Genetic profiling from challenging samples: Direct PCR of touch DNA

We report on a novel direct PCR approach for retrieving touch DNA from handled items. Trace levels of DNA on handled items can be difficult to recover and analyse using standard methodology. The lack of a full nuclear STR DNA profile may be related to insufficient DNA being present initially, the presence of PCR inhibitors, or the loss of nucleic acid during sample collection and processing. The aim of this study was to optimise the swabbing method used to collect DNA and to improve the success rate of STR-based DNA profiling from touched items. A comparison was carried out to evaluate the use of three common swab types, nylon, cotton and foam at retrieving and releasing template DNA for amplification by direct PCR. To test the effectiveness of our method at processing low levels of DNA, complete STR DNA profiles were obtained from fingerprints deposited onto sterile plastic slides, which were swabbed and subjected to direct PCR. Our findings indicate the potential use of direct PCR when analysing samples that contain limited DNA.