Residual DNA and cleaning protocols: a comparative analysis of forensic evidence examination methods.

The present study aimed to assess how effective commonly used cleaning protocols are in removing residual DNA from forensic evidence examination tools, thereby evaluating their ability to prevent contamination. The research question focused on whether standard cleaning techniques reliably remove residual DNA to mitigate contamination risks in forensic casework. Simulated forensic evidence samples—including bloodstains, buccal swabs, clothing, and bench surfaces—were processed using scissors, tweezers, and scalpels. After initial conservative cleaning, the tools were subjected to five experimental cleaning techniques derived from publicly available laboratory protocols. Each technique varied in terms of bleach concentration, ethanol use, and contact time, and all the techniques lacked an abrasive wiping motion. Swabs collected post-cleaning were subjected to DNA extraction (QIAamp® DNA Investigator Kit) and quantitation (Qubit™ 4 Fluorometer). Residual DNA was classified as positive (> 2.5 pg/µL), near negative, or negative (< 0.2 pg/µL). All the techniques resulted in detectable DNA in at least one trial. Among the 60 swabs, 11 were classified as positive for residual DNA, and 10 were classified as near negative for residual DNA. Only one technique incorporated a waiting period before removing bleach, and this was the only method that had no samples classified as positive for residual DNA. No tool type demonstrated lower contamination risk, and variability was observed across trials. Current single-phase cleaning solution-only cleaning practices may be insufficient for complete DNA removal. These findings underscore the need for standardized, multistep cleaning protocols, enhanced analyst training, and quality control measures to minimize contamination risk in casework.