Whose blood is it? Application of DEPArray™ technology for the identification of individual/s who contributed blood to a mixed stain.

The interpretation and statistical evaluation of mixed DNA profiles often presents a particular challenge in forensic DNA investigations. Only in specific combinations can single cellular components of a mixture be assigned to one contributor. In this study, the DEPArray™ technology, which enables image-assisted immunofluorescent-sorting of rare single cells using dielectrophoretic (DEP) forces, was applied together with different preliminary tests to identify the individual/s who contributed blood to a given mixture. The technique was successfully applied in two routine casework samples. In order to ascertain how old a stain can be and still be processed successfully, white blood cells from two 10- and one 27-year-old stains were investigated. Depending on the stain's age, the associated DNA degradation level and the number of target cells successfully isolated, the final profile reflects a compromise between the gain of information due to isolation of pure cells of a specific cell type from a single contributor and the loss of discriminatory power due to incomplete profiles caused by DNA degradation.