Impact of heated passive headspace concentration on DNA recovery from semen in fire-scene evidence

Heated passive headspace concentration (HPHC) is routinely employed to recover ignitable-liquid residues from fire debris, but the elevated temperatures used may compromise subsequent DNA analysis when biological traces are present on the same exhibit. This study evaluated the feasibility of sequential chemical and biological examinations by investigating the impact of HPHC on semen DNA. Semen diluted 1 : 50 was deposited on cotton swabs and exposed to HPHC at 90 °C for 6 h or 16 h. The influences of dithiothreitol (DTT) pretreatment and gasoline contamination were also assessed. DNA yield, degradation index (DI) and short tandem repeat (STR) profiles served as outcome measures.When not contaminated with gasoline, about 60 ng of DNA (DI≈1.6) could still be recovered from normal semen samples after HPHC treatment for 6 hours, and a complete STR profile with high peak heights was obtained. DNA loss increased by 20–30 % and the peak height was significantly reduced after extending the heating time to 16 hours. DTT pretreatment further reduced the DNA recovery of semen samples, but there was no significant difference between the two groups after 16 hours of heating, suggesting that the disulfide bonds of sperm cells only provided short-term thermal protection. For unheated swabs with gasoline, quantitative polymerase chain reaction (qPCR) amplification of long-target amplicon signals (T.Large) was undetectable or extremely low, while interpretable STR profiles were still obtained. After 6 hours of heating at 90 °C, gasoline-contaminated samples regained measurable T.Large signals, however, the quality of STR profiles were severely impacted. Overall, when both ignitable-liquid analysis and DNA examination are required, an HPHC run at 90 °C for up to six hours prior to DNA profiling is a workable compromise. This temperature and time setting could minimize additional DNA loss and DNA degradation. Negative qPCR results from gasoline-contaminated samples must be interpreted cautiously. These findings offer empirical guidance for integrated workflows in complex fire-scene evidence processing.

Author dc:creator

• Li, Jialing

Advisor dc:contributor.advisor

• Wareing, Celeste M.

• Biochemistry

Statement dc:rights

• Attribution-NonCommercial-ShareAlike 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-sa/4.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

https://hdl.handle.net/2144/53175

OAI identifier oai:identifier

oai:open.bu.edu:2144/53175