The Metropolitan Police Service currently uses cotton swabs to retrieve DNA for forensic profiling. Recently, a new nylon flocked swab type has become available from Copan (MicroRheologics, Brescia, Italy) that it is claimed, offers increased sample recovery and release yields. If true, the flocked swab may have important applications in DNA evidence retrieval. This study examines the DNA retrieval capability of cotton and nylon flocked swabs when extracted using three common extraction platforms (QIAcube, BioRobot EZ1 and manually processed QIAamp DNA investigator kit). Results indicate that both swab types are capable of recovering high percentages of DNA (>50%); however, the extraction platform selected was shown to have a significant effect upon DNA retrieval. Across all experiments, the cotton swab combined with the spin-column extractions was shown to be most effective, with the nylon swab and BioRobot EZ1 combination being the least effective. These findings illustrate the importance of extraction method selection.
: Four presumptive blood tests, Hexagon OBTI, Hemastix®, Leucomalachite green (LMG), and Kastle‐Meyer (KM) were compared for their sensitivity in the identification of dried bloodstains. Stains of varying blood dilutions were subjected to each presumptive test and the results compared. The Hexagon OBTI buffer volume was also reduced to ascertain whether this increased the sensitivity of the kit. The study found that Hemastix® was the most sensitive test for trace blood detection. Only with the reduced buffer volume was the Hexagon OBTI kit as sensitive as the LMG and KM tests. However, the Hexagon OBTI kit has the advantage of being a primate specific blood detection kit. This study also investigated whether the OBTI buffer within the kit could be utilized for DNA profiling after presumptive testing. The results show that DNA profiles can be obtained from the Hexagon OBTI kit buffer directly.
It is important that contamination from extraneous DNA should be minimised on items used at crime scenes and when dealing with exhibits within the laboratory. Four sterilisation techniques (UV, gamma and beta radiation and ethylene oxide treatment) were examined for their potential to degrade contaminating DNA to such an extent that subsequent DNA profiling was impossible. This work indicated that the most successful technique to reduce DNA contamination was ethylene oxide treatment. Of the radiation techniques tested in this study, gamma was the most successful at eradicating DNA and UV radiation was the least. None of the contaminated samples treated with ethylene oxide and subsequently subjected to DNA analysis met the DNA profile criteria necessary for acceptance on the UK National DNA Database. Contaminated cotton swabs and micro-centrifuge tubes treated with ethylene oxide showed a marked decrease in amplifiable DNA post-treatment. Ethylene oxide treatment to sterile swabs and tubes did not significantly affect subsequent DNA analysis.
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