The use of non-thermal plasma for DNA decontamination in a forensic vacuum metal deposition chamber: A proof of concept study

Vacuum Metal Deposition (VMD) is routinely deployed for fingermark development on various types of evidence. In efforts to implement a sequential forensic workflow where fingermarks are processed before DNA collection to maximise evidential value, it is essential to prevent cross-contamination between analysed items. Non-thermal plasma (NTP) presents a potential advantage in DNA decontamination as it can reach areas that are inaccessible to conventional UV-C light and eliminates the need for solvents that might interfere with the vacuum-based systems. In this study, different NTP conditions generated within a VMD chamber were tested on human cells with known DNA concentrations, and cell-free DNA. This included variations in power (maximum and medium), exposure times (0.5 h, 1 h, 2 h), and pressures (1.68, 2, 4.27 ×10⁻¹ mbar). Overall, a reduction of approximately 100-fold in DNA concentration was observed after plasma treatment. Out of the tested conditions 1 h, 2 × 10⁻¹ mbar and maximum power proved to be the most stable plasma for the DNA removal. While UV-C light was more efficient at degrading cell-free DNA in direct line of sight by reducing DNA levels below the limit of detection and showing significant degradation, NTP was more effective at eliminating DNA out of the line of sight. These findings suggest that NTP could be a promising tool for DNA decontamination of forensic instruments like VMD. Future research should focus on optimizing NTP settings, including power output and vacuum conditions, to ensure complete DNA removal.