A systematic evaluation of 'Bidi - a hand-rolled cigarette' as a forensic DNA evidence

Bidis are small handmade cigarettes consisting of ~0.2 g of tobacco flakes rolled in a dried leaf of 'Tendu' (Diospyros melanoxylon) or Piliostigma racemosum and tied with a thin thread. They have gained worldwide popularity among smokers and are often collected as forensic DNA evidence from crime scenes and processed similarly to cigarette butts. However, bidi's composition and manufacturing process differs distinctly from the cigarette, and hence the optimal processing for DNA analysis should not be assumed to be similar to cigarette butts. In the present study, the methodical evaluation of the bidi for DNA analysis is reported and an additional process of cell elution from bidi stubs prior to DNA extraction is systematically compared with the direct lysis of bidi stubs which is identical to the standard practice in forensic labs for cigarette butts. In terms of cell recovery from bidi stubs, the SDS based Cell Elution Buffer (CEB) proved to be better than Tween20 based CEB. The three components (cell-elute, supernatant, and processed stub) obtained after the cell elution process of smoked bidi stubs showed varying amounts of DNA. The cell-elute and processed stub exhibited high quality DNA, resulting in 90-100% of the samples giving a full STR profile. On the contrary, the directly lysed stubs yielded high quantity but low quality of DNA, resulting in only 40% of the samples with full STR profiles. The cell elution process enables three components namely cell-elute, supernatant and processed stub from the same bidi to be used for forensic DNA analysis, although the cell-elute proved to be the best source of DNA for STR profiling. The current study demonstrates that the additional cell elution process proved to be an essential step prior to DNA extraction procedure for bidi stubs.