DNA Profiles Generated from a Range of Touched Sample Types

Direct PCR from touch DNA has a range of potential applications in the field of forensic investigation for exhibit examination that, under standard extraction methods, rarely produce informative DNA profiles. Previous studies from ‘touch DNA’ have focussed on fingermarks created under laboratory conditions. Here we report on successful STR DNA profiling from a range of touched items. Direct PCR, with no increase in cycle number, was performed after eight different sample types, typical of those submitted for forensic investigation, were handled by volunteers for a maximum of 15 s to deposit trace amounts of their DNA. Amplifications were performed using either GlobalFiler^® or Identifiler^® Plus following manufacturer's instructions. These two kits were chosen deliberately as many laboratories worldwide have adopted and validated them in their workflow, thus allowing for direct PCR to be incorporated within their practises easily. It was found that informative STR profiles were obtained from all eight substrates using both STR kits. Identifiler^® Plus out-performed GlobalFiler^® in terms of the percentage of alleles amplified using the direct PCR approach. Both generated informative profiles from all items and all individuals, at different rates, with Identifiler^® Plus being informative in a larger percentage of samples. GlobalFiler^® produced profiles with an average of 60% ± 24% (36 ± 15 alleles) alleles present while Identifiler^® Plus produced profiles with an average of 96% ± 4% (31 ± 1 alleles) alleles present. A comparison was made between the direct PCR approach and subjecting touched samples to a standard DNA extraction process, both using Identifiler^®. An average of 4% of profiles were informative for samples that underwent extraction with 100% being informative from the same subset of samples amplified by direct PCR. Our findings further demonstrate the success of direct PCR to enhance the STR DNA profiles from touch DNA. Further, Identifiler^® Plus was found to generate informative profiles more often than GlobalFiler^®. Direct PCR is fast, simple, and non-destructive of evidence with the ability to generate informative genetic data where standard methods are likely to fail.