Time Since Deposition for Touch DNA Evidence

The goal of this project is to test a new method for determining the time-since-deposition for epithelial cell populations that can be used for a variety of sample types including touch or trace biological evidence. Establishing the age of evidentiary samples is a critical need for caseworking laboratories as it can provide probative context to DNA profiling results. Currently, few methods have been described for determining the age of epithelial cell samples and, of those methods, none have been validated for casework. Previous research from our group has established a novel workflow that analyzes the autofluorescence and morphological signatures of cell populations that varies with time following sample deposition. Using predictive algorithms based on a reference dataset, the time since deposition can be estimated for unknown biological samples. The primary advantage of this method for forensic casework is that all aspects of the workflow are high-throughput and inherently non-destructive which is ideal for evidence samples since these are typically compromised and low in template quantity.  The goal of this project is fully test time-since-deposition signatures for the most challenging and realistic sample types commonly encountered by DNA caseworking laboratories (e.g., cell mixtures) and optimize the method to increase the probative value of time estimates as well as the range of samples it can be used on. Our specific aims include (1) increasing the resolution and precision of time-since-deposition through novel computational approaches; (2) testing autofluorescence-based time-since-deposition on cell mixture samples, (3) applying signatures to epithelial cell samples derived relevant to sexual assault casework, and (4) development of age-of-evidence signatures both as a screening tool for rapidly assessing DNA quantity and quality, and a means to link time-since-deposition with specific contributors to DNA mixtures. The expected outcomes for the project include peer-reviewed manuscripts describing the workflow and developmental validation of this method within a DNA caseworking unit (VA-DFS). This research will provide a fast, high-throughput, and non-destructive front-end analysis techniques within a forensic DNA caseworking laboratory that can enhance the probative value of many types of biological samples. CA/NCF