Conclusion

This study investigated the persistence of touch cells on six common surfaces over a period of one year while also assessing the utility of Diamond Dye™ cell visualisation method for this purpose, including method optimisation. We determined that the use of a continuous device at 20 cm provided the least disruption to the cells and the most consistent dye coverage. We found that the uptake and retention of fluorescence is dependent on the substrate type, with some surfaces providing a delay in the amount of cellular material visualised until up to 24 h after staining while others exhibited maximum fluorescence instantly. Additionally, each substrate had different times where there were large drops in fluorescence. Further, respraying the surface after a period of time appears to improve visualisation of cellular material with all substrates. The surface characteristics and their interactions with the deposited cells as well as the dye likely resulted in these discrepancies. To further understand substrate and dye interactions with touch deposits, future studies may benefit from inclusion of the effects of surface topography (roughness, porosity, shape and presence of gloves), chemical composition and functional group interactions as well as the hydrophobicity on both deposited cells and the dye that stains them. The persistence of cellular material visualised over time, even upon respraying showed a larger decrease with porous and textured substrates compared to non-porous substrates. Furthermore, future studies should also investigate the reasons for the lack of a relationship between the cell counts and quantification results and expand the analysis to include STR profiling and the relationship, or lack thereof, between cell counts and STR data.

Based on these findings when triaging exhibits for examination during the initial stages of the investigative process the vetting personnel should consider, not just the probative value of an exhibit, but also the potential losses associated with each item type. Thus, it may be that while the exhibit is low on the examination priority list and previously would have been stored until it was to be examined at a later date, now may be prioritised with the knowledge that if not examined soon, the potential evidence may be lost to future analysis.