Evaluation of a direct PCR method and the Qiagen Investigator 24plex GO! Kit for typing blood, saliva and touch DNA on multiple substrates

Abstract

In forensic DNA typing, omitting the DNA extraction procedure and adding the sample directly to the polymerase chain reaction (direct PCR) mixture has several advantages. Without extraction and purification, there is less of a risk of sample loss, sample mix up, or contamination. This study tested the feasibility of direct PCR using the Qiagen® Investigator® 24plex GO! Kit, a megaplex kit that amplifies 22 polymorphic STR markers and the Amelogenin sex determination alleles. Test samples included blood, saliva and skin cells on porous substrates, specifically denim, white cotton, polyester fabric, and paper tissue. Glass slides were used to represent non-porous surfaces. Body fluids like blood and saliva were collected using the following: Scotch™ double-sided tape, Zots™ dots, Sellotape® and two different FLOQSwabs™ from Copan© (microFLOQ® and a nylon FLOQSwab™). The results show that utilization of Sellotape® as a sample collection method was the most successful in generating a profile. This collection yields fast PCR-STR results and is non-destructive, so that the remaining sample can be re-tested if necessary. For touch samples, collection employed a double swab technique using the nylon FLOQSwab™ from Copan, a single Fitzco CEP swab, as well as a cutting method for the fabric substrates. The use of swabs had better success than cutting, probably due to the swab covering a larger surface area, thereby collecting a larger quantity of sample. Touch samples on glass were problematic. This sample type showed some PCR inhibition for samples collected with the FLOQSwab™ and had the lowest overall success rate