Persistence of Touch DNA for Forensic Analysis

The purpose of this project is to quantify how different factors (including surface type, temperature, humidity, UV exposure, and time) affect the persistence and stability of touch DNA. “Touch DNA” refers to the trace amounts of DNA that can be deposited on objects by touch. As DNA detection methods have increased in sensitivity and sophistication over the past 20 years, touch DNA samples have become increasingly important in criminal investigations.

This project addresses an operational requirement put forth by the NIJ Forensic Science Technology Working Group for “comprehensive, systematic, well controlled studies that provide foundational knowledge and practical data about ‘touch evidence’ persistence in the real world.” This two-year applied research project is a collaboration between the Massachusetts Institute of Technology Lincoln Laboratory (MIT LL), which will contribute to study design and perform all relevant experiments, and researchers at South Dakota State University, who will help with study design, statistical analysis, and model development. In the first year, we will:

• Conduct a formal Design of Experiments to optimize the statistical power and cost effectiveness of the proposed experiments
• Perform controlled experiments to assess how DNA quantity and stability are affected by a range of environmental exposures (using test surfaces on which we have deposited controlled amounts of cell suspensions or purified DNA)
• Generate a predictive model of DNA persistence based on environmental exposure

In year two, we will:

• Use the results of our initial experiments and modeling efforts to design experiments involving real-world touch DNA samples
• Perform controlled experiments to assess how the quantity and stability of touch DNA are affected by a down-selected range of environmental exposures
• Conduct additional model validation and refinement
• Prepare a publication describing study results and providing recommendations to the forensic science community

DNA persistence will be assessed by measuring total DNA concentration and degradation index as well as by performing DNA typing analysis by short tandem repeat (STR) analysis or single nucleotide polymorphism (SNP) sequencing. These studies will leverage the advanced SNP sequencing capabilities developed by MIT LL as well as our experience conducting rigorous fielding/sampling campaigns. Collectively, these studies will provide the most comprehensive information to date regarding basic properties of touch DNA evidence and will enable improved recommendations to be made to the forensic science community regarding best practices for the interpretation and evaluation of touch DNA evidence.