DNA analysis by polymerase chain reaction of saliva traces on cigarette butts exposed to indoor and outdoor environmental conditions

Abstract

Cigarette butts are one of the most common carriers of saliva traces in forensic practice. There is a growing need to perform trace analyses such as DNA salivary analyses on cigarette butts found at a crime scene for identification purpose. However, examination of saliva traces left on cigarette butts as evidences are complicated due to the availability of the biological material in trace amounts for analysis and its rapid degradation due to extreme effects of environmental factors. The aim of this study was to compare the DNA quality and quantify the amount of DNA preserved in saliva found on cigarette butts subjected to various temperatures and humidity. Several cigarette butt samples were smoked, collected and were exposed to outdoors and indoors for 1 day, 3 days and 7 days. The samples were subjected to DNA extraction, quantification, DNA amplification using polymerase chain reaction (PCR) for the locus YNZ-22 and DNA typing. The results from this study showed that the purity of the DNA in the indoor experiment were higher (A260/280 1.76 – 1.91) than the purities of the outdoor experiment (A260/280 1.26 – 1.65) of cigarette butts. The concentration of the DNA found on the saliva traces on cigarette butts can be very variable in the outdoor experimental set-up (377.99 – 585.83 ng/µL) compared to the indoor (266.38 – 290.18 ng/µL); attributable to the differences in the humidity as well as the temperature. In conclusion, the purity obtained in this study ranges from low to high, and samples with intermediate to high purity was proven to enable successful DNA profiling. Since the concentration of DNA reported in this study may constitute human as well as non-human DNA, the interpretation of the DNA purity is a better mean for elucidating its potential value in forensic aspect compared to the DNA concentration.