Latent DNA detection on items of forensic relevance

This review focusses on the use of DNA binding dyes to detect and record the presence of latent DNA on items of forensic relevance. Latent DNA can be crucial in forensic investigations and remains invisible unless an enhancement method is applied. Latent DNA is deposited on items of forensic relevance through various modes of transfer, with direct contact between skin and the item being the most common. Skin cells, otherwise called dead keratinocytes or corneocytes, have been shown to contain highly variable amounts of DNA. There is no standardised presumptive test for skin cells, but the advent of DNA-binding dyes allowed for the first time, the presence and number of stained corneocytes to be recorded. A commonly used DNA binding dye is Diamond™ Nucleic Acid Dye (DD). The dye has been used to detect the presence of latent DNA within biological deposits on a range of substrates and has been used to assess shedder status. This review discusses the many potential benefits of staining a substrate with a dye to detect latent DNA and then being able to target collection of a sample only where there is cellular material present. Despite advantages, the use of dyes to detect cellular material has not transitioned into forensic science practice; the reasons for this are discussed including some of the problems of dye staining of substrates. The review concludes by highlighting opportunities for conducting research to monitor cell deposition, persistence and transfer.