Persistence of cellular material after exposure to water

Abstract

Disposing of items of forensic relevance in bodies of water is one countermeasure offenders can use to avoid detection. The impact of immersion in water has been explored for blood, saliva, and semen; however, few studies have assessed touch DNA. Here we report on the effect of exposure to water on the persistence of touch DNA over prolonged periods of time. To evaluate the persistence of cells from touch DNA, after water exposure, three substrates and two water types were tested: plastic, metal, and ceramic, submerged into seawater or tap water. Diamond™ Nucleic Acid Dye was used to stain cells deposited by touch. Cell counts before and after water exposure were compared to investigate cell loss over time, ranging from 6 hours to 5 days. A logarithmic increase in the percent of cells lost was observed over time when the data for substrate and water type conditions were combined. Substrate type influenced the persistence of cells, with the metal substrate retaining cells longer than plastic or ceramic. The influence of water type appeared dependent on the substrate, with varied cell persistence on metal whereas plastic and ceramic recorded similar cell loss over time between water types. The ability to visualize cells after exposure to water could assist in triaging evidence within operational forensic laboratories and allow for targeted sampling. This proof‐of‐concept study demonstrated that greater than 50% of cells can persist on various items submerged in aqueous environments for at least 5 days, highlighting the possibility for downstream DNA testing.

Nucleic Acids Persistence—Benefits and Limitations in Forensic Genetics

“…Recent reports prove that the type of material on which contact DNA has been deposited in water is very important. Metal surfaces provide an environment that is more conducive to the survival of the applied cellular material compared to plastic or ceramics [ 174 ]. Schmidt et al [ 175 ] reported that the amount of genetic material obtained from blood stains located on the shoe sole was significantly lower when shoes were used on a wet surface compared to a dry surface.…”

Cell counting to monitor swab efficiency

“…Visualization of the cells deposited via touch can be achieved using Diamond™ Nucleic Acid Dye (DD) and a fluorescence microscope. This method has been used in a variety of contexts [27][28][29][30][31][32], but the use of this technique to determine the efficiency of DNA recovery from a surface is limited. Visualization of cells before and after swabbing for evaluation of a swab's efficiency has been completed in a study by Haase et al [17] in 2019.…”