Nanoscale Imaging and Chemical Analysis of Extracellular DNA in Trace Evidence Samples

As submitted by the proposer:

Humans shed tens of thousands of skin cells each day, and these cells are transferred to every surface our skin comes in contact with. At crime scenes, "touch DNA" refers to the DNA that is left behind from skin cells when a perpetrator touches, or comes into contact with an item, including physical interaction between two individuals. Analysis of this trace cellular evidence has become an integral part of a forensic laboratory's workload, and an important tool for investigators. However, the relationship between the genetic profile from a touched object and the transferred DNA of cells in the layers of epidermal cells has not been fully elucidated. In fact, there are no conclusive ways even to identify the kind of epithelial cell itself (skin, vaginal, buccal, etc.).

To optimize the recovery and profiling of trace DNA from a scarce sample, it is therefore critical to improve our understanding of the source (epithelial cells) and nature of DNA (whether it is free or anchored to the surface) transferred through touch or contact. Often, investigators have to work only with a few recovered cells, underscoring the need for new kinds of ultra-sensitive tools that can also be rapid and reliable.

The objective of this project is to advance the fundamental science of understanding epithelial cell surfaces for forensic analysis. Using nanoscale and traditional analytical tools the researchers propose to probe cells based on the hypothesis that the outer surfaces of epithelial cells holds the key to answering fundamental forensic questions.

These include the differences between various cells as well as the spatial and biochemical context of DNA on the cell surface. Using high-resolution, non-destructive tools, the researchers will be able to gain a unique look at the cell surface - its morphology, its mechanical properties and the presence of specific cell surface signatures including extracellular DNA. These spatial and temporal signatures will lead to a better understanding and handling of cellular samples collected as evidence; provide guidelines on storage; develop ultra-sensitive tools for cell attribution; and precise analysis of touch and contact DNA.

Note: This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

ca/ncf