A comprehensive evaluation of Cell Elution Method (CEM) for forensic DNA analysis from smoked cigarettes

Abstract

Cigarette stubs are commonly encountered trace DNA samples at crime scenes. Standard laboratory practice typically involves direct lysis of the stub for DNA extraction, leading to the co-extraction of DNA-degrading and inhibiting constituents from smoke and tobacco. This process can result in lower-quality DNA profiles. There has been limited focus on developing specific sample processing techniques that minimize these degrading agents and inhibitors before DNA extraction, which could significantly enhance the quality of DNA profiles. This study evaluates a previously established Cell Elution Method (CEM) against the conventional Direct Lysis Method (DLM) for DNA extraction from cigarette stubs. DNA quantity, quality, and subsequent STR profiles were assessed in 80 smoked cigarette stubs, comprising both flavoured and unflavoured types. While CEM exhibited comparable DNA yield from both flavoured (0.17 ng) and unflavoured (0.19 ng) cigarettes, DLM showed significant variability in average DNA yield for unflavoured (0.05 ng) and for flavoured (0.25 ng) cigarettes. Notably, CEM-treated samples demonstrated lower Degradation Index (DI) values compared to DLM-treated ones for both the types of cigarettes. Consequently, STR profiling success rates were higher with CEM, with 95 % of flavoured and 55 % of unflavoured samples yielding informative profiles, compared to 80 % and 0 %, respectively, for DLM. In unflavoured stubs, Amelogenin marker amplification was achieved in 35 % of CEM-treated samples, significantly outperforming the 5 % success rate with DLM. Additionally, CEM resulted in higher average allele recovery rates for both flavoured (58.98 %) and unflavoured (33.41 %) samples compared to DLM. These findings indicate that CEM outperforms DLM in producing higher-quality DNA profiles from cigarette stubs. Thus, CEM can be a choice of method for processing cigarette stub prior to DNA extraction.