Evaluating the impact of sandy surface contamination on trace DNA recovery from wearable fabrics: A comparative study of collection methods and extraction kits

Touch DNA evidence plays a pivotal role in forensic investigations, particularly in the absence of visible biological fluids. However, trace DNA recovery is influenced by multiple factors, including substrate type, collection technique, extraction method, and environmental exposure. Despite widespread adoption of both cotton swabbing and tapelifting methods, little is known about their comparative performance under real-world environmental stressors such as sand contamination, which is common in arid and desert regions. This study evaluated the efficiency of two collection methods Copan cotton swabs (CS) and SceneSafe Fast™ minitapes (MT) and two DNA extraction kits PrepFiler Express BTA™ and QIAamp® DNA Investigator Kit in recovering Touch DNA from 100 fabric-based items (face masks, T-shirts, and caps) exposed to sandy outdoor environments. DNA concentration, STR profile completeness, and total allele count were analyzed using standardized protocols. Statistical methods included factorial ANOVA, chi-square analysis, and Pearson correlation to assess method performance and inter-variable relationships. Cotton swabs consistently outperformed minitapes in DNA yield and profile integrity across all fabric types. The combination of cotton swabs with Prep Filer extraction produced the highest DNA concentrations (mean >2.0 ng/μL) and yielded full STR profiles in a majority of cases. In contrast, minitape sampling, particularly when combined with QIAamp extraction, resulted in lower recovery and an increased rate of partial or mixed profiles. A strong positive correlation (r > 0.8) was observed between DNA concentration and STR profile completeness. These findings indicate that adhesive-based sampling methods are substantially hindered by sand interference, reducing their forensic value in contaminated conditions. The results emphasize the need for adaptive forensic DNA protocols that account for environmental contaminants such as sand. Cotton swabbing in combination with Prep Filer Express BTA™ extraction represents a robust and reliable strategy for maximizing trace DNA recovery from wearable items in sandy or dusty outdoor settings. This research provides critical guidance for improving DNA evidence collection in real-world casework and supports the development of optimized trace DNA workflows for challenging environments.