Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
J. Thomas McClintock
While several improvements have been made in recent years to optimize the recovery of ‘touch’ DNA, relatively little research has been conducted to understand the relationship between ‘touch’ DNA and the binding affinity of that DNA to metal surfaces, specifically those with a significant copper presence. Furthermore, characterization of cell-free DNA (cfDNA) and its contribution to ‘touch’ samples and those cfDNA-metal interactions from objects commonly identified at crime scenes (cartridge casings, knives, doorknobs) have been lacking. Research has identified the tendency of copper ions to intercalate with DNA helices, resulting in sample degradation among other damaging conformational changes; however, while these effects have been observed in aqueous solutions under controlled conditions, virtually no examples of this phenomenon exist out of solution. It is therefore of critical importance to first evaluate if similar interactions are taking place on copper containing surfaces once dried on the surface, as are the conditions of ‘touch’ DNA samples usually collected at a crime scene. Additionally, research pertaining to ‘touch’ DNA recovery from metals has focused on developing optimized mechanical recovery techniques to include the M-Vac® wet-vacuum DNA collection system. However, recovery remains problematic due to those approaches having been developed to retrieve as much cellular material i.e., intracellular nuclear DNA (nDNA) as possible when it has recently been suggested that circulating cfDNA comprises the majority of DNA in a ‘touch’ sample. Therefore, maximizing the amount of both cellular and cfDNA acquired from metal surfaces is critical to successful DNA profiling. To generate an optimized workflow regarding collection and extraction procedures for ‘touch’ DNA from metal surfaces, the binding effects of metal ions with cfDNA, as well as the composition of ‘touch’ DNA samples, need to be further evaluated. As such, a three-fold study was designed with the following objectives: evaluate DNA-metal interactions at the surface level using ATR-FTIR, investigate efficacy of three collection methods (wet:dry double-swabbing method, tape-lifting, M-Vac® wet-vacuum DNA collection system) in recovery of ‘touch’ DNA from metal substrates, and test a centrifugal separation method for more efficient extraction of cellular and cfDNA. This study contributes to the ongoing research concerning the efficient collection of ‘touch’ DNA at the scene and from evidentiary items and provides investigators with a framework for which to collect and process such samples from commonly encountered metals.
Thornton, Jessica E., "Analysis of ‘touch’ DNA recovered from metal substrates: an investigation into cfDNA-metal interactions and the efficacy of different collection techniques on DNA yield" (2023). Graduate Theses, Dissertations, and Problem Reports. 11810.