saliva (Phadebas paper) had success rates of 85% and 73.33%, respectively. Moreover, the substrate type also had an effect, with the highest success rate seen with cotton. The developed direct PCR protocol can be used to generate STR profiles from even with 6 months-old biological samples. The benefits of this research include increasing amount of DNA obtainable from evidence, as the protocol can be performed directly from filter paper that had been used for presumptive testing; reducing the risk of DNA contamination from extraction procedures; and most importantly, using minimal samples for analysis.