DNA alloys: The enduring story of touch DNA on metals

The successful analyses of DNA obtained from cellular deposits on metal substrates is an on-going issue with many metallic substrates inhibiting downstream enzymatic reactions. To examine this problem further, we report on the monitoring of persistence of cells deposited by touch on a range of metal surfaces using the DNA binding dye, Diamond Dye. Fingerprints were deposited in defined areas on metal substrates and stained with Diamond Dye. The cells were recorded at time points from initial deposition through to four weeks. Cells deposited on a glass microscope acted as a control. Little cell loss was recorded over the 4-week period on cells deposited on glass, nickel, stainless steel, and zinc. Unusual patterns of cell loss were recorded for cells deposited on copper and brass. Cells deposited on aluminium showed the greatest cell loss, nearly 22 %, contrasting with a loss of 4.5 % for cells deposited on glass (control). Whole thumbprints were deposited on the same substrates and stored for four weeks after which cellular material was removed using a swab and the DNA analysed using quantification and STR amplification. While cells deposited on copper did not record the greatest cell loss over the four weeks compared to the other metal substrates, when quantified and profiled, the whole thumbprints produced the least informative DNA profiles. No notable inhibition was recorded by qPCR for any sample, but degradation was indicated for both the brass and copper deposits. The data confirms that there are interactions between metallic surfaces and DNA and the substrate and DNA binding dye, which made cell visualisation difficult on brass and copper substrates. However, it also highlights that these metal-DNA interactions are causing DNA degradation on the copper and brass substrates that affect subsequent profile quality.