Persistence of touch deposits on a range of substrates assessed using an optimised application of Diamond Dye™.

The persistence of biological material on various substrates over extended periods of time and the visualization of cellular degradation are an important area of consideration in DNA-TPPR research. This study investigates long-term cell persistence of touch deposits and the ability to visualise them on different substrates. A key focus of the study was optimisation of the Diamond Nucleic Acid Dye™ (DD) application to minimise disruption to cells while ensuring effective cell visualisation. Three spray methods were tested across seven distances, with performance evaluated based on fluorescence intensity and the spread of cellular material outside of the deposit circle.Using the optimised method persistence of touch cells on six substrates: glass, plastic, melamine, aluminium, leather, and cotton were assessed at several timepoints up to a year including effect of respraying.Results revealed diminishing and significant variation in. cell persistence across substrates, with cotton and leather displaying lowest persistence. Further, the results of the re-spraying, point to the need for respraying items after initial staining to ensure the best visualisation of cellular material over time. The DNA amounts in the deposits were then assessed, showing that the amount of DNA recovered was considerably less than what would be expected based on the cell counts.This research provides valuable baseline data for forensic caseworkers to prioritise, where possible, sample collection based on substrate-specific cell persistence. Additionally, the study aids the work towards establishing best practices for Diamond Dye™ application to maximise visualisation efficiency with minimal cell disruption.