Monitoring cell loss through repetitive deposition.

Touch DNA deposited on items can be visualised by using fluorescent nucleic acid staining dyes. It might be expected that if a person contacts items multiple times, then at each contact fewer cells should be transferred and deposited. Here we report on the use of Diamond Dye (DD) to monitor any reduction in cellular deposition during multiple contacts. A volunteer, who was assigned as a heavy shedder, was asked to deposit a thumbprint using both left and right thumbs for 15 s onto separate clean glass slides. Thumbprints were collected in triplicate with each mark made for 15 s. Immediately after deposition, a second and then third mark was made in the same way. The three consecutive depositions were repeated 30 times to create 90 tested thumbprints. The number of cells within each entire thumbprint was scored using a cell-counting program, developed in-house. The number of cells deposited by the second and third depositions showed a decrease in the cell number compared to the first deposition, by ~70% and ~85% respectively. There was no difference between the percentage of cell persistence from whole thumbprints (16 frames) compared to only scoring part of thumbprints (4 frames). The data obtained provide insight into how cells are deposited by touch and how many cells remain on the thumb for subsequent contact events. Such information may account for cell deposition when performing actions (e.g. loading a firearm or repetitively opening a closing zip-lock bag).