Evaluation of low trace DNA recovery techniques from ridged surfaces

The first step in the DNA profiling process is the recovery of DNA from the crime scene or item. Such surfaces can be varying with absorbent and non-absorbent surfaces. Ridged surfaces, such as those encountered on bottle-tops or firearms, are also common. Although low trace DNA or “touch DNA” is problematic in forensic casework, ridged surfaces should be a more effective surface for the recovery of such DNA due their abrasive nature. The aim of this study was to evaluate six recovery techniques; single wet swab, dry-wet double swab, wet-dry double swab, flocked swab, PCR square, and tape lifts. 36 falcon tubes with screw top lids were sterilised before DNA was deposited on the screw-top lids. Each of the recovery techniques were then utilised on 6 screw-top lids. All recovery media then underwent standard DNA extraction prior to DNA quantification by UV/Vis spectroscopy and quantitative PCR. The data indicated that the tape lifts recovered significantly more DNA from the ridged surface than the other techniques. There was no significant difference between the remaining 5 techniques, although on average, flocked swabs recovered the least amount. This suggested that the success in recovery of DNA is not down to the particular technique used, but down to the competence of the individual examiner and the amount of DNA deposited onto the surface.