Collaborative swab performance comparison and the impact of sampling solution volumes on DNA recovery

The collection of DNA traces marks the first step determining the success of genetic analysis. This study aimed to identify and validate a suitable alternative to the currently used ForensiX Evidence Collection Kit containing a cardboard box for swab storage. This box has to be folded at the crime scene, which is time-consuming and carries the risk of potential contamination and handling difficulties. A collaboration study involving three police departments and one laboratory for forensic genetics was performed to compare the currently used swab against three challenger swabs: ForensiX SafeDry, Copan 4N6FLOQSwab™ Genetics and Copan 4N6FLOQSwab™ Crime Scene. Mock samples consisted mainly of touch DNA, but also blood, saliva and semen were applied to twelve items with different surfaces. Every organisation contributed with three DNA collectors, whose individual collection efficiencies were investigated. The challenge of preparing homogenous traces, especially touch DNA, was addressed by enhancing hand contact frequency and sampling area. As a further part of the swab comparison study, we describe for the first time the influence of different swabbing solution volumes on the sampling efficiency of the different swabs. The application of touch DNA was also tested for a further swab type, the Sarstedt Forensic Swab, which yielded such low DNA concentrations that it was excluded from the collaboration study. The Copan Genetics and Copan Crime Scene swabs yielded significantly lower DNA concentrations than the currently used ForensiX Evidence Collection Kit and ForensiX SafeDry swab. The inter-individual performance results of the operators revealed significant differences in sampling skills. Comparing different swabbing solution volumes showed higher DNA yields or no significant difference for the ForensiX Evidence Collection Kit and ForensiX SafeDry than the Copan Genetics, depending on the item or trace type swabbed. Our results highlight the importance of validating first-step components that are decisive to the success of DNA typing in the context of specific sampling procedures and laboratory methods. Also, the significance of individuals' securing variations, principally unknown for crime scene investigation and laboratory teams, is emphasised for the first time, offering a practical approach for improving and training DNA collecting activities and ensuring the optimal securing evidence process. These findings increase the knowledge of impacts on DNA collection and, thus, benefit other laboratories and forensic services, particularly when using the same extraction methods.